VALENCE ELECTRONS & BONDING

VALENCE ELECTRONS

• Valence electrons:

• found in the outermost shell of an atom

• determines the atom’s chemical properties.

• So how do we know the number of valence electrons an element has?

• It based on their group on the periodic table.

Chapter 4

1 ve

2 ve3 ve

4 ve5 ve

6 ve7 ve

8 ve

VALENCE ELECTRONS

• Lets find some valence electrons.• Si • Xe• K• Ba• I• O• Al• P

OXIDATION NUMBERS

• charge an atom would have if it were in a compound composed of ions.

• AKA: charge

• change in oxidation number represents number of electrons gained or lost in a chemical reaction.

+1

+2+3

+4-3

-2

-1

OXIDATION NUMBERS

• Lets find some oxidation numbers• In• F• Rb• Sn• Ca• N• O

Lewis Structures

• AKA: electron-dot structures or electron-dot diagrams.

• Uses the number of valence electrons.• indicated by dots placed around the element’s

symbol. • diagrams that show the bonding between atoms

of a molecule.• Always place the element with the largest

number of valence electrons first, next largest …• They can form ionic & covalent bonds

Ionic Bonds

• TRANSFER of electrons from one bonding atom to another

Ionic Bonds• BaO

• FIRST WE SEE HOW MANY ELECTRONS THEY ARE FOR EACH ELEMENT.

• Ba = 2

• O = 6

• DRAW LEWIS STRUCTURE FOR OXYGEN

Ionic Bonds

oBa

Ionic Bonds

MgCl2

COVALENT BONDING

• chemical bond resulting from SHARING of electrons between 2 bonding atoms.

COVALENT BONDING

• H2O

• FIRST WE SEE HOW MANY ELECTRONS THEY ARE FOR EACH ELEMENT.

• H = 2

• OXYGEN = 6

• DRAW LEWIS STRUCTURE FOR OXYGEN

COVALENT BONDING

OH

H

BONDINGBONDING

REVIEWREVIEW

Directions: Each slide provides information in a question answer format. Click once to see the question and then again for the answer.

Bonds Between Atoms

Covalent

Ionic

Polyatomic Ions

Metallic

Molecular Substance Polar

NonpolarCoordinate Covalent

Network Solids

What are we going to learn about???

See if you can define the following words before starting the lesson…

• Anion- negative ion• Cation-positive ion• Octet Rule- rule that states that atoms tend to gain,

lose, or share electrons so that each atom has full outermost energy level which is typically 8 electrons.

• Polyatomic Ion- charged group of covalently bound atoms

• Monatomic Ion- ion formed from a single atom• Molecule-neutral group of atoms united by covalent

bonds• Alloy- homogeneous mixture of metals

• Unshared Pair- pair of electrons that is not involved in bonding but instead is held exclusively by one atom.

Marriage

Divorce

Forming of a bond is like marriage

•More stable

•exothermic

The breaking of a bond relates to a divorce.

•Less stable

•Endothermic

Ionic Bonds•What is an Ionic Bond?

- An Ionic Bond is a chemical bond resulting from the TRANSFER of electrons from one bonding atom to another

• When is an ionic bond formed?

- An ionic bond is formed when a cation (positive ion) transfers electrons to an anion (negative ion).

What are some characteristics of an ionic bond?

1. Crystalline at room temperatures

2. Have higher melting points and boiling points compared to covalent compounds

3. Conduct electrical current in molten or solution state but not in the solid state

4. Polar bonds

Covalent Bonds•What is an Covalent Bond?

- A covalent bond is a chemical bond resulting from SHARING of electrons between 2 bonding atoms.

• What forms a covalent bond?

- A covalent bond is formed between two nonmetals.

What are some characteristics of a covalent bond?

1. Covalent bonds have definite and predicable shapes.

2. Very strong

3. Low melting and boiling points

Covalent Bonds can have multiple bonds, so you should be familiar with the following…

Single Covalent Bond- chemical bond resulting from sharing of an electron pair between two atoms.

Double Covalent Bond- chemical bond resulting from sharing of two electron pairs between two atoms.

Triple Covalent Bond-chemical bond resulting from sharing of three electron pairs between two atoms.

There are five different categories associated with covalent bonds. What are the 5 different categories?

Covalent

Molecular Substance Polar

NonpolarCoordinate Covalent

Network Solids

c

First, we are going to look at Polar Covalent…

What is polar covalent?

-Polar covalent is a description of a bond that has an uneven distribution of charge due to an unequal sharing of bonding electrons.

The boy is not equally sharing with anyone else but rather taking all the food for himself.

Next, we are going to look at Non-Polar Covalent…

What is non-polar covalent?-Non polar covalent is a covalent bond that has an even distribution of charge due to an equal sharing of bonding electrons.

This couple is non- polar because they are sharing the drink equally between them.

Next, we are going to look at Molecular Substances…

What is a molecular substance?-A molecular substance is a substance that has atoms held together by covalent bonds.

Name 2 Characteristics of a Molecular Substance.

1. Weak

2. Low melting and boiling points

Next, we are going to look at Coordinate Covalent…

What is a Coordinate Covalent Bond?-A coordinate covalent bond is a bond formed when one atom donates both electrons that are shared.

*Think about the party analogy!

People donate their blood to help others just like atoms “donate” electrons to form stable octets.

Now, we are going to look at Network Solids…

What is a Network Solid?-A network solid is a solid that has covalently bonded atoms linked in one big network or one big macromolecule.

Name 3 Characteristics of a Network Solid.

1. Poor conductors of heat and electricity

2. Hard / Strong

3. High melting and boiling points

Diphenylglycoluril assembles into a unique, two-dimensional hydrogen bonding network in the solid state, while exhibiting a twisted molecular structure.

Metallic BondingWhat is a Metallic Bond?

- A metallic bond occurs in metals. A metal consists of positive ions surrounded by a “sea” of mobile electrons.

Name 4 Characteristics of a Metallic Bond.

1. Good conductors of heat and electricity

2. Great strength

3. Malleable and Ductile

4. Luster

This shows what a metallic bond might look like.

Polyatomic Bonds

What is a Polyatomic Bond?

- A polyatomic bond is charged group of covalently bonded atoms. It is made up of more than one atom.

Polyatomic ions usually have a charge because the collection of atoms has either gained an extra electron or else it has lost an electron.

Trigonal Planer

Tetrahedral

Linear

Octahedral

Trigonal Bipyramidal

Notice all the different types of shapes that the atoms Notice all the different types of shapes that the atoms can take on because of their bonding…can take on because of their bonding…

Just as a summary to what each bond looks like…

Now that you have completed the review provided you may wish to practice for your test by answering the following regents questions. The question is presented in the same way that http://regentsprep.org/ does them. If you would like to get reasons to why your answers were incorrect you can find the explanations there. After you have gotten your answer, click the mouse and the right answer will show up.

REVIEW

If you chose…

If you chose…

If you chose…

If you chose…

If you chose…

If you chose…

Atom – the smallest unit of matter “indivisible”

Heliumatom

electron shells

a) Atomic number = number of Electrons

b) Electrons vary in the amount of energy they possess, and they occur at certain energy levels or electron shells.

c) Electron shells determine how an atom behaves when it encounters other atoms

Electrons are placed in shells according to rules:

1) The 1st shell can hold up to two electrons, and each shell thereafter can hold up to 8 electrons.

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons

C would like to N would like toO would like to

Gain 4 electronsGain 3 electronsGain 2 electrons

Why are electrons important?

1) Elements have different electron configurations different electron configurations mean

different levels of bonding

Electron Dot Structures

Symbols of atoms with dots to represent the valence-shell electrons

1 2 13 14 15 16 17 18

H He:

Li Be B C N O : F :Ne :

Na Mg Al Si P S :Cl :Ar :

Chemical bonds: an attempt to fill electron shells

1. Ionic bonds –

2. Covalent bonds –

3. Metallic bonds

Learning Check

A. X would be the electron dot formula for

1) Na 2) K 3) Al

B. X would be the electron dot formula

1) B 2) N 3) P

IONIC BONDbond formed

between two ions by the

transfer of electrons

Formation of Ions from Metals

Ionic compounds result when metals react with nonmetals

Metals lose electrons to match the number of

valence electrons of their nearest noble gas

Positive ions form when the number of

electrons are less than the number of protons

Group 1 metals ion 1+

Group 2 metals ion 2+

• Group 13 metals ion 3+

Formation of Sodium Ion

Sodium atom Sodium ion

Na – e Na +

2-8-1 2-8 ( = Ne)

11 p+ 11 p+

11 e- 10 e-

0 1+

Formation of Magnesium Ion

Magnesium atom Magnesium ion

Mg – 2e Mg2+

2-8-2 2-8 (=Ne)

12 p+ 12 p+

12 e- 10 e-

0 2+

Some Typical Ions with Positive Charges (Cations)

Group 1 Group 2 Group 13

H+ Mg2+ Al3+

Li+ Ca2+

Na+ Sr2+

K+ Ba2+

Learning Check

A. Number of valence electrons in aluminum1) 1 e- 2) 2 e- 3) 3 e-

B. Change in electrons for octet1) lose 3e- 2) gain 3 e- 3) gain 5

e-

C. Ionic charge of aluminum 1) 3- 2) 5- 3) 3+

Solution

A. Number of valence electrons in aluminum3) 3 e-

B. Change in electrons for octet1) lose 3e-

C. Ionic charge of aluminum 3) 3+

Learning Check

Give the ionic charge for each of the following:A. 12 p+ and 10 e-

1) 0 2) 2+ 3) 2-

B. 50p+ and 46 e-

1) 2+ 2) 4+ 3) 4-

C. 15 p+ and 18e-

2) 3+ 2) 3- 3) 5-

Ions from Nonmetal Ions

In ionic compounds, nonmetals in 15, 16,

and 17 gain electrons from metals

Nonmetal add electrons to achieve the octet

arrangement

Nonmetal ionic charge:

3-, 2-, or 1-

Fluoride Ion

unpaired electron octet

1 -

: F + e : F :

2-7 2-8 (= Ne)

9 p+ 9 p+

9 e- 10 e- 0 1 -

ionic charge

Ionic Bond

• Between atoms of metals and nonmetals with very different electronegativity

• Bond formed by transfer of electrons

• Produce charged ions all states. Conductors and have high melting point.

• Examples; NaCl, CaCl2, K2O

Ionic Bonds: One Big Greedy Thief Dog!

1). Ionic bond – electron from Na is transferred to Cl, this causes a charge imbalance in each atom. The Na becomes (Na+) and the Cl becomes (Cl-), charged particles or ions.

COVALENT BONDbond formed by the sharing of electrons

Covalent Bond

• Between nonmetallic elements of similar electronegativity.

• Formed by sharing electron pairs

• Stable non-ionizing particles, they are not conductors at any state

• Examples; O2, CO2, C2H6, H2O, SiC

Bonds in all the polyatomic ions

and diatomics are all covalent bonds

when electrons are shared

equally

NONPOLAR COVALENT BONDS

H2 or Cl2

2. Covalent bonds- Two atoms share one or more pairs of outer-shell electrons.

Oxygen AtomOxygen Atom Oxygen AtomOxygen Atom

Oxygen Molecule (O2)

when electrons are shared but

shared unequally

POLAR COVALENT BONDS

H2O

Polar Covalent Bonds: Unevenly matched, but willing to share.

- water is a polar molecule because oxygen is more electronegative than hydrogen, and therefore electrons are pulled closer to oxygen.

METALLIC BONDbond found in

metals; holds metal atoms together

very strongly

Metallic Bond

• Formed between atoms of metallic elements

• Electron cloud around atoms

• Good conductors at all states, lustrous, very high melting points

• Examples; Na, Fe, Al, Au, Co

Metallic Bonds: Mellow dogs with plenty of bones to go around.

Ionic Bond, A Sea of Electrons

Metals Form Alloys

Metals do not combine with metals. They form Alloys which is a solution of a metal in a metal.Examples are steel, brass, bronze and pewter.

Formula Weights

• Formula weight is the sum of the atomic masses.

• Example- CO2

• Mass, C + O + O

12.011 + 15.994 + 15.994

43.999

Practice

• Compute the mass of the following compounds round to nearest tenth & state type of bond:

• NaCl; • 23 + 35 = 58; Ionic Bond

• C2H6;

• 24 + 6 = 30; Covalent Bond

• Na(CO3)2;

• 23 + 2(12 + 3x16) = 123; Ionic & Covalent

CHEMICAL CHEMICAL BONDINGBONDINGCHEMICAL CHEMICAL BONDINGBONDING

Cocaine

Chemistry I – Chapter Chemistry I – Chapter 88

Chemistry I Honors – Chemistry I Honors – Chapter 12Chapter 12

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Chemical Chemical BondingBondingProblems and questions —Problems and questions —

How is a molecule or How is a molecule or polyatomic ion held together?polyatomic ion held together?

Why are atoms distributed at Why are atoms distributed at strange angles?strange angles?

Why are molecules not flat?Why are molecules not flat?

Can we predict the structure?Can we predict the structure?

How is structure related to How is structure related to chemical and physical chemical and physical properties?properties?

Review of Chemical Review of Chemical BondsBonds

• There are 3 forms of bonding:There are 3 forms of bonding:• __________________—complete —complete transfer transfer of of

1 or more electrons from one atom 1 or more electrons from one atom to another (one loses, the other to another (one loses, the other gains) forming oppositely charged gains) forming oppositely charged ions that attract one anotherions that attract one another

• __________________——some valence some valence electrons electrons sharedshared between atoms between atoms

• __________________ – holds atoms of a – holds atoms of a metal togethermetal together

Most bonds are Most bonds are somewhere in somewhere in between ionic between ionic and covalent.and covalent.

The type of bond can The type of bond can usuallyusually be be calculated by finding the difference calculated by finding the difference in electronegativity of the two atoms in electronegativity of the two atoms

that are going together.that are going together.

Electronegativity Difference

• If the difference in electronegativities is between:

– 1.7 to 4.0: Ionic

– 0.3 to 1.7: Polar Covalent

– 0.0 to 0.3: Non-Polar Covalent

Example: NaClNa = 0.8, Cl = 3.0Difference is 2.2, sothis is an ionic bond!

Ionic BondsIonic BondsIonic BondsIonic BondsAll those ionic compounds were made All those ionic compounds were made

from ionic bonds. We’ve been from ionic bonds. We’ve been through this in great detail already. through this in great detail already. Positive cations and the negative Positive cations and the negative anions are attracted to one another anions are attracted to one another (remember the Paula Abdul Principle (remember the Paula Abdul Principle of Chemistry: Opposites Attract!)of Chemistry: Opposites Attract!)

Therefore, ionic Therefore, ionic compounds are usually compounds are usually between metals and between metals and nonmetals (opposite nonmetals (opposite ends of the periodic ends of the periodic table).table).

Electron Electron Distribution Distribution

in in MoleculesMolecules

Electron Electron Distribution Distribution

in in MoleculesMolecules

• Electron distribution is Electron distribution is

depicted withdepicted with Lewis Lewis (electron dot) (electron dot) structuresstructures

• This is how you This is how you decide how many decide how many atoms will bond atoms will bond covalently! covalently!

(In ionic bonds, it (In ionic bonds, it was decided with was decided with charges)charges)

G. N. Lewis G. N. Lewis 1875 - 19461875 - 1946

Bond and Lone Bond and Lone PairsPairs

Bond and Lone Bond and Lone PairsPairs• Valence electrons are Valence electrons are

distributed as shared ordistributed as shared or BOND PAIRSBOND PAIRS and and unshared orunshared or LONE PAIRS.LONE PAIRS. •

••

•

••

H Cllone pair (LP)

shared orbond pair

This is called a This is called a LEWIS LEWIS structure.structure.

Bond Bond FormationFormation

Bond Bond FormationFormation

A bond can result from anA bond can result from an overlapoverlap of of atomic orbitals on neighboring atoms.atomic orbitals on neighboring atoms.

ClH H Cl••

••

••

••

••

••

+

Overlap of H (1s) and Cl (2p)

Note that each atom has a single, Note that each atom has a single, unpaired electron.unpaired electron.

Review of Valence Review of Valence ElectronsElectrons

Review of Valence Review of Valence ElectronsElectrons

• Remember from the electron Remember from the electron chapter that valence electrons are chapter that valence electrons are the electrons in the OUTERMOST the electrons in the OUTERMOST energy level… that’s why we did energy level… that’s why we did all those electron configurations!all those electron configurations!

• B is 1sB is 1s22 2s 2s22 2p 2p11; so the outer ; so the outer energy level is 2, and there are energy level is 2, and there are 2+1 = 3 electrons in level 2. 2+1 = 3 electrons in level 2. These are the valence electrons!These are the valence electrons!

• Br is Br is [Ar] 4s[Ar] 4s22 3d 3d1010 4p 4p55

How many valence electrons are How many valence electrons are present?present?

Review of Valence Review of Valence ElectronsElectrons

Review of Valence Review of Valence ElectronsElectrons

Number of valence electrons of a main Number of valence electrons of a main (A) group atom = Group number(A) group atom = Group number

Steps for Building a Dot Steps for Building a Dot StructureStructureSteps for Building a Dot Steps for Building a Dot StructureStructure

Ammonia, NHAmmonia, NH33

1. Decide on the central atom; never H. 1. Decide on the central atom; never H. Why?Why?

If there is a choice, the central atom is atom of If there is a choice, the central atom is atom of lowest affinity for electrons. lowest affinity for electrons. (Most of the time, this is (Most of the time, this is the the least electronegative atomleast electronegative atom…in advanced chemistry …in advanced chemistry we use a thing called formal charge to determine the we use a thing called formal charge to determine the central atom. But that’s another story!)central atom. But that’s another story!)

Therefore, N is central on this oneTherefore, N is central on this one

2. Add up the number of valence electrons 2. Add up the number of valence electrons that can be used.that can be used.

H = 1 and N = 5H = 1 and N = 5

Total = (3 x 1) + 5 Total = (3 x 1) + 5

= 8 electrons / 4 pairs= 8 electrons / 4 pairs

3.3. Form a single bond Form a single bond between the central atom and between the central atom and each surrounding atom (each each surrounding atom (each bond takes 2 electrons!)bond takes 2 electrons!)

H H

H

N

Building a Dot StructureBuilding a Dot Structure

H••

H

H

N4.4. Remaining electrons form Remaining electrons form LONE PAIRS to complete the LONE PAIRS to complete the octet as needed (or duet in the octet as needed (or duet in the case of H).case of H).

3 BOND PAIRS and 1 LONE 3 BOND PAIRS and 1 LONE PAIR.PAIR. Note that N has a share in 4 pairs (8 Note that N has a share in 4 pairs (8

electrons), while H shares 1 pair.electrons), while H shares 1 pair.

5.5.Check to make sure there are Check to make sure there are 8 electrons around each atom 8 electrons around each atom except H. H should only have except H. H should only have 2 electrons. This includes 2 electrons. This includes SHARED pairs. SHARED pairs.

Building a Dot StructureBuilding a Dot Structure

6. 6. Also, check the number of electrons in Also, check the number of electrons in your drawing with the number of your drawing with the number of electrons from step 2. If you have more electrons from step 2. If you have more electrons in the drawing than in step 2, electrons in the drawing than in step 2, you must make double or triple bonds. If you must make double or triple bonds. If you have less electrons in the drawing you have less electrons in the drawing than in step 2, you made a mistake!than in step 2, you made a mistake!

H••

H

H

N

Carbon Dioxide, COCarbon Dioxide, CO22Carbon Dioxide, COCarbon Dioxide, CO22

1. Central atom = 1. Central atom =

2. Valence electrons =2. Valence electrons =

3. Form bonds.3. Form bonds.O OC4. Place lone pairs on outer atoms.4. Place lone pairs on outer atoms.

This leaves 12 electrons (6 pair).This leaves 12 electrons (6 pair).

5. Check to see that all atoms have 8 electrons 5. Check to see that all atoms have 8 electrons around it except for H, which can have 2.around it except for H, which can have 2.

C 4 e-C 4 e-O 6 e- X 2 O’s = 12 e-O 6 e- X 2 O’s = 12 e-Total: 16 valence Total: 16 valence electronselectrons

Carbon Dioxide, COCarbon Dioxide, CO22Carbon Dioxide, COCarbon Dioxide, CO22

••O OC

•• ••

••••••

••O OC

•• ••

••••••

••O OC

•• ••

••

••O OC

•• ••

••

6. There are too many electrons in our drawing. 6. There are too many electrons in our drawing. We must form DOUBLE BONDS between C and O. We must form DOUBLE BONDS between C and O. Instead of sharing only 1 pair, a double bond Instead of sharing only 1 pair, a double bond shares 2 pairs. So one pair is taken away from shares 2 pairs. So one pair is taken away from each atom and replaced with another bond.each atom and replaced with another bond.

C 4 e-C 4 e-O 6 e- X 2 O’s = 12 e-O 6 e- X 2 O’s = 12 e-Total: 16 valence electronsTotal: 16 valence electrons

How many are in the drawing?How many are in the drawing?

Double and Double and even triple even triple bonds are bonds are commonly commonly observed for observed for C, N, P, O, C, N, P, O, and Sand S

••O OC

•• ••

••

••O OC

•• ••

••

HH22COCO

SOSO33

CC22FF44

Now You Try One!Now You Try One!Draw Sulfur Dioxide, SODraw Sulfur Dioxide, SO22

Now You Try One!Now You Try One!Draw Sulfur Dioxide, SODraw Sulfur Dioxide, SO22

Violations of the Violations of the Octet RuleOctet Rule

(Honors only)(Honors only)

Violations of the Violations of the Octet RuleOctet Rule

(Honors only)(Honors only)Usually occurs with B and Usually occurs with B and elements of higher periods. elements of higher periods. Common exceptions are: Be, Common exceptions are: Be, B, P, S, and Xe. B, P, S, and Xe.

BF3BF3

SF4SF4

Be: 4Be: 4

B: 6B: 6

P: 8 OR 10P: 8 OR 10

S: 8, 10, OR 12S: 8, 10, OR 12

Xe: 8, 10, OR Xe: 8, 10, OR 1212

MOLECULAR MOLECULAR GEOMETRYGEOMETRY

MOLECULAR MOLECULAR GEOMETRYGEOMETRY

VSEPRVSEPR • VValence alence SShell hell EElectron lectron

PPair air RRepulsion theory.epulsion theory.

• Most important factor in Most important factor in determining geometry is determining geometry is relative relative repulsion repulsion between electron pairs.between electron pairs.

Molecule Molecule adopts the adopts the shape that shape that minimizes the minimizes the electron pair electron pair repulsions.repulsions.

Molecule Molecule adopts the adopts the shape that shape that minimizes the minimizes the electron pair electron pair repulsions.repulsions.

MOLECULAR MOLECULAR GEOMETRYGEOMETRY

MOLECULAR MOLECULAR GEOMETRYGEOMETRY

Some Common Some Common GeometriesGeometries

LinearLinear

Trigonal PlanarTrigonal Planar TetrahedrTetrahedralal

VSEPR chartsVSEPR charts

• Use the Lewis structure to determine the geometry Use the Lewis structure to determine the geometry of the moleculeof the molecule

• Electron arrangement establishes the bond anglesElectron arrangement establishes the bond angles• Molecule takes the shape of that portion of the Molecule takes the shape of that portion of the

electron arrangementelectron arrangement• Charts look at the CENTRAL atom for all data!Charts look at the CENTRAL atom for all data!• Think REGIONS OF ELECTRON DENSITY rather Think REGIONS OF ELECTRON DENSITY rather

than bonds (for instance, a double bond would than bonds (for instance, a double bond would only be 1 region)only be 1 region)

Other VSEPR chartsOther VSEPR charts

Structure Determination Structure Determination by VSEPRby VSEPR

Structure Determination Structure Determination by VSEPRby VSEPR

Water, HWater, H22OO The electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL

The electron pair The electron pair geometry is geometry is TETRAHEDRALTETRAHEDRAL

The molecular The molecular geometry is geometry is BENTBENT..

The molecular The molecular geometry is geometry is BENTBENT..

H O H••

••

H O H••

••

2 bond 2 bond pairspairs

2 lone 2 lone pairspairs

Structure Determination Structure Determination by VSEPRby VSEPR

Structure Determination Structure Determination by VSEPRby VSEPR

Ammonia, NHAmmonia, NH33

The electron pair geometry is tetrahedral.The electron pair geometry is tetrahedral.

H

H

H

lone pair of electronsin tetrahedral position

N

The The MOLECULAR GEOMETRYMOLECULAR GEOMETRY — the — the positions of the atoms — is positions of the atoms — is TRIGONAL TRIGONAL PYRAMIDPYRAMID..

The The MOLECULAR GEOMETRYMOLECULAR GEOMETRY — the — the positions of the atoms — is positions of the atoms — is TRIGONAL TRIGONAL PYRAMIDPYRAMID..

Bond PolarityBond PolarityBond PolarityBond PolarityHCl is HCl is POLARPOLAR because it because it

has a positive end and a has a positive end and a negative end. (difference negative end. (difference in electronegativity)in electronegativity)

Cl has a greater share Cl has a greater share in bonding electrons in bonding electrons than does H.than does H.

Cl has a greater share Cl has a greater share in bonding electrons in bonding electrons than does H.than does H.

Cl has slight negative charge Cl has slight negative charge (-(-)) and H and H has slight positive charge has slight positive charge (+ (+ ))

H Cl••

••

+ -••H Cl

••

••

+ -••

• This is why oil and water will not This is why oil and water will not mix! Oil is nonpolar, and water mix! Oil is nonpolar, and water is polar.is polar.

• The two will repel each other, The two will repel each other, and so you can not dissolve one and so you can not dissolve one in the otherin the other

Bond PolarityBond PolarityBond PolarityBond Polarity

Bond PolarityBond PolarityBond PolarityBond Polarity

• ““Like Dissolves Like”Like Dissolves Like”

–Polar dissolves Polar dissolves PolarPolar

–Nonpolar Nonpolar dissolves dissolves NonpolarNonpolar

Ch. 11 - Chemical Bonds

II. Kinds of Chemical Bonds (p.304-308)

Ionic Bond

Covalent Bond

Comparison Chart

A. Ionic Bond

• Attraction between 2 oppositely charged ions– Ions - charged atoms– formed by

transferring e-

from a metal to a nonmetal

A. Ionic Bond

– ions form a 3-D crystal lattice

NaCl

B. Covalent Bond

• Attraction between neutral atoms– formed by sharing e- between two nonmetals

B. Covalent Bond

– covalent bonds result in discrete molecules

Cl2 H2ONH3

• Nonpolar Covalent Bond– e- are shared equally

– usually identical atoms

B. Covalent Bond

• Polar Covalent Bond– e- are shared unequally between 2 different

atoms

– results in partial opposite charges

+ -

B. Covalent Bond

• Nonpolar

• Polar

• Ionic

View Bonding Animations.

B. Covalent Bond

C. Comparison Chart

IONIC COVALENT

Electrons

MeltingPoint

Soluble in Water

Conduct Electricity

OtherProperties

transferred from metal to nonmetal

high

yes (solution or liquid)

yes

crystal lattice of ions, crystalline solids

shared between nonmetals

low

no

usually not

molecules, odorous liquids & gases

C h e m i c a l B o n d i n g

V a l e n c e E l e c t r o n s

• E l e c t r o n s i n t h e o u t e r e n e r g y l e v e l a r e c a l l e d v a l e n c e e l e c t r o n s .

• I t i s t h e s e e l e c t r o n s t h a t d e t e r m i n e t h e f o r m a t i o n o f c h e m i c a l b o n d s .

V a l e n c e E l e c t r o n s

• C e r t a i n n u m b e r s o f v a l a n c e e l e c t r o n s a r e m o r e s t a b l e t h a n o t h e r s .

• A t o m s w i l l g a i n o r l o s e e l e c t r o n s t o b e c o m e m o r e s t a b l e .

C h e m i c a l B o n d T y p e s

• I o n i c

• C o v a l e n t

• M e t a l l i c

I o n i c B o n d

E l e c t r o n s a r e t r a n s f e r r e d f r o m o n e a t o m t o a n o t h e r .

E l e c t r o n T r a n s f e r

L i t h i u m Neon

I o n i c B o n d

• W h e n t h i s h a p p e n s , t h e c h a r g e s w i t h i n e a c h a t o m a r e n o l o n g e r b a l a n c e d .

• T h e a t o m s h a v e b e c o m e i o n s - o n e w i t h a p o s i t i v e c h a r g e , t h e o t h e r w i t h a n e g a t i v e

c h a r g e .

C o v a l e n t B o n d

E l e c t r o n s a r e s h a r e d b e t w e e n a t o m s .

C o v a l e n t B o n d

• T h e n u c l e u s o f b o t h a t o m s h a s a n e q u a l a t t r a c t i o n f o r t h e e l e c t r o n s .

• T h e s h a r e d e l e c t r o n s s p e n d m o s t o f t h e i r t i m e b e t w e e n t h e t w o a t o m s .

Polar covalent B o n d

Atoms share the electron unequally,

There is a slight difference in charge between the two poles of the bond; water is an example.

Hydrogen Bonding

In a hydrogen bond, an atom or a molecule interacts weakly with a hydrogen atom already taking part in a polar covalent bond.

I o n i z a t i o n E n e r g y

• T h e e n e r g y n e e d e d t o r e m o v e a n e l e c t r o n f r o m a n a t o m .

• T h e a t t r a c t i o n b e t w e e n t h e n e g a t i v e l y c h a r g e d e l e c t r o n a n d t h e p o s i t i v e l y c h a r g e d n u c l e u s m u s t b e o v e r c o m e .

E l e c t r o n A f f i n i t y

• T h e t e n d e n c y o f a n a t o m t o a t t r a c t e l e c t r o n s .

• M e t a l s h a v e a l o w e l e c t r o n a f f i n i t y .

• N o n m e t a l s h a v e a h i g h e l e c t r o n a f f i n i t y .

D i a t o m i c M o l e c u l e s

C o v a l e n t b o n d i n g o c c u r s b e t w e e n a t o m s o f t h e s a m e e l e m e n t .

D i a t o m i c M o l e c u l e s

H y d r o g e n

N i t r o g e n

O x y g e n

F l o r i n e

C h l o r i n e

B r o m i n e

I o d i n e

7

P o l y a t o m i c I o n s

• A g r o u p o f c o v a l e n t l y b o n d e d a t o m s a c t i n g l i k e a s i n g l e a t o m w h e n f o r m i n g

c o m p o u n d s .

• T h i s g r o u p o f a t o m s i s n o t e l e c t r i c a l l y b a l a n c e d a n d h a s a n o v e r a l l c h a r g e .

P r e d i c t i n g B o n d T y p e s

• W i l l t h e s e p a i r s f o r m i o n i c o r c o v a l e n t b o n d s ?

– s o d i u m & c h l o r i n e– c a l c i u m & o x y g e n– c a r b o n & o x y g e n– a l u m i n u m & s u l f u r

C h e m i c a l B o n d i n g

E n dE n d

Ch. 11 - Chemical Bonds

IV. Naming Ionic Compounds(p. 314-320)

Oxidation Number

Ionic Names

Ionic Formulas

A. Oxidation Number

• The charge on an ion.• Indicates the # of e- gained/lost to

become stable.1+

2+ 3+ 4+ 3- 2- 1-

0

• Write the names of both elements, cation first.

• Change the anion’s ending to -ide.

• Write the names of polyatomic ions.

• For ions with variable oxidation #’s, write the ox. # in parentheses using Roman numerals. Overall charge = 0.

B. Ionic Names

• NaBr

• Na2CO3

• FeCl3

– sodium bromide

– sodium carbonate

– iron(III) chloride

B. Ionic Names

• Write each ion. Put the cation first.

• Overall charge must equal zero.– If charges cancel, just write the symbols.

– If not, crisscross the charges to find subscripts.

• Use parentheses when more than one polyatomic ion is needed.

• Roman numerals indicate the oxidation #.

C. Ionic Formulas

• potassium chloride

• magnesium nitrate

• copper(II) chloride

– K+ Cl KCl

– Mg2+ NO3 Mg(NO3)2

– Cu2+ Cl CuCl2

C. Ionic Formulas

• calcium oxide

• aluminum chlorate

• iron(III) oxide

– Ca2+ O2 CaO

– Al3+ ClO3 Al(ClO3)3

– Fe3+ O2 Fe2O3

C. Ionic Formulas

Chemical Bonds

– Atoms gain or lose electrons through chemical reactions to gain a filled outer shell and therefore a lower energy level.

– A chemical reaction forms a chemical bond that is an attractive force that holds atoms together in a compound.

– Ionic bonds are formed when an atom transfers an electron to another atom during a chemical reaction• The opposite charges resulting forms an

electrostatic attraction between the ions that are formed.

– Covalent bonds form when atoms share electrons in a chemical bond.

– Metallic bonds form in metals.– These new bonds form compounds which can be

described in several ways.– Molecular orbital theory describes the electrons

as belonging to the whole molecule which gives the orbital its own shape, orientation, and energy levels.

– Isolated atom description considers the electrons around the atoms as being isolated from the rest of the molecule.

• Ionic Bonds

– Ionic bonding occurs when one atom transfers an electron to another atom

• The difference in electrical charge results in an electrostatic attraction between unlike electrical charges

• This occurs when a metal reacts with a nonmetal

Na+1 + Cl-1 NaCl (table salt)

– Energy and Electrons in Ionic Bonding• Example:

energy + Na+ Na+ + e-

Cl + e- Cl- + energy

Na+ + Cl- NaCl + energy• The energy that is released in steps 2 and 3

is greater that that absorbed in step one and an ionic bond is formed.

–This energy is called the heat of formation.

• Two rules for keeping track of electrons in ionic bonding reactions.

–Ions are formed when atoms gain or lose electrons to achieve a noble gas configuration

–The number of electrons that are lost must equal the number of electrons that are gained.

– Ionic Compounds and Formulas• The formula of a compound describes what

elements are in the compound and in what proportions.

• Compounds that are held together by ionic bonds are called ionic compounds.

• The elements in Group IA and IIA tend to lose electrons for form positive ions

• The elements in Group VIA and VIIA tend to gain electrons to form negative ions.

• Covalent Bonds– A covalent bond is a chemical bond that is formed

when two atoms share a pair of electrons.–H. + H. H:H

– Covalent Compounds and Formulas• Since a pair of electrons is shared in a covalent

bond, the electrons move throughout the entire molecular orbital.

• In the above example, since both hydrogen share the electron pair, each hydrogen has a filled valence shell, since it has the electron configuration of helium.

• Compounds that are held together by covalent bonds are called covalent compounds.

• Covalent compounds form from atoms on the right side of the periodic table

– Multiple Bonds.• In electron dot notations, a pair of electrons

can be represented by a pair of dots : .–This can be a bonding pair or a lone pair

(non-bonding pair).• Bonding pairs can also be represented by

lines connecting atoms.

»H:H = H—H• When one pair of electrons is shared, it is

called a single bond.»H-H

• When two pairs of electrons are shared it is called a double bond.

H H \ / C C / \ H H

• When three pairs of electrons are shared it is called a triple bond.

H-C C-H

• Electronegativity.– Electronegativity is the ability of an atom to

attract bonding electrons.– Elements with higher values have the greatest

attraction for bonding electrons.– The difference in electronegativity can be used

to predict whether a bond will be ionic or covalent.• If the absolute difference is 0.5 or less, the

bond will be covalent.• If the absolute difference is 1.7 or more the

bond will be ionic.

– When the absolute difference is between 0.5 and 1.7 a covalent bond is formed, but one in which the electron pair is not shared equally.

– This type of bond is called a polar covalent bond.

– A polar covalent bond results in areas of partial positive charge and areas of partial negative charge since the electrons spend more time around the more electronegative atom.

• Naming chemical Compounds

• Ionic Compound Names– Ionic compounds that are formed from metal

ions are named by naming the metal ion (electropositive ion) first, followed by the nonmetal (electronegative ion)

– The ending of the nonmetal is changed to end in -ide

– When a metal can have various oxidation states the oxidation state is give by roman numerals in parenthesis after the name of the metal.

Naming the ions

Names of main-group monatomic ions are straightforward. A cation takes the name of the element plus the word "ion."

Na Sr Ba

Na+

sodium ionSr2+

strontium ionBa2+

barium ion

N O Cl

N3-

nitride ionO2-

oxide ionCl-

chloride ion

For anions, the element name has its ending replaced with  ide.

Some transition metals can form more than one ion. Iron, for example, forms both Fe2+ and Fe3+. To name such an ion unambiguously, we use the name of the element, a Roman numeral in parentheses to denote the charge, and the word "ion." Fe2+ and Fe3+ would be iron(II) ion and iron(III) ion, respectively.

• Ionic Compound Formulas–Rules

• The symbol for the positive element is written first, followed by the symbol of the negative element

• Subscripts are used to indicate the numbers of ions needed to produce an electrically neutral compound.

Example calcium chloride

–calcium is Ca2+ and chlorine is Cl-

–in order to balance charges there needs to be two negative charges to balance the 2+ on the calcium

–the formula is therefore CaCl2

Most of the common polyatomic ions are anions, although a few are cations. It is important to know the names, charges, and formulas of all of these ions.

Common polyatomic ion names

Formula Name

NH4+ Ammonium ion

CO32- Carbonate ion

PO43- Phosphate ion

SO42- Sulfate ion

OH- Hydroxide ion

NO3- Nitrate ion

Anions + Cations = ionic compound name

F- Fluoride ion

CO32- Carbonate ion

PO43- Phosphate ion

SO42- Sulfate ion

OH- Hydroxide ion

NO3- Nitrate ion

Cl- Chloride ion

O2- Oxide ion

S2- Sulfide ion

NH4+ Ammonium ion

Na+ Sodium ion

Ca2+ Calcium ion

Fe3+ Iron(III) ion

Ag+ Silver ion

Al3+ Aluminum ion

Ammonium fluorideIron phosphateSilver oxide

Note: Ag has a charge of +1 and oxide has a charge of –2 sothe chemical formula of silver oxide must be Ag2O

What is the correct name for the ionic compound Na2SO4?

A. disodium sulfateB. sodium sulfoxideC. sodium sulfateD. sodium sulfide

The procedures used for naming binary (two-element)molecular compounds are similar to those used for naming ionic compounds:

1. The name of the element farthest to the left in theperiodic table is usually written first.

2. If both elements are in the same group in the periodic table, the lower one is named first.

3. The name of the second element is given an -ide ending. 4. Greek prefixes (Table 2.6) are used to indicate

the number of atoms of each element. The prefix mono- is never used with the first element. When the prefix ends in a or o and the name of the anion begins with a vowel (such as oxide), the a or o is often dropped.

CO2

Carbon Dioxide

H2O

Dihydrogen Monoxide

Carbon tetrachloride isA. CCl4

B. CClO4

C. C2Cl4

D. CCl5

TETRA = 4

• Once you understand chemical names and formulas, you can figure out what chemical compounds are contained in different household products. For example, (A) washing soda is sodium carbonate (Na2CO3) and (B) oven cleaner is sodium hydroxide (NaOH), which is also known as lye.

Using Lewis Dot structure to help you move electrons around

The number of valence electrons of any element is the same as the group number of the element in the periodic table. • For example, the Lewis symbol for oxygen, a member of group 6A, shows 6 dots. •A maximum of eight dots can be placed around a symbol, where each dot represents a valence electron.• Dots are placed above, below, to the left, and to the right of the element symbol. •Each position can accommodate two electrons, and electrons are not "paired" until each of the four positions contains a single electron.

The Lewis dot structure for Oxygen

OOxygen is in group VIA so it has 6 valence electrons

The Lewis dot structure for Chlorine

Clchlorine is in group VIIA so it has 7 valence electrons

The Lewis dot structure for calcium

Cacalcium is in group IIA so it has 2 valence electrons

Making calcium chloride

+Ca Cl Cl

Ca( Cl )2

Lewis dot structure of a compound

NH3

1) How many valence electrons does N have?N is in group VA so it has 5 valence electrons

2) How many valence electrons does H have? H is in group IA so each H has one valence electron

3) How many total valence electrons are there in this molecule?

3 x 1 + 5 = 8You know it had to be 8 because it has NO CHARGE!

Lewis dot structure of a compound

NH3

N

H

H

H

Lewis dot structure and making ammonium ion

NH4+

H+

H

N H

H

H

+

Forces.

• A force is viewed as a push or a pull, something that changes the motion of an object.

• Forces can result from two kinds of interactions.

– Contact interactions.

– Interaction at a distance.

• The net force is the sum of all forces acting on an object.

– When two forces act on an object the forces are cumulative (the are added together.

– Net force is called a resultant and can be calculated using geometry.

• Four important aspects to forces.

– The tail of a force arrow is placed on the object that feels the force.

– The arrowhead points in the direction of the applied force.

– The length of the arrow is proportional to the magnitude of the applied force.

– The net force is the sum of all vector forces.

The rate of movement and the direction of movement of this ship are determined by a combination of direction and magnitude of force from each of the tugboats. A force is a vector, since it has direction as well as magnitude. Which direction are the two tugboats pushing? What evidence would indicate that one tugboat is pushing with greater magnitude of force? If the tugboat by the numbers is pushing with a greater force and the back tugboat is keeping the ship from moving, what will happen?

(A)When two parallel forces are acting on the cart in the same direction, the net force is the two forces added together.

• (B) When two forces are opposite and of equal magnitude, the net force is zero.

• (C) When two parallel forces are not of equal magnitude, the net force is the difference in the direction of the larger force.

• You can find the result of adding two vector forces that are not parallel by drawing thetwo force vectors to scale, then moving one so the tip of one is the tail of the other.

• A new arrow drawn to close the triangle will tell you the sum of the two individual forces.

(A) This shows the resultant of two equal 200 N acting at an angle of 90O, which gives a single resultant arrow proportional to a force of 280 N acting at 45O. (B) Two unequal forces acting at an angle of 60O give a single resultant of about 140 N.

Horizontal Motion on Land.

• It would appear as though Aristotle's theory of motion was correct as objects do tend to stop moving when the force is removed.

– Aristotle thought that the natural tendency of objects was to be at rest.

– Objects remained at rest until a force acted on it to make it move.

• Aristotle and Galileo differed in how they viewed motion.

– Again, Aristotle thought that the natural tendency of objects was to be at rest.

– Galileo thought that it was every bit as natural for an object to be in motion.

• Inertia.

– Galileo explained the behavior of matter to stay in motion by inertia.

– Inertia is the tendency of an object to remain in motion in the absence of an unbalanced force such as:

• friction

• gravity.

Galileo (left) challenged the

Aristotelian view of motion and focused

attention on the concepts of distance,

time, velocity, and acceleration.

Chemical Bonding

Physical Science

Chemical Bonds

• When two or more atoms attach to each other, they form a chemical bond

• Compounds are any two elements chemically bonded– Water– Sugar– Salt– And almost all other substances!!!!

• Electrons are responsible for the type, strength, and size of a chemical bond

Lewis Structures

• Bohr-Rutherford diagrams are large and difficult to show relationships between multiple atoms

• Lewis diagrams are used to show multiple atoms

• Lewis diagrams show only the valence electrons

Lewis Structures

• Valence electrons form the charge of an atom

• Electrons are always trying to get together in groups of 8 (forget shells for a minute)

• Elements that have 8 valence electrons have FULL outer groups

• We call these elements NOBLE or INERT gases, they are found in group 8

Lewis Structures

• Label the Nobel (Inert) gases on your chart

Lewis Structures

• Elements with 1 valence electron are called the Alkali metals (group 1) (Label)

Lewis Structures

• Elements with 2 valence electrons are called the Alkaline Earth metals (group 2) (Label)

Lewis Structures

• Elements with 7 valence electrons are called the Halogens (group 7) (Label)

Lewis Structures

• Consist of– Element Symbol– Electrons in each open spot

Sy

Lewis Structures

• Draw the element symbol• Determine the # valence electrons• Starting at the top, going clockwise, place one

electron in each spot around the element symbol

Cl

7

Lewis Structure

• Draw the Lewis Structure for Aluminum!

Al

Quick Recap!

• Draw the Lewis Structure for Lithium!

• Draw the Rutherford-Bohr Diagram for Lithium!

Li 3P

3N

-

-

-

A note about charges…

• Writing a charge– Valence electrons, Bohr-Rutherford, and Lewis

diagrams are used to determine charge– Charges are a shortcut to determining bonding

properties– RULES OF CHARGE

• IF the # of valence electrons is GREATER than 4, the charge is negative (Mostly)

• IF the # of valence electrons is less than 4, the charge is positive (Mostly)

• Charges are in reference to a full shell of 8

A note about charges…

• For example, Aluminum has 3 valance electrons– The possible charges are +3 OR -5– It either has 3 OVER a full shell, or 5 LESS

than a full shell– Because the number 3 is less than 4, we use

the charge of +3

Charges

• Any element with a charge is called an ION, the charge is an ionic charge

• What are the ionic charges of the elements in the table?

Sodium?

Nitrogen?

Oxygen?

Argon?

Sodium? +1Nitrogen? -3Oxygen? -2

Argon? 0

Charges

Charges

• A few exceptions!– Metals are always a positive charge!!– Non metals are always negative!!– Metalloids can go either way (you are not

responsible for choosing – I will tell you)

• Example: Boron– According to rule of 4’s….its a +3 charge– But since it’s a nonmetal, we use -5!

Rules of Bonding

1. All compounds must have neutral charges

2. (That means the positive charges (cations) and the negative charges (anions) must equal

3. Subscript numbers are used to show the number of ions

4. Coefficients are used to show the number of molecules

Rules of Bonding

2H2OSubscript

2 atoms of H

Coefficient

Subscript1 atom of O

“1’s” are implied and not written

Rules of Bonding

H2O

HH

O

Rules of Bonding

H2O

HHO

Rules of Bonding

• Try this one!

NaCl (table salt)

Na Cl

Rules of Bonding

• Last One!

Aluminum Bromide

Br AlBr

Br

Chemical Bonding

• Several Types including– Covalent Bonds*– Ionic Bonds*– Metallic (only between metals)

Covalent Bonds

• Electrons are shared between two or more atoms

• Covalent bonds can exist between atoms of the same type…for example N-N (N2) or O-O (O2)

• Covalent bonds can form single, double, or triple bonds

• Covalent bonds are strong and usually result in stable molecules

• Carbon always forms covalent bonds and forms the basic molecules for all life substances

Ionic Bonds

• Usually formed by members of the Alkali group (ones with +1 electron)

• Electrons are donated to another molecule

• Between elements from opposite sides of the chart

• Forms crystals (salts) & most dissolve in water

Forming Compounds

1. Write ions with charges

2. Cross charges

3. Write subscripts (omit “1’s”)

4. Use parenthesis if needed

Forming Compounds

• What is the molecular formula of water?

H+1 O-2

H2 O1

H2O HHO

Forming Compounds

• What is the molecular formula of carbon dioxide? C+4 O-2

C2 O4

C2O4

CO2

Yikes!Reduce like a

fraction to lowest denominator

****note****

Forming Compounds

• What is the molecular formula of a compound that has aluminum and sulphur?

Al+3 S-2

Al2 S3

Al2S3

Any guesses on the name?