November 25, 2014

Chemical Bonding: Ch 7 and 8

http://www.youtube.com/watch?v=QqjcCvzWwww

http://www.youtube.com/watch?v=UR4eG60jjQQ

http://www.youtube.com/watch?v=QXT4OVM4vXI

Chemical BondingA chemical bond is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together.

Why are most atoms bound together?Most atoms are at relatively high potential energy by

themselves and are more stable when combined with other elements!

We will be discussing ionic vs. covalent bonding.Chapter 7- Ionic BondingChapter 8- Covalent Bonding

Chemical Bonding-Vocabulary

A chemical bond

-Attractive force between atoms or ions that binds them together as a unit.

-bonds form in order to:-decrease potential energy (PE)-increase stability

Chemical Bonding-Vocabulary

Chemical Formula

covalentionic

Formula Unit

NaClMolecular Formula

H2O

Chemical Bonding-Vocabulary

Compound

more than 2 elements2 elements

Binary Compound

NaClTernary Compound

NaNO3

Chemical Bonding-Vocabulary

Ion

2 or more atoms1 atom

Monoatomic Ion

Na+

Polyatomic Ion

NO3-

November 25, 2014B) Types of Bonds

Ionic Covalent Metallic

Bond Formation

electrons transferred from metal to nonmetal

electrons shared between two nonmetals

electrons are delocalized among metal atoms.

Type of Structure crystal lattice true molecules "electron sea"

Physical State solid liquid or gas solid

Melting Point high low very high

Solubility in Water yes usually not no

Electrical Conductivity

yes (solution or liquid) no yes (any form)

Other Properties odorousmalleable, ductile, lustrous

Example NaCl, BaCl2, CaO, etc. H2O, NO, NO2 Al, Fe, etc.

1) Ionic Bonding

-Transfer of electrons from one atom to another.

Metal + Nonmetal Ionic Compound

Valence electrons are usually the only electrons used in chemical bonds.

Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level.

Atoms of some non-metals tend to gain electrons or to share electrons with another nonmetal to achieve a complete octet.

Example: Sodium ChlorideThe chemical formula: NaCl because Na+1 and Cl-1

Steps:1. Look at the charge2. Determine the ratio of charges3. Criss-Cross the charges and simplify to the lowest ratio.

Practice Problems:

Determine the charge of the ions and the final formula unit of the following:

1. potassium and iodine

2. aluminum and oxygen

3. magnesium and chlorine

Nomenclature of Ionic Compounds1. Keep the name of the cation the same and change the name of the anion to an -ide ending.

a) NaCl= sodium chlorideb) CaCl2= calcium chloride

c) BaF2=

d) KCl=

e) MgO=

November 25, 2014

Coordination patterns and packing depends on the size of the ions. Remember the trends from the Periodic Table!

Body Centered Cubic Every atom has 8 neighborsEx: (Na, K, Fe)

Face Centered CubicEvery atom has 12 neighborsEx: (Ag, Au, Al, Pb)

Hexagonal close-packedEvery atom ALSO has 12 neighbors but is pattern is different. Ex: (Zn, Mg, and Cd)

http://www.youtube.com/watch?v=ZVqocQLAEr0

http://www.youtube.com/watch?v=Rm-i1c7zr6Q&feature=related

http://www.youtube.com/watch?v=KNgRBqj9FS8Oxidation Numbers (Honors)

-Can figure out from the formula-Unpaired electrons in d orbitals

Fe: (+2 and +3)

Section 7.3 Bonding in Metals*Similar to structure of ionic!The valence electrons of metal atoms can be modeled as a sea of electrons.The valence electrons are mobile and can drift freely from one part of the metal to another.The electrons can drift because of the vacant d orbitals just below their highest energy level.

These orbitals can overlap and the overlapping is what causes the electrons to move about freely.

http://www.drkstreet.com/resources/metallic-bonding-animation.swf

Bonding in MetalsMetallic bonds:consist of the attraction of the free-floating valence electrons for the positively charged metal ions.

November 25, 2014

Crystalline Structure of Metals Alloys:Mixtures composed of two or more elements, at least one of which is a metal.

*Alloys are important because their properties are often superior to those of their component elements.

Types of AlloysSubstitutional- atoms of different components are of similar size.Ex: Brass

Interstitial- solute atoms occupy "gaps" because they are different sizes.Ex: Carbon for steel

Electrons shared between nonmetals

3) Covalent Bonding

Potential Energy Diagram

1. The separated atoms do not affect each other.2. Potential energy decreases as the atoms are drawn together.3. Potential energy is at a minimum when attractive forces are balanced by repulsive forces.4. Potential increases when repulsion between like charges outweighs attraction between opposite charges.

1. 2. 3. 4.

Mr. BrINClHOF

B(r)illiantHarvardNerdsOftenFindC(l)hemistry Interesting

Most elements can form diatomics, HOWEVER, only at very high temperatures.

Kinetic Theory (Random movement)

The "7" exist free at normal conditions.

November 25, 2014

The Nature of Covalent BondingIn covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases.

Why would atoms want to do that?

We will be looking at three different types of covalent bonds:

1. Single Covalent2. Double and Triple Covalent

3. Coordinate Covalent

1. Single Covalent BondStructural formula:Represents the covalent bonds by dashes and shows the arrangement of covalently bonded atoms. One dash represents two electrons.

Unshared Pair:

A pair of valence electrons that are not shared between atoms.

(lone pair or nonbonding pair).

2. Double and Triple Covalent Bonds

Atoms form double or triple covalent bonds if they can attain a noble gas structure by sharing two pairs or three pairs of electrons.

Double covalent bond: A bond that involves two shared pairs of electrons

Triple covalent bond: A bond formed by sharing three pairs of electrons.

3. Coordinate Covalent BondsCoordinate Covalent Bond:

A covalent bond in which one atom contributes both bonding electrons.

In a coordinate covalent bond, the shared electron pair comes from one of the bonding atoms.

Electron-Dot Notation (Lewis Dot Structures)Why the exceptions??

Incomplete Octet: (Group 3A)

Group 3A: Boron 1s2 2s2 2p1 (only 3 valence electrons)

Expanded Octet: (3rd Period)

Beyond the 3rd period with the "d" orbitals

Sulfur: [Ne]3s2 3p4 (6 valence electrons)

Odd-Electron Molecules (Radicals)(NO and NO2 )

Lewis Structures-Steps1. Find the total # of valence electrons2. Arrange atoms-singular atom is usually in the middle (usually carbon)3. Form bonds between atoms (2 electrons)4. Distribute remaining electrons to give each atom an octet.5. If there are not enough electrons to go around, you will have to make double or triple bonds.· Don't forget the exceptions.· Boron and Aluminum only need 6· Sulfur and Phosphorus can have an expanded octet.

November 25, 2014

Lewis Structures-Practice

NH3

CO2

Polyatomic Ions

-a tightly bound group of atoms that have a positive or negative charge and behaves as a unit.

The charge is on the whole ion but the individual components can be held together covalently.

Example is the ammonium ion (NH4+ )

Polyatomic Ions-Practice

ClO4-

NH4+

Exceptions to Lewis Structures1. Odd number of valence electrons

*Central atom will not have an octet*Examples: ClO2 and NO

2. Central atom with less than eight electrons*These compounds tend to be very reactive*Examples: BF3, BH3

3. Central atom with more than eight electrons*Most common exception*Expanded octet*extra electrons fill in the empty d-sublevel*Examples: SF6, XeF4

Resonance

Resonance-Practice

O3

SO3

November 25, 2014

Bond Dissociation EnergiesBond Dissociation Energy:The energy required to break the bond between two covalently bonded atoms.

The larger the bond dissociation energy, the stronger the bondExample: C2H2 vs. C2H6

Nomenclature (Intro)

Nomenclature (Intro)Name the following binary molecular compounds:

1. SF6 is sulfur hexafluoride

2. CO

3. CO2

4. N2 O

5. Cl2 O8

Nomenclature (Intro)

Resonance(Honors Only)

Formal Charge is used to determine the best overall resonance structure.

Handout