to the world of

• Chemical Bonding is the joining of atoms to form molecules and compounds

• Atoms bond to achieve a state of stability (stable outer shell of electrons)

• It is the transfer or sharing of electrons

• Bonding occurs during a chemical reaction and results in a chemical change (example: Na+ and Cl-

ions react to give a molecule, NaCl)

Question 1

• What are atoms trying to achieve?

• A – a full inner shell

• B – a stable state

• C – 6 outer electrons

• D – Halogen gas structures

Question 2

• When does bonding occur?

• A - During a physical change

• B – When a current flows in a metal

• C – During a chemical reaction

• D – As a result of heating

Question 3

• What do electrons do during bonding?

• A- They double in mass

• B - They go to new levels

• C - They share or transfer

• D - They move to lower energy levels

• A measure of the attraction an atom has for bonding electrons

• Fluorine is the most reactive non-metal, and therefore has the greatest attraction for the electron – it is the most electronegative element

• On the periodic table, the general trend is that electronegativity increases going up a group and right across a period

• The difference in electronegativites can help predict what type of bond will be formed

Question 4

• Which is the most electronegative atom?

• A – Chlorine

• B – Argon

• C - Francium

• D - Fluorine

Question 5

• Electronegativity shows which trend?

• A- Decreases going down a period

• B – Increases going across a period

• C – Increases going down a group

• D – Decreases going across a group

Question 6

• Electronegativity means:

• A – how easy it conducts

• B – how many electrons it has

• C – the type of anion it forms

• D – the attraction for bonding electrons

Metals Nonmetals

Conduct heat and electricity

Typically shiny

Can be hammered into sheets or drawn into wire

Lose electrons to form cations

80% of elements are metals

Bad conductor of heat and electricity

Brittle, waxy, or gaseous

Cannot be hammered into sheets or drawn into wire

Gain electrons to form anions

20% of elements

Question 7

• What is NOT a property of Non - metals?

• A- Bad conductor of heat and electricity

• B- Brittle, waxy, or gaseous

• C- Cannot be hammered into sheets or drawn into wire

• D- Typically shiny

Question 8

• What is NOT a property of metals?

• A- Conduct heat and electricity

• B- Can be hammered into sheets or drawn into wire

• C- Brittle

• D- Lose electrons to form cations

Question 9

• A new element conducts electricity, is shiny and can be bent into shape. Is it?

• A – Metalloid

• B- Metal

• C- Non metal

• D – A halogen

• Ionic

• Covalent

• Metallic

Question 10

• Which is not a type of bond?

• A- Metallic

• B- Covalent

• C- Allotropic

• D- Ionic

• Occurs between a metal and a nonmetal• Occurs between two atoms with a large

difference in electronegativity (typically 1.7 or greater)

• Electrons are completely transferred, forming atoms with net positive and net negative charge

• Salts are often formed

Continued

• tend to have high melting and boiling points• can't melt them with a Bunsen burner

• very hard and very brittle• conduct electricity when they dissolve in

water

Continued

Question 11

• What type of elements are involved in ionic bonding?

• A- 2 metals

• B- A metal and a non metal

• C- 2 non metals

• D- A noble gas and a metal

Sodium and Chlorine The sodium atom has one valence electron and a very low electronegativity, so it will lose an electron and become an ion with a charge of +1.

The chlorine atom has a very high electronegativity, so it will attract an electron and become and ion with a charge of -1

The reaction is thus: Na+ + Cl-

NaCl (table salt)

Question 12

• In sodium chloride what has happened to the electrons?

• A- One electron has shared

• B- One electron has transferred to Cl+

• C- One electron has transferred to Na+

• D- One electron has transferred to Cl-

• Occurs between atoms with similar or identical electronegativities (difference less than 1.7)

• Atoms “gain” electrons to obtain a stable configuration

• Occurs between two nonmetals• Common examples are diatomic molecules

(Cl2, F2, N2, etc.)

• generally have much lower melting and boiling points

• are soft and squishy (compared to ionic compounds)

• tend to be more flammable than ionic compounds

• don't conduct electricity in water• aren't usually very soluble in water

Question 13

• Covalent bonding occurs between?

• A- 2 metals

• B- A metal and a non metal

• C- 2 non metals

• D- A noble gas and a metal

Question 14

• What happens to the electrons in a covalent bond?

• A- They are transferred

• B- They are shared

• C- They become delocalized

• D- They form a sea of electrons

Chlorine Molecule (Cl2)

Each chlorine atom has seven valence electrons, so by sharing one, the atoms can obtain stable electron configurations.

Question 15

• Chlorine is in group 17. How many electrons does it need to share to have a stable octet?

• A – 0

• B- 1

• C- 2

• D- 3

• Occurs between atoms with low electronegativity

• Occurs between atoms with 1, 2, or 3 valence electrons (many vacancies in shell)

• Electron clouds overlap, allowing electrons to become delocalised (move freely inside the structure)

• Positively charged nuclei and negatively charged electrons hold the metal together with strong forces of attraction

Question 16

• Why are metals good conductors?

• A- They have high melting point

• B – They have delocalized electrons

• C – They have low densities

• D – They are malleable

Question 17

• Which of the following is covalently bonded?

• A - NaCl

• B – CO

• C – KBr

• D – An alloy of copper and zinc (brass)

Question 18

• Which compound will transfer electrons?

• A – NH3

• B – H2O

• C – CH4

• D - CaO

REMEMBER!!

• Electronegativity – the relative ability of an atom in a molecule to attract shared electrons to itself

Polarity

• when a molecule acts like a little magnet

• one side of the molecule has more electrons than the other side

Polarity

• Only covalent bonds can be polar

• A polar covalent bond results when electrons are shared unequally by nuclei

• One atom attracts the electrons more than the other atom

Polarity

• The polarity of a bond depends on the difference of electronegativity.

• This difference also helps to predict which type of bond will form.

• The larger the difference the more ionic the bond will be.

Dipole Moment

• A dipole moment results when a polar molecule has a center for positive charge separate from a center for negative charge

• The arrow starts on the positive side and points to the negative side.

• All polar bonds have a dipole moment.

Dipole Moment

• Ex. Water

Dipole Moment

• The polarity of water affects its properties • Permits ionic compounds to dissolve in it

• Causes water to remain liquid at higher temperature

Can we rank the polarity?

Bond Electronegativity Difference in values

Bond Type Ranking

H - H (2.1)(2.1) 2.1 – 2.1 = 0 COVALENT

S – H

F – H

Cl - H

O – O

O - H

Ions and Compounds

Ions and Compounds

• Lets take a look at this chart.

Ions and Compounds

• Why do the formation of an ion cause the electron configuration to change to a noble gas?

• BECAUSE IT’S STABLE!!!

Ions and Compounds

• Ionic Compounds• When representative metal and nonmetals react,

they transfer electrons in such a way that both the cation and the anion have noble gas electron configurations.

• Covalent Compounds• When nonmetals react they share electrons in a

way that leads to both atoms having noble gas electron configurations

• Octet rule - every atom wants to have eight valence electrons, just like the nearest noble gas

• Duet rule – hydrogen only wants 2 valence electrons

• *one exception* - boron (B) – it only needs 6 valence electrons.

Predicting Compounds

• Chemical compounds are always electrically neutral.

• That helps up figure out formulas.

• Ex. Li+ and F- => LiF

• Practice

• Fe2+ and P3- K+ and S2+

• Mg and Cl Al and O

Practice on your own

What compound would form from these atoms? Ex. Li+ and F- => LiF

• Rb and I

• C and Cl

• P and H

• C and O

Size Does Matter

• When atoms loose or gain electrons their relative size changes.

• Cations are smaller than parent atom

• Anions are larger than parent atom

Size Does Matter

Structure

• All the large anions get packed closely together. • Forms rows and columns

• Small cations fill in the small spaces. • Still in the same rows and columns.

Structure

• Ions are packed together to maximize the attractions between ions