IPC 03B Chemical Bonding

Number of Valence ElectronsValence Electrons: Are electrons in the highest

energy level.

The noble gases have 8 electrons.

Gro

up

1 h

as 1

v.e

-

Gro

up

2 h

as 2

v.e

-

Gro

up

13

has

3 v

.e-

Gro

up

17

has

7 v

.e-

Gro

up

18

has

8 v

.e-

Valence electrons are represented using dot diagrams.

Valence electrons (dots) are placed around the four sides of the element symbol.

Electrons (dots) begin to pair up only when no more single spaces are left.

Octet Rule: atoms will gain, lose, or share e- in order to have 8 valence e- and become

stable.

Exception: the first energy level only needs 2 valence electrons to be stable.

So, Helium is stable and will not bond with other atoms.

Stable Atoms

Atoms with less than 8 valence electrons are not very stable.

Atoms with 8 valence electrons are very stable. Helium is stable with two electrons.

Chlorine has 7 valence electrons (not stable).

Chlorine gains an electron to have 8 valence electrons (stable).

Are these elements stable?

A neon atom is stable because it has an octet (8 valence e-).

A sodium atom is unstable because it has only one valence e-.

Stable atoms have full valence shells.

Lithium atoms have 3 e-. Since the 1st energy level only holds 2 e-, lithium has 1 valence e-.

If lithium loses that electron, it will have a full valence shell with 2 e- and an oxidation number of +1.

Li Li +

Net Ionic Charges

Metals will lose electrons to form positive ions.

Nonmetals will gain electrons to form negative ions.

Groups/Families

Group Number Group Name Valence Electrons Oxidation Number

1 Alkali Metals 1 +1

2 Alkaline Metals 2 +2

3-12 Transition Metals 2 Vary

13 Boron Family 3 +3

14 Carbon Family 4 +/4

15 Nitrogen Family 5 3

16 Oxygen Family 6 2

17 Halogens 7 1

18 Noble Gases 8 0

Chemical Bonds

Compounds are made up of more than one atom.

When atoms combine to make molecules, they form chemical bonds.

Types of Bonds:Ionic BondsCovalent BondsMetallic Bonds

Ionic Bonding

Ions: atoms with a positive (+) or negative (-) charge.

Metals tend to lose electrons to form positive ions called cations.

Chloride ion

Sodium ion

• Nonmetals tend to gain electrons to form negative ions called anions.

Bond Formation:

opposite charges attract

electrons are transferred from a metal atom to a nonmetal atom

+11-11

+11-10

+17-17

+17-18

Oxidation Numbers

No

Ion

s!

-1

Write the charges on your periodic table!

6 Steps to Writing Ionic Compounds

1. Identify the (+) ion and the () ion.

2. Write the symbols with their charges.

3. Cross the charges.

4. Remove the charges.

5. Simplify the numbers.

6. Remove the “1”s and write the formula.

1. Magnesium Sulfide

2. Mg+2 S-2

3. Mg-2 S+2

4. Mg2 S2

5. Mg1 S1

6. MgS

______________(+) ion

_________() ion

see periodic table

Both #’s are divisible by

2.

Metal first; then

nonmetal.

Tutorial

Practice Steps

Sodium Chloride

Aluminum Sulfide

1. Identify the (+) ion and the () ion.

2. Write the symbols with their charges.

3. Cross the charges.

4. Remove the charges.

5. Simplify the numbers.

6. Remove the “1”s and write the formula.

Na+1 Cl-1

__________(+) ion

__________() ion

Na-1 Cl+1 Na1Cl1

NaCl

Al+3 S-2Al-2 S+3 Al2S3

Al2S3

_____________(+) ion

__________() ion

Reason: Total Charges = ZeroAluminum Sulfide

Al3+ S2-

S2-Al3+

S2-

Need 2 Al+3 ions

Al2S3

+6 + -6 = 0

Al+3 S-2

-2 +3Need 3 S-2 Ions

Polyatomic Ions (EOC)

Combining Atoms

Positive ions must cancel the negative ions to make a neutral molecule.

Ca2+

-1

-1

Ca(OH)2

If you need more than one polyatomic ion, use ( ).

Aluminum Sulfate

Al3+

Al3+

Need 2 Al+3 ions

Al2(SO4)3

+6 + -6 = 0

Al+3 (SO4)-2

-2 +3Need 3 SO4

-2 Ions

Put ( )’s around the polyatomic ions so you don’t get the numbers confused.

Properties of Ionic Compounds (Salts)

solid, crystalline structure

high melting point

Made up of metal w/ nonmetal

hard or brittle (not malleable)

conduct electricity when melted or dissolved

nonconductor as a solid

Some soluble in water

Covalent Bonding in Action

Covalent Bonding

•Covalent Bond: Shared pair of electrons between two nonmetals.•Covalent compounds are called molecular compounds.

Atoms share electrons in order to get 8 valence electrons. (Remember the Octet Rule) (Exception: only 2 e- for H)

Diatomic Elements7- Up

Diatomic means “2 atoms” These 7 elements exist in

nature as diatomic molecules (covalently bond).

H2 (g) O2 (g) F2 (g) Br2 (l) I2 (s) N2 (g) Cl2 (g)

“HOFBrINCl”

Greek Prefixes

Prefix Meaning

Mono- 1

Di- 2

Tri- 3

Tetra- 4

Penta- 5

Hexa- 6

Hepta- 7

Octa- 8

Nona- 9

Deca- 10

Don’t use prefix “mono” on the first element, only on the second.

Certain vowel combinations are not allowed: oo and aoEx. Don’t write tetraoxide; do write tetroxide.

Naming Molecular Compounds

1) First Nonmetal: (Greek prefix + element name)

2) Second Nonmetal: (Greek prefix + element root + -ide ending)

Practice:

1. CCl4

2. SO3

3. N2O

4. P2O5

5. CO2

6. SF6

Carbon Tetrachloride

Sulfur Trioxide

Dinitrogen monoxide

Diphosphorous pentoxide

Carbon Dioxide

Sulfur Hexafluoride

Writing Molecular Compounds

1) nonmetal with nonmetal: Write the element symbol followed by the Greek prefix as a subscript for both elements.

Practice:

1. Dinitrogen tetroxide

2. Carbon monoxide

3. Sulfur dioxide

4. Phosphorus pentachloride

N2O4

CO

SO2

PCl5

Type of Chemical Bond

Ionic Bonds have ions!Metal & NonmetalPolyatomic ion & NonmetalPolyatomic ion & Polyatomic ionAttraction between pos. & neg. ions

Covalent Bonds have nonmetals!Nonmetal & NonmetalSharing of electrons

Metallic Bonds (free e-)

Metallic BondThe metal is held together by the strong forces of attraction between the positive nuclei of the metallic cation and the “free floating” valence electrons known as a “Sea of Electrons”.

Sea of Electrons