Chemical Bonding

Unit 4

Why chemical bonds form?• It takes energy to

separate atoms that are bonded together.

• The same energy is released when chemical bonds form.

• Atoms form bonds to reach a lower energy state.

Valence electron are what get transferred or shared to form the chemical bond

A chemical bond forms when atoms transfer or share valence electrons.

Forming Chemical Bonds

• Octet Rule Atoms will form bonds by: – Sharing– Giving or – Taking

electrons to

complete

their octet

Or be like a Noble Gas

Higher energy farther away from nucleus

Forming Chemical Bonds

• Lithium–Better to lose 1 electron or

to gain 7 electrons?

X

Ionization• Neutral element: # protons = # electrons

-wants to lose an e’

Na 1+

- wants to gain an e’

Cl 1-

OXIDATION #s

Oxidation Numbers

- indicate # of e’ lost or gained

PRACTICE:

Oxygen Potassium Fluorine2- 1+ 1-

What is the oxidation number for sulfur?

1+ 2+ 3+ 0 1- 2- 3-

0% 0% 0% 0%0%0%0%

1. 1+

2. 2+

3. 3+

4. 0

5. 1-

6. 2-

7. 3-

What is the oxidation number for aluminum?

1+ 2+ 3+ 0 1- 2- 3-

0% 0% 0% 0%0%0%0%

1. 1+

2. 2+

3. 3+

4. 0

5. 1-

6. 2-

7. 3-

What is the oxidation number for all halogens?

1+ 2+ 3+ 0 1- 2- 3-

0% 0% 0% 0%0%0%0%

1. 1+

2. 2+

3. 3+

4. 0

5. 1-

6. 2-

7. 3-

What is the oxidation number for all noble gases?

1+ 2+ 3+ 0 1- 2- 3-

0% 0% 0% 0%0%0%0%

1. 1+

2. 2+

3. 3+

4. 0

5. 1-

6. 2-

7. 3-

PRACTICE

• Mg

• Fe (III)

• Cl• S

• Be

2+

3+

1 –

2 –

2 +

• Cu (II)

• Br

• Na

• Cu (I)

• N

2+

1-

1 +

1 +

3 _

Ionic Bonds

• Forms between a metal and nonmetal

• Atoms LOSE or GAIN its valence electrons

• ve’ are transferred from one element to another

+

NaCl - salt

Covalent Bond• Forms between 2 nonmetals

• Atoms SHARE electrons– H wants to give an e’ – O wants to take 2 e’

– SHARE between – highest energy level.

DIATOMIC MOLECULES• Covalent molecules that like to bond

with atoms of the same type

“Have No Fear Of Ice Cold Beverages”

H2

N2

F2

O2

I2

Cl2

Br2

Ionic Covalent

• Gain / Losee’

• 2 opposite charged ions

• Bonds between metals and nonmetals

• Compound

•Share e’

•2 same charged elements

•Bonds between 2 nonmetals

•Molecules

Why do Atoms form Bonds? Are most atoms stable?

Electronegativity

• Electron pairs in covalent bonds may be shared unequally.– Strong electronegativity pulls the e’ more towards

one atom– Group 17 (VII) strong electronegativity– Group 1 (I) weak electronegativity

CopperAtom

CopperAtom

CuCu CuCu CuCu CuCu CuCu CuCu

CuCu CuCu CuCu CuCu CuCu CuCu

CuCu CuCu CuCu CuCu CuCu CuCu

CuCu CuCu CuCu CuCu CuCu CuCu

CuCu CuCu CuCu CuCu CuCu CuCu

CuCu CuCu CuCu CuCu CuCu CuCu

CuCu

CuCu

CuCu

CuCu

CuCu

CuCu

The Atom

Metallic Bond

• Formed between atoms of metallic elements

• Electron cloud around atoms

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

• Examples; Fe, Al, Au, Co

Metallic 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 metalExamples: steel, brass, bronze and pewter.

Identify the type of bonding in the following substance: KBr

Ionic

Covalent

Metallic

0% 0%0%

1. Ionic

2. Covalent

3. Metallic

Identify the type of bonding in the following substance: Fe

Ionic

Covalent

Metallic

0% 0%0%

1. Ionic

2. Covalent

3. Metallic

Identify the type of bonding in the following substance: CuCl

Ionic

Covalent

Metallic

0% 0%0%

1. Ionic

2. Covalent

3. Metallic

Identify the type of bonding in the following substance: NO2

Ionic

Covalent

Metallic

0% 0%0%

1. Ionic

2. Covalent

3. Metallic

Learning Check• Identify the following as Ionic,

Covalent or Metallic

•LiBr Na3N

•FeCl3 CaBr2

•CO Cu

•Steel NO2

Ionic

Ionic

Covalent

Metallic

Ionic

Ionic

Metallic

Covalent

Chemical Formulas – Ionic Compounds

• Transition Metal

• Iron (III) + Oxygen

• Fe 3+ + O 2- =

Fe O = Fe2 O3

• Criss-cross the oxidation #s not the + or- signs

Solving Problems

• Iron and oxygen combine to form a compound. Iron (Fe) has an oxidation number of 3+. Oxygen (O) has an oxidation number of 2–.

• Predict the chemical formula of this compound.

1. Looking for:

– …formula for a binary compound

2. Given– … Fe3+ and O2–

3. Relationships:– Write the subscripts so that the sum of the oxidation

numbers equals zero.

4. Solution– Two iron atoms = 2 × (3+) = 6+

– Three oxygen atoms = 3 × (2–) = 6–

Solving Problems

Fe3+

O2-

3 2x = 6

Solving Problems

Fe3+

+

= +6

Fe3+

O2-

+

O2-

+

O2-

= -6+6-6

0

Solving Problems

Fe3+

O2-

32

Solving Problems

Naming Ionic Bonds• Must be - metal + nonmetal• Given Formula

– Write the name of 1st element– Write the name of the 2nd element – but

change end to “ide”.

• Given Name– Write the Ox #’s above each element– Write the chemical symbol of each

element– Criss-Cross the oxidation numbers

Naming Covalent Bonds• Must be - nonmetal + nonmetal

• Given Formula– Look at the subscript for each element – Use the Greek prefix to show the #

• “mono not necessary on 1st element, but is on 2nd

– Change the ending of the 2nd element to “ide”

• Given Name– Use the Greek prefixes to determine the

subscripts for each element.– Write the chemical symbol then subscript.

Naming Ionic Compounds

• Simple Ionic– Name first element– Root name of 2nd

element (change “ine” to “ide”

– Ex: NaCl• Sodium + chlorine • = sodium chloride

Naming Covalent Compounds• AKA molecular

compounds• Binary Compounds –

have only 2 elements• Name the + ion• Name the – ion (change

“ine” to “ide” AND give the # of atoms

• Ex: CO – carbon monoxide

• Prefix Meaning mono- 1 di - 2 tri - 3 tetra - 4 penta - 5 hexa - 6 hepta 7 octa 8 nona - 9

Formulas• Empirical

– Simplest whole # ratios by which the elements combine

• Ex: CH2O

• Molecular– The actual # of atoms of

each element in the compound

• Ex: 6 x CH2O ---C6H12O6

How many carbon atoms?

Hydrogen?

Oxygen?

Compounds Vs Mixtures• Compounds

– Chemical bonds hold the atoms or ions together

– same # of atoms or ions

– elements proportional

• Mixtures

– Just are placed together

– Can vary

– Can Vary