Chapter 8Chemical Bonding

Octet Rule

Octet Rule: Atoms will gain, lose, or share valence electrons in order to obtain a stable outer shell electron configuration of 8 valence electrons. (H and He only need 2)

Lewis Electron Dot Structures

Lewis Structures – use dots to represent valence electrons

3 6 4 2 7 1 5 8

X

Lewis Electron Dot Structures

Another way

Draw the Lewis Structure for:

1. Phosphorus 2. Chlorine

3. Magnesium Ion 4. Oxygen Ion

Chemical Bonds

1. Chemical Bonds: Attractive forces that hold atoms together due to the mutual attraction between the nuclei and their valence electrons.

2. Three types of Chemical Bonds Ionic Covalent (Polar & Nonpolar) Metallic

Metallic Bonds

Metallic bonds: result from the delocalized sharing of valence electrons between metal atoms.

Example: Aluminum, Copper, Iron

Electronegativity

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

Metals = low values(Ionization energy too)

Nonmetals = high values(Ionization energy too)

Note Trend:Across increaseDown decrease

Types of Bonds

Type Ionic Polar

CovalentNonpolar Covalent

Electronegativity Difference…

>1.7(equal to or more

than 1.7)

1.7>x>0(less than 1.7 but more than zero)

= zero

Valence Electrons are…

Transferred Shared unequally

Shared Equally

How to Recognize…

Metal & Nonmetal

2 Different Nonmetals

2 of the same Nonmetals

Chemical Formula for one example…

NaCl H2O H2

Ionic Bonding

1. Metals lose electrons and form cations . Na +

2. Nonmetals gain electrons and form anions. Cl –

3. Ionic Bonds form due to the attractions between the metal ions and nonmetal ions.

Lattice Energy

1. Lattice Energy is the energy needed to separate an ionic lattice into gaseous ions.

2. Lattice Energy increases with: Increasing charge on the ions LE stronger in MgO than NaCl Decreasing distance between the ions (LE is stronger between smaller radii ions) LE stronger in LiF than in CsBr3. The greater the LE, the higher the melting point.

Explain These Trends in Lattice Energy

1. NaCl > RbBr2. BaO > KF3. CaF2 > BaF2

HW - Textbook

#8.1#8.8#8.12ab#8.14#8.19#8.21#8.22

Covalent Bonds vs Ionic Bonds

Covalent Bonds: form when valence electrons are shared between atoms of 2 nonmetals

Ionic Bonds: form when valence electrons are transferred from a metal atom to a nonmetal atom

Covalent Bonds1. Single Bond – sharing of 1 electron pair

2. Double Bond – sharing of 2 electron pairs

3. Triple Bond – sharing of 3 electron pairs

Bond Length & Strength

Single bonds: Longer Bond Lengths Lowest Bond Energies (weak bonds)Triple bonds: Shorter Bond Lengths Highest Bond Energies (strong bonds)

Bond Polarity

1. Nonpolar Covalent Bond – electrons are shared equally between two atoms

Br2

2. Polar Covalent Bond – one atom exerts a greater attraction for the bonding atoms

H2O

3. The greater the electronegativity difference between the atoms, the more polar the bond.

Which Bond is Most Polar?

C – O or Si – F

B – Br or S - Cl

Rules for Drawing Lewis Structures for Molecules & Polyatomic Ions

1. Find the number of valence electrons in each atom and add them up.

(Note: - ions have gained e-, + ions have lost)2. Draw symbols of the atoms near each other in the

way they will bond. 3. Connect the atoms by single bonds (1 e- pair)4. Complete octets on atoms bonded to the central

atom. (except hydrogen gets 2)5. Place leftover electrons on the central atom.6. If there aren’t enough electrons to give the central

atom an octet, try double or triple bonds.

Do These

Note: The central atom is often written first, but not always. It is usually the less electronegative element.

PCl3 CH2Cl2

HCN BrO3 -