Covalent Bonding

Covalent Bonding

• Electrons are

shared

between two

nonmetals

•

Weaker

attractive force than ionic bonding

State at SATP Structure

Properties of Molecular Compounds

Typically gases & liquids, but some solids Variable (waxy to brittle) Melting & Boiling Points Low Electrical Conductivity Nonelectrolyte Solubility in Water Variable (low to high) Confused?? Don’t worry…more answers to come

Covalent Bonding

Lone pairs

, valence electrons

not

involved in covalent bond • Formation of hydrogen chloride: H  +  Cl   H  Cl    H - Cl 

Covalent bond

, shared electrons

Structural Formula:

H-Cl (lone pairs are not drawn)

Lewis Structures

H 2 Cl 2 : : H  +  H  H H or H H  Cl  +  Cl     Cl Cl    or Cl Cl   

Structural Formula:

Cl-Cl

Double and Triple Bonds

• Atoms can share 4 electrons to form a double bond or 6 electrons to form a triple bond.

O 2 :   =   N 2 : • The number of shared electron pairs (covalent bonds) that an atom can form is the

bonding capacity

.

Multiple Covalent Bonds

• N • • • • N • • N • • N • N • • N N N

Multiple Covalent Bonds

• O • • • • • C • • • • O • • • O •• • C • • O •• • O •• • C • • O •• •• O •• C •• O ••

Drawing Lewis Structures

1. Arrange the element symbols. • • • Central atoms are generally those with the highest bonding capacity. Carbon atoms are always central atoms Hydrogen atoms are always peripheral atoms 2. Add up the number of valence electrons from all atoms. • For polyatomic ions, add one electron for each negative charge and subtract one for each positive charge.

3. Draw a skeleton structure with atoms attached by

single bonds

.

4. Complete the octets of peripheral atoms.

5. Place extra electrons on the central atom.

6.

If the central atom doesn’t have an octet, try forming multiple bonds by moving lone pairs.

Practice Problems

• Examples – Methanal CH 2 O – Chlorate (polyatomic ion) • p.77-81 #1-15

Strategy for Writing Lewis Structures

Draw Lewis structures and the structural formula for: H HF: 2 NH CH O: 3 4 : :  H F   H O H   H N H  H H  H C H  H  or H F   or H O H   or H N H H H or H C H H

Molecular formula Atom placement Sum of valence e -

For NF : F : 3 N : : F :

Remaining valence e -

Zero: NF 3 is uncharged

Lewis structure

N = 5e F = 7e X 3 = 21e Total 26e -

SAMPLE PROBLEM 10.1

PROBLEM: Writing Lewis Structures for Molecules with One Central Atom

Write a Lewis structure for CCl 2 F 2 , one of the compounds responsible for the depletion of stratospheric ozone.

SOLUTION:

Step 1:

Carbon has the highest bonding capacity and is the central atom. The other atoms are placed around it.

Steps 2-4:

C has 4 valence e , Cl and F each have 7. The sum is 4 + 4(7) = 32 valence e . Make bonds and fill in remaining valence electrons placing 8e around each atom.

Cl Cl C F F

:

Cl

: :

Cl C

:

F

::

F

:

SAMPLE PROBLEM 10.2

PROBLEM: Writing Lewis Structure for Molecules with More than One Central Atom

Write the Lewis structure for methanol (molecular formula CH 4 O), an important industrial alcohol that is being used as a gasoline alternative in car engines.

SOLUTION:

Hydrogen can have only one bond so C and O must be next to each other with H filling in the bonds. There are 4(1) + 4 + 6 = 14 valence e .

C has 4 bonds and O has 2. O has 2 pair of nonbonding e .

H H C O H H

SAMPLE PROBLEM 10.3

PROBLEM: Writing Lewis Structures for Molecules with Multiple Bonds.

Write Lewis structures for the following:

(a)

Ethylene (C 2 H 4 ), the most important reactant in the manufacture of polymers

(b)

Nitrogen (N 2 ), the most abundant atmospheric gas

PLAN:

For molecules with multiple bonds, there is a

Step 5

which follows the other steps in Lewis structure construction. If a central atom does not have 8e , an octet, then e can be moved in to form a multiple bond.

SOLUTION:

H H C

(a)

There are 2(4) + 4(1) = 12 valence e . H can have only one bond per atom. C H H H H C C H H

(b)

N 2 has 2(5) = 10 valence e . Therefore a triple bond is required to make the octet around each N.

: .

.

:

N

.

N

.

:

N

.

N

.

: :

N N

:

Polyatomic Ions

• • Many compounds contain a combination of covalent and ionic bonds.

• E.g. NaOH • OH is a polyatomic ion

bond

between O and H with a

covalent Ionic bond

between Na + and OH -

Coordinate Covalent Bonds

A covalent bond in which both of the shared electrons come from the same atom.

E.g. NH 3 (ammonia) and H + (hydrogen ion) to form NH 4 (ammonium)

Drawing Lewis Structures

COCl 2 HOCl ClO 3  24 ve’s 14 ve’s 26 ve’s  O    Cl C Cl   H O Cl     O  O Cl O      CH 3 OH 14 ve’s H  H C O H  H