COVALENT BONDING

COVALENT BONDS Covalent bonds = Sharing electrons

Octet rule: Atoms still need to become stable by having 8 electrons in their outer energy level!!

Instead of losing or gaining valence electrons, atoms in covalent bonds share valence electrons

These bonds take place between nonmetals and nonmetals

COVALENT BONDS Atoms that combine through covalent bonds

(electron sharing) form molecules

Example:

Nonmetal

COVALENT BONDSCOMPOUND PROPERTIES

Have lower melting and boiling points than ionic compounds

- No bonds to be broken as in ionic compounds

- Molecules are very close to each other, but not bonded

Are soft and “squishy,” compared to ionic compounds

- Molecules move very easily around each other because there are no bonds between them

- These makes them flexible and not hardhttp://www.mhhe.com/physsci/chemistry/animations/chang_7e_esp/

bom1s2_11.swf

COVALENT BONDSCOMPOUND PROPERTIES

They are more flammable than ionic compounds

- Most covalent compounds have carbon and hydrogen which burn very easily with oxygen

- Those without carbon and hydrogen do not burn

They do not conduct electricity in water

- Ion (charge carriers) movement in water is the conduction of electricity

- Covalent compounds do not have ions

They are usually not very soluble in water

- “Like dissolves like” rule

- Compounds dissolve in compounds with similar properties

- Water is polar solvent and most covalent compounds are nonpolar = then do not dissolve in water

SINGLE COVALENT BONDS Made up of two shared electrons

Usually, one of the shared electrons comes from one of the atoms in the bond and the other electron from the other atom in the bond

Halogen (Group 7A) elements exist as molecules of single covalent bonds (more stable)

Example: Hydrogen molecule (H )

2

SINGLE COVALENT BONDSHYDROGEN MOLECULE

H H. .+..HH

Bonding pairEach hydrogen atom has 1 valence electron

Another way to represent the hydrogen covalent bond:

H HBonding pairhttp://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm

SINGLE COVALENT BONDSWATER MOLECULE

H H H

H

OO. .. . .. ....

+ + ...

..

.

OR

H

H O....

http://web.jjay.cuny.edu/~acarpi/NSC/5-bonds.htm

MULTIPLE COVALENT BONDS

Covalent bonds can have more than one pair of shared electrons

Atoms of the elements carbon, nitrogen, oxygen, and sulfur very often form multiple covalent bonds

Multiple bonds can be double or triple covalent bonds

DOUBLE COVALENT BONDSOXYGEN MOLECULE

O O. .+.. OO

Bonding pairs

Each oxygen atom has 6 valence electrons

..... .

.... .. ....

TRIPLE COVALENT BONDSNITROGEN MOLECULE

N N. .+ .. NN

Bonding pairs

Each nitrogen atom has 5 valence electrons

... .

.... ..

http://www.tutorvista.com/content/chemistry/chemistry-i/chemical-bonding/covalent-bond-animation.php

HOW DO ELEMENTS COMBINE?

NAMING COVALENT COMPOUNDS

Names are usually composed of two words

- First is the name of the first element in the formula

- Second is the name of the second element in the formula, but changing the ending to –Ide

Example: HF = hydrogen fluoride

NAMING COVALENT COMPOUNDS

If there is more than one atom of an element in the molecule, then we need to use prefixes to tell us how many are there

Number of Atoms Prefix

1 Mono- (use only for oxygen)

2 di-

3 tri-

4 tetra-

5 penta-

6 hexa-

7 hepta-

8 octa-

9 nona-

10 deca-

NAMING COVALENT COMPOUNDS

Some common names to some very important covalent compounds

Formula Common

NameMolecular Compound Name

H O water dihydrogen monoxide

NH ammonia nitrogen trihydride

N O nitrous oxide (laughing gas)

dinitrogen monoxide

NO nitric oxide nitrogen monoxide

CH methane carbon tetrahydride

2

3

2

4

NAMING COVALENT COMPOUNDS

Examples……

P O = diphosphorus pentaoxide

CO = carbon monoxide

CF = carbon tetrafluoride

2 5

4