Bonding

A Chemical Bond• The forces that hold groups of atoms

together and make them function as a unit• Bonding involves only the valence electrons

• There are 2 types of bonds:– Ionic: Transfer of electrons from a metal and to

a nonmetal

– Covalent: Sharing of electrons between 2 nonmetals

– Note: When 2 metals bond an alloy is formed

Ionic Bonding

• Chemical bonding that results from the electrical attraction between cations and anions is called ionic bonding.

• Cations give up electrons to anions.

• Ionic compounds form between metallic ions and non-metallic ions.

Covalent Bonds

• A covalent bond results from the sharing of electrons between two atoms.

• The most familiar examples of covalent bonding are seen in the interactions of nonmetallic elements with one another. (CO2, NO)

• Diatomic molecules are held together by covalent bonding (N2, O2, F2 Cl2, Br2, I2, As2, H2).

• Electrons are transferred or shared to give each atom a noble gas configuration (stable octet)– This is known as the octet rule

Octet Rule

• Noble gases have a very stable structure and are somewhat unreactive.

• According to the octet rule, atoms bond in order to achieve an electron configuration that is the same as the electron configuration of a noble gas.

• As an example, Chlorine will gain an electron to have 18, which is how many the atom Argon has. These two atoms are said to be isoelectronic with each other.

Lewis Diagrams

• Valence electrons involved in bonding can be represented by Lewis dot diagrams

• A chemical symbol represents the nucleus and the core electrons (not involved in bonding).

• Dots around the symbol represent valence electrons.

Drawing Lewis Diagrams1. Write the element symbol.

2. Draw dots, one for each valence electron

3. Dots should be spread over 4 sides• It does not matter what side the dots are

placed, but do not start to pair dots until there is one on each side

Cl

• Lewis diagrams for the first 20 elements

Representing Ionic CompoundsLewis Diagrams

• Formation of sodium chloride:

Na · + ® [Na]+ [ ]Cl · ·

· ·

·· ··Cl

· ·

· · ···

Bohr Diagram

Lewis Diagram

It takes two Na to satisfy one sulfur.

Lewis Structures for Ionic Compounds

Ba•

• O•••

•••

••O••

••

••Ba

2+ 2-

Mg•

•

Cl•••

••

••Cl•••

••••

••Cl••

••

••Mg

2+ -2

Ba and O

Mg and Cl

BaO

MgCl2

Covalent Bonding

• Formation of hydrogen chloride:

H · + Cl · ·

· ·

··· ® Cl

· ·

· ·

·· ··H ® H - Cl

· ·

· ·

··

Covalent bond, shared electrons

Lone pairs, valence electrons not involved in covalent bond

Structural Formula: H-Cl (lone pairs are not drawn)

Lewis Structures

H · · H+

® Cl Cl ·· ·· · ·

· ·

· ·

· ·

··

H2or H H

Cl2 Cl · ·

· · ···Cl

· ·

· ·

·· · +

or Cl Cl ·· ··

· ·

· · · ·

· ·

® H H

Structural Formula: Cl-Cl

Multiple Bonds

• Atoms sometimes need to share more than a pair of electrons.

• If an atom is sharing two pairs of electrons, this is a double covalent bond.

• If an atom is sharing three pairs of electrons, this is a triple bond.

Double and Triple Bonds

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

• The number of shared electron pairs (covalent bonds) that an atom can form is thebonding capacity.

O2:

N2:

=O O · ·

· · · ·

· ·

·· ··N N

Multiple Covalent Bonds

N••

••

•N N

•

••

•

•

••

•N••

••

•

N N•

•• ••

•N N •

•

••

Multiple Covalent Bonds

C••

••

O••

• •

• •O••

• •

• •CO O

•

••

•••

••

••

••

•CO O ••

•••

••

••

••CO O

••

••

••

••