Bonding

Introduction to Bonding:Chemical bond: the force that holds two atoms together• Bonds may be formed by the

attraction of a cation to an anion ionic bond

• Bonds may be formed by sharing electrons covalent bond

Significance of Bonding

Formation of bonds (or breaking bonds) is a chemical change.Formation of bonds (or breaking bonds) is a type of reactivity.

Octet RuleOctet Rule: atoms will gain, lose, or share electrons in order to acquire the stable electron configuration of a noble gas.Try to have 8 electrons around each atom

Li + F Li F::

::

: ::

This is an example of an ionic compound

Octet RuleSince C only has 4 valence electrons, it can form more than one bond:

Note that C achieves an octet of electrons This is an example of a covalent compound

Learning Check• Draw the Lewis dot structure for

H2

• Draw the Lewis dot structure for F2

• Draw the Lewis dot structure for a water molecule, H2O

Practice Work with your partner to draw the following compounds:

CCl4 NF3H2SSiH4 O2 COCO2SO2NO2

Ionic versus Covalent Bonding

Ionic: electrical force of attraction between a cation and anion; the anion donates both electrons for the bond

cation anion

Each cation in the solid ionic compound is surrounded by anions, and each anion is surrounded by cations. Solid ionic compounds form a crystal lattice.

Na Cl

Endlessly repeating Lattice of Ions

All ionic compounds form crystal lattices, in which the positive and negative ions alternate.

stress

If the ion layers shift slightly ions with the same charge are brought side-by-side causing repulsion.

Ionic compounds have high melting and boiling points. This is due to the strong attraction of the oppositely charged ions. It takes a lot of heat energy to overcome these strong attractions.

Attractions are strongest for smaller ions or ions with greater charge (Mg 2+ O 2- vs. Na + Cl- ). These ionic compounds will have the highest melting and boiling points.

Characteristics of ionic compounds:High melting points and boiling

points (usually solid at room temp)Very hard and crystal-like;

interactions between molecules are strong

Occurs between metals and nonmetals (requires atoms to have very different electronegativity)

High polarity Conduct electricity when meltedTypically dissolve in water

Formation of Ionic Compounds  Reacting Compound

Example Groups General Formula

Simple Binary Ionic Compounds Table

Covalent: sharing electrons to form a bond; each atom contributes an electron to the bond

C OC + O

Representing Covalent BondsCovalent bonds are shown by a line, representing the shared pair of electrons

CH

H

H

H

Multiple BondsCovalent compounds sometimes form multiple bonds between 2 atoms: a double bond:

O O a triple bond:

N N

Multiple BondsDouble bonds are shorter and stronger than single bondsTriple bonds are shorter and stronger than double bondsIt takes more energy to break a double or triple bond

Characteristics of covalent compounds:Low melting points and boiling points

(usually liquid or gas at room temp)Relatively soft and even flexible;

interactions between molecules are weak, allowing the molecules to move

Occurs between 2 nonmetals (requires atoms to have similar electronegativity)

Nonpolar or low polarityPoor conductors of electricity Often do not dissolve in water, but

dissolve in nonpolar liquids

Ionic, Covalent, or Polar CovalentIonic bonds form between metals and

nonmetals with large differences in electronegativity

Covalent bonds form between nonmetals with smaller differences in electronegativity

Some covalent bonds are polar. The bonding atoms have different electronegativity, causing one atom to pull the shared electrons towards it.

Polar Covalent BondsPolar covalent bonds share

electrons unequally

Polarity of Bonds

Comparison of ionic solid and covalently

bonded solidNa Cl

Ionic solid: strong electrostatic interactions

Molecular solid: weak intermolecular forces

Covalent bonds CH4

Summary