BONDING
Def: A chemical bond is a link between atoms that results from the electrostatic
attraction of their positively charged nuclei for negatively charged electrons.
I. Elements react to form compounds, e.g. HCl, CH4, H2O, NaCl, SiO2
Combining in a specific way depending on the Electron arrangement i.e. configuration
Periodic trends: Atom size, I.E., E. A, m.p. b.p.
A. 2 Basic ways for bonding to occur-valence electrons, the
outermost e- in an incomplete shell are available for bonding:
1. Electron transfer: form ions (Ionic bond)
lose, gain electrons and their ionic radius changes:
cations Na+ and anions Cl2. Electrons Sharing:(covalent bond)
II. Types of Chemical bonds
A. Bonds are classified by comparing the electronegativities
of the bonding atoms.
B. Ionic bond: One atom gives up one or more e- and another gains one or more eA + B 
A+ :B-
ionic bonding
(EN diff. of 1.7 or more )
C. Covalent bond results from sharing of electrons between two atoms
Fig. 6-3, p. 163
1. nonpolar-covalent bond: the bonding electrons are
shared equally by the bonded atoms
(EN diff. of 0 - 0.3)
e.g. H2
2. polar-covalent bond: atoms have an unequal
attraction for the shared electrons
(EN diff. of greater than 0.3) e.g. EN=2.5 C-O EN=3.5
partial charge
+ or  -
Sample problems 6-1, p. 163; (in class)
p.1
III. Why Chemical Bonding Occurs
Energy in Bonding: (Why?) Fig. 6-5 p. 165
A. Potential energy is lowered when two atoms form a chemical bond.
In nature, changes that decrease potential energy are favored.
B. Chemical bond formation
1. exothermic - products have less potential energy and are more
stable than reactants
2. endothermic: products have more pot. energy and are less stable
than reactants
Often breaking of a chemical bond is endothermic.
C. Covalent, ionic, and metallic bonding all decrease the potential
energy of the combined atoms.
IV. Ionic Bonding
A. electron transfer between outer shells
1s 2s 2p 3s 3p
Na
Cl
B. After e-transfer, atoms are no longer neutral e.g. Na and Cl
1. Na+ ion single excess positive charge
2. Cl- ion single excess neg. charge
1s 2s 2p
3s 3p
Na+
ClCrystal Lattice: ions are arranged systematically in crystals of NaCl
in ratio of 1:1
p.2
V. Relative size of atoms and ions
atom great diff in radius from ion
Metals form + ions called cations
nonmetals form - ions called anions
A. Metallic cations smaller than atoms: the outer shell is removed and the
remaining shells are closer to the nucleus
B. Nonmetallic anions larger than atoms since outer shell octet:
average force of
attraction for each electron decrease as
# protons remains the same
1. Within a group, ion size increases with at # because of shell addition
2. Within a period Grp I, II, III cations show a sharp decrease in size
Grp I & II same electron configuration, greater + charge of II draws
electrons closer
Grp VI & VII anions have identical e. c. but VII anion's greater
nuclear charge pulls in electrons closer
p.3
III. Covalent Bonding and Molecular Compounds
A. Definitions:
1. Molecule is the smallest unit quantity of matter which
can exist by itself and retain all the properties of the original
substance.
2. diatomic: contains two atoms
3. molecular compound: a chemical compound whose simplest
formula units are molecules
4. chemical formula: represents the relative numbers of
atoms of each kind in a chemical compound by using atomic
symbols and numerical subscripts
5. molecular formula: shows the types and numbers of atoms
combined in a single molecule
p.4