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COVALENT BONDING
[MH5; Chapter 7]
•Covalent bonds occur when electrons are equally shared between two
atoms.
• The electrons are not always equally shared by both atoms; these
bonds are said to be polar covalent.
• We assume that only electrons in the valence shell are involved in
forming covalent bonds.
• These electrons are simultaneously attracted to both nuclei; a
favourable, lower - energy, arrangement.
• The nuclei are “insulated” from each other by electrons; so the
electrons feel attraction of 2 nuclei.
• Two bonded atoms are in a lower energy state than two separate
atoms; resulting in the formation of a stable covalently bonded
molecule:
H(g) + H(g) !H
2
(g)
• Two electrons are shared; a single bond is formed.
• Lewis dot structure: H H ! H H
• Since each H atom has electron configuration 1s
1
, H atoms form only
one bond:
EXAMPLES:
O
/ \
H — H H — C
R
H H
