Chemical Bonding
BIOB111
Session 2

Valency

bonding power of an atom

electrons in the outer most shell of the atom

Group 1 - 1 valence electron

Group 2 - 2 valence electrons

Group 3 - 3 valence electrons

Group 4 - 4 valence electrons

elements in the same group on the periodic table have the same number of valence electrons

maximum number of valence electrons = 8

Octet Rule

atoms of elements tend to react together in order to achieve a stable outer shell of 8 valence electrons

applies to Groups I. A to VII. A (Representative Group Elements)

to form molecules, elemental atoms LOOSE, GAIN or SHARE their valence electrons to produce a stable arrangement of their valence electrons

Ions

when an atom (form on the period table = no charge) looses/gains one or more electrons to become more stable

Nonmetal
Anion (-ve)

Metal
Cation (+ve)

doesn't apply to Transition Group Elements #

Transition Group
Element Cations

Ionic Bond

combination of metal cation + and nonmetal anion -

bonding between charged ions - attraction between positive and negative ions

Covalent Bond

complete transfer of valence - GIVE OR TAKE

generates two oppositely charged ions

ionic compounds do not exist as molecules, they have a definite ratio = their formulas

  • NaCl = 1:1
  • MgCl2 = 1:2

Polyatomic ions

contain more than 1 atom

have an overall charge (mostly negative)

there is only 1 polyatomic cation (ammonium)

atoms SHARE their valence shell electrons to achieve stable state (Octet rule) #

doesn't rely on positive or negative charge

only form between non-metal atoms

Lewis symbols/
notation

overlap between electron shells/orbitals (only ones sharing electrons)

Bonding vs.
Nonbonding
Electrons

Bonding
pairs of valence of electrons that are shared between atoms in a covalent bond

Nonbonding
pairs of valence electrons that are not involved in electron sharing

Non-polar
covalent bonds

Single
sharing 1 pair of electrons

Double
sharing 2 pairs of electrons

Triple
sharing 3 pairs of electrons

Polar
covalent
bonds

Oxygen

  • 2 single bonds
  • 1 double bond

Nitrogen

  • 3 single
  • 1 single and 1 double
  • 1 triple
  • bond dependent on what the other atoms are

Carbon

  • all 4 valence electrons unpaired
  • 4 single
  • 2 single and 1 double bond
  • 2 double bonds
  • 1 single and 1 triple

Electronegativity

the ability of an atom in a molecule to attract shared electrons to itself



increases from left to right going across the Periodic Table

decreases going down a Group in the Periodic Table

nonmetals have a high electronegativity

gains electrons into valence shell

negatively charged ion

more electrons (negatively charged) than protons (positively charged)

looses electrons out of their valence shell

positively charged ion

more protons (positively charged) than electrons (negatively charged)

looses electron/s out of their valence shell. Can form more than one cation with 3 exceptions (Ag+, ZN2+, Cd2+)

can form more than one type of cation (at least 2)

Octet rule DOES NOT apply

Nomenclature: Roman numeral in bracket after the name of the metal to indicate charge

Fe2+ Iron (II) Ferrous
Fe3+ Iron (III) Ferric
Cu+ Copper (I)
Cu2+ Copper (II)

electrons spend more time around the atom with higher polarity

the more electronegative the more the electrons are attracted to it

unequal sharing of valence electrons between atoms

intermediate between extremes of covalent and ionic bonds

δ+ and δ-

H2O: H(δ+)‒O(δ-)‒H(δ+)
‒OH: ‒O(δ-)‒H(δ+)
HF: H(δ+)‒F(δ-)

equal sharing of electrons between atoms