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Chemical Bonding BIOB111 Session 2 (Covalent Bond (Non-polar covalent…
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
doesn't apply to Transition Group Elements
#
Ions
when an atom (form on the period table = no charge) looses/gains one or more electrons to become more stable
Nonmetal
Anion (-ve)
gains
electrons into valence shell
negatively
charged ion
more electrons (negatively charged) than protons (positively charged)
Metal
Cation (+ve)
looses
electrons out of their valence shell
positively
charged ion
more protons (positively charged) than electrons (negatively charged)
Transition Group
Element Cations
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)
Ionic Bond
combination of
metal cation +
and
nonmetal anion -
bonding between charged ions - attraction between positive and negative ions
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
Covalent Bond
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
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
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
equal sharing of electrons between atoms
Polar
covalent
bonds
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-)
Polyatomic ions
contain more than 1 atom
have an overall charge (
mostly negative
)
there is only 1 polyatomic cation (ammonium)
Lewis symbols/
notation
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
