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