Download Chemical Bonding Notes for 2016

Why are electrons
important?
• Chemical bonding involves electrons in the
outermost energy level (valence electrons) .
• When chemical bonds are formed, atoms
gain, lose or share electrons to have 8
electrons in their valence level.
• Exception: He (duet rule)
C would like to
N would like to
O would like to
Gain 4 electrons
Gain 3 electrons
Gain 2 electrons
Chemical bonds
• Atoms attempt to fill electron shells.
• When electrons are gained, lost or shared, an
attractive force is formed
called a BOND, which holds elements
together.
-Ionic bonds (metal & non metal)
-Covalent bonds (2 non metals)
-Metallic bonds (2 metals)
Ionic Bonding
• Occurs between a metal and a non-metal.
• Electrons are moved from one atom to another.
• The charged particle that results is called an
ION.
IONS
• When an atom loses (or gives away) its
electrons, it becomes a positively charged.
• This is known as a CATION.
• Metals commonly
form positive ions.
IONS
Continued..
• When an atom gains electrons, it becomes
negatively charged.
• This is known as an ANION.
• Non metals commonly form
negative ions.
Formation of Ions
from Metals
 Positive ions form when the number of electrons are
less than the number of protons
Group 1 metals 
ion 1+
Group 2 metals 
ion 2+
Group 13 metals 
ion 3+
Formation of
Sodium Ion
Sodium atom
Na 
2-8-1
11 p+
11 e0
– e
Sodium ion

Na +
2-8 ( = Ne)
11 p+
10 e1+
Formation of
Magnesium Ion
Magnesium atom
Magnesium ion

Mg 
2-8-2
12 p+
12 e0
– 2e

Mg2+
2-8 (=Ne)
12 p+
10 e2+
Typical Ions with
Positive Charges
(Cations)
Group 1
Group 2
Group 13
H+
Mg2+
Al3+
Li+
Ca2+
Na+
Sr2+
K+
Ba2+
Learning Check
A. Number of valence electrons in aluminum
1) 1 e2) 2 e3) 3 eB.
C.
Change in electrons for octet
1) lose 3e2) gain 3 eIonic charge of aluminum
1) 32) 5-
3) gain 5 e-
3) 3+
Solution
A. Number of valence electrons in aluminum
3)
3 eB.
Change in electrons for octet
1)
lose 3e-
C.
Ionic charge of aluminum
3) 3+
Formation of Ions
from Nonmetals
•
In ionic compounds, nonmetals in 15, 16, and 17
gain electrons from metals
•
Nonmetals gain electrons to achieve a stable octet
•
Nonmetal ionic charge: -3, -2, or -1
Fluoride Ion
unpaired electron

:F

2-7
9 p+
9 e0
+ e
octet

1-
: F:

2-8 (= Ne)
9 p+
10 e-1
ionic charge
Ionic Bond
Properties
• Crystal lattice: repeating 3D pattern
Ionic Bond
Properties
• Strong attraction between ions result in
brittleness.
Ionic Bond
Properties
• High melting points & usually solid at room
temperature.
Ionic Bond
Properties
• Soluble
• Good Conductors
Ionic Bonds:
One Big Greedy Thief Dog!
http://web.jjay.cuny.edu/~acarpi/NSC/salt.htm
1). Ionic bond – electron from Na is transferred to Cl,
this causes a charge imbalance in each atom. The Na
becomes (Na+) and the Cl becomes (Cl-), charged
particles or ions.
Oxidation
Numbers
• The number of electrons that an element can
lose, gain or share is called the
OXIDATION NUMBER.
• Some elements have more than one
oxidation number, example Fe +2 or Fe+3
Formula Weights
Or
Molecular mass
• Formula weight is the sum of the atomic
masses.
• Example- CO2
• Mass, C + O + O
12.011 + 15.994 + 15.994
43.999
Covalent
Bond
• Between 2 or more nonmetal elements.
• Formed by sharing electron pairs.
• Smallest unit of a covalently bonded
compound is called: molecule
• Examples; O2, CO2, C2H6, SiC
Covalent Bond
Properties
• Low melting point & boiling point
• They are not conductors at any state.
.
POLAR COVALENT
BONDS
Electrons are shared but shared unequally
H2O
Polar Covalent Bonds
Unevenly matched, but willing to share
polyatomic
ions
A covalently bonded group of atoms
acting as one that have a positive or
negative charge.
Diatomic
Molecules
• Some elements exist in nature as covalent
bonds.
• Composed of only 2 elements
Diatomic
Molecules
• Nonmetals called the “Heavenly 7”
Heavenly 7
Mnemonic
• HONClBrIF The Chemistry Goose
• Pronounced “Honk-Cool-Brief”
Metallic
Bond
• Formed between atoms of metallic elements
• Metal atoms become cations surrounded by
a pool of electrons
• Good conductors at all states, lustrous, very
high melting points
• Examples; Na, Fe, Al, Au, Co
Metallic Bonds:
Mellow dogs with plenty of bones to go around.
Metallic Bond
Attraction between a metal cation and
shared electrons.
Metals Form
Alloys
• Metals do not combine with metals.
• They form alloys which is a solution of a metal in a metal.
• Examples are steel, brass, bronze and pewter.
Practice
• Compute the mass of the following compounds
round to nearest tenth & state type of bond:
• NaCl;
• 23 + 35 = 58; Ionic Bond
• C2H6;
• 24 + 6 = 30; Covalent Bond
• Na(CO3)2;
• 23 + 2(12 + 3x16) = 123; Ionic & Covalent
The End