Post on 06-Oct-2020
Bonding: An Overview
LHSE Presents
Molecules and Compounds
Bonding: An Overview
• What is a bond?
• Bonding and Energy
– Bond Dissociation Energy
– Underlying Forces
• Types of bonds
– Covalent
– Polar Covalent
– Ionic
– Metallic
• Bonding Topics in other Lectures
What is a Bond?
A bond is the joining of two or more
atoms or ions under a force of attraction
When ANY atoms or ions join they
are considered a compound
before
after
Release
energy
Bonding and Energy
Reaction coordinate
Favorable
time
ener
gy
reactants
products
Activation
energy
Bonding and Energy
time
ener
gy
Consume
energy
before
after
Reaction coordinate
Unfavorable
bond
dissociation
energy
braking
bonds takes
energy!
Bonding and Energy
time
ener
gy
Consume
energy
before
after
Reaction coordinate
Unfavorable
+ +
- -
- -
-
-
1. Electrons (-) in Atom A are ATRRACTED to nucleus (+) in Atom B
2. Electrons (-) in Atom B are ATRRACTED to nucleus (+) in Atom A
3. Electrons (-) in Atoms A and B REPULSE each other
4. Nuclei (+) in Atoms A and B REPULSE each other
Atom A Atom B
Bonding: Underlying Forces
Distance between nuclei
Pote
nti
al E
ner
gy
Net attraction
Net repulsion
+
-
-
-
Bond length
Bond Dissociation
Energy
1. e- in Atom A are ATRRACTED nucleus in Atom B
2. e- in Atom B are ATRRACTED to nucleus in Atom A
3. e- in Atoms A and B REPULSE each other
4. Nuclei (+) in Atom s A and B REPULSE each other Atom A Atom B
+
-
-
-
Types of Bonds
CHEMICAL
• Within a compound
• Stronger
INTERMOLECULAR
• Between compounds
• Weaker
• van der Waals
• dipole
• hydrogen bonds
1. Covalent Bond:
• 2 Non-metal atoms share
some electron(s); ~equally
• molecule
• Bond drawn as line; C-H
• Orbitals overlap
1. Covalent
H
H
H
H C
Types of Bonds
CHEMICAL
• Within a compound
• Stronger
Types of Bonds
CHEMICAL
• Within a compound
• Stronger
1. Covalent
2. Polar covalent
2. Polar Covalent Bond:
• 2 Non-metal atoms share
some electron(s); unequally
• Partial charges ( +, -)
• Molecule
• Bond drawn as line; O-H
• Orbitals overlap
+
+
-
3. Ionic Bonds:
• results from the attraction of a
positive ion to a negative ion
• Often a metal (cation) to
non-metal (anion).
• A compound
• No orbital overlap
1. Covalent
2. Polar covalent
3. Ionic
Types of Bonds
CHEMICAL
• Within a compound
• Stronger
Na+ Cl-
Types of Bonds
CHEMICAL
• Within a compound
• Stronger
1. Covalent
2. Polar covalent
3. Ionic
4. Metallic
4. Metallic Bonds:
• Pure metals
• Valence electrons are not
strongly held by atoms nucleus.
• Delocalized valence electrons
• Sea of electrons around an array
of the positively charged core of
atoms
+
+
+
+
+ +
- -
-
- - -
- -
- -
-
-
-
H
H O
H
H
H
H C
covalent polar covalent ionic
A B
Electrons spend EQUAL
time around A and B
A B
Electron spend MORE
time around A than B
A B - +
Types of Bonds
How well do the share electrons?
Sharing means time!
Electron spend ALL
the time around A
covalent polar ionic
sharing
Electronegativity Electronegativity (EN): The capacity of an atom
in a molecule to attract shared electrons from
another atom
Difficult to actually measure
dec
rease
increase
Artificial scales are used to give relative strengths
This scale goes from 0.8 to 4.0
Electronegativity
Bond type between 2 atoms (AB):
1. Get the electronegativity for both atoms
2. Subtract the smaller value from the larger one
3. Compare result of subtraction to the bond scale.
1 2 3 0 0.4
ionic covalent polar
Electronegativity
Bond type between 2 atoms (AB):
1. Get the electronegativity for both atoms
2. Subtract the smaller value from the larger one
3. Compare result of subtraction to the bond scale.
1 2 3 0 0.4
ionic covalent polar
Bond type between 2 atoms (AB):
1. Get the electronegativity for both atoms
2. Subtract the smaller value from the larger one
3. Compare result of subtraction to the bond scale.
Electronegativity
Determine the bond type for:
C-H
2.5 2.1 2.5 2.1 - = 0.4
D EN
1 2 3 0 0.4
ionic covalent polar
Bond type between 2 atoms (AB):
1. Get the electronegativity for both atoms
2. Subtract the smaller value from the larger one
3. Compare result of subtraction to the bond scale.
Electronegativity
1 2 3
ionic covalent polar
0 0.4
Determine the bond type for:
Na Cl
0.9 3.0 3.0 0.9 - = 2.1
D EN
Electronegativity Bond type between 2 atoms (AB):
1. Get the electronegativity for both atoms
2. Subtract the smaller value from the larger one
3. Compare result of subtraction to bond scale.
1 2 3 0 0.4
Determine the bond type for:
O-H
3.5 2.1 3.5 2.1 - = 1.4
D EN
ionic covalent polar
Bonding Topics in other Lectures
Valence electrons : Covalent Bonding
Simple dot structures
Topic: Lecture
Formula Unit: Ionic Bonding
Lattice
Compound & : Naming Compounds
Polyatomic naming
RECAP
• A bond is the joining of two or more atoms or ions under a
force of attraction
• When atoms or ions join they are considered a compound
• Bond formation is Favorable when energy is released upon
bonding
• The energy for breaking a bond is called the bond dissociation
energy
• Bond formation is Unfavorable when energy is consumed upon
bonding
• Bonding (A-B) is driven by the net sum of 4 forces:
1. e- in Atom A are ATRRACTED nucleus in Atom B
2. e- in Atom B are ATRRACTED to nucleus in Atom A
3. e- in Atoms A and B REPULSE each other
4. Nuclei (+) in Atoms A and B REPULSE each other
RECAP
• When the distance between nuclei is plotted against energy:
– The minimum energy is where the net attraction is at its maximum.
• The energy required to break the bond: bond dissociation energy
– The distance between nuclei, at the minimum energy, is the bond length
• There are 4 types of chemical bonding covered in this lecture:
1.Covalent
• atoms share some electron(s) ~equally; molecule
2.Polar covalent
•atoms share some electron(s) ~unequally; molecule; ( +, -)
3.Ionic
• results from the attraction of a cation to an anion; compound
4. Metallic
• Sea of e- around an array of the positively charged core of atoms
• The difference in electronegativity between 2 atoms determines
their bond type
– 0-0.4 covalent; 0.5-1.9 polar covalent; >2 ionic
Go check out the Covalent
Bonds and Ionic Bonds
lectures!