Download chapter 6 sec 2 resonance structure

Chapter 6 section 2
• Covalent bonding
• Molecular compounds
A molecule is a neutral group of atoms that are
held together by a covalent bond
• A molecular compound is a chemical compound whose simplest
units are molecules
• A molecular formula show the types and numbers of atoms
combined in a single molecule of a molecular compound.
• A chemical formula indicates the relative numbers of atoms of
each kind in a chemical compound by using atomic symbols and
numerical subscripts.
Two H atoms bond with one O atom to form
H2O
• if we look at the difference in electronegativity, we see that
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H is 2.1 and O is 3.5. 3.5 – 2.1 = 1.4 so the bond between H and O is
a polar covalent bond.
By definition a neutral group of atoms held together by covalent
bonds is a molecule.
So, the H2O particle is a molecule
H2O is a molecule which makes H2O a molecular compound and a
molecular formula.
But H2O is also a chemical formula because we use atomic symbols
and subscripts to describe it.
Diatomic molecule
• A diatomic molecule is a molecule containing only two
atoms of the same element.
• There are seven elements that exist as diatomic molecules
in nature
• Ex: H2 N2 O2 F2 Cl2 I2 Br2
Formation of a covalent bond
Bond energy is the energy required to break a
chemical bond and form neutral isolated atoms.
Octet rule
• Chemical compounds tend to form so that each
atom, by gaining, losing, or sharing electrons, has
an octet (8) of electrons in it’s highest energy level.
Electron dot notation
• On board
Lewis Structure
• On board
Multiple covalent bonds
• On board
Resonance Structures
Resonance Structures
• Resonance structures refers to bonding in molecules or
ions that cannot be correctly represented by a single
Lewis structure
Resonance Structures
• For example: NH3 – ammonia has only one correct structure
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N
• H H H
Resonance Structures
• But some structures have more than one Lewis Structure;
• O3 - Ozone
•O
O
O
or
O
O
O
Resonance Structures