Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Lewis Electron-Dot Structures
In 1920,G.N. Lewis, the American chemist came up with a system to represent
the valence electrons of an atom. This system - known as electron-dot diagrams
or Lewis structures - uses dots to represent valence electrons. Lewis’s system
is a valuable model for covalent bonding.
A Lewis structure shows only the valence electrons in an atom or molecule.
The nuclei and the electrons of the inner energy levels (if any) of an atom
are represented by the symbol of the element.
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Group #
# Valence e-
1
1
2
2
13
3
14
4
15
5
16
17
18
6
7
8
Electron Dot Structure
(example)
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Rules for Electron Dot Structures
1. Each atoms is drawn with its symbol surrounded by one dot for each of
its valence numbers. No more than 2 dots to a side.
2. Determine if you are drawing an ionic or covalent substance.
Ionic – Must show the charges due to lose/gain of electron(s), anions
are to be placed in brackets [ X]2Covalent – Must show the shared pair(s) of electrons
3. No more than 8 electrons around any atom.
(H, He, B, and Be will only have 2)
4. Covalent may have up to 3 bonds between atoms.
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Draw dot structures for CH4
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Draw dot structures for NaCl
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Draw dot structures for H2O
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Draw dot structures for NH4+
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Draw dot structures for CaSO4
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Draw dot structures for MgCl2
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Draw dot structures for CO2
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Draw dot structures for F2
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Naming Covalent Compounds
Covalent compounds made of two elements are named by using a
method similar to the one used to name ionic compounds.
Covalent Compounds usually list the most electronegative element last.
This element will have the “–ide” ending that is usually found on ions.
The first element listed will keep its periodic table name.
For example, SO2
The first element keeps its periodic name -- Sulfur
The last element picks up the “–ide” ending -- Oxide
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Prefixes Indicate How Many Atoms Are in a Molecule
Prefixes are used to tell how many of each element are found in each
molecule. A prefix is added to the name of the first element and one is
added to the second element.
Prefix Number Prefix Number
Mono
1
Hexa
6
Di
2
Hepta
7
Tri
3
Octa
8
Tetra
4
Nona
9
Penta
5
Deca
10
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Prefixes are not used on the first element if there is only one of them.
SO2
Nitrogen Dioxide
Sulfur Dioxide
SO3
NO2
Carbon Monoxide
Sulfur Trioxide
P4 O 6
Tetraphosphorus Hexaoxide
CO
Dinitrogen Tetraoxide
N2O4
The diatomic 7
There are seven molecules that commonly bond with themselves and
form a diatomic molecule (molecule with two atoms). These molecules
are never found in nature as atoms, only in their diatomic form. They
will keep their atomic name.
Hydrogen
Nitrogen
Oxygen
Fluorine
Chlorine
Bromine
Iodine
H2
N2
O2
F2
Cl2
Br2
I2
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Review
Which is the correct electron-dot formula for a molecule of chlorine?
Which electron-dot diagram best represents a compound that contains
both ionic and covalent bonds?
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Review
Which molecule contains a polar covalent bond?
What is the correct Lewis electron-dot structure for the compound
magnesium fluoride?
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Review
Which diagram below shows the correct Lewis electron-dot diagram
for a molecule of phosphorus trichloride, PCl3?
Which Lewis electron-dot diagram is correct for CO2?
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Review
What is the IUPAC name for P2O5?
1. Phosphorus Oxide
2. Diphosphorus Pentaoxygen
3. Diphosphorus Oxide
4. Diphosphorus Pentaoxide
What is the formula for Nitrogen Disulfide?
1. NS
2. N2S
3. NS2
4. N2S2
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Review
Chapter 6 -Covalent compounds
Section 2 - Drawing and Naming Molecules
Review