Section 3.1:
Compounds
Compounds
 A compound is a pure
substance made up of
two or more kinds of
elements that are
chemically
combined.
 Q: What is a pure
substance?
Chemical Bonds
 Formed when atoms combine together to form
molecules or compounds.
 Two main types:
 Covalent
 Ionic
Covalent Compounds
 Formed from a sharing of electrons between atoms.
 Always formed from non-metals.
 Results in the formation of a molecule.


The atoms in molecules are held together by shared electrons.
ALL atoms end up with the FULL NUMBER of electrons.
 They are ALL satisfied!!!
 Examples:


Water – H2O
Glucose – C6H12O6
Covalent…….cont..
 Covalent compounds (molecules) are best shown with
Lewis Dot Diagrams or a Ball and Stick Model.
 What do you
notice about the
number of electrons
in A?
 What molecule is this? What is it’s formula?
Practice Question –
Draw a Lewis Dot Diagram for each of the following atoms.
Place only the valence electrons.
Atom
Structure
(Put the
symbol in the
middle and
space the
electrons
evenly around
the outside. If
there’s more
than 4, you
must have
pairs.
C
H
O
S
Lewis Dot Structures of Molecules
Formula
Structure of
individual
Atoms
Structure of
Molecule
H2O
CO2
CH4
Pause for Thought
 What is the key idea behind Covalent Bonding?
 Do questions 1-3 on page 75 and 1-3 and 7 on page 79.
Ionic Compounds
 Ionic Compounds form when two ions are attracted to
each other.
 Ions form when atoms loose or gain electrons to become
like the nearest noble gas.
 Q: Which noble gas does the Na+ ion resemble? Cl-?
Ionic compounds cont…
 Look at this diagram again:
 Q: Where did sodium’s extra electron go?
 Q: What does this do to the sodium atom?
 Q: What happens to the chorine atom as a result?
Formation of Ions
Ions
Atoms
Atom
Energy Level Diagram
Ion
Sodium
Sodium
Chlorine
Choride
Flourine
Flouride
Energy Level
Diagram
Symbol
with
Charge
Ionic Compounds cont….
 When a metal atom forms an ion, it becomes
positively charged.
 When a non-metal forms an ion, it becomes negatively
charged.
 These oppositely charged ions attract each other.
 When huge numbers of negative and positive ions
attract each other they form an ionic lattice.
 Positives attract negatives, positives repel positives and
negatives repel negatives.
NaCl
lattice
This shows how
several Na+ and Clions form an ionic
lattice.
You see it as table
salt!!!!
Q: How many
sodium ions are
there for every
chloride ions?
Ionic vs. Covalent Compounds
Ionic
Covalent




 Non-metals only.
Metal and non-metal combo.
Transfer of electrons.
Solid at room temperature.
High melting and boiling
points.
 Not electrically conductive as
solids but very conductive
when dissolved in water.
 Are referred to as salts.
 E.g. CaCO3 – Calcium
carbonate
 Sharing of electrons.
 Do not conduct electricity.
 May be solids, liquids or gases
at room temperature.
 Have many uses.
 E.g. Crude oil has many
covalent compounds mixed
together.
Pause for thought
 Q: What is the main idea behind ionic bonding?
 Do questions 4 and 5 on page 75 and 1-11 on page 79.