Chapter 3
Elements combine to form
compounds
What you will learn
 Distinguish
between covalent and ionic
compounds
 Demonstrate understanding of chemical
names and formulas of ionic compounds
 Differentiate between chemical and
physical changes
Objectives
By the end of the lesson you should be able
to:
 Describe compounds
 Compare and contrast ionic and
covalent compounds
 Describe polyatomic ions
Importance
 Almost
everything in our world is made of
compounds and mixtures of compounds
 Our society depends on the production
and wise use of compounds
Recall: Metals vs Non-metals
 Metals

have positive (+) charges.
Therefore, they want to donate an e- from
their outer shells.
 Most
non-metals have negative (–)
charges.

Therefore, they want to accept an e- into
their outer shells.
Recall

Compounds are made up of 2 or more elements
that have been chemically bonded

Electrons are located in the shells around the
nucleus

Only electrons can move – protons and neutrons
are “locked” in the nucleus

Golden Rule: all atoms want to have full outer
shells and will gain/lose electrons to do achieve
this
Atomic Structure
review
How will sodium achieve a full
outer shell: gain 7 electrons or
lose 1?
 Way easier to lose 1, so has an
overall charge of 1+

How will fluorine achieve a full
outer shell: gain 1 electron or lose
7 electrons?
 Way easier to gain 1, so has an
overall charge of 1
Question
 Where
do the electrons that are gained
when making a full outer shell come
from??
 Where
do the electrons that are lost when
making a full outer shell go??
 ANSWER:
from other atoms!
But how?
Making Compounds
There are two ways to make compounds:
1.
Ionic Compounds: electrons can be
transferred from one atom (losing electrons)
to another atom (gaining electrons)

2.
Covalent Compounds: electrons are shared
between two atoms that are both gaining
electrons
You never has a situation where two atoms are
both losing electrons
Ionic Compounds
 Transfer
of electrons
from a metal to a nonmetal
 The metal have positive
charges because they
are losing electrons
 The non-metals have
negative charges
because they are
gaining electrons
Ionic Bonding Example:
Chlorine and Sodium

How many valence
electrons does sodium
have?


How many valence
electrons does chlorine
have?


1
7
Thus to gain full outer shells –
sodium will donate its outer
shell electron to chlorine
Ionic Bond
 To
show an ionic
bond draw an
arrow to show
where electrons
are moving from
and to
Your Turn
 Draw
a magnesium and oxygen atom
 How would they bond?
 Draw arrows to show where the electrons
would move.
Ionic Compounds as solids
 When
ionic compounds occur as solids
there are more than one pair of atoms
involved
 These
occur as an “Ionic Lattice”
 Notice
the + and –
are in an alternating
pattern
Covalent Compounds

What happens when 2 non-metals try to bond
when they both need to gain electrons?


They have to share electrons to gain full outer
shells!
A molecule is formed when a group of atoms bond
together by sharing electrons
Covalent Bonding Example
(Water (H2O)

How many valence electrons does
hydrogen have?
◦

How many valence electrons does
oxygen have?
◦

2
How many electrons can hydrogen
give to oxygen?
◦

6
When hydrogen and oxygen bond
how many electrons does oxygen
need?
◦

1
1
So how many hydrogen atoms are
needed to make water?
◦
2
Covalent Bonding Example
(Water (H2O)
 Notice
that the
outer shells of
each atom are
overlapping to
show and that
the electrons are
in that “shared
zone”
 Video
Polyatomic Atoms

Covalent and ionic bonds can be found in
the same compound!! WOW!...but how?!?!

It is possible for some molecules to gain/lose
electrons as the atoms combine to form a
compound.
So, because they are gaining/losing electrons
they are called ions....specifically polyatomic
ions
“Poly” means many...so, there are many
atoms in this type of ion


Polyatomic Atoms
 There
are many types of polyatomic ions.
 One kind, Carbonate, helps form the
delicate shell of a robin’s egg and the
enamel on your teeth