IONS
SO FAR . . .
So
far we’ve discussed how to
find the number of protons and
neutrons in an element.
How many electrons do we
have in an element?
WHAT DO YOU THINK?
ANSWER
If
an element is neutral (does
not have a charge), then the
element has the same number
of electrons and protons
All of the (+) from the protons
is cancelled out by the same
number of (-) from the
electrons
IONS
 In
chemical reactions, atoms often
gain or lose electrons (e-) to form
charged particles
 IONS: an atom or group of atoms
that has an electric charge
because it has lost or gained
electrons
 NOTE: From now on, I will
abbreviate (e-) for electrons
VOCABULARY
DISTINCTION
 If
an element has the same number
of protons and electrons (neutral), it
is called an atom
 If
an element has a different
number of protons and electrons
(has a charge), it is called an ion
IONS
 Atoms
start of with a neutral charge
 In other words, they have the same
number of e- and protons
 Example: Oxygen (O) has an
atomic number of 8
 This means it has 8 protons
 Therefore a neutral oxygen atom
also has 8 e-
IONS
 When
an atom gains or loses
electrons the atom forms a charge
 Example: Neutral oxygen (O)
atom has 8 protons and 8
electrons
 In a chemical reaction, O gains 2
electrons
 8 protons (+) and 10 electrons (-)
gives a net (-2) charge
IONS
 Formula
for calculating ion charge:
 #protons - #electrons = ion charge
 How
do we show an ion using a symbol?
 Neutral atom is the normal atomic
symbol
 For example: Neutral oxygen = O
 An ion shows the charge associated
with the atom
 For example: Oxygen with a -2 charge
= O-2
IONS

Calculate the charge on the following
ions and write out the ion symbol:
1. Chlorine (Cl) atom with 18 electrons
2. Aluminum (Al) atom with 10
electrons
3. Copper (Cu) atom with 27 electrons
4. Potassium (K) atom with 18
electrons
5. Sulfur (S) atom with 18 electrons
IONS

Answers:
1. Cl2. Al+3
3. Cu+2
4. K+
5. S-2
 NOTE: When an ion has a (+1) or a
(-1) charge, we only write a (+) or
a (-)
ION TYPES
 Definition
of ions
Cation:
an ion that has a
positive charge
Anions: an ion that has a
negative charge
IONS
 Ions
behave differently than the atoms
from which they are formed.
 Na (neutral sodium)  very reactive
and will explode in pure water
 Na+ (sodium ion)  very stable (is in
the table salt we eat)
 Cations and anions combine together
to form neutral compounds
AGAIN, LOOK AT YOUR
PERIODIC TABLES
 Group
1 (alkali metals): lose 1 e- to
form (+1) charge
 Group 2 (alkali earth metals): lose 2 eto form (+2) charge
 Group 7 (halogens): gain 1 e- to form (1) charge
 Group 16: gain 2 e- to form (-2) charge
 Group 15: gain 3 e- to form (-3) charge
 Transition metals: lose different
amounts of e-
HOW DO WE COMBINE THE
SYMBOLS FOR IONS AND ISOTOPES
Previously,
we looked at how to
show the symbol for atoms that
have a certain number of
protons and neutrons
Today, we will combine this
with the number of electrons
also
EXAMPLE
 How
would you write the symbol for
an atom that has 29 protons, 34
neutrons and 27 electrons?
 Step 1: Find the symbol
 Step 2: Number of protons goes in
the bottom left
 Step 3: Protons + neutrons goes in
the upper left
 Step 4: Charge (protons –
electrons) go in the upper right
ANSWER
63
29
Cu
+2
TRY THESE
1.
2.
3.
An atom with 35 protons, 45
neutrons, and 36 electrons.
An atom with 12 protons, 13
protons, and 10 electrons.
An atom with 10 protons, 10
neutrons and 10 electrons.
TRY THESE


Write down the number of
protons, neutrons and
electrons for the following:
32S-2
16

56Fe+3
26

39K+
19