Chapter 7

7-1
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How are ions different from atoms?

An ion is an atom that has gained or lost
one or more electrons.

An ion is like an atom, but the number of
electrons does not equal the number of
protons.

The following equation shows the
formation of a sodium ion from a sodium
atom.
Na
Na+ + e-

Using the same name for both the atom
and the ion indicates that the nucleus is
unchanged.

The ion still has same number of protons
and neutrons, like the atom.
Changes in electron arrangements
change chemical properties.

Cations- ions with a positive charge.
 They have more protons than
electrons.

Anions- ions with a negative charge.
 They have more electrons than
protons.

Collections of cations are never found
without a similar number of anions nearby.

This happens because the charges must
be balanced.

The concept of having equal numbers of
opposite charges is called
electroneutrality.
Many simple ions have a noble gas
configuration.

Atoms and ions with the same electron
configuration are said to be isoelectronic
with each other.
Transition metals form stable ions
too.

Not all simple ions are isoelectronic.

Transitions metals, for example, are all
cations.
Concept check

How does an atom form a negative ion?

How does an atom form a positive ion?
Names and Formulas for Ions

Ions borrow their names from the names
of elements.
When an element forms two or more ions,
the ions are distinguished by roman
numerals to indicate charge. (transition
metals only)
Cu+ copper (I) ion
Cu2+ copper (II) ion


An ionic compound composed of a simple
cation and a simple anion is called a
binary ionic compound.

Common table salt
Na+Cl-

Binary ionic compounds are easy to name.

Bi- means two. In this case two elements.

To name a simple anion, just add –ide to
the end of the element name.

Cl- is the chloride ion.

Naming binary compounds is simple.

The name has two words:
 The
name of the cation (the positive ion)
Followed by…
 The name of the anion (the negative ion)
Na+Cl-
- sodium chloride
Writing Formulas

The formulas must indicate the numbers of
anions and cations.

You must combine cations and anions in
such a way that the negative charges
equals the positive charges.

Subscripts are used to denote the number
of ions represented in the compound.

Example:
Mg3N2
How To:
What is the formula for aluminum oxide?
 Symbol for aluminum cation : Al3+
 Symbol for oxide anion :O 2

Step 1: Write the ions
side by side.

Step 2: Draw arrows
that cross each other.
Al3+ O2-
Al3+
O2-

Step 3: Put the
number of charges at
the ends.
Al3+
2
O23

Step 4: Write the formula as follows:
a.) write the positive ion without its charge
Al
b). Write the number as a subscript
Al2
c.) write the negative ion without its charge
Al2O
d.) write the number as a subscript
Al2O3
FINISHED!!