The Octet Rule and forming Ions

http://njctl.org/video/?v=iO8YcvrugDg

The Octet Rule
and Forming Ions

Return to Table
of Contents

Atoms tend towards having a full outer shell consisting of:

·2 electrons in their outer s-orbital
·6 electrons in their outer p-orbital

That yields an outer electron configuration of ns2p6

Where "n" is the element's highest principal quantum number.

The number "n" is also equal to the period in which the atom is located.

Octet Rule

Atoms tend towards having a total of 8 valence electrons.

This can also be called an octet of valence electrons.

This is why the ideal gases (Group 18) are nonreactive.

They have an outer electron configuration of ns2p6, so they want to
neither gain nor lose electrons.

They are stable.

Octet Rule

Valence Electrons

Valence electrons are usually the electrons in the outermost s and
p subshells.

Valence electrons determine the chemical properties of an element.

Valence
electron

Valence Electrons

The number of valence electrons in an atom in the Main Group
(Groups 1, 2, and 13-18) is the last digit in the group number.

·For example, atoms in group 2 have 2 valence electrons.

·Atoms in group 17 have 7 valence electrons.

The number of valence electrons in groups 3 - 12, the transition
metals, can vary and cannot be determined by their Group
Number.

Valence Electrons

1 2 3 4 5 6 7 8

1 or more

There is one exception:
helium has only 2 valence electrons.

Number of valence
electrons in neutral atoms:

Cations are positive and are
formed by elements on the
left side of the periodic table
(the metals).

Ions

Anions are negative and
are formed by elements on
the right side of the periodic
table (the nonmetals).

Ions are atoms or groups of atoms that have become charged
by either gaining or losing electrons.

The Formation of Cations

Main Group metals usually give up valence electrons so as to
have 8 electrons in their outermost shell.

This often results in their outer shell having a noble gas electron
configuration (ns2p6).

Here, sodium (Na) loses its valence electron to become a cation
with the same electron configuration as neon.

Na : [Ne] 3s1 Na+1 : [Ne]

1s

2s

2p

3s

1s

2s

2p

3s

Loss of
valence
electron

The Formation of Cations

Shown below are electron configurations of the sodium cation Na+1
side-by-side with the electron configuration of neon (Ne).

The difference is that neon is electrically neutral while the sodium
ion has a charge of +1.

Na+1 : [Ne]

Ne atom

1s

2s

2p

3s

1s

2s

2p

3s

The Formation of Cations

Na atom

Na+ ion

loses e-

11p
11e-
11p
10e-

The Na+ ion is smaller than the Na atom since it's outer shell is no
longer occupied.

Group 2 cations
always have a
charge of +2.

The Formation of Cations

1

2

Group 1 cations
always have a
charge of +1.

For example, Mg will
lose two electrons to
become Mg2+.

The Formation of Cations

1

2

For example, Na will
lose one electron to
become Na+.

Mg

Mg2+

2e-

+

Na

Na+

e-+

The + symbol in Na+
indicates 1 unit of
positive charge.

The 2+ symbol in Mg2+
indicates 2 units of
positive charge.

Nonmetals usually gain valence electrons.

The result is a noble gas electron configuration of
8 valence electrons.

The Formation of Anions

Cl: [Ne] s23p5

Cl-: [Ne] 3s23p6

1s

2s

2p

3s

Gain of
valence
electron

3p

1s

2s

2p

3s

3p

The Formation of Anions

Shown below are electron configurations of the chlorine anion Cl-1
side-by-side with the electron configuration of argon (Ar).

They look the same. The difference is that argon is electrically
neutral while the chlorine ion has a charge of -1.

Cl-: [Ne] 3s23p6

1s

2s

2p

3s

3p

1s

2s

2p

3s

3p

Argon atom [Ar]

The Formation of Anions

Cl atom

Cl- ion

Gains an e-
17P

17e-
17p

18e-

The Cl- ion is larger than the Cl atom since it has an additional
valence electron.

The Formation of Anions

15 16

17
Group 15 anions always have a charge of 3-

Group 16 anions always have a charge of 2-

Group 17 anions always have a charge of 1-

Multiple Choice

1 How many valence electrons does potassium have?

• 3

• 1

• 19

• 4

Multiple Choice

2 How many valence electrons does
Aluminum have

• 5

• 7

• 3

• 27

Multiple Choice

How many valence electrons does Barium
have?

• 1

• 2

• 52

• 3

Multiple Choice

Metals tend to __________ electrons and
nonmetals tend to __________ electrons.
A gain, gain

• lose, lose

• gain, lose

• lose, gain

• gain, gain

Multiple Choice

Anions tend to be __________ and cations
tend to be __________.

• metals, metals

• nonmetals, nonmetals

• nonmetals, metals

• metals, nonmetals

Multiple Choice

This is the ion formed from a calcium atom.

• Ca+

• Ca2+

• Ca-

• Ca2-

Multiple Choice

Phosphorous forms an ion with a charge of
__________.

• 1+

• 2-

• 3-

• 3+

Multiple Choice

Aluminum forms an ion with a charge of
__________.

• 2+

• 1-

• 2_

• 3+

Multiple Choice

Of the following, __________ contains the
greatest number of electrons.

• P3+

• P

• P2-

• P3-

Multiple Choice

Oxygen forms an ion with a charge of __________.

• 2-

• 2+

• 3+

• 3-

Multiple Choice

Iodine forms an ion with a charge of __________.

• 7-

• 1+

• 2-

• 1-

Multiple Choice

This is the ion formed from nitrogen.

• N-

• N3+

• N3-

• N3+

Multiple Choice

Predict the charge of the most stable ion of S.

• +3

• -1

• +6

• 2-

Multiple Choice

What would be the expected charge on the gallium (Ga)
ion?

• +1

• +2

• +3

• +13