C AT I O N S A N D A N I O N S

IONS

OBJECTIVES

• When you complete this presentation you will be able to …• determine the number of valence electrons in an atom of

a representative element.• explain how the octet rule applies to atoms of metallic

and nonmetallic elements.• describe how cations form.• describe how anions form.

VALENCE ELECTRONS

• Valence electrons• The total number of s- and p-electrons• For Groups 1 and 2, it is the same as the group number• For Groups 13 – 18, it is the group number minus ten

• Electron dot structures• Illustration of the number of electron dot structure• It is a combination of both• Paired electrons (lone pairs).• Single electrons.

• Octet Rule• Most atoms will want a total of 8 electrons as shared

bonding electrons and lone pairs.

CATIONS

• Definition:• Cations are ions with a positive charge.• Due to a loss of one or more electrons

• In general, metals become cations.

• Formation• For groups 1, 2, and 13, the loss of electrons will help to

bring the atoms closer to an octet• Closer to the electron configuration of a noble gas.

• Group 1 elements lose one electron.• Group 2 elements lose two electrons.• Group 13 elements lose three electrons.

CATIONS

• For example:

Na (1s2 2s2 2p6 3s1) → Na+ (1s2 2s2 2p6) + e-

Mg (1s2 2s2 2p6 3s2) → Mg2+ (1s2 2s2 2p6) + 2 e-

Al (1s2 2s2 2p6 3s2 3p1) → Al3+ (1s2 2s2 2p6) + 3 e-

ANIONS

• Definition:• Anions are ions with a negative charge.• Due to a gain of one or more electrons

• In general, nonmetals become anions.

• Formation• For groups 15, 16, and 17, the gain of electrons will help

to bring the atoms closer to an octet• Closer to the electron configuration of a noble gas.

• Group 15 elements gain three electrons.• Group 16 elements gain two electrons.• Group 17 elements gain one electron.

ANIONS

• For example:

P (1s2 2s2 2p6 3s2 3p3) + 3 e- → P3- (1s2 2s2 2p6 3s2 3p6)

S (1s2 2s2 2p6 3s2 3p4) + 2 e- → S2- (1s2 2s2 2p6 3s2 3p6)

Cl (1s2 2s2 2p6 3s2 3p5) + e- → Cl- (1s2 2s2 2p6 3s2 3p6)

CHECK

• What is the ion produced by each of the following elements?

F N S

O K Na

Ga Sr O

Ca I Ra

CHECK

• What is the ion produced by each of the following elements?

F- N3- S2-

O2- K+ Na+

Ga3+ Sr2+ O2-

Ca2+ I- Ra2+