Ions

Chapter 7 Section 1

Valence Electrons

• Electrons in the highest occupied energy level of an element

• The number of valence electrons largely determines the chemical properties of an element

• The group number of the representative elements corresponds to the number of valence electrons

Lewis Structure

• The valence electrons are the only electrons used in chemical bonds.

• Therefore, only the valence electrons are shown in an electron dot structure also called a Lewis Structure

• Electron dot structures show the valence electrons as dots

Lewis Structures

• N

• O

• Na

• B

The noble gases are unreactive in chemical reactions because they

all have 8 valence electrons except for He which has 2.

Octet Rule

• Gilbert Lewis explained why atoms form certain kinds of ions and molecules

• He called his explanation the octet rule: In forming compounds, atoms tend to achieve the electron configuration of a noble gas

• An octet is a set of 8 electrons (noble gases have 8 valence electrons)

Octet Rule

• Elements will behave differently based on the type of element

• Metals will lose their valence electrons so that their last energy level will have 8 valence electrons (Sodium wants an electron configuration like Ne)

• Nonmetals will gain electrons or share electrons with another nonmetal to gain electrons so the current energy level is an octet (Cl wants an electron configuration like Ar)

Ions

• Atoms are electrically neutral because it has equal numbers of protons and electrons

• An ion forms when an atom or groups of atoms loses or gains electrons

7.1

Formation of Cations

• An atom’s loss of valence electrons produces a cation or a positively charged ion

• Cations are produced by the loss of valence electrons from a metal

• The name of the cation has the same name as the element

• The sodium atom forms the sodium cation

Formation of Cations

• Sodium has 11 electrons, including 1 valence electron

• The sodium Ion has an electron configuration of Ne

• Sodium is now left with an octet

7.1

Formation of Cations

• The electron configuration of the sodium ion is the same as that of a neon atom.

7.1

Loss of a valence electron

Formation of Cations

• Using electron dot structures, you can show the ionization more simply.

7.1

Formation of Cations• A magnesium atom attains the electron

configuration of neon by losing both valence electrons. The loss of valence electrons produces a magnesium cation with a charge of 2+.

7.1

Formation of Cations

• Cations of Group 1A elements always have a charge of 1+.

• Cations of group 2A elements always have a charge of 2+.

• Cations of group 3A elements always have a charge of 3+

7.1

Transition Metal Cations

• Transition metals will not lose electrons to match the noble gas before or after it.

• Silver would have to lose eleven to match krypton and gain seven to match xenon

• Instead it will lose its 5s1 electron• Pseudo noble gas configuration

• Ag 1s22s22p63s23p64s23d104p65s14d10

• Ag+ 1s22s22p63s23p64s23d104p64d10

Formation of Anions• The gain of negatively charged electrons by

a neutral atom produces an anion.• The name of an anion typically ends in -ide.– Chlorine becomes Chloride– Oxygen becomes Oxide

• Because they have almost full valence shells nonmetal elements gain noble gas configuration by gaining electrons

7.1

Formation of Anions

• A gain of one electron gives chlorine an octet and converts a chlorine atom into a chloride ion.

• It has the same electron configuration as the noble gas argon.

7.1

Formation of Anions

• Both a chloride ion and the argon atom have an octet of electrons in their highest occupied energy levels.

7.1

Gain of valence electrons

Formation of Anions

• In this equation, each dot in the electron dot structure represents an electron in the valence shell in the electron configuration diagram.

7.1

Formation of Ions

• Ions produced when chlorine and other halogens gain electrons are called halide ions

• All halide ions have a charge of 1-

Formation of Anions

• Oxygen is in Group 6A.

7.1

Gain of valence electrons

Formation of Anions

• Anions of Group 5A elements always have a charge of 3-.

• Anions of group 6A elements always have a charge of2-.

• Anions of group 7A elements always have a charge of 1-