7.1 Ions

• Ions are atoms that have gained or lost electrons….

• Have a net electrical charge

• Cations

• Anions

• Valence electrons are gained or lost

What are valence electrons?

• Electrons in the highest energy level of an atom

• Elements within a group have the same number of valence electrons

• Number of valence electrons largely determines properties of the element and its group

• Number of ve’s indicated by the group A group numbers, IA, IIA, IIIA, etc.

Valence Electrons

1s1 1s22s22p2 1s22s22p3 1s22s22p4

Electron Dot Structures

Valence electrons represented as dots

What is the octet rule?

• Noble gases are extremely unreactive, i.e. very stable

• When forming ions or compounds, representative elements (Group A) gain, lose, or share electrons in order to achieve a noble gas electron configuration

• i.e. an octet, ns2np6

Metals vs. Nonmetals

• Metals tend to give up ve’s to achieve an octet

• Nonmetals tend to gain or share ve’s to achieve an octet

Formation of Cations

• When Na loses its valence electron, there is an octet in the next lowest energy level

Formation of Cations

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

Transition Metals• Do not follow the octet rule• “Pseudo-noble gas” configuration

Formation of Anions

• Non-metals tend to gain ve’s to achieve an octet (noble gas e- configuration)

Formation of Anions

Formation of Anions

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

How can you predict the charge of a monatomic ion?

• Determine number of ve’s

• Representative elements will gain or lose the least number of ve’s to achieve an octet

Common Anions:Monatomic and Polyatomic

7.2 Ionic Compoounds

• Usually composed of a metal and non-metal

Ionic Bonds & Ionic Compounds

• Ionic Compounds– Composed of ions

• Cations and anions

– Held together by ionic bonds– Are electrically neutral

Ionic Bonds

• Ionic Bonds are….– electrostatic forces of attraction between oppositely

charged ions

Formula Unit

• Chemical formula for an ionic compound• Lowest whole number ratio of ions in the

compound producing an electrical neutrality • What is the formula unit for…

Sodium chloride

Magnesium chloride

Sodium sulfide

Magnesium oxide

What are the properties of ionic compounds?

• Solids

• High melting points

• 3D arrangement of ions

• Coordination number

• Conduct electric current when dissolved in water

Crystalline Solids:Specific 3D Arrangement of Ions

“crystal lattice”

Coordination Number

• Number of ions surrounding an oppositely charged ion

High melting temperatures (mp)

• Because ionic bonds are very strong, it takes much energy to break them

• Therefore, their mp’s are high

Sample mp’s of ionic compounds

Compound Name

Formula Unit mp (ºC)

NaCl 801

MgO 2852

LiF 845

Sr(NO3)2 570

KNO3 334

Conduct electricity if molten or dissolved in water (aqueous)

Electrical current is a movement of charge

Because ions are free to move in the molten or aqueous state

Structure of Metals

“Electron sea” model of metals

valence electrons are free to move about in metals

Metallic bonds: attraction between valence electrons and the metal cations

Properties of Metals are due to the Structure of Metals

• Ductility• Malleability• Electrical conductivity• Luster• Thermal conductivity

Compare Properties of Metals and Ionic Compounds

Property MetalsIonic

Compounds

Malleability & ductility

High Brittle

Electrical conductivity as solid

High None

Luster High Low or none

Thermal conductivity

High Low or none

Compare Structure of Metals & Ionic Compounds

Crystal Structure of Metals• Metal atoms arranged in orderly, compact

patterns• Unit Cell & Crystal Lattice

Alloys

• Mixtures of which at least one component is a metal

• Have superior properties to the pure metal, – hardness, tensile strength, durability,etc.

Some bicycle frames are often made of titanium alloys that contain aluminum and vanadium.

Steel

There are many alloys of steel used for different applications

Vocational & Professional Opportunities…

Metallurgy & metallurgical engineering

Welding & welding engineering