Types of Bonding Valence Electrons: S & P electrons in the outer most energy level involved in the bonding process.

To show valence electrons we use dot structures:

Electron Dot Structures of Some Elements Group

Period

1 s1

2 s2

13 s2p1

14 s2p2

15 s2p3

16 s2p4

17 s2p5

18 s2p6

1 2 3 4

•Notice group 18 has 8 electrons called an octet, that is what all the other elements wants to achieve by losing, gaining or sharing of electrons. How many electron dots would all the transition metals have in common?

The Octet Rule • Atoms of metals tend to lose their valence electrons, so that their highest electron configuration will replicate a noble gas and form an octet. What are they called? • Atoms of some nonmetals tend to gain electrons so that their highest electron configuration will replicate a noble gas and form an octet. What are they called if they gain electrons?

Formation of Cations •The figure at right lists the symbols of the cations formed by metals 1 2 •in Groups 1 and 2. • Cations of Group 1 elements always have a charge of 1+. • Cations of Group 2 elements always have a charge of 2+.

•Atoms of nonmetals and metalloids form anions by gaining enough valence electrons to attain the octet of the nearest noble gas.

15 16 17

• An ionic compound is a compound composed of cations and anions or a metal and a nonmetal. •The total positive charge of the cations equals the total negative charge of the anions. •Anions and cations have opposite charges and attract one another by means of electrostatic forces.

•The electrostatic forces that hold ions together in ionic compounds are called ionic bonds.

Formation of Ionic Compounds When sodium and chlorine react to form a compound, the sodium atom transfers its one valence electron to the chlorine atom. • Sodium and chlorine atoms combine in a one-toone ratio, and both ions have stable octets. Hence the chemical formula is NaCl A chemical formula shows the numbers of atoms of each element in the smallest representative unit of a substance.

Sample Problem 7.1

Predicting Formulas of Ionic Compounds •Use electron dot structures to predict the formulas of the ionic compounds formed from the following elements:

a. potassium and oxygen b. magnesium and nitrogen

2 Solve Apply the concepts to this problem.

a. Start with the atoms. ••

•• • K and •O • a. In order to have a completely filled valence shell, the oxygen atom must gain two electrons. These electrons come from two potassium atoms, each of which loses one electron. + K• K •• • • 2– O + •O • •• • •• ••

••

K

K+

•The formula of the compound formed is K2O

Sample Problem 7.1

2 Solve Apply the concepts to this problem.

b. Start with the atoms. •

••

•

Mg and • N •

•

Sample Problem 7.1

2 Solve Apply the concepts to this problem.

b. Each nitrogen atom needs three electrons to have an octet, but each magnesium atom can lose only two electrons. Three magnesium atoms are needed for every two nitrogen atoms. •

•

Mg •

•

Mg2+

• N•

•• N ••

3–

••

3–

•• ••

Mg

+

••

•

•

• N•

Mg2+

•• ••

•

•

••

Mg

Mg2+

N

••

•Formula would be Mg3N2 Now its your turn: Use electron dot structures to predict the formulas of the ionic compounds formed from the following elements: Calcium and Fluorine

Aluminum and Sulfur

Formula Units Ionic compounds do not exist as discrete units, but as collections of positively and negatively charged ions arranged in repeating patterns.

The chemical formula of an ionic compound refers to a ratio known as a formula unit. • A formula unit is the lowest wholenumber ratio of ions in an ionic compound.

Properties of Ionic Bonds • Composed of a metal and a nonmetal. •Ionic compounds made up of a cation and anion. •Although they are composed of ions, ionic compounds are electrically neutral.

•Most ionic compounds are crystalline solids at room temperature. •Ionic compounds generally have high melting points.

•Ionic compounds can conduct an electric current when melted or dissolved in water. When the bonds break the ions are free and are charged so they can conduct an electric current.

•A structure of an ionic compound is called a crystalline structure.

Metallic bonds are the forces of attraction between the free-floating valence electrons and the positively charged metal ions. • These bonds hold metals together. • Metals are good conductors of electric current because electrons can flow freely in the metal. • As electrons enter one end of a bar of metal, an equal number of electrons leave the other end.

Metallic Bonds and Metallic Properties Properties of Metals When a metal is subjected to pressure, the metal cations easily slide past one another. Sea of electrons

Force

Metal cation

Metal

Metallic Bonds and Metallic Properties Properties of Metals When a metal is subjected to pressure, the metal cations easily slide past one another. Sea of electrons

Force

Force Nonmetal anion

Metal cation

Metal cation Strong repulsions

Metal

Ionic crystal

• If an ionic crystal is struck with a hammer, the blow tends to push the positive ions close together. • The positive ions repel one another, and the crystal shatters.