c hapter 7 ionic and metallic bonding. s ection 1 ions

CHAPTER 7Ionic and Metallic Bonding

SECTION 1Ions

LEARNING TARGETS

7.1.1 – I can determine the number of valence electrons in an atom of a representative element.

7.1.2 – I can explain how the octet rule applies to atoms of metallic and nonmetallic elements.

7.1.3 – I can describe how cations form.7.1.4 – I can explain how anions form.

VALENCE ELECTRONS

Valence electrons – electrons in the highest occupied energy level of an elements atoms.

Valence electrons determine an elements properties.

To find the number of valence electrons simply look at the group number.

Helium is the only exception to this, only has 2 electrons.

Electron dot structure – diagrams that show the valence electrons as dots.

THE OCTET RULE

Octet rule – in forming compounds, atoms tend to achieve the electron configuration of noble gases.

Or the configuration of ns2np6

Atoms of metallic elements tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level.

Atoms of nonmetallic elements tend to gain electrons or share electrons with another nonmetallic element to achieve a complete octet.

FORMATION OF CATIONS

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

Usually metal atoms – very few nonmetals lose electrons.

Transition metals will achieve the most stable configuration possible so they may be exceptions to the octet rule.

Also called a pseudo-noble gas electron configuration.

Which looks like

FORMATION OF ANIONS

The gain of negatively charged electrons by a neutral atom produces an anion.

Nonmetals form anions and change their name endings to –ide.

Halide ion – ions produced when atoms of chlorine and the other halogens gain electrons.

Which looks like

SECTION 2Ionic Bonds and Ionic Compounds

LEARNING TARGETS

7.2.1 – I can explain the electrical charge of an ionic compound.

7.2.2 – I can describe three properties of ionic compounds.

FORMATION OF IONIC COMPOUNDS

Ionic compound – compounds composed of cations and anions.

Although they are composed of ions, ionic compounds are electrically neutral.

Sodium reacting with chlorine 1 Sodium reacting with chlorine 2 Aluminum reacting with bromine Sodium reacting with bromine Aluminum reacting with iodine

IONIC BONDS

Ionic bonds – electrostatic forces that hold ions together in ionic compounds.

Think about sodium and chloride Sodium has 1 valence electron. Chlorine has 7 valence electron. When they combine sodium gives chlorine its 1

valence electron so they both satisfy the octet rule.

FORMULA UNITS

Chemical formulas – shows the kinds and numbers of atoms in the smallest representative unit of a substance.

Formula unit – lowest whole-number ratio of ions in an ionic compound.

EXAMPLES:

Look at sodium and oxygen

EXAMPLES:

Look at aluminum and oxygen

EXAMPLES:

Pick a metal from the representative elements. Pick a nonmetal from the representative

elements

PROPERTIES OF IONIC COMPOUNDS

Most ionic compounds are crystalline solids at room temperature.

Ionic compounds generally have high melting points.

Coordination number – number of ions of opposite charge that surround the ion in a crystal

Ionic compounds can conduct an electric current when melted or dissolved in water.

SECTION 3Bonding In Metals

LEARNING TARGETS

7.3.1 – I can model the valence electrons of metal atoms.

7.3.2 – I can describe the arrangement of atoms in a metal.

7.3.3 – I can explain the importance of alloys.

METALLIC BONDS AND METALLIC PROPERTIES

The valence electrons of metal atoms can be modeled as a “sea” of electrons.

Metallic bonds – attraction of the free-floating valence electrons for the positively charged metal atoms.

METALLIC BONDS AND METALLIC PROPERTIES

Good conductors of electrical current because of the free-floating electrons.

Malleable (pounded into sheets) Ductile (pulled into wires)

CRYSTALLINE STRUCTURE OF METALS

Metal atoms are arranged in very compact and orderly patterns.

Body-centered cubic (8 neighbors)

Face-centered cubic (12 neighbors)

Hexagonal close-packed (12 neighbors)

ALLOYS

Alloy – mixtures composed of two or more elements at least one of which is a metal.

Alloys are important because their properties are often superior to those of the component elements.

Substitutional alloy – components are about the same size and one replaces (substitutes) another.

Interstitial alloy – components are different sizes and smaller fits into the spaces (intercies) of the larger.