ionic bonding

Chapter 7

Ions

• Elements within each group of the periodic table behave similarly because they have the same number of valence electrons.

• Valence electrons are the electrons in the highest occupied energy level of an elements atoms.– Valence electrons determine the chemical

properties of an element.

Valence Electrons

• To find the number of valence electrons in an atom of a representative element, simply look at its group number.

• In forming compounds, atoms tend to gain or lose electrons in order to achieve the electron configuration of a noble gas!!!

OctetRule

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons

C would like to N would like toO would like to

Gain 4 electronsGain 3 electronsGain 2 electrons

Key Concept

• Atoms of metals lose their valence electrons.

• Atoms of some nonmetals ten to gain electrons or to share with other nonmetallic elements to achieve a complete octet

Formation of Cations

• When an atom loses an electron it produces a positively charged ion, or a cation.

• The most common cations are those produced by the loss of valence electrons from metal atoms.

Electron–Dot Structures for Ions

• Remove electrons for cations

Sodium Atomic number 11 1s22s22p63s1 1 Valence electron Na

Remove electron to form ion

Sodium Ion Atomic number 11 1s22s22p63s0 Na+

Now has full shell with similar electronic configuration to Neon --Stable noble gas configuration

Formation of Anions

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

Electron–Dot Structures for Ions

• Add electrons for anions

Chlorine atomic number 17 1s22s22p63s23p5 Cl7 Valence electrons

Add electron to form ion

Chloride ion atomic number 17 1s22s22p63s23p68 Valence electrons Cl

-

Now has full shell with similar electronic configuration to Argon --Stable noble gas configuration

Mg example

1s22s22p6

3s2[Ne]

3s2

Lewis Dot StructuresThe valence shell is the outermost shell of electrons of an atom.

2 electrons in the valence Shell

MgUse dots to represent Valence Electrons

Electron-Dot Structures• Valence electrons represented by dots

• Electron-dot symbols– Examples: Na•, •Mg•, …

Ionic Bonds

• Compounds composed of cations and anions are called ionic compounds.

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

The electrostatic forces that hold ionsTogether in ionic compounds areCalled Ionic bonds.

Ionic Bonds: One Big Greedy Thief Dog!

Formula Units

• A chemical formula shows the kinds and numbers of atoms in the smallest representative unit of a substance.

• Because an ionic compound exists as a collection of positively and negatively charged ions arranged in repeating patterns, its chemical formula refers to a ratio known as a formula unit.

• A formula unit is the lowest whole-number ratio of ions in an ionic compound.

• For NaCl the ratio of the ions is 1:1 (one Na+ to one Cl-)

• What is the formula unit for Magnesium Chloride?

Practice, Practice, Practice

• Use electron dot structures to determine formulas of the ionic compounds formed when

• 1. potassium reacts with iodine.

• 2. Aluminum reacts with oxygen.

Properties of Ionic Compounds

1. Most are crystalline solids at room temperature.

2. High melting points.

3. Conduct electricity when melted or dissolved in water.

Practice, Practice

• Write the formulas for each compound.

1. Barium chloride2. Lithium oxide3. Magnesium oxide4. Calcium flouride

7.3 Bonding in Metals

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

• That is, the valence electrons are mobile and can drift freely from one part of the metal to another.

• Metallic Bonding Animation

Metallic Bonds: Mellow dogs with plenty of bones to go around.

Alloys

• Mixtures composed of two or more elements, at least one of which is a metal.

• Their properties are often superior to those of their component elements.

Learning Check

Give the ionic charge for each of the following:A. 12 p+ and 10 e-

1) 0 2) 2+ 3) 2-

B. 50p+ and 46 e-

1) 2+ 2) 4+ 3) 4-

C. 15 p+ and 18e-

2) 3+ 2) 3- 3) 5-

Learning Check

A. Number of valence electrons in aluminum1) 1 e- 2) 2 e- 3) 3 e-

B. Change in electrons for octet1) lose 3e- 2) gain 3 e- 3) gain 5

e-

C. Ionic charge of aluminum 1) 3- 2) 5- 3) 3+

Solution

A. Number of valence electrons in aluminum3) 3 e-

B. Change in electrons for octet1) lose 3e-

C. Ionic charge of aluminum 3) 3+

Review..

• What is a chemical bond?– Force that holds two atoms together

• What is an ionic bond?– An electrostatic force that holds

oppositely charged particles together in an ionic compound

– Forms when….?• What are atoms and compounds always

trying to achieve?– Stability– Complete set of valence electrons…