Ionic Bonding

Chapter 7 Ionic and Metallic Bonding

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!!!
Octet Rule

Octet Rule = atoms tend to gain, lose or share electrons so as to have 8 electrons
C would like to
N would like to
O would like to
Gain 4 electrons Gain 3 electrons Gain 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 1 s 2 2 s 2 2 p 6 3 s 1 1 Valence electron Na Remove electron to form ion Sodium Ion Atomic number 11 1 s 2 2 s 2 2 p 6 3 s 0 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 1 s 2 2 s 2 2 p 6 3 s 2 3 p 5 7 Valence electrons Add electron to form ion Chloride ion atomic number 17 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 8 Valence electrons - Now has full shell with similar electronic configuration to Argon --Stable noble gas configuration Cl Cl

Lewis Dot Structures Mg example 1 s 2 2 s 2 2 p 6 3 s 2 [Ne] 3 s 2 The valence shell is the outermost shell of electrons of an atom. 2 electrons in the valence Shell Mg Use 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 ions Together in ionic compounds are Called 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
Most are crystalline solids at room temperature.
High melting points.
Conduct electricity when melted or dissolved in water.

Practice, Practice
Write the formulas for each compound .
Barium chloride
Lithium oxide
Magnesium oxide
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 aluminum
1) 1 e - 2) 2 e - 3) 3 e -
B. Change in electrons for octet
1) 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 aluminum
3) 3 e -
B. Change in electrons for octet
1) 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…

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Ionic Bonding

by Currituck County High School on Oct 10, 2008

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