ionic bonding

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CHAPTER 6Ionic Bonding

© 2013 Marshall Cavendish International (Singapore) Private Limited

6.1 The Stable Electronic Configuration of a Noble Gas

6.2 Forming Ions

6.3 Ionic Bond: Transferring Electrons

6.4 Chemical Formulae of Ionic Compounds

6.5 Structure and Physical Properties of Ionic Compounds

Chapter 6 Ionic Bonding

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Learning Outcome


• describe the stable electronic configuration of a noble gas.

At the end of this section, you should be able to:

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What are Noble Gases?

• Elements that belong to Group 0 of the Periodic Table

• Examples: He, Ne, Ar, Kr and Rn

• Atoms of noble gases are stable and unreactive.

• They exist in nature as single atoms.

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What is the Noble Gas Structure?

• Noble gases have full or complete outer shells.

Helium has a duplet configuration

All other noble gases have an octet configuration

(2 outer electrons).

(8 outer electrons).5


Why Do Atoms React?

• Atoms of most other elements are reactive because they do not have the noble gas structure (i.e. their outer shells are not fully-filled).

• Atoms of these elements lose, gain or share outer electrons to attain the noble gas configuration and form compounds.

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Chemical Bonding

Ionic bonding Covalent bonding

Atoms share electrons to attain noble gas

configuration

Atoms gain or lose electrons to attain

noble gas configuration

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6.2 Forming Ions




• describe the formation of positive ions (cations) and negative ions (anions) to achieve the noble gas configuration.

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Learning Outcome


6.2 Forming Ions

What is an Ion?

Recall: Atoms have an equal number of protons and electrons. They are

electrically neutral.

• An atom loses or gains electrons to form ions.

• Ions are charged particles.

No. of electrons ≠ No. of protons10

6.2 Forming Ions

• Ions can be positively- or negatively-charged.

• Positively-charged ions are called cations.

• Negatively-charged ions are called anions.

URL11

6.2 Forming Ions

What is an Ion?

http://www.bbc.co.uk/schools/gcsebitesize/science/add_aqa/atomic/ionicact.shtml

Formation of Cations

• Atoms of metals lose electrons to form positively-charged ions called cations.

•In this way, they achieve the noble gas configuration.

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6.2 Forming Ions

The Na atom loses one outer electron to form the Na+ ion. Why?

To achieve stable octet (noble gas) configuration.

Example 1: Formation of sodium (Na+) ion

Na atom

Electronic configuration: 2, 8, 1

Number of protons = 11

Number of electrons = 11

Neon (2, 8) 13

6.2 Forming Ions

Na atom: 11p, 12n, 11e

2, 8, 1 2, 8

sodium atom loses one outer electron

+

NeutralNa atom

Positively-chargedNa+ ion

Charge = 11p + 11e = (+11) + (–11) = 0

Na+ ion: 11p, 12n, 10e

Charge = 11p + 10e = (+11) + (–10) = +1

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6.2 Forming Ions

Example 1: Formation of sodium (Na+) ion

Charge = 20p + 20e

Ca2+ ion: 20p, 20n, 18e

2, 8, 8, 2 2, 8, 8

Ca atom: 20p, 20n, 20e

2+calcium atom loses two outer electrons

NeutralCa atom

Positively-chargedCa2+ ion

= 20(+1) + 20(–1) = (+20) + (–20) = 0

Charge = 20p + 18e

= 20(+1) + 18(–1)

= (+20) + (–18) = +2

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6.2 Forming Ions

Example 2: Formation of calcium (Ca2+) ion

Metal Ion Formula of ion

sodium sodium ion Na+

potassium potassium ion K+

calcium calcium ion Ca2+

magnesium magnesium ion Mg2+

aluminium aluminium ion Al3+

Common Cations and Their Charges

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6.2 Forming Ions

Formation of Anions

• Atoms of non-metals gain electrons to form negatively-charged ions called anions.

•In this way, they achieve the noble gas configuration.

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6.2 Forming Ions

Cl atom

Electronic configuration: 2, 8, 7

Number of protons = 17

Number of electrons = 17

What happens in the formation of a chloride ion?

The chlorine atom gains one electron in its outer shell to achieve a stable octet (noble gas) configuration.

Argon (2, 8, 8) 18

6.2 Forming Ions

Example 1: Formation of chloride (Cl–) ion

chlorine atom gains one electron

2, 8, 7

Cl atom: 17p, 18n, 17e Cl– ion: 17p, 18n, 18e

NeutralCl atom

Negatively chargedCl– ion

Charge = 17p + 17e = (+17) + (–17) = 0

Charge = 17p + 18e = (+17) + (–18) = –1

2, 8, 8

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6.2 Forming Ions

Example 1: Formation of chloride (Cl–) ion

oxygen atom gains two electrons

O atom: 8p, 8n, 8e O2– ion: 8p, 8n, 10e

NeutralO atom

Negatively chargedO2– ion

Charge = 8p + 8e = (+8) + (–8) = 0

Charge = 8p + 10e = (+8) + (–10) = –2

2, 82–

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2, 6

6.2 Forming Ions

Example 2: Formation of oxide (O2–) ion

Non-metal Ion Formula of ion

chlorine chloride ion Cl–

bromine bromide ion Br–

oxygen oxide ion O2–

sulfur sulfide ion S2–

Common Anions and Their Charges

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6.2 Forming Ions

Why do metals lose electrons to form positive ions (cations) but non-metals gain electrons to form negative ions (anions)?

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6.2 Forming Ions




Learning Outcome

• describe how an ionic bonds are formed between metals and non-metals.


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Examples:Group VII: Fluorine, chlorineGroup VI: Oxygen, sulfur

Examples:Group I: Sodium, potassiumGroup II: Magnesium, calcium

Ionic Bonding

• Ionic bonds are formed between metals and non-metals.

• This is done through the transfer of electron(s) from metals to non-metals.

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Metallic atom Non-metallic atom

loses electron(s) gains electron(s)

Positive ion(cation)

Negative ion(anion)

electrostatic forces of attraction

Ionic Bonding

(hold oppositely charged ions together) 26


Step 1: Formation of Positive Ions

Each sodium atom (Na) loses its single outer electron to form a positively-charged sodium ion (Na+).

Na Na+ + e−

2, 8, 1 2, 8

Formation of Ionic Compound

Example 1: Sodium chloride

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Step 2: Formation of Negative Ions

Each chlorine atom gains an electron from a sodium atom to form a negatively-charged chloride ion (Cl−).

Cl –Cl

2, 8, 7 2, 8, 8

+ e−

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Sodium and chlorine react in the ratio of 1 : 1 to form sodium chloride (NaCl).

Sodium atom2, 8, 1

Chlorine atom2, 8, 7

Sodium ion2, 8

Chloride ion2, 8, 8

Electrostatic forces of attraction

Step 3: Formation of Ionic Bonds

Gains one electron

Loses one electron

URL29


http://www.youtube.com/watch?v=QqjcCvzWwww&NR=1

Chlorine atoms gain one electron each.

Chloride ion2, 8, 8

Chloride ion2, 8, 8

Magnesium ion2, 8

Magnesium atom loses two

electrons.

Magnesium reacts with chlorine in the ratio of 1 : 2 to form magnesium chloride (MgCl2).

Example 2: Magnesium chloride

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6.2 Forming Ions




Learning Outcome

• deduce the chemical formula of an ionic compound from the charges on the ions and vice versa.


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Chemical Formulae of Ionic Compounds

• The formula of an ionic compound is constructed by balancing the charges on the positive and negative ions.

• All the positive charges must equal all the negative charges in an ionic compound.

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Since 1 × (+2 charge) balances out 1 × (−2 charge),

Example: Magnesium oxide

Magnesium forms Mg2+ ions.

Oxygen forms O2− ions.

Mg2+ O2−

The formula is MgO.

Charge: +2 Charge: −2

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Since 1 × (+2 charge) balances out 2 × (−1 charge),

Copper ion Hydroxide ion

Cu2+ OH−

The formula is Cu(OH)2.


To balance the charges, multiply the smaller charge (−1) by 2 to make it equal to +2.

Example: Copper(II) hydroxide

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Example 1

Write the chemical formula of aluminium oxide.

aluminium ion oxide ion

Al 3 + O 2 −

Al2O3


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Therefore, the formula is Al2O3.


Since ‘2’ is a common factor, it can be removed. Therefore, the formula is CaCO3.

CaCO3

URL

Example 2Write the chemical formula of calcium carbonate.

calcium ion carbonate ion

Ca 2 + CO3 2 −

Ca2(CO3)2


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http://www.learner.org/interactives/periodic/groups_interactive.html


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6.2 Forming Ions




Learning Outcomes

• state that ionic compounds form giant lattice structures;


• deduce the formulae of ionic compounds from their lattice structures;

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• relate the physical properties of ionic compounds to their lattice structures.


Ionic compounds form giant ionic structures.

Structure of Ionic Compounds

Also known as giant lattice structures or crystal lattices

Consist of an endlessly repeating three-dimensional lattice of positive and negative ions

Ions are closely packed, arranged in an orderly manner and held in place by ionic bonds

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Sodium ions and chloride ions alternate with each other.

Structure of NaCl

Three-dimensional arrangement of sodium ions and chloride ions

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Sodium chloride crystal


Strong forces of attraction between ions in crystal lattice

A large amount of energy is required to overcome these forces of attraction between ions.

Structure of NaCl

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–

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Each sodium ion is surrounded by six chloride ions.

Each chloride ion is surrounded by six sodium ions.

Cl− ion

Na+ ion

The ratio of sodium ions to chloride ions is 1 : 1.Hence, the formula unit of sodium chloride is NaCl.

Structure of NaCl


• High melting and boiling points

• Non-volatile

• Exist as solids at room temperature

Melting and Boiling Points of Ionic Compounds

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Na+

Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–Cl–

Cl–Cl–

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• Usually soluble in water

Solubility of Ionic Compounds

• Usually insoluble in organic solvents E.g. ethanol, turpentine, petrol

Water molecules

dissolve in water

URL

Cl–Na+ Na+

Cl–Na+ Na+

Cl–Na+Cl–

Na+

Cl–

Na+

Cl–

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http://www.youtube.com/watch?v=EBfGcTAJF4o&feature=related

aqueous NaClsolid NaCl

molten NaCl

Electrical Conductivity of Ionic Compounds

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Electrical Conductivity of Ionic Compounds

• Ionic compounds conduct electricity in the molten and aqueous states.

• They do not conduct electricity in the solid state.

• In the molten and aqueous states, mobile ions are

present.

• Mobile ions conduct electricity.

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Concept Map

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ionic bonding

Education

noble gas structure

ions example

noble gaswhy

number of electrons

octet configuration

gains electrons

e charge

duplet configuration