Ionic CompoundsIonic Compounds

Chapter 6Chapter 6

Chapter OutcomesChapter Outcomes

At the end of this chapter you should be able At the end of this chapter you should be able to:to: Describe the ionic bonding modelDescribe the ionic bonding model Use the model to explain the properties of ionic Use the model to explain the properties of ionic

compoundscompounds Explain how ions are produced when metals and Explain how ions are produced when metals and

non-metals reactnon-metals react Write chemical formulas for ionic compoundsWrite chemical formulas for ionic compounds Describe the uses of some ionic compoundsDescribe the uses of some ionic compounds

Ionic CompoundsIonic Compounds Ionic compounds are made up by the chemical Ionic compounds are made up by the chemical

combination of combination of metallicmetallic and and non-metallicnon-metallic elements.elements.

Most rocks, minerals and gemstones are ionic Most rocks, minerals and gemstones are ionic compounds.compounds.

Ceramics, bricks and kitchen crockery are Ceramics, bricks and kitchen crockery are made from clays which contain ionic made from clays which contain ionic compounds.compounds.

While most of the above are made up of While most of the above are made up of mixtures of different ionic compounds table salt mixtures of different ionic compounds table salt is a pure ionic compound made up of sodium is a pure ionic compound made up of sodium chloride (NaCl)chloride (NaCl)

Properties of Ionic Properties of Ionic CompoundsCompounds

Think of the properties of rocks, bricks, Think of the properties of rocks, bricks, crockery and table salt. What properties do crockery and table salt. What properties do they share?they share? Have high melting and boiling temperatures.Have high melting and boiling temperatures. Are hard but brittleAre hard but brittle

They also:They also: Do NOT conduct electricity in the solid stateDo NOT conduct electricity in the solid state They will only conduct electricity if they are melted They will only conduct electricity if they are melted

or dissolved in wateror dissolved in water

Structure of ionic Structure of ionic compoundscompounds

The physical properties of ionic The physical properties of ionic compounds are very different from compounds are very different from metals.metals.

The structure of ionic compounds must The structure of ionic compounds must therefore be very different from those therefore be very different from those present in metals.present in metals.

What do we already know about ionic What do we already know about ionic compounds.compounds.

What do the properties What do the properties tell us?tell us?

StructureStructure

From the properties we can conclude:From the properties we can conclude: The forces between the particles are strong.The forces between the particles are strong. There are no free-moving electrons present, There are no free-moving electrons present,

unlike in metals.unlike in metals. There are charged particles present, but in There are charged particles present, but in

solid state they are not free to move. solid state they are not free to move. When an ionic compound melts, however, When an ionic compound melts, however,

the particles are free to move and the the particles are free to move and the compound will conduct electricity.compound will conduct electricity.

The ionic bonding modelThe ionic bonding modelChemists believe that when metallic and non-metallic atoms Chemists believe that when metallic and non-metallic atoms

react to form ionic compounds the following steps occur:react to form ionic compounds the following steps occur:

Metal atoms lose electrons to non-metallic atoms and Metal atoms lose electrons to non-metallic atoms and become positively charged metal ions.become positively charged metal ions.

Non-metal atoms gain electrons from the metal atoms Non-metal atoms gain electrons from the metal atoms and so become negatively charged non-metal ions.and so become negatively charged non-metal ions.

Large numbers of positive and negative ions formed in Large numbers of positive and negative ions formed in this way then combine to form a three-dimensional lattice.this way then combine to form a three-dimensional lattice.

The three dimensional lattice is held together strongly by The three dimensional lattice is held together strongly by electrostatic forces of attraction between positive and electrostatic forces of attraction between positive and negative ions. This electrostatic force is called ionic negative ions. This electrostatic force is called ionic bonding.bonding.

How many chlorine ions surround each sodium ion and vice versa?

Using the ionic bonding Using the ionic bonding model to explain the model to explain the properties of sodium properties of sodium chloridechloride

High Melting High Melting TemperatureTemperature

Ever noticed that when you eat fish and chips Ever noticed that when you eat fish and chips the food may be hot but the salt does not melt.the food may be hot but the salt does not melt.

This is because to melt and ionic solid energy This is because to melt and ionic solid energy must be provided to allow the ions to break must be provided to allow the ions to break free and move.free and move.

NaCl has a high melting temp, this indicates a NaCl has a high melting temp, this indicates a large amount of energy is needed to reduce large amount of energy is needed to reduce the electrostatic attraction between the the electrostatic attraction between the oppositely charged ions and allow them to oppositely charged ions and allow them to move freely.move freely.

Hardness and BrittlenessHardness and Brittleness

Unlike metals ionic compounds are not Unlike metals ionic compounds are not malleable. They break when beaten.malleable. They break when beaten.

A force can disrupt the strong electrostatic A force can disrupt the strong electrostatic forces holding the lattice in place. forces holding the lattice in place.

A sodium chloride crystal cannot be scratched A sodium chloride crystal cannot be scratched easily but if a strong force (a hammer blow) is easily but if a strong force (a hammer blow) is applied it will shatter.applied it will shatter.

This is because the layers of ions will move This is because the layers of ions will move relative to each other due to the force. relative to each other due to the force.

During this movement, ions of like charge will During this movement, ions of like charge will become adjacent to each other. Resulting in become adjacent to each other. Resulting in repulsionrepulsion

Hardness and BrittlenessHardness and Brittleness

Figure 6.4 Figure 6.4 The repulsion The repulsion between like charges causes between like charges causes this sodium chloride crystal to this sodium chloride crystal to shatter when it is hit sharply.shatter when it is hit sharply.

Electrical ConductivityElectrical Conductivity

In the solid form, ions in sodium chloride are In the solid form, ions in sodium chloride are held in the crystal lattice and are not free to held in the crystal lattice and are not free to move so cannot conduct electricity. move so cannot conduct electricity.

When the solid melts the ions are free to move. When the solid melts the ions are free to move. The movement of these charged particles to an The movement of these charged particles to an

electrode completes an electrical circuit.electrode completes an electrical circuit. In a similar way, when sodium chloride In a similar way, when sodium chloride

dissolves in water, the ions separate and are dissolves in water, the ions separate and are free to move towards the opposite charge.free to move towards the opposite charge.

Conducting ElectricityConducting Electricity

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Reactions of metals with Reactions of metals with non-metalsnon-metals

Metallic atoms have low ionisation Metallic atoms have low ionisation energies and low electronegativities.energies and low electronegativities.

Non-metallic atoms have high ionisation Non-metallic atoms have high ionisation energies and low electronegativities.energies and low electronegativities.

In other words metallic atoms lose In other words metallic atoms lose electrons easily and non-metallic atoms electrons easily and non-metallic atoms gain electrons easily.gain electrons easily.

Ionic CompoundsIonic Compounds

So the metal atoms lose an electron to So the metal atoms lose an electron to the non-metal atoms.the non-metal atoms.

In doing so, both atoms will often achieve In doing so, both atoms will often achieve the electronic configuration of the nearest the electronic configuration of the nearest noblest gas, which is particularly stable.noblest gas, which is particularly stable.

Sodium ChlorideSodium Chloride

When sodium reacts with chlorine:When sodium reacts with chlorine: Na atom (1sNa atom (1s2 2 2s2s2 2 2p2p6 6 3s3s11) loses an ) loses an

electron to become 1selectron to become 1s2 2 2s2s2 2 2p2p6 6 (the same (the same as Neon)as Neon)

Cl atom (1sCl atom (1s2 2 2s2s2 2 2p2p6 6 3s3s1 1 3p3p55) gains an ) gains an electron to become 1selectron to become 1s2 2 2s2s2 2 2p2p6 6 3s3s1 1 3p3p66 (the same as argon)(the same as argon)

Electron ConfigurationElectron Configuration

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Electron Transfer Electron Transfer DiagramsDiagrams

When sodium and chloride react together When sodium and chloride react together sodium loses an electron and chlorine sodium loses an electron and chlorine gains an electron. gains an electron.

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Sodium ChlorideSodium Chloride

What is happening:What is happening: Chlorine molecules splitting into separate Chlorine molecules splitting into separate

chlorine atomschlorine atoms Electrons being transferred from sodium atoms Electrons being transferred from sodium atoms

to chlorine atoms – positively charged sodium to chlorine atoms – positively charged sodium and negatively charged chlorine ions are being and negatively charged chlorine ions are being formed.formed.

Sodium and chloride ions combining to form a Sodium and chloride ions combining to form a three dimensional lattice.three dimensional lattice.

Notes:Notes:

When a non-metal atom gains one or When a non-metal atom gains one or more electrons, the name of the negative more electrons, the name of the negative ion ends in –ide. ion ends in –ide.

When a metal atom loses one or more When a metal atom loses one or more electrons the name of the positive ion is electrons the name of the positive ion is the same as the metal and is always the same as the metal and is always named first.named first.

For example: sodium chlorideFor example: sodium chloride

ElectrovalencyElectrovalency

The charge on an ion is known as its The charge on an ion is known as its electrovalency. electrovalency.

That is the little positive or negative That is the little positive or negative number to the top right of a chemical number to the top right of a chemical symbol. symbol.

Sodium has an electrovalency of +1 whilst Sodium has an electrovalency of +1 whilst chlorine has an electrovalency of -1chlorine has an electrovalency of -1

NaNa+1+1 and Cl and Cl-1-1

Magnesium OxideMagnesium Oxide

What are the electron configurations for What are the electron configurations for Magnesium and Oxygen?Magnesium and Oxygen?

How many electrons does magnesium How many electrons does magnesium need to lose to get a full outer shell?need to lose to get a full outer shell?

How many electrons does oxygen need How many electrons does oxygen need to gain to get a full outer shell?to gain to get a full outer shell?

Draw an electron transfer diagram.Draw an electron transfer diagram. What is the electrovalency of a What is the electrovalency of a

magnesium ion and an oxide ion?magnesium ion and an oxide ion?

Magnesium ChlorideMagnesium Chloride

What are the electron configurations for What are the electron configurations for Mg and Cl?Mg and Cl?

So a Mg atom will have a stable outer So a Mg atom will have a stable outer shell if 2 electrons are removed.shell if 2 electrons are removed.

A Cl atom only needs to gain one A Cl atom only needs to gain one electron.electron.

So how can this work?So how can this work?

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MgClMgCl22

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Chemical FormulasChemical Formulas

Almost every compound in which a metal Almost every compound in which a metal is combined with a non-metal displays is combined with a non-metal displays ionic bonding.ionic bonding.

The formulas of simple ionic compounds, The formulas of simple ionic compounds, such as NaCl and MgClsuch as NaCl and MgCl22 can be can be

predicted from the electron configurations predicted from the electron configurations of the atoms. of the atoms.

ElectrovalenciesElectrovalencies

Elements in groups 1 all have an Elements in groups 1 all have an electrovalency of +1 (they all have only electrovalency of +1 (they all have only one electron to lose)one electron to lose)

Elements in group 17 all have an Elements in group 17 all have an electrovalency of -1electrovalency of -1

What about groups 2 and groups 16?What about groups 2 and groups 16? Does this formula work for all atoms?Does this formula work for all atoms?

Writing Formulas: RulesWriting Formulas: Rules

Chemical formulas are part of the Chemical formulas are part of the language of chemists. To understand and language of chemists. To understand and use this language, you need to follow a use this language, you need to follow a number of fules.number of fules.

Simple IonsSimple Ions The positive ion is place first in the formula, the The positive ion is place first in the formula, the

negative ion is second. negative ion is second. For example, Kf, CuOFor example, Kf, CuO Positive and negative ions are combined so that the Positive and negative ions are combined so that the

total number of positive charges is balanced by the total number of positive charges is balanced by the total number of negative charges. total number of negative charges.

For example, CuS, CuClFor example, CuS, CuCl22, AlCl, AlCl3 3 and Aland Al22OO33

When there are two or more of a particular ion in a When there are two or more of a particular ion in a compound, then in the chemical formula the number is compound, then in the chemical formula the number is written as a subscript after the chemical symbol.written as a subscript after the chemical symbol.

For example, AlFor example, Al22OO33

Writing Formulas: RulesWriting Formulas: Rules

Polyatomic ionsPolyatomic ions Some ions contain more than one atom.Some ions contain more than one atom. These are called polyatomic ions.These are called polyatomic ions. They include nitrate (NOThey include nitrate (NO33

--) and hydroxide (OH) and hydroxide (OH--). ). What else?What else?

If more than one of these ions is used to If more than one of these ions is used to balance the charge of a compound, then it is balance the charge of a compound, then it is placed in brackets with the required number placed in brackets with the required number written as a subscript after the brackets.written as a subscript after the brackets.For example Mg(NOFor example Mg(NO33))22 and Al(OH) and Al(OH)33

Brackets are not required for the formula of Brackets are not required for the formula of sodium nitrate NaNOsodium nitrate NaNO33, where there is only one , where there is only one nitrate ion present for each sodium ion.nitrate ion present for each sodium ion.

Different ElectrovalenciesDifferent Electrovalencies Some elements form ions with different charges. Some elements form ions with different charges. Iron ions can have a charge of +2 or +3.Iron ions can have a charge of +2 or +3. In this situation you need to specify the electrovalency In this situation you need to specify the electrovalency

when naming the compound. when naming the compound. This is done by placing a Roman numeral representing This is done by placing a Roman numeral representing

the electrovalency of the ion immediately after the the electrovalency of the ion immediately after the metal in the name of the compound.metal in the name of the compound.

For exampleFor example Iron(II) chloride contains FeIron(II) chloride contains Fe2+2+ ions and so the formula is ions and so the formula is

FeClFeCl22 Iron(III) chloride contains FeIron(III) chloride contains Fe3+3+ ions and so the forumla ions and so the forumla

is FeClis FeCl33

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