© Boardworks Ltd 2003 CHEMICAL BONDING PART 1 IONIC BONDING

© Boardworks Ltd 2003

CHEMICAL BONDINGPART 1

IONIC BONDING


Elements

• Elements are the simplest substances. There are about 100 different elements N

S

OC

Fe

K

NN

N

N

N N

NN

• Each elements has just one particular type of atom that is different to the atoms in any other element

• Even in elements atoms usually join (bond) together.

• In some elements atoms bond to form small simple structures.

• In other elements atoms bond into giant structures with millions of atoms.


Compounds

• Compounds are formed when different elements chemically react together.

• In these reactions different types of atom become chemically bonded.

• Like elements some compounds have small simple structures with just a few atoms bonded together

• Other compounds have large, complex structures containing thousands or even millions of bonded atoms.

OH H

Water – a simple structure

DNA – a large & complex structure


Compounds are not just mixtures

• Reacting is different to just mixing.• The physical and chemical properties of compounds are

veryvery different to their original elements.

Carbon + oxygen Carbon dioxide

COMPOUNDELEMENTS

C O O CO O

(black solid) (colourless gas,that supportscombustion)

(a colourless gas, that extinguishes fire)


Copy the Table and fill in the last column.

SiO2Sand

HgMercury

Fe2O3Rust

O2Oxygen

H2OWater

CuSO4Copper sulphate

NiNickel

NaClSodium chloride

Element or compound

FormulaName

compound

element

compound

compound

element

compound

element

compound

Rust consists of

iron combined

with oxygen

Activity


Bonding and atoms

–Protons } These exist in –Neutrons } the nucleus.

To understand bonding we must know a little about the atoms from which elements are made.

Atoms consist of three types of particles that are even smaller than atoms:

–Electrons }

exist in layers (or shells) around the outside of the nucleus


No charge on element atoms

Two of the three particles in atoms have an electrical charge.

Protons +1 Neutrons 0 Electrons -1

BUTBUT atoms have equal numbers of protons and electrons. This means their overall charge = zero.

FluorineFluorine

9 protons 9+

9 electrons 9-

10 neutrons 0

Total Charge 0

19

F9

For example 20

Ne10

Neon Copy & Fill in the gapsNeon Copy & Fill in the gaps

___ protons ___

___ electrons ___

___neutrons ___

Total Charge ___

10

10

10

10+

10-

0

0


Noble Gases: full shells

The electrons around the outside of atoms are arranged in layers called shells

Each shell has a maximum number of electrons that it can hold.

In noble gases the shells are completely full rather than partially full. During bonding other atoms try to attain the “full electron shell” structure of the noble gases.

1st Shell: 2 electrons

2nd Shell: 8 electrons

3rd Shell: 8 electrons


Types of bonding

Atoms can be joined together in 3 possible ways

All three types involve changes in the electrons in the outermost electron shells of the atoms

Ionic Bonding

Metal and non-metal

Covalent Bonding

Non-metals only

Metallic Bonding

Metals only


IONIC BONDING


Most ionic compounds contain a metal and a non-metal.

When metals react they lose outer shell electrons to leave a full electron shell.

This produces a charged atom (ion) with a + charge.

Lose 1 or more electrons

Neutral atom

n+

Positive ion

When non-metals react with a metal they gain electrons to achieve a full electron shell.

Gain 1 or more electrons

Neutral atom

n-

Negative ion

IONIC BONDING


opposites

attract

Opposites attract – lattices

The oppositely charged ions are attracted into a lattice that gets bigger and bigger until it consists of millions of ions

+

++

+

+

+

-

--

-

--

+ -+ -+-

+ -+-

+

-+ -

+-+

--+ +

And ion, and ion, and ion!


Lattices are 3-Dimensional

We have shown ions attracting and building into a 2 dimensional sheet.

In fact the whole process will be going on in three dimensions to build up a giant 3-D lattice.

+ -+-

+

--+ +

+ -+-

+

--+ +

+-+

-

- --+

++ -

+-+

--+ +

+-+

-

- --+

+

+ -+-

+

--+ +

+-+

-

- --+

++ -

+-+

--+ +

+ -+-

+

--+ +

+-+

-

- --+

+

And so on to build a giant 3-D lattice with

millions of ions.


Ions and electron structures

Metals lose electrons to form positive(+) ions called cations.

Non-metals gain electrons to form negative (–) ions called anions.

n+

n-

We know that the atoms lose or gain electrons to achieve full electron shells.

To understand more about how ionic compounds form we must look at what is happening to the outer shell electrons.


Formation of sodium chloride1. Formation of sodium ions

Sodium has 1 electron in its outer shell.

If it loses this it will have no partially filled shells.

Loses 1 electron

Sodium 1+ ion (2.8.0)Sodium atom (2.8.1)

This only happens if there is another atom able to accommodate the lost electron.

Na Na+


Formation of sodium chloride 2.Formation of Chloride ions

Chlorine has 7 electrons in its outer shell.

If it gains 1 electron it can achieve a full outer electron shell. It is, therefore, going to be able to accept the electron that the sodium wants to lose.

Chlorine atom (2.8.7)

Gains 1 electron(from sodium)

Chlorine I - ion (2.8.8)

Cl Cl


Formation of Sodium Chloride- the overall process.

ClNa

Na Cl

Sodium loses itsouter electron.Chlorine gains it.The result is both end up with full shells

Two oppositelycharged ionsare formed, which attract.Millions of such pairs form a giant lattice


Simpler electron diagrams

We can assume full inner electron shells. We can therefore sometimes shorten bonding diagrams by omitting to draw the inner electron shells.

Na Cl

Na Cl


OMg

2.8.2. 2.6

Magnesium atom

Oxygen atom

Bonding in Magnesium Oxide

More than one electron may be transferred between atoms in ionic bonding.

Mg2+ O2-

2.82.8

Magnesium Oxide


Draw a simplified bonding diagram (omitting inner shells) for magnesium oxide.

MgO

Magnesium atom

Oxygen atom

Mg2+ O2-

Magnesium Oxide


Sodium Fluoride

Sodium atom Fluorineatom

Copy the diagram and draw another box showing the electron configuration in sodium fluoride.

Na+

2.82.8

FNa

2.8.1. 2.7

F-


Bonding in Lithium Oxide

The bonding in lithium oxide is more complicated in that there are different numbers of each atom.

Li

Li

OLi+

Li+

O2-


Bonding in Lithium Nitride

The bonding in lithium nitride similarly involves different numbers of each atom.

N

Li

Li

Li

Li+

Li+

N3-

Li


Bonding in Aluminium Fluoride

In aluminium fluoride it is the non-metal atoms that we need more of.

F

F

F

Al Al

F

F

F


Following the previously shown slides draw bonding diagrams for the compounds formed from the following atoms:

1. Lithium (2.1) and fluorine (2.7)2. Sodium (2.8.1) and sulphur (2.8.6)3. Magnesium (2.8.2) and sulphur (2.8.6)4. Magnesium (2.8.2) and fluorine (2.7)5. Aluminium (2.8.3) and nitrogen (2.5)

Remember that the total number of electrons lost by the metal must equal the total number of electrons gained by

the non-metal

Activity


2 electrons

Electrons Lost = Electrons Gained

Both sodium chloride and magnesium oxide are simple ionic compounds.

In both cases the metal and non-metal need to lose or gain the same number of electrons respectively.

Na Cl1 electron Na+ Cl-

OMg O2-Mg2+

This is not always the case.


Different numbers of electrons

Consider the reaction of sodium with oxygen.– Sodium (2.8.1) needs to lose 1 electron.– Oxygen (2.6) needs to gain 2 electrons

This can only happen if there are two sodium ions formed for every one oxygen ion formed.

The formula will be Na2O.

NaO

Na

Na+

O2-

Na+

1 electron per sodium


Consider the reaction of magnesium with chlorine.– Magnesium (2.8.2) needs to lose 2 electron.– Chlorine (2.8.7) needs to gain 1 electrons

We need 2 chlorines for every one magnesium.

The formula will be MgCl2

ClMg

Cl

Mg2+

Cl-

Cl-

2 electrons

Different numbers of electrons


Charges on ions

• When atoms form ions they aim to attain electron shells that are either completely full or completely empty.

• If we know the electron configuration of an atom we can usually work out how many electrons it must lose or gain to achieve a noble gas configuration.

• This will tell us the charge on its ion.


Charges and Metal ions

• Metals usually lose electrons to empty this outer shell. • The number of electrons in the outer shell is usually

equal to the group number in the Periodic Table. For example,

Mg

2.8.2 Mg2+

Al

2.8.3 Al3+

Li

2.1Li+


Charges and non-metal ions

• Outer shells with 5 or more electrons usually gain electrons to fill up the outer shell. For example,

• Oxygen (2.6) gains 2 electrons to form O2-

• Chlorine (2.8.7) gains 1 electron to form Cl-

ClO

2.62.8 O

O2-

2.8.7 2.8.8 Cl Cl-


Copy out and fill in the Table below showing what charge ions will be formed from the elements listed.

H He

Li

Na

K

Be

Sc Ti

Mg

V Cr Mn Fe Co Ni Cu Zn Ga Ge Se BrCa Kr

Al P

N O

S Cl

F Ne

ArSi

B C

As

Mg

C

Cl

K

Na

Charge

Outer electrons

NeBrOAlKCaClNLiSymbol

1 5 7 2 1 3 6 7 1 8

1+ 3- 1- 2+ 1+ 3+ 2- 1- 1+ 0

Activity


The formulae of ionic compounds

This is most quickly done in 5 stages.Remember the total + and – charges must =zeroRemember the total + and – charges must =zeroFor example, For example, the formula of calcium bromide.

1. Symbols: Ca Br2. Charge on ions 2+ 1-3. Need more of Br4. Ratio of ions 1 25. Formula CaBrCaBr22

BrCa

Br

Ca2+

Br-

Br-

2 electrons


For example, the formula of aluminium bromide.

1. Symbols: Al Br2. Charge on ions 3+ 1-3. Need more of Br4. Ratio of ions 1 35. Formula AlBrAlBr33

BrAl

Br

Br

3 electrons

Al3+ Br-

Br-

Br-



For example, the formula of aluminium oxide.

1. Symbols: Al O2. Charge on ions 3+ 2-3. Need more of O4. Ratio of ions 2 3 (to give 6 e-)5. Formula AlAl22OO33

OAl

O

OAl

2e-

2e-

2e-

Al3+

O2-

O2-

O2-

Al3+



Using the method shown on the last few slides, work out the formula of allall the ionic compounds that you can make from combinations of the metals and non-metals shown below:

•Metals: Li Ca Na Mg Al K

•Non-Metals: F O N Br S Cl

Activity


More Complicated Formulae

• Ionic compounds may contain ions consisting of groups of atoms rather than a single atom.

• Here are some more complicated ions you may come across.

Atoms presentChargeFormulaIon

2-

1-

1+

2-

1-

CO32-

OH-

NH4+

SO42-

NO3-

carbonate

hydroxide

ammonium

sulphate

nitrate N O O O

OS OOO

N H H H H

O H

C O O O


1. Symbols: Li NO3-

2. Charge on ions 1+ 1-

3. Need more of neither

4. Ratio of ions 1 1

5. Formula LiNOLiNO33

• When working out formula you simply treat the entire group of atoms as though it were a single atom.

• The only difficulty is to do with how we write down the final answer.

• For example, what is the formula of lithium nitrate?



1. Symbols: Mg NO3-


3. Need more of NO3-


5. Formula Mg(NOMg(NO33)2

• What is the formula of magnesium nitrate?

• The brackets around the NO3- ion show that the 2 refers

to two complete NO3- ions.

• It represents a total of 2 nitrogens and 6 oxygens with each magnesium ion.



• What is the formula of sodium sulphate?

1. Symbols: Na+ SO42-


3. Need more of Na+


5. Formula NaNa22SOSO44

• No brackets here as only one SO42- ion needed.

• Note although Na contains 2 letters it only represents a single atom – so no brackets!



1. Symbols:

2. Charge on ions

3. Need more of

4. Ratio of ions

5. Formula

Again we need brackets as 3 complete OH- ions are needed meaning that for each aluminium there are 3 oxygens and 3 hydrogens.

Al3+ OH-

3+ 1-

OH-

1 3

Al(OH)Al(OH)33

Write down how to work out the formula of aluminium hydroxide.


1. Symbols:

2. Charge on ions

3. Need more of

4. Ratio of ions

5. Formula

Again we need brackets as 2 complete NH4+ ions are needed meaning

that for each sulphate ion there are 2 nitrogen and 8 hydrogens.

NH4+ SO4

2-

1+ 2-

2 1

(NH(NH44))22SOSO44

NH4+

Write down how to work out the formula of ammonium sulphate.


1. Symbols:

2. Charge on ions

3. Need more of

4. Ratio of ions

5. Formula

No brackets for Al as only one atom even though it’s 2 letters.

We do need brackets around the SO4 to show it is 3 complete sulphate ions.

Al3+ SO42-

3+ 2-

2 3

AlAl22(SO(SO44))33

Need to get total charge =6

Write down how to work out the formula of aluminium sulphate.


• Formed when a _____ and non-metal react.• Metals ___ electrons to empty their outer

electron shell.• Non-metals _____ electrons to fill their outer

electron shell.• The ratio of metal ions to non-metal ions will

depend upon the number of ________ lost and gained.

• The ions formed join up into giant _____.

Copy this choosing words from below to fill the gaps.

lose lattices

electrons gain metal

metal

lose

gain

electrons

lattices.


Which of the following will have ionic bonding?

A. Copper chloride

B. Iron

C. Brass

D. Sulphur dioxide


Which of the following is NOTNOT true of ionic bonding?

A. Metal ions have a + charge

B. Non-metal ions have a - charge

C. They form a 2 dimensional lattice

D. They have giant structures


Which of the following is true about the oxide ion?

A. Formed by oxygen atoms losing 2 electrons.

B. Oxygen ions have an empty second shell

C. Exist in pairs

D. Have a 2- charge16

O8


Which of the following is true about the sodium ion?

A. Has a 2,8,1 electron arrangement

B. Formed by sodium atoms gaining 1 electron.

C. Sodium ions have an empty second shell

D. Have a 1+ charge23

Na11


What formula compound will be formed from Mn4+ and O2- ions?

A. Mn2O4

B. MnO2

C. Mn2O

D. MnO4


What formula compound will be formed from Ga3+ and SO4

2- ions?

A. Ga2(SO4)3

B. Ga3(SO4)2

C. Ga2S3O12

D. Ga (SO4)3

Documents

© Boardworks Ltd 2003 CHEMICAL BONDING PART 1 IONIC BONDING