1 | p a g e j u n e 2 0 2 1 v e r s i o n 2 a l e v e l c

1 | P a g e J u n e 2 0 2 1 V e r s i o n 2 a l e v e l c h e m i s t r y @ s t d o m s

Bridging the

Gap –

GCSE to A’

Level

Chemistry Atomic Structure + Structure and Bonding


The development of atomic structure The Greek philosopher Democritus first suggested that matter was made up of atoms in about 350 BCE. However, it is only much more recently that scientists realised that atoms are made up of even smaller particles.

In 1897, the British scientist J. J. Thomson discovered the electron while carrying out experiments on the conduction of electricity through gases. Thomson suggested a theory for the structure of the atom known as the plum pudding model. He suggested that the atom was a tiny sphere of positive charge (the pudding) with much lighter negatively charged electrons (the plums) spread throughout the atom.

Thomson’s model was replaced by Rutherford and Bohr’s model. Ernest Rutherford developed his new

ideas following:


The development of atomic structure (continued)

Rutherford realised that the results did not fit in with Thomson ’s model. He proposed a new theory to explain these results. He said that most of the mass and positive charge in an atom must be concentrated in a tiny nucleus which is much smaller than the atom itself. The electrons move in the space around the nucleus.

Rutherford realised that his model was not totally correct as the negative electrons would be attracted into the nucleus, which has positive charge. In 1913, Neils Bohr, working with Rutherford, used the new ‘quantum physics’ to develop the model further. He proposed that the electrons moved in stable orbits called shells or energy levels.

In 1932, James Chadwick developed the model further when he discovered the neutron. Scientists knew that there was some extra mass in atoms that could not be explained by the Rutherford-Bohr model. Chadwick’s model proposed that neutrons were in the nucleus as well as the protons.

These ideas have been developed further since then, but the basic idea of a tiny nucleus containing protons and neutrons surrounded by electrons remains. Science works by people proposing theories which fit and explain known facts and experimental results. As new discoveries are made, theories have to be altered or replaced by new ones. When a scientist suggests a theory, it is a proposed explanation rather than a statement of fact.

1 Describe the current model of atomic structure.

2 What new contribution did each of the following people make to the current model?

a Thomson

b Rutherford

c Bohr

d Chadwick

3 In Geiger and Marsden’s experiments, only a tiny fraction of the alpha particles were deflected or bounced back. It would have been very easy to ignore these results, as most alpha particles passed straight through the gold foil. Explain why it was very important that they did not ignore these results.

4 The development of ideas about atomic structure helps to show how science works.

a Explain, in simple terms, why Thomson’s model was replaced by Rutherford’s.

b Describe why scientific theories change or are replaced.


Atomic and electronic structure

Complete the table below. You will need to use the Periodic Table to help with the last three.

Atom Atomic

number

Mass number Number of

protons

Number of

neutrons

Number of

electrons

K 19 39

B 5 11

P 15 16

Ca 20 20

26 30

78

55

120 50

2 Complete the table below.

Atom Atomic

number

Mass

number

Number of

protons

Number of

neutrons

Number of

electrons

Electronic

structure

Mg 12 24

Ar 18 22

Si 28 2, 8, 4

Na 11 12

S 16 16

Cl 17 35

Cl 17 37


Atoms and ions

You will need to look at the Periodic Table to help you answer the following questions.

1 Fill in the passage below using these words: electrons gain lose negative positive

Ions are particles that have a different number of protons and _______________. Ions are electrically charged. Ions can be formed when a metal reacts with a non-metal. Metal atoms _______________ electrons to form _______________ ions. Non-metals _______________ electrons to form _______________ ions.

2 a Complete the table to show the electronic structure of the following ions. The first one has been done for you.

Ion O2– Ca2+ Li+ Mg2+ Cl– Be2+

Electronic

structure

b The table shows the electronic structure of some Group 0 elements (noble gases). Place the ions from part a into the correct row of the table. One has been done for you.

Element Electronic

structure

Ions with the same electronic structure

He 2

Ne 2, 8 F–

Ar 2, 8, 8

c What is the link between the electronic structure of ions and the electronic structure of Group 0 elements (noble gases)?

Ion F– Na+ Al3+ K+ S2– H+

Electronic

structure 2, 8


3 Magnesium oxide (MgO) contains magnesium ions (Mg2+) and oxide ions (O2–). Draw the electronic structure of these ions on the diagram.

4 Calcium atoms react with chlorine atoms to form the ionic compound calcium chloride. Calcium atoms each lose two electrons to form calcium ions. Chlorine atoms each gain one electron to form chloride ions. This means that calcium atoms react with chlorine atoms in the ratio of one calcium atom for every two chlorine atoms.

Complete the diagram on the right to show the electronic structure of the calcium and chlorine atoms and the calcium and chloride ions.


Writing formulae Use the table of ions to write the formula of the following ionic compounds. You will need to use your knowledge of electronic structure, ions and the Periodic Table to work out the charge and formula of some ions in questions 3 and 4.

Positive ions Negative ions

aluminium Al3+ lead Pb2+ bromide Br– oxide O2–

ammonium NH4+ lithium Li+ carbonate CO3

2– sulfate SO42–

barium Ba2+ magnesium Mg2+ chloride Cl– sulfide S2–

calcium Ca2+ potassium K+ fluoride F–

copper (II) Cu2+ silver Ag+ hydrogencarbonate HCO3–

hydrogen H+ sodium Na+ hydroxide OH–

iron (II) Fe2+ zinc Zn2+ iodide I–

iron (III) Fe3+ nitrate NO3–

1 a potassium iodide 2 a potassium sulfate

b sodium oxide b magnesium sulfate

c aluminium bromide c magnesium hydroxide

d magnesium chloride d copper (II) nitrate

e silver oxide e zinc carbonate

f iron (II) oxide f potassium hydroxide

g iron (III) oxide g sodium carbonate

h calcium sulfide h aluminium hydroxide

i copper (II) chloride i ammonium hydroxide

j lithium fluoride j ammonium chloride

k barium chloride k aluminium sulfate

l lead sulfide l iron (III) nitrate

m zinc iodide m ammonium nitrate

n aluminium sulfide n sodium hydrogencarbonate

o barium oxide o potassium nitrate


Ionic substances

Ionic substances have high melting and boiling points. This is because there are strong attractions between positive and negative ions. They conduct electricity when they are melted and if they dissolve in water. This is because the ions can move. They do not conduct electricity as solids because their ions cannot move around. The formula of an ionic compound represents the ratio of ions in the structure.

1 Explain why ionic compounds have high melting and boiling points.

________________________________________________________________________

2 Explain why ionic compounds conduct electricity when melted or dissolved in water.

________________________________________________________________________

________________________________________________________________________

3 Explain why ionic compounds do not conduct electricity as solids.

________________________________________________________________________

________________________________________________________________________

4 Look at the following table of data and give the letters of the substances which are ionic.

________________________________________________________________________

Substance Melting

point (°C)

Boiling

point (°C)

Electrical conductivity as

Solid Liquid Solution (aq)

A 650 1107 conducts conducts insoluble

B 114 184 does not conduct does not conduct does not

conduct

C 801 1467 does not conduct conducts conducts

D 2040 2980 does not conduct conducts insoluble

E 119 445 does not conduct does not conduct insoluble

F 1610 2230 does not conduct does not conduct insoluble


Three forms of carbon

Diamond and graphite are both forms of carbon which have giant covalent structures. They have both been used for hundreds of years.

1 Complete the table using the words and phrases below. When you have finished, it should summarise the properties of diamond and graphite.


Three forms of carbon (continued)

In 1996, Professor Sir Harry Kroto won the Nobel Prize for Chemistry for his discovery of a third form of carbon. It was made by the action of a laser on some graphite. It was called buckminsterfullerene after the American architect Buckminster Fuller who built buildings in complex geometric shapes.

Buckminsterfullerene is the same shape as a football.

2 Buckminsterfullerene has the formula C60. Is it a simple molecular substance or a giant covalent substance?

Explain your answer.

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________


Metals 1 Fill in the blanks to complete the passage.

Metallic substances have a giant structure. In the structure, the atoms are packed _______________

together. The outer shell _______________ are lost from each atom leaving _______________ metal

ions. There is a _______________ attraction between the metal ions and the delocalised electrons.

This means the metals have _______________ melting and boiling points. Metals conduct electricity

and heat because the outer energy level (shell) _______________ are free to move around. Metals

can be bent and shaped because the layers of ions can _______________ over each other yet there

are strong forces of attraction between the positive ions and the delocalised electrons.

2 Use this Periodic Table to decide whether the following elements are metals.

3 Look at the following table of data and give the letters of the substances which are metallic.

____________________________________________________________________________________

Substance Melting point (°C)

Boiling point (°C)

Electrical conductivity as

Solid Liquid

A 1887 2482 conducts conducts

B –39 357 conducts conducts

C 636 1300 does not conduct conducts

D 64 774 conducts conducts

E 119 445 does not conduct does not conduct

F 1923 2002 does not conduct conducts

4 Describe some tests that could be done to find out if a substance is a metal.


Structure types Complete the table to show the properties of the five different types of substances.

The answers to choose from are in the last column.

Property Monatomic Ionic Simple

molecular

Giant

covalent Metallic

Melting and

boiling points

Very high

High

High

Low

Very low

Conductivity

as solid

conducts

does not conduct

does not conduct

does not conduct

does not conduct

Conductivity

when melted

conducts

conducts

does not conduct

does not conduct

does not conduct

Solubility in

water

soluble (usually)

insoluble (usually)

insoluble

insoluble

insoluble

Conductivity

of solution

conducts

insoluble (usually)

insoluble

insoluble

insoluble

2 Which type of structure does each of the following substances have? Complete the table with your answers.

Substance Melting

point

(°C)

Boiling

point

(°C)

Electrical conductivity as Type of

structure Solid Liquid Solution (aq)

A 963 1560 does not

conduct

conducts conducts

B 1063 2967 conducts conducts insoluble

C 123 187 does not

conduct

does not

conduct

insoluble

D –7 59 does not

conduct

does not

conduct

does not

conduct

E 3527 4027 does not

conduct

does not

conduct

insoluble

F 30 2397 conducts conducts insoluble

G 1713 2230 does not

conduct

does not

conduct

insoluble

H –138 0 does not

conduct

does not

conduct

insoluble

I –189 –188 does not

conduct

does not

conduct

insoluble

J 1100 1501 does not

conduct

conducts insoluble


Extension work - Electrolysis Electrolysis is the decomposition of ionic compounds using electricity. Ionic compounds can be electrolysed when molten or dissolved in water because the ions can move to the electrodes. Oxidation and reduction take place at the electrodes. Oxidation is the loss of electrons. Reduction is the gain of electrons.

1 Complete the table about the electrolysis of some ionic compounds.

Molten

substance

Formula Ions

contained

Product at negative

electrode

Product at positive

electrode

Calcium bromide CaBr2 Ca2+, Br–

Iron oxide Fe2O3 Fe3+, O2–

Sodium iodide NaI Na+, I–

Nickel chloride NiCl2 Ni2+, Cl–

Aluminium is made by the electrolysis of aluminium oxide. Aluminium oxide is insoluble in water and melts at over 2000°C. It is mixed with a substance called cryolite. This mixture melts at a much lower temperature of about 950°C. Aluminium oxide contains aluminium (Al3+) and oxide (O2–) ions.

2 The Al3+ ions go to the negative electrode. The O2– ions go to the positive electrode. Explain why this happens.

________________________________________________________________________

________________________________________________________________________

3 The half equation for the process at the negative electrode is: Al3+ + 3 e– → Al

Is this oxidation or reduction? Explain your answer.

________________________________________________________________________

4 The half equation for the process at the positive electrode is: 2O2– → O2 + 4 e–

Is this oxidation or reduction? Explain your answer.

________________________________________________________________________

5 Explain why aluminium oxide does not conduct electricity as a solid.

________________________________________________________________________


Electrolysis of solutions

Electrolysis of ionic compounds dissolved in water can form different products to the electrolysis of molten ionic compounds. The following table gives some examples of the products of electrolysis of solutions using graphite electrodes.

Negative electrode (positive ions) Positive electrode (negative ions)

Solutions containing ions of

metals low in the reactivity

series

the metal Solutions containing halide

ions (chloride, bromide,

iodide)

the halogen

(chlorine,

bromine,

iodine)

Solutions containing ions of

metals high in the

reactivity series

hydrogen Solutions containing other

negative ions

oxygen

1 Predict the products of the electrolysis of each of the following.

Substance Negative electrode Positive electrode

potassium iodide (l) KI(l)

potassium iodide (aq) KI(aq)

sodium bromide (l) NaBr(l)

sodium bromide (aq) NaBr(aq)

magnesium chloride (l) MgCl2(l)

magnesium chloride (aq) MgCl2(aq)

lead nitrate (aq) Pb(NO3)2(aq)

sulfuric acid (aq) H2SO4(aq)

2 Balance the following half equations.

a Ag+ + ________ e– → Ag

b Cr3+ + ________ e– → Cr

c _______ Br– → Br2 + ______ e–

d _______ H+ + _______ e– → H2

e _______ OH– → _______ H2O + O2 + _____ e–

3 Oxidation can be defined as the loss of electrons and reduction as the gain of electrons. The following half equations show what happens in the electrolysis of calcium chloride.

Half equation 1: Ca2+ + 2 e– → Ca

Half equation 2: 2 Cl– → Cl2 + 2 e–

a Which half equation takes place at the positive electrode?

b Which half equation takes place at the negative electrode?

c Which half equation represents an oxidation process?

d Which half equation represents a reduction process?


NOTES

1 | p a g e j u n e 2 0 2 1 v e r s i o n 2 a l e v e l c

Documents