National 5
Bonding, Structure and
Properties of Elements
and Compounds
1
Bonding, structure and properties
Bonding Atoms Together
Why should atoms combine with each other? We found in the Topic 'Atomic
Theory' that all elements with the same number of electrons in their outer shell
would have similar chemical reactions.
We have also found that the Noble Gases had either a complete outer ener gy level of
electrons or had 8 electrons in their outer energy level. This arrangement of the
electrons in their outer energy level (called an 'octet') makes them very stable and
explains why they do not easily combine with other atoms.
In fact they are just single atoms and as such are called Monatomic Elements.
(mon =1 atomic = atom).
Other elements would be more stable if they too could somehow have this 'stable
octet' arrangement of their outer shell electrons – just like the Noble Gases!
Bonding
To get this arrangement they are prepared to join or make bonds to other atoms.
How many bonds they make depends on the way the electrons are arranged in the
outer shells of the elements.
To work out how they are arranged you must remember some rules:
1.
The shell nearest the nucleus fill up first, and then the next one out and so on.
2.
Each shell (energy level) has special 'compartments' called orbitals which can
hold a maximum of 2 electrons.
This means the first shell only has 1 orbital since it can only hold 2 electrons
before it is full up. The second shell can hold 8 electrons so it has 4 orbitals.
3.
Electrons try to go into different orbitals within a shell if possible. They will only
pair up in an orbital if there is no empty one for them to go into.
Activity: Collect Notes 1.13 a and b and insert them into your notes.
Complete the electron shell diagrams in 1.13b for the elements using the above
3 rules. Use a • to represent an electron.
2
If two or more atoms of non-metal elements bond together they will form a molecule.
e.g. 2 atoms of oxygen bonding together will make a molecule of oxygen. Notice how the
electrons are shred in the bond.
Oxygen molecule:
When two or more atoms of different elements bond together a compound is
formed. e.g. hydrogen and oxygen bonding together make the compound called
water (H2 O) while sodium and chlorine bonding together make the compound
called sodium chloride (common salt).
In this Topic we will concentrate on the bonding in elements and compounds.
If you look at a Periodic Table of the Elements or even examine some elements
yourself, you will see that at room temperature some elements like copper and tin are
shiny metals, some like carbon and sulphur are black or yellow solid non -metals while
others like hydrogen and oxygen are gases.
Why should they look so differently ? Does this mean that their atoms are joined
together in different ways ? Is there more than one way what atoms of an element can
form bonds with each other ?
3
1.1 Bonding and structure of covalent compounds
Compounds are made up of atoms of more than one element. Energy is required to
separate the elements in a compound because the different kinds of atoms are chemically
joined together.
The chemical join between different atoms in a compound is called a bond. One kind of
bond is called a covalent bond. A discrete (small) group of non-metal atoms held
together by covalent bonds is called a molecule. Molecules made up of only two atoms
are called diatomic (two atom).
The chemical formula gives the number of atoms of each element in a molecule. The
number of atoms of each element in the molecule is indicated by a subscript after the
symbol of the element (the subscript "1" is not written in), e.g. there is one carbon and
four hydrogen atoms in a molecule of CH4.
Activity 1.26
1.
2.
Take a set of models.
Identify the colour which represents - a carbon atom,
- a nitrogen atom,
- an oxygen atom,
- a chlorine atom,
- a hydrogen atom.
Join hydrogen and chlorine atoms together to make a molecule of
hydrogen chloride.
Note the formula (see table on next page)
3.
Now make molecules of
(i)
(ii)
(iii)
(iv)
hydrogen oxide,
nitrogen hydride,
carbon chloride,
carbon dioxide.
Note the formula for each molecule.
Answer the following questions:
1.
What is meant by atoms being bonded together?
2.
What is meant by a molecule?
3.
What is meant by a diatomic molecule?
4.
What kind of bonding is found in molecules?
5.
What information is given by the chemical formula?
6.
Copy and complete the table on the next page.
4
Name
Formula
hydrogen
chloride
hydrogen
oxide
nitrogen
hydride
carbon
chloride
carbon
dioxide
7.
Which compound is made up of diatomic molecules?
8.
Is it atoms of metal or non-metal elements that bond to form molecules?
9.
Hydrogen Iodide, formula HI, is a compound. Is it diatomic? Explain.
1.2
Arrangements of atoms: Drawing Covalent Molecules
The chemical formula indicates the number of atoms of
each element in the molecule. It does not give any
information about how atoms are arranged. In some
molecules the atoms are arranged in a straight line,
some molecules are flat, others are three-dimensional.
Molecules are usually drawn "flattened-down" with the number of covalent bonds to each
atom shown.
One line ( - ) represents a single covalent bond, e.g. H - Cl;
two lines ( = ) represent a double covalent bond, e.g. O= C = O.
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Activity 1.27 – Making Discrete Covalent Molecules
1.
Take a set of models.
2.
Use carbon and chlorine atoms to make a molecule of carbon tetrachloride.
Note the formula.
The arrangement is flattened-down
to look like:
3.
Now make molecules of and Draw a diagram to show the flattened-down
arrangement of atoms in each of the following molecules:
(i)
hydrogen chloride
(ii)
hydrogen oxide
(iii)
nitrogen hydride
(iv)
carbon hydride
(v)
carbon dioxide

Note the molecules in which the atoms are arranged in a straight line.

Note the molecule which is flat.

Note the molecules which are three-dimensional.
1.
What is meant by a single covalent bond?
2.
What is meant by a double covalent bond?
3.
Draw flattened down structures of hydrogen iodide and
carbon tetrabromide.
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1.3 Covalent bonding in elements – Diatomic Elements
Certain elements normally exist as diatomic molecules. In the Periodic table there are only
7 diatomic elements! They are all non-metals. The first is hydrogen (H2). Use the term ‘H,
NOF down ↓’ to help you find the rest of them.
Diatomic molecules contain two atoms.
Activity 1.28
1.
Take a set of models and make a molecule of each of
(i) hydrogen,
(ii) chlorine,
(iii) oxygen,
(iv) nitrogen.
Note the formula for each element.
Note the elements which are made up of atoms joined by
- a single covalent bond,
- a double covalent bond,
- a triple covalent bond.
2.
Try to make a diatomic molecule of carbon.
Decide whether carbon can exist as C2 molecules
The elements which exist as diatomic molecules are:
hydrogen, oxygen, nitrogen, fluorine, chlorine, bromine and iodine.
(‘H, NOF down ↓’)
Copy and complete the table below for the elements which exist as diatomic molecules.
Element
Formula
Type of covalent bond
1.4 Covalent bonding: A Sharing of Electrons and Lewis Diagrams
Take a copy of Notes 1.14a, 1.14b read them and stick them into your notebook. Your
teacher may also introduce you to Lewis diagrams. Then read Notes 1.14c.
Write the heading Covalent Bonding. Now collect the Standard Grade Chemistry
text book. Read pages 37 to 39 and answer questions 1-4 on these pages.
Qu1. Explain in detail why the melting and boiling points of discrete covalent molecules are
so low.
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1.5 Showing the shapes of molecules
The shapes of many molecules are based on the tetrahedral 3-D arrangement of atoms
held together by strong covalent bonds. E.g. Methane (CH4) and Carbon tetrachloride.
Molecules can also be flat in shape E.g. hydrogen chloride and hydrogen oxide (water).
Activity 1.30 – Building and Drawing Flat & 3-D Covalent
Molecules
A.
Methane
1.
Make up a model of a molecule of methane, CH4
2.
Copy the three-dimensional representation of methane on to a piece
of paper.
3. Turn the model to match the drawing.
4.
Now turn the model to another position.
Make another drawing.
5.
Now turn the model to another position.
Make another drawing.
B. Ammonia
6.
Make up a model of a molecule of ammonia, NH3.
7.
As like methane, make a three-dimensional drawing on a sheet of paper.
8.
Turn the model to another position.
Make another drawing.
9.
Turn the model to another position.
Make another drawing.
8
C. Water
10. Make up a model of a molecule of water, H2O.
11. Make a drawing of a water molecule.
A two-dimensional molecule is "flat".
1.
The shape of many molecules is based on what structure?
2.
Using the guidance draw diagrams to show the shape of each of the following
molecules:
(i)
methane (carbon hydride)
(ii)
ammonia (nitrogen hydride)
(iii) water (hydrogen oxide)
3. Which molecules are three-dimensional?
4.
Which molecule is flat?
1.42 Covalent network substances
Most covalent substances exist as discrete molecules but a few consist of a giant
lattice of covalently bonded atoms. These substances are said to have a covalent
network structure.
Activity 1.31 Covalent Network Solids
Look at models showing the bonding and structure in some covalent
network substances.
Collect Notes 1.15, read it and paste it into your notebook.
1.
2.
3.
4.
5.
What is meant by a covalent network structure?
Name three substances which have a covalent network structure.
Why can graphite conduct electricity?
Why does diamond have such a high melting point?
Does diamond conduct electricity? Explain
.
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2. Bonding and structure - Ionic Compounds
2.1 Charged particles - Ions
Have you heard of the terms ion or ionic before? Think of your phone’s battery!
An ion is the charged particle which is formed when an atom either loses or gains
one or more electrons from its outer shell so the arrangement of the electrons in its
shells is then the same as that of a stable Noble Gas.
The element itself does not change into a Noble Gas since the number of protons it
has in its nucleus does not change. Its just that the number of protons and electrons
it has is no longer equal so it is no longer an atom.
There are 2 types of ion:
1.
Positive ions – made from metal atoms
2.
Negative ions – made from non-metal elements

Take a copy of notes 1.18 and stick it into your notes.

Now try Exercise 1.4.
2.1 Ionic compounds
Ionic compounds involve metals bonding to non-metals through a transfer of
electron(s). This is different from non-metals making a covalent bond as this
involves a sharing of electrons!
Take a copy of notes 1.19a and 1.19b and stick them into your notes.
Using different colours, colour in the positive and negative ions.
Activity 1.32: Ionic Lattice Structures
Look at a model showing the bonding and structure of an ionic compound.
1.45 The significance of formula

Take a copy of Notes 1.20 and stick it into your notes.
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3. Bonding and structure - Metals
3.1 Metals – Metallic Bonding
Can metals conduct electricity? If so why?
Take a copy of Notes 1.21 and 1.21 cont. Read them, and stick them it into your notes
4. Properties of Elements (Metals and non-metals)
4.1 Conduction of Electricity
Metals & Non-Metals
It is hard to imagine life without electricity - we use it for cooking, for heating and for
lighting. What is electricity?
Atoms are made up of a nucleus which contains positive particles. Negative particles
called electrons move around outside the nucleus.
Electricity is a flow of these electrons (or other charged particles) in a definite direction.
Materials that conduct electricity are called conductors; materials that do not allow
electrons to pass through are called non-conductors (insulators).
The elements in the Periodic Table can be classified as conductors and non-conductors.
Activity 1.33: Testing the Conductivity of Meals and Non-Metals
The following elements are to be tested for electrical
conduction:
copper, iron, nitrogen, sulphur, magnesium, silicon,
oxygen, aluminium, lead, iodine, mercury, tin.
The terminals through which electrical current enters and leaves the substance under test
are called electrodes. These are made of carbon - an element which conducts electricity
but is comparatively unreactive.
Before you attempt the experiment below, copy the results table on the next p[age into
your notes.
1.
2.
Set up the circuit shown.
CLEAN THE ELECTRODES AFTER EACH TEST.
Dip the electrodes into each powder.
DO NOT GET IODINE ON YOUR HANDS.
Press the other elements between the electrodes.
4.
Ask your teacher for the sealed flask of mercury.
Disconnect the electrodes from your circuit and test the mercury.
Complete the table for oxygen and nitrogen of the air.
5.
11
Copy and complete the table below using a tick (√) or a cross (x) to indicate whether
or not the element conducts electricity.
Metal or
Non-metal
Element
Conduction
1. What is meant by electricity?
2. What is meant by an electrical conductor?
3. What is meant by an electrical insulator?
4. Draw a labelled diagram of the circuit used to test some elements to see if they
conduct electricity?
5. What is meant by the electrode?
6. Why are the electrodes made of carbon?
7. What kind of element conducts electricity? Explain.
8. What can be said about all the elements which do not conduct?
9. Which element is the exception? (Look at the electrodes.)
10. What must be present in this form of the element?
11. Do metals in the liquid state conduct electricity?
12. Which liquid metal was tested in the experiment?
4.3
Conductivity Properties of Covalent compounds
Covalent compounds consist of molecules which do not have a charge. The elements in
covalent substances are non-metal elements.
Covalent compounds in solid form, liquid form and in solution are to be tested for
electrical conduction.
Copy and complete the table below complete the column to indicate whether or not the
compound conducts electricity.
Conduction
Name
Formula
Solid
Liquid
Solution
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Activity 1.34: Testing Conductivity of Covalent Compounds
Use the circuit
shown to test
the following
covalent
compounds:
1.
Do covalent compounds contain charged particles? How can you tell?
1.
What type of element is found bonded in together in covalent substances?
2. Do covalent compounds conduct electricity in any state?
13
4.4 Testing the conductivity of Ionic compounds – Solids and Solutions
Ionic compounds consist of oppositely charged ions. Ionic compounds contain both metal
and non-metal ions.
Samples of compounds are to be tested for electrical conduction - in solid form and in
aqueous solution.
Copy and complete the table below using a tick () or a cross (x) to indicate whether or
not the compound conducts electricity.
Use the following ionic compounds:
copper sulphate, sodium chloride, potassium nitrate, potassium bromide.
Activity 1.35 Testing the Conductivity of Ionic compounds
Use the circuit show
1. CLEAN THE ELECTRODES after each
test. Dip the electrodes into the solid in the jar.
2.
CLEAN THE ELECTRODES after each test.
Add the solid to water in a small beaker.
Stir to dissolve.
1. Do ionic compounds contain charged particles?
2.
What type of elements are found bonded together in ionic compounds?
3. Do ionic solids conduct electricity?
4.
Do solutions of ionic compounds conduct electricity?
5.
What test can be used to distinguish between covalent and ionic compounds?
14
Copy and complete: In ionic compounds it is the charged particles that allow
conduction of electricity, but only if the ions can move. Solid ionic compounds
do/don’t conduct electricity as the ions are free/not free to move. Ionic
solutions do/don’t conduct electricity at the ions are free/not free to move.
4.5 Conductivity of Melted (Molten) Ionic Compounds
Ions are present in ionic compounds in the solid. Positive ions attract negative ions. The
forces of attraction keep the ions locked together in the crystal lattice. Since ions in a solid
are unable to move, the solids do not conduct electricity.
In a solution, the ions in the dissolved solid become free to move and so the solution
conducts.
Some solid ionic compounds can be melted by a Bunsen burner. Will the melt conduct?
Activity 1.36 – Conductivity of Ionic Melts
Your teacher may demonstrate the following experiment where the conductivity of
solid lead iodide is tested. The solid is them melted and the conductivity of molten
lead iodide is tested. It is then cooled down and again the conductivity is tested. Look
at the questions below before the demo. You will need to answer them after it!
1.
2.
3.
Is there a reading on the meter before the solid lead iodide has melted? Explain.
Does the molten lead bromide conduct electricity? Explain in terms of ions why
this is.
What happens to the meter-reading after the heating is stopped and the melt has
cooled down? Explain in terms of movement of ions why this is so.
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4.6 Electrolysis of Ionic Compounds
Passing electricity through a solution (or a melt) results in chemical reactions
taking place at the electrodes, and new products being formed. This process is
called electrolysis. The ionic solution (or a melt) between the electrodes
which does the conducting is called the electrolyte.
A DC (direct current) supply is used as the electrode which is connected to
the positive terminal of the supply will always be "positive" (+ve); the other
will always be "negative" (-ve). The electrodes will attract oppositely-charged
ions in a solution (or a melt).
In this experiment the positive ions gain electrons at the negative electrode
and the negative ions lose electrons at the postive electrode. Both types of ion
are changed to neutral atoms.
Activity 1.37 – Electrolysis of Copper chloride
1. Half-fill a small beaker with copper chloride
solution.
2. Clean the electrodes with sandpaper. Set up the
circuit.
3. Examine the reaction taking place at the
positive electrode.
4. Remove the electrodes and examine the
negative one for evidence of a chemical
reaction.
1.
What is the definition of electrolysis?
2.
Explain why the electrolysis process is only applies to ionic compounds.
3.
What is meant by an electrolyte?
4.
Draw a labelled diagram of the circuit.
5.
Why is a D.C. (direct current) supply used for this experiment?
6.
How is the product at the positive electrode identified?
7.
What is this product?
16
8.
What must be the charge on the chloride ions?
9.
What happens to the chloride ions at the positive electrode?
10.
How can the product at the negative electrode be identified?
11.
What is this product?
12.
What must be the charge on the copper ions?
13.
What happens to the copper ions at the negative electrode?
Revision: Electrolysis of a melt – look back to 4.5
The term electrolysis applies to the passage of electricity through both a melt and a
solution. A substance which conducts electricity in solution or as a melt is called an
electrolyte.
Refer back to Activity 1.36 – Conductivity of Molten Ionic
Compound
Electrolysis of Lead Iodide – Think back to the demo and use your knowledge of electrolysis
to answer the following questions.
1.Draw a labelled diagram of the circuit used.
2.What is observed at the positive electrode?
3.What is this product?
4.What must be the charge on the iodide ions?
5.What happens to the iodide ions at the positive electrode?
6.What is observed forming at the negative electrode?
7.What must be the charge on the lead ions?
8.What happens to the lead at the negative electrode?
17
4.7 Colours of Ionic compounds (i)
Some ions are colourless, e.g. Na+ and Cl- . In the solid form they appear white due to
reflection of light from the crystals; in solution they are colourless.
Some ions are coloured, e.g. Cu2+. For an ionic compound, X+Y- , the colour of the
compound is determined by the colour of X+ and of Y-. These compounds dissolve in
water to give coloured solutions.
Ions are not usually the same colour as the atoms of the element, e.g. copper ions are
blue, copper atoms are brown, iodide ions are colourless, iodine molecules are grey.
Activity 1.39: Working out the Colours of Ions
This is a problem solving exercise. Look at the samples to find out the colour of the
compound, then deduce the colour of the ions. Copy and complete the table below
using this info.
Compound
Name
Positive ion
Colour
Name
Colour
Negative ion
Name
sodiumchloride
none
sodium
none
chloride
potassium sulphate
none
potassium
none
sulphate
sodium nitrate
none
sodium
Colour
none
chloride
copper chloride
copper sulphate
copper nitrate
nickel nitrate
nickel sulphate
sodiumdichromate
potassium dichromate
sodium chromate
potassium chromate
potassium permanganate
Questions:
1.
2.
What gives an ionic compound colour?
What colour are the ions which make up a colourless compound (white solid)?
18
3.
What is the colour of most copper compounds?
4.
Explain why the colour of copper in copper compounds is different from the colour
of the metal.
5.
What is the colour of most nickel compounds?
6.
Why is potassium permanganate purple?
7.
Why are most chromate compounds yellow?
4.8 Using the Colour of Ions - Electrolysis of copper chromate solution
1.What is meant by electrolysis?
2.What is the colour of the copper ions?
3.What is the colour of the chromate ions?
4.During the electrolysis of copper chromate solution, predict what colour will be seen
at the negative electrode. Explain.
5.Predict what colour will be seen at the positive electrode. Explain
The colour of copper chromate will be a blend of the colours of the copper and
chromate ions.
A solution of copper chromate, Cu2+ CrO42-, is electrolysed.
Passing electricity through an electrolyte separates out the positive and
negative ions.
Positive ions will be attracted to the negative electrode.
Negative ions will be attracted to the positive electrode.
Activity 1.41 Electrolysis of copper chromate solution
Your teacher will set up the following experiment. Draw a labelled diagram of
the apparatus.
1.
2.
Complete the diagram to show what is actually observed.
Do the experimental observations fit in with the predictions? Explain.
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5. Other Properties OF Elements and Compounds
5. 1 Melting and boiling points
Take a copy of Notes 1.22 read it, and stick it into your notes.
Activity 1.42
Linking Bonding to States; (s), (l) and (g)
Look at each substance in turn.
Check the bonding and note whether the substance is a solid, liquid or
gas at room temperature. Then copy and complete the table below.
.
Substance
Type of bonding
Solid, liquid or gas
1. Are all the ionic compounds solid, liquid or gas at room temperature? Explain.
2. What about the metal elements? Explain.
3. Which metal is an exception?
4. What about the discrete covalent compounds? Explain.
5. What about the covalent network compounds? Explain.
6. What can be concluded about the strength of bonding holding a compound together
which is a liquid or gas at room temperature?
7. What can be concluded about the strength of bonding holding a compound together
which is a solid at room temperature?
Extention: Take the Standard Grade Chemistry Text book, read page 43 and answer
questions 2 and 3.
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5.2 Solubility of Ionic and Covalent Compounds
The most common solvent is water. Some substances, e.g. paints and nail-polish are not
soluble in water. These substances dissolve in non-aqueous solvents (solvents without
water)
This experiment compares the solubility of ionic and covalent compounds in water, and
also non-aqueous solvents.
Activity 1.43 Solubility of Ionic and Covalent
Compounds
Safety
Do not empty non-aqueous solvents down the sink.
USE THE RESIDUE BOTTLE.
1.
Add 1 or 2 cm depth of a nonaqueous solvent to each of four testtubes.
2.
Check which substances are soluble by adding a very small quantity
- a few crystals, or a tiny lump of the four substances
into separate test-tubes.
3.
Repeat the experiment using the other non-aqueous solvent, then
using water.
Note: Some paints are made from covalent substances. Stains caused by these paints
cannot be removed by water – the non-aqueous solvent turpentine is used.
1.
2.
3.
4.
5.
What is meant by a non-aqueous solvent?
Give everyday examples of substances which are insoluble in water but which
dissolve in a non-aqueous solvent.
Are ionic compounds generally soluble in water?
Are covalent compounds generally soluble in water?
Are covalent compounds generally soluble in non-aqueous solvents?
21
5.3 A comparison of properties
A comparison of some of the properties of substances can be found in Notes 1.23.
Take a copy, read it, and stick it into your notes.
Revision and Study Questions
Collect a copy of Standard Grade Chemistry Text book. Use your notes and the notes in the
text book to help you answer questions 1-16 on page 44 and Questions 1-11 on page 75.
22
Exercise 1.3
Covalent bonding - a bit more
Draw Lewis diagrams or similar diagrams to show how the outer electrons overlap and hence
obtain the formula for each of the following substances.
a)
hydrogen fluoride
b)
phosphorus chloride
c)
nitrogen hydride
d)
oxygen
e)
sulphur chloride
f)
hydrogen sulphide
g)
carbon dioxide
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Exercise 1.4
Charge on ions
Use the table showing the electron arrangements to write the symbol and charge for
each of the following ions.
a)
potassium
b)
sulphur
c)
nitrogen
d)
aluminium
e)
iodine
f)
magnesium
g)
potassium
h)
bromine
i)
strontium
j)
rubidium
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