THE PERIODIC TABLE
1.
Atomic Structure
Type of particle
proton
neutron
electron
Mass
1
1
Almost 0
Charge
+1
0
-1
Where found
Nucleus
Nucleus
shells
Atoms have the same number of protons and electrons so are neutral overall.
a)
protons
Protons are found in the nucleus of an atom.
The number of protons (or electrons) is called the atomic number.
The atomic number determines the name of the atom, so you can name an atom by
looking at its atomic number.
Elements are arranged in the Periodic Table in order of increasing atomic number.
Exercise 1
What name would you give to an atom containing
a)
six protons;
b)
ten protons;
c)
fifty protons?
How many protons will you find in the nucleus of
d)
a helium atom;
e)
a chlorine atom;
f)
an iron atom?
b)
neutrons
Neutrons are found in the nucleus of an atom.
The mass of an atom depends on the number of protons and neutrons.
The sum of the number of protons and neutrons is called the mass number.
The number of neutrons can vary. This means that two atoms of the same element can
have different mass numbers.
Eg
An atom has 14 protons and 15 neutrons.
What is the atomic number? 14
What is the mass number? 29
29
What atom is it?
Silicon-29
or
Si
Exercise 2
Name an give the correct symbols for the following atoms:
An atom with 2 protons and 2 neutrons
An atom with 3 protons and 4 neutrons
An atom with 26 protons and 30 neutrons
An atom with 6 protons and 6 neutrons
An atom with 6 protons and 7 neutrons
An atom with 6 protons and 8 neutrons
An atom with 17 protons and 18 neutrons
An atom with 17 protons and 20 neutrons
How many protons, neutrons and electrons in these atoms?
130
Xe
H
81
Br
235
U
2
Atoms with the same number of protons but different numbers of neutrons are called
isotopes.
Eg carbon-12 and carbon-13 are isotopes
Eg chlorine-37 and chlorine-35 are isotopes
The relative atomic mass of an atom is the weighted average mass of the different
isotopes. It can be found in the Periodic Table and can be worked out if the
abundances of the different isotopes are known:
Eg
75% of chlorine exists as chlorine-35
25% of chlorine exists as chlorine-37
What is the average mass of a chlorine atom?
(35 x 75) + (37 x 25)
100
= 35.5 (average mass = relative atomic mass)
Exercise 3
a)
80% of boron exists as boron-11
20% of boron exists as boron-10
What is the average mass/relative atomic mass of a boron atom?
(11 x 80) + (10 x 20)
100
b)
= 10.8
50% of bromine exists as bromine-79
50% of bromine exists as bromine-81
What is the average mass/relative atomic mass of a bromine atom?
(79 x 50) + (81 x 50)
100
= 80.0
As isotopes have the same number of protons and electrons, they have the same
chemical properties.
c)
electrons
Electrons are found in shells.
In atoms, the number of electrons is the same as the number of protons.
Shells are filled starting with the innermost shells.
The first shell can hold 2 electrons.
The second and third shells can hold 8 electrons each.
Exercise 4
Draw an atom of lithium
Draw an atom of sodium
Draw an atom of potassium
What do these three atoms have in common?
Draw an atom of fluorine
Draw an atom of chlorine
What do these two atoms have in common?
Draw an atom of helium
Draw an atom of neon
Draw an atom of argon
What do these three atoms have in common?
What do sodium, chlorine and argon have in common?
What do lithium, fluorine and neon have in common?
All elements in the same column of the Periodic Table have the same number of
electrons in the outer shell. A column in the Periodic Table is called a GROUP.
All elements in the same row of the Periodic Table have the same number of shells. A
row in the Periodic Table is called a PERIOD.
2.
Bonding
Atoms need a full or empty outer shell in order to be stable.
Atoms can form full or empty shells by gaining electrons, losing electrons or sharing
electrons.
a)
forming molecules
A molecule if formed when two or more atoms join together by sharing electrons.
The process of sharing electrons is called covalent bonding.
Sharing electrons is one way in which atoms can form full outer shells.
Examples of molecules are: Cl2, H2, HCl, CH4, CO2, H2O
b)
giant covalent structures
Sometimes atoms join together by sharing electrons, but form giant structures, in
which all the atoms are held together by covalent bonds.
Examples are diamond and graphite (both made up of carbon atoms).
b)
forming ions
Atoms in group 1 (lithium, sodium, potassium) can form a full outer shell by losing 1
electron.
Atoms in group 7 (chlorine, fluorine) can form a full outer shell by gaining 1 electron.
Atoms in group 8 (or 0) are already stable and do not gain or lose electrons.
When you add electrons, the overall charge becomes negative.
Adding electrons to an atom is known as reduction.
When you take away electrons, the overall charge becomes positive.
Taking away electrons from an atom is known as oxidation.
An atom or molecule which has an overall charge is called an ion.
Exercise 5
Write equations to show how the following atoms can become stable by forming ions.
In each case, state whether oxidation or reduction is taking place:
Na
Mg
Cl
O
Al
S
F
Ne
Ar
K
Exercise 6
State whether the following particles are atoms, molecules or ions
Na, Cl2, Na+, Cl-, SO2, SO42-, H2O, OH-
3.
Elements and Compounds
a)
elements




An element is a substance which contains only one type of atom.
Elements cannot be broken down chemically.
There are just over 100 elements
Each atom is listed in the Periodic Table in order of increasing atomic number.

b)
Some elements make full outer shells by sharing and forming molecules (like
hydrogen, nitrogen and chlorine).
Some exist as giant structures containing covalent bonds (eg carbon).
Some exist as free atoms (like helium and xenon)
Most give up their electrons and form metallic structures with free electrons
(like magnesium, aluminium and iron).
compounds







Eg
A compound is a substance which contains different atoms joined together.
These can be joined by ionic bonds (like in sodium chloride) or with covalent
bonds (like water).
There are a very large number of different compounds.
Ionic compounds are formed when electrons are transferred from one atom to
another, and then the different ions attract together.
The atom which loses electrons becomes a positive ion (cation).
The atom which gains electrons becomes a negative ion (anion).
The ions attract to form an ionic compound.
Sodium has one electron in its outer shell
Chlorine has seven electrons in its outer shell
So the sodium gives its electron to the chlorine.
The Na+ and Cl- ions join together to make the ionic compound NaCl.
Exercise 7
For each of the following pairs of atoms, state how the electrons will be transferred,
deduce the formula of the compound formed and draw a dot-cross diagram to show
the bonding in the ionic compound
a)
b)
c)
d)
sodium and chlorine
magnesium and oxygen
magnesium and fluorine
sodium and oxygen
Now work out the formula of:
d)
e)
f)
g)
h)
Sodium sulphide
Aluminium fluoride
Potassium oxide
Magnesium sulphide
Aluminium oxide
Now try:
CD6 Exercise 1
c)
properties of different compounds
Some covalent compounds, like carbon dioxide and water, have low melting points
because there are weak intermolecular forces between the different molecules. They
do not conduct electricity because there are no free electrons.
Some covalent substances like diamond and graphite have high melting points
because there are strong covalent bonds between all the atoms. Graphite conducts
electricity because it has free electrons, but diamond does not.
PRACTICAL 1
1.
2.
3.
4.
What properties do ionic compounds have?
Find out whether sodium chloride and magnesium oxide conduct
electricity.
Find out whether they dissolve in water.
Find out whether the conduct electricity when dissolved in water.
Find out if they have a high melting point.
Compound
Does it conduct
electricity?
Does it have a high
melting point?
Does it dissolve in water?
Does it conduct electricity
when dissolved in water?
Does it conduct electricity
when it is molten?
Sodium chloride
no
Magnesium oxide
No
yes
Yes (very high)
yes
yes
No
It didn’t dissolve
yes
Yes
Property
Ionic compounds have a high melting
point
Ionic compounds do not conduct
electricity in the solid state
Ionic compounds can conduct electricity
when molten
Sodium chloride conducts electricity
when dissolved in water
Explanation
Strong attraction between positive and
negative ions in a giant lattice
The ions cannot move in a solid
The ions can move in a liquid
The ions can move when dissolved in
water
Now try: CD6 Exercise 2
4.
Group 1 Elements
The group 1 elements are lithium, sodium, potassium, rubidium and caesium.
a)
Reaction with water
They all react vigorously with water.
PRACTICAL 2
How do group 1 metals react with water?
Drop pieces of sodium and potassium into water and observe what happens. Add
universal indicator to the water and observe what happens.
Video: Macromedia videos: lithium, sodium, potassium, rubidium and caesium with
water
Eg
sodium + water  sodium hydroxide + hydrogen
potassium + water  potassium hydroxide + hydrogen
symbol equation:
2Na + 2H2O  2NaOH + H2
2K + 2H2O  2KOH + H2
The reaction produces a metal hydroxide, which dissolves in water to give an alkaline
solution.
Hence group 1 metals are often called ALKALI METALS
Group 1 metals are so reactive to air and water that they have to be kept under oil.
b)
Reactivity of Group 1 metals
Group 1 metals become more reactive as you descend the group.
Lithium < Sodium < Potassium < Rubidium < Caesium
Least reactive
Most reactive
Group 1 metals react by losing one electron.
The more reactive the metal the more easily it can lose one electron.
As you go down a group, there are more shells and so the electron in the outer shell is
further and further away from the nucleus. This means that the attraction is less and
the electron is more easily lost.
c)
Testing for lithium, sodium and potassium in compounds
How can you distinguish between compounds of lithium, sodium and potassium?
Answer: carry out a flame test.
PRACTICAL 3
Flame Tests
Method:
-
dip a nichrome wire loop into some dilute hydrochloric acid
then dip the wire loop into a sample of the solid
then put the wire loop into a blue Bunsen flame
what colour is the flame?
Compound containing…
Lithium
Sodium
Potassium
5.
Group 7 elements
a)
Structure and appearance
Colour of flame……
Red
Yellow
Purple/lilac
The first four group 7 elements are fluorine, chlorine, bromine and iodine.
Elements in group 7 are called halogens.
They have the chemical formula F2, Cl2, Br2, I2
Chlorine is a pale green gas
Bromine is a reddy brown liquid
Iodine is a purple/brown/grey solid
They all dissolve in water to give coloured solutions.
b)
Reactivity of the halogens
When the halogens react they gain one electron.
The greater the tendency to gain an electron, the more reactive the halogen.
In smaller atoms (like fluorine), the electron gained is closer to the nucleus so it is
attracted to the nucleus more strongly. So the smaller atoms are more reactive.
So reactivity decreases down group 7:
Fluorine > Chlorine > Bromine > Iodine
Most reactive
Least reactive
c)
Reaction with group 1 elements
Group 1 metals react vigorously with group 7 elements.
Video: Macromedia videos: sodium with chlorine, sodium with chlorine
Eg
Sodium + chlorine  sodium chloride
2Na + Cl2  2NaCl
Exercise 8
Write word and symbol equations for the following reactions.
a)
sodium with fluorine
b)
potassium with chlorine
c)
lithium with bromine
d)
rubidium with water
d)
Displacement reactions
The more reactive halogens are more likely to form compounds. They can displace
less reactive halogens from their compounds.
PRACTICAL 4 – Displacement reactions of the halogens









Pour 3 cm of potassium bromide solution into two test tubes
Add 1 cm of chlorine water to the first test tube and note any colour changes
Add 1 cm of iodine water to the second test tube and note any colour changes
Pour 3 cm of potassium iodide solution into two test tubes
Add 1 cm of chlorine water to the first test tube and note any colour changes
Add 1 cm of bromine water to the second test tube and note any colour
changes
Pour 3 cm of potassium chloride solution into two test tubes
Add 1 cm of bromine water to the first test tube and note any colour changes
Add 1 cm of iodine water to the second test tube and note any colour changes
In which of the above experiments does a chemical reaction actually take place?
Chlorine + sodium bromide  bromine + sodium chloride
Chlorine + sodium iodide  iodine + sodium chloride
Bromine + sodium iodide  iodine + sodium bromide
Exercise 9
Predict whether there will be a reaction between the following substances. If there is,
write the word and symbol equations.
i)
chlorine and sodium bromide
ii)
chlorine and potassium iodide
iii)
bromine and sodium chloride
iv)
bromine and potassium iodide
v)
iodine and potassium chloride
vi)
iodine and sodium bromide
e)
Uses of the halogens
-
6.
chlorine is used to sterilise water
chlorine is used to make pesticides
bromine is used to test for alkenes
iodine is used to sterilise wounds
Group 8 elements
Group 8 elements are unreactive because they have full outer shells.
They are sometimes called noble gases.
Down the group, the relative atomic mass of the atoms increases. This means that the
density increases:
Helium > Neon > Argon > Krypton > Xenon
Least dense
Most dense
Because they are unreactive, they can be used in light bulbs.
Because helium has a lower density than air, it can be used in balloons.
Now try: CD6 Exercise 3
7.
Transition metals
Transition metals are found in between groups 2 and 3 of the Periodic Table.
a)
Properties
They have some characteristic properties:
- shiny
- hard
- high density
- high tensile strength
- high melting and boiling points
b)
Uses
Iron is used to make cars and bridges because it is strong.
Copper is used to make brass and electrical wiring because it is a good electrical
conductor.
Transition metals make useful catalysts:
- Iron is used in the Haber process to make ammonia.
- Nickel is used in the hydrogenation of alkenes.
c)
colours of transition metal compounds
Unlike many compounds in the other groups, transition metals are normally coloured:
Copper compounds are blue
Iron (II) compounds (containing Fe2+) are light green
Iron (III) compounds (containing Fe3+) are orange/brown
d)
Reactions of transition metal ions in solution
The presence of these ions in solution can be confirmed by adding dilute sodium
hydroxide.
PRACTICAL 5 – Identifying transition metal ions in solution
 Pour 3 cm of a solution containing Cu2+ ions into a test tube
 Pour 3 cm of a solution containing Fe2+ ions into a second test tube
 Pour 3 cm of a solution containing Fe3+ ions into a third test tube
 Pour 1 cm of dilute sodium hydroxide solution into each of the three test tubes
What do you see?
Solution
containing…
Fe2+
Fe3+
Cu2+
Initial colour of
solution
Pale yellow
yellow
Pale blue
Colour of solid
formed
Green/grey solid
Orange/brown solid
Blue solid
When transition metal ions combine with hydroxide ions in solution, a neutral
transition metal hydroxide is formed which does not dissolve in water so forms a
solid. The formula of the hydroxide depends on the charge on the metal ion:
Eg
Cu2+ + 2OH-  Cu(OH)2
Fe3+ + 3OH-  Fe(OH)3
Solids formed by combining two solutions are called precipitates.
A reaction in which a solid is formed from two solutions is called precipitation.
These reactions can be used to identify transition metal ions in solution.
Exercise 10
Write balanced ionic equations for the precipitation reaction between:
a)
Fe2+ and OHb)
Fe3+ and OHc)
Cu2+ and OHIn each case, give the colour before and after the reaction.
e)
Reaction of transition metal carbonates
PRACTICAL 6 – Thermal decomposition of transition metal carbonates
 Place three spatulas of copper carbonate into a test tube
 Attach a bung with delivery tube to the top of the test tube
 Half-fill another test-tube with limewater
 Immerse the delivery tube from the test tube containing the solid into the
limewater
 Heat the solid in a medium Bunsen flame
What happens to the colour of the solid? What does that tell you?
What happens to the limewater? What does that tell you?
Copper
carbonate
Colour before
heating
Green
Colour after
heating
Black
Was carbon
dioxide evolved?
Yes
Manganese
carbonate
Zinc
Carbonate
Brown
Black
Yes
White
Yellow
Yes
When a metal carbonate is heated, it breaks down into the metal oxide and carbon
dioxide:
Eg
copper carbonate  copper oxide + carbon dioxide
CuCO3  CuO + CO2
A reaction in which one substance is broken down into two or more other substances
by heat is called thermal decomposition.
Exercise 11
Write word and symbol equations to show the following reactions:
a)
thermal decomposition of copper carbonate
b)
thermal decomposition of manganese carbonate
c)
thermal decomposition of zinc carbonate
d)
thermal decomposition of iron carbonate
You can tell that the gas is carbon dioxide because it turns limewater cloudy.
Now try:
CD6 Exercise 4
END OF TOPIC