OCR Additional Science

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OCR Additional Science
The Periodic Table
W Richards The Weald School
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Elements
If a solid, liquid or gas is made up of only one
type of atom we say it is an element. For
example, consider a tripod made up of iron
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Compounds
Compounds are formed when two or more elements
are chemically combined. Some examples
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Some simple compounds
Carbon dioxide, CO2
Water, H2O
Ethyne, C2H2
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Chemical formulae
The chemical formulae of a molecule or compound
is simply a way of showing the ratio of atoms in
it. For example
sodium chloride (NaCl)
potassium iodide (KI)
potassium nitrate (KNO3)
K
N
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Chemical formulae

• Try drawing these
• Water H2O
• Carbon dioxide CO2
• Calcium sulphate CaSO4
• Magnesium hydroxide Mg(OH)2

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Naming compounds
Rule 1 If two identical elements combine then
the name doesnt change
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Naming compounds
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Naming compounds

1. Potassium hydrogen oxygen
2. Lithium hydrogen oxygen
3. Calcium hydrogen oxygen
4. Mg(OH)2

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Naming compounds
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Simple formulae to learn
Covalent formulae
Ionic formulae
H2O CO2 NH3 H2 O2 N2 SO2
Water Carbon dioxide Ammonia Hydrogen Oxygen Nitro
gen Sulphur dioxide
NaCl CaCl2 MgO HCl H2SO4 HNO3 NaOH Ca(OH)2 CaCO3 A
l2O3 Fe2O3
Sodium chloride Calcium chloride Magnesium
oxide Hydrochloric acid Sulphuric acid Nitric
acid Sodium hydroxide Calcium hydroxide Calcium
carbonate Aluminium oxide Iron oxide
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Balancing equations
Consider the following reaction


This equation doesnt balance there are 2
hydrogen atoms on the left hand side (the
reactants and 3 on the right hand side (the
products)
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Balancing equations
We need to balance the equation


Now the equation is balanced, and we can write it
as
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Some examples
2 2 2 3
2 2 2 2 3
2 2 2 2 2 4
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The structure of the atom
The Ancient Greeks used to believe that
everything was made up of very small particles.
I did some experiments in 1808 that proved this
and called these particles ATOMS
Dalton
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Mass and atomic number
Particle Relative Mass Relative Charge
Proton 1 1
Neutron 1 0
Electron Very small -1
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Mass and atomic number
How many protons, neutrons and electrons?
1
11
16
H
B
O
1
5
8
23
35
238
Na
Cl
U
11
17
92
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Isotopes
An isotope is an atom with a different number of
neutrons
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Electron structure
Consider an atom of Potassium
Potassium has 19 electrons. These electrons
occupy specific energy levels shells
The inner shell has __ electrons The next shell
has __ electrons The next shell has __
electrons The next shell has the remaining __
electron
Electron structure 2,8,8,1
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Bonding
Hi. My names Johnny Chlorine. Im in Group 7,
so I have 7 electrons in my outer shell







Id quite like to have a full outer shell. To do
this I need to GAIN an electron. Who can help me?
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Bonding
Here comes my friend, Sophie Sodium
Hey Johnny. Im in Group 1 so I have one
electron in my outer shell. I dont like having
just one electron so Im quite happy to get rid
of it. Do you want it?
Okay
Now weve both got full outer shells and weve
both gained a charge. Weve formed an IONIC bond.
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Ions
An ion is formed when an atom gains or loses
electrons and becomes charged
If we take away the electron were left with
just a positive charge
This is called an ion (in this case, a positive
hydrogen ion)
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Ionic bonding
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Some examples of ionic bonding
Magnesium chloride

MgCl2
Calcium oxide
CaO
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Balancing ions

• Determine the formula of the following compounds
• Sodium chloride
• Magnesium oxide
• Magnesium chloride
• Ammonium chloride
• Sodium sulphate
• Sodium oxide

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Periodic Table Introduction
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Periodic table







Horizontal rows are called PERIODS
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The Periodic Table
Fact 1 Elements in the same group have the same
number of electrons in the outer shell (this
corresponds to their group number)
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg

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The Periodic Table
Fact 2 As you move down through the periods an
extra electron shell is added
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg

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The Periodic Table
Fact 3 Most of the elements are metals
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg

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The Periodic Table
Fact 4 (Most important) All of the elements in
the same group have similar PROPERTIES. This is
how I thought of the periodic table in the first
place. This is called PERIODICITY.
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg

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Bonding Revision
Hi. My names Johnny Chlorine. Im in Group 7,
so I have 7 electrons in my outer shell







Id quite like to have a full outer shell. To do
this I need to GAIN an electron. Who can help me?
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Ionic Bonding Revision
Here comes my friend again, Sophie Sodium
Hey Johnny. Im in Group 1 so I have one
electron in my outer shell. Unlike Harry, this
electron is far away from the nucleus so Im
quite happy to get rid of it. Do you want it?
Okay
Now weve both got full outer shells and weve
both gained a charge. Weve formed an IONIC bond.
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Covalent Bonding
Here comes another one of my friends, Harry
Hydrogen
Hey Johnny. Ive only got one electron but its
really close to my nucleus so I dont want to
lose it. Fancy sharing?
Now were both really stable. Weve formed a
covalent bond.
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Covalent bonding
Consider an atom of hydrogen
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Dot and Cross Diagrams
Water, H2O
O
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Dot and Cross Diagrams
Oxygen, O2
O
O
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Dot and cross diagrams
Water, H2O
Step 1 Draw the atoms with their outer shell
Step 2 Put the atoms together and check they all
have a full outer shell
Oxygen, O2
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Dot and cross diagrams
Nitrogen, N2
Methane CH4
Ammonia NH3
Carbon dioxide, CO2
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Other ways of drawing covalent bonds
Consider ammonia (NH3)
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Group 1 The alkali metals
Li
Na
K
Rb
Cs
Fr







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Group 1 The alkali metals
Some facts







1) These metals all have ___ electron in their
outer shell.
2) Density increases as you go down the group,
while melting point ________
2) Reactivity increases as you go _______ the
group. This is because the electrons are further
away from the _______ every time a _____ is
added, so they are given up more easily.
3) They all react with water to form an alkali
(hence their name) and __________, e.g
Words down, one, shell, hydrogen, nucleus,
decreases
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Trends in Group 1
Consider a sodium atom
Sodium ion
Now consider a potassium atom
Potassium ion
Potassium loses its electron more easily because
its further away potassium is MORE REACTIVE
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Flame tests
Compounds containing lithium, sodium, potassium,
calcium and barium can be recognised by burning
the compound and observing the colours produced
Lithium Red
Sodium Yellow
Potassium Lilac
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Group 0 The Noble gases
He
Ne
Ar
Kr
Xe
Rn







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Group 0 The Noble gases
Some facts







1) All of the noble gases have a full outer
shell, so they are very ______
2) They all have _____ melting and boiling points
3) They exist as single atoms rather then
_________ molecules

1. Helium is ________ then air and is used in
   balloons and airships (as well as for talking in
   a silly voice)

1. Argon is used in light bulbs (because it is so
   unreactive) and argon , krypton and ____ are used
   in fancy lights

Words neon, stable, low, diatomic, lighter
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Group 7 The halogens
F
Cl
Br
I
At








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Group 7 The Halogens
Some facts







1) Reactivity DECREASES as you go down the group
(This is because the electrons are further away
from the nucleus and so any extra electrons
arent attracted as much).
2) They exist as diatomic molecules (so that
they both have a full outer shell)
3) Because of this fluorine and chlorine are
liquid at room temperature and bromine is a gas
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The halogens some reactions
1) Halogen metal

2) Halogen non-metal

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Properties
Element Melting Point (OC) Boiling Point (OC) Density (g/cm3)
Flourine -220 -188 0.0016
Chlorine -101 -34 0.003
Bromine -7 59 3.12
Iodine 114 184 4.95
Astatine 302? 337? ??
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Trends in Group 7
Consider a flourine atom
Flouride ion
Now consider a chlorine atom
Chloride ion
Chlorine doesnt gain an electron as easily as
flourine so it is LESS REACTIVE
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Electrolysis
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Electrolysis
Electrolysis is used to separate a metal from its
compound.
When we electrolysed copper chloride the _____
chloride ions moved to the ______ electrode and
the ______ copper ions moved to the ______
electrode OPPOSITES ATTRACT!!!
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Electrolysis equations
We need to be able to write half equations to
show what happens during electrolysis (e.g. for
copper chloride)
2
2
2
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Electrolysis of sulfuric acid
Sufuric acid is an electrolyte it contains
cations (H) and anions (OH-)
Anode
Cathode
2 2
4 4 2
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Testing for Hydrogen
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Testing for Oxygen
Oxygen will relight a glowing splint
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Extracting Aluminium
Aluminium has to be extracted from its ore
(called ________) by electrolysis. This is
because aluminium is very ___________. The ore
is mixed with cryolite to lower its ________
________. The ore is then melted so that the
ions can ______. The positively charged
aluminium ions gather at the ___________
electrode. Oxygen forms at the positive
electrode and causes it to wear away, which means
that they have to be __________ frequently.
Words melting point, replaced, negative,
bauxite, reactive, move
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Electrolysis of Aluminium Oxide
Overall
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The Transition Metals







Some facts
1) This section includes metals like gold,
mercury, iron, copper
2) They are all ______ and solid (except
_________)
3) They are ____ reactive than the alkali metals
4) They can form __________ compounds, usually
_______
5) They can be used as a ______ (a chemical that
speeds up a reaction)
Words hard, coloured, mercury, less, catalyst,
insoluble
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Thermal decomposition
Thermal Decomposition is when a substance breaks
down into a simpler substance through the action
of heat. For example, consider copper carbonate
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Metal ions and precipitates
Some metal ions form precipitates, i.e. an
insoluble solid that is formed when sodium
hydroxide is added to them. Consider calcium
chloride
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Metal ion Precipitate formed Colour
Calcium Ca2 Calcium hydroxide Ca2(aq) OH-(aq) Ca(OH)2 (s) White
Aluminium Al3
Magnesium Mg2
Copper(II) Cu2
Iron(II) Fe2
Iron(III) Fe3
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Metals
Metal atoms are very closely packed together in a
regular arrangement. The atoms are held together
by metallic bonds.
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A closer look at metals
Metals are defined as elements that readily lose
electrons to form positive ions. There are a
number of ways of drawing them
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Properties of metals
Metals have very high melting points (which means
that they are usually _____) whereas non-metals
will melt at lower ___________ All metals conduct
heat and __________ very well, whereas non-metals
dont (usually) Metals are strong and ______ but
bendable. Non-metals are usually _____ or they
will snap. Metals will _____ when freshly cut or
scratched, whereas non-metals are usually
dull. Metals have higher _______ than non-metals
(i.e. they weigh more) Metals can be used to make
______ (a mixture of different metals)
Words - alloys, electricity, solids, weak,
densities, temperatures, tough, shine
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Superconductors
At low temperatures metals can become
superconductors. A superconductor has very
little or no resistance to the flow of
electricity. Current research is being done to
see if this will happen at room temperature, as
it is only possible at very low temperatures at
the moment.