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OCR Additional Science
The Periodic Table
Elements
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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:
These atoms are
ALL iron – there’s
nothing else in here
Compounds
Compounds are formed
when two or more
elements are
chemically combined.
Some examples:
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Methane
Sodium
chloride (salt)
Glucose
Some simple compounds…
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Methane, CH4
Water, H2O
Carbon
dioxide, CO2
Key
Hydrogen
Ethyne, C2H2
Oxygen
Sulphuric
acid, H2SO4
Carbon
Sulphur
Chemical formulae
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The chemical formulae of a molecule or compound is simply a
way of showing the ratio of atoms in it. For example…
Na
Cl
= sodium chloride (NaCl)
K
I
= potassium iodide (KI)
O
K
N
O
O
= potassium nitrate (KNO3)
Chemical formulae
Try drawing these:
1) Water H2O
2) Carbon dioxide CO2
3) Calcium sulphate CaSO4
4) Magnesium hydroxide Mg(OH)2
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Naming compounds
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Rule 1– If two identical elements combine then the
name doesn’t change
This happens with the following elements:
1) H2
4) F2
2) N2
5) Cl2
3) O2
6) Br2
These elements always go
around in pairs (diatomic
molecules). For example,
hydrogen looks like this:
Naming compounds
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Rule 2 – When two elements join and one is a halogen,
oxygen or sulphur the name ends with ____ide
e.g. Magnesium + oxygen
magnesium oxide
1) Sodium + chlorine
6) KBr
2) Magnesium + fluorine
7) LiCl
3) Lithium + iodine
8) CaO
4) Chlorine + copper
9) MgS
5) Oxygen + iron
10)KF
Naming compounds
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Rule 3 – When three or more elements combine and two of
them are hydrogen and oxygen the name ends with
hydroxide
e.g. Sodium + hydrogen + oxygen
Sodium hydroxide
1) Potassium + hydrogen + oxygen
2) Lithium + hydrogen + oxygen
3) Calcium + hydrogen + oxygen
4) Mg(OH)2
Naming compounds
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Rule 4 – When three or more elements combine and
one of them is oxygen the ending is _____ate
e.g. Copper + sulphur + oxygen
Copper sulphate
1) Calcium + carbon + oxygen
6) AgNO3
2) Potassium + carbon + oxygen
7) H2SO4
3) Calcium + sulphur + oxygen
8) K2CO3
4) Magnesium + chlorine + oxygen
5) Calcium + oxygen + nitrogen
Simple formulae to learn
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“Covalent” formulae
“Ionic” formulae
H2O
Water
NaCl
Sodium chloride
CO2
Carbon dioxide
CaCl2
Calcium chloride
NH3
Ammonia
MgO
Magnesium oxide
H2
Hydrogen
HCl
Hydrochloric acid
Sulphuric acid
O2
Oxygen
H2SO4
HNO3
Nitric acid
N2
Nitrogen
NaOH
Sodium hydroxide
SO2
Sulphur dioxide
Ca(OH)2
Calcium hydroxide
CaCO3
Calcium carbonate
Al2O3
Aluminium oxide
Fe2O3
Iron oxide
Balancing equations
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Consider the following reaction:
Sodium + water
Na
+
sodium hydroxide + hydrogen
Na
O
H
H
O
H
+
H
H
This equation doesn’t balance – there are 2 hydrogen
atoms on the left hand side (the “reactants” and 3 on
the right hand side (the “products”)
Balancing equations
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We need to balance the equation:
Sodium + water
sodium hydroxide + hydrogen
Na
O
H
Na
+
Na
H
O
O
H
Na
H
O
H
+
H
H
Now the equation is balanced, and we can write it as:
2Na(s) + 2H2O(l)
2NaOH(aq) + H2(g)
H
Some examples
2Mg
O2
2 MgO
Zn
+ 2 HCl
ZnCl2
2 Fe
+ 3Cl2
2 FeCl3
NaOH
CH4
Ca
+
+
HCl
+ 2 O2
NaCl
CO2
+
+
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H2
H 2O
+ 2H2O
+ 2 H2O
Ca(OH)2
+
+
H2SO4
Na2SO4
+ 2H2O
2 CH3OH
+ 3 O2
2 NaOH
2 CO2
+ 4H2O
H2
The structure of the atom
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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
NEUTRON –
neutral, same
mass as
proton (“1”)
PROTON –
positive, same
mass as
neutron (“1”)
ELECTRON –
negative, mass
nearly nothing
Mass and atomic number
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Particle
Relative Mass
Relative Charge
Proton
1
+1
Neutron
1
0
Electron
Very small
-1
MASS NUMBER = number of
protons + number of neutrons
SYMBOL
PROTON NUMBER = number of
protons (obviously)
Mass and atomic number
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How many protons, neutrons and electrons?
Isotopes
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An isotope is an atom with a different number of neutrons:
Notice that the mass number is different. How many
neutrons does each isotope have?
Each isotope has 8 protons – if it didn’t then it just
wouldn’t be oxygen any more.
Electron structure
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Consider an atom of Potassium:
Potassium has 19 electrons.
These electrons occupy
specific energy levels “shells”…
Nucleus
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
Bonding
Cl
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Hi. My name’s Johnny Chlorine.
I’m in Group 7, so I have 7
electrons in my outer shell
I’d quite like to have a full outer
shell. To do this I need to GAIN
an electron. Who can help me?
Cl
Bonding
Here comes my friend,
Sophie Sodium
Cl
Na
Hey Johnny. I’m in Group 1 so I have one
electron in my outer shell. I don’t like
having just one electron so I’m quite
happy to get rid of it. Do you want it?
Okay
+
Cl
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Na
Now we’ve both got full outer shells
and we’ve both gained a charge.
We’ve formed an IONIC bond.
Ions
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An ion is formed when an atom gains or loses electrons and
becomes charged:
+
-
The electron is negatively charged
The proton is positively charged
If we “take away” the electron
we’re left with just a positive
charge:
+
+
This is called an ion (in this case, a positive hydrogen ion)
Ionic bonding
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This is where a metal bonds with a non-metal (usually). Instead of sharing
the electrons one of the atoms “_____” one or more electrons to the
other. For example, consider sodium and chlorine:
Na
Sodium has 1 electron on its outer shell
and chlorine has 7, so if sodium gives
its electron to chlorine they both have
a ___ outer shell and are ______.
+
A _______
charged
sodium ion
(cation)
Na
Cl
-
Cl
A _________
charged
chloride ion
(anion)
As opposed to covalent bonds, ionic bonds form strong forces
of attraction between different ions due to their opposite
______, causing GIANT IONIC STRUCTURES to form (e.g
sodium chloride) with ______ melting and boiling points:
Some examples of ionic bonding
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-
Magnesium
chloride:
Mg
2+
Cl
Cl
Mg
+
-
Cl
Cl
MgCl2
Calcium oxide:
Ca
+
2+
O
Ca
2-
O
CaO
Balancing ions
Some common ions:
Sodium – Na+
Chloride – Cl-
Potassium – K+
Bromide – Br-
Magnesium – Mg2+
Oxide – O2-
Ammonium – NH4+
Sulphate – SO42-
Determine the formula of the following compounds:
1) Sodium chloride
2) Magnesium oxide
3) Magnesium chloride
4) Ammonium chloride
5) Sodium sulphate
6) Sodium oxide
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Periodic Table Introduction
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Periodic table
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The periodic table arranges all the elements
in groups according to their properties.
Vertical
columns are
called GROUPS
Mendeleev
Horizontal rows are called PERIODS
The Periodic Table
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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
Br
Kr
I
Xe
Fe
Ni
Cu
Zn
Ag
Pt
E.g. all group 1 metals
have __ electron in
their outer shell
Au
Hg
These elements have
__ electrons in their
outer shells
These elements
have __ electrons
in their outer shell
The Periodic Table
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Fact 2: As you move down through the periods an
extra electron shell is added:
Li
Be
Na
Mg
K
Ca
E.g. Lithium has 3
electron Hin the
configuration 2,1
He
Ni
Sodium hasFe11
electrons in the
configuration 2,8,1
Pt
Cu
Zn
Ag
Au
Potassium has 19 electrons in
the configuration __,__,__,__
Hg
B
C
N
O
F
Ne
Al
Si
P
S
Cl
Ar
Br
Kr
I
Xe
The Periodic Table
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Fact 3: Most of the elements are metals:
H
These elements
are metals
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar
K
Ca
Br
Kr
I
Xe
Fe
Ni
Cu
Zn
Ag
Pt
Au
This line divides
metals from nonmetals
Hg
These elements are
non-metals
The Periodic Table
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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
Br
Kr
I
Xe
Fe
Ni
Cu
Zn
Ag
Pt
Au 1Hgmetals. They all:
E.g. consider the group
1) Are soft
2) Can be easily cut with a knife
3) React with water
Bonding Revision
Cl
Hi. My name’s Johnny Chlorine.
I’m in Group 7, so I have 7
electrons in my outer shell
I’d quite like to have a full outer
shell. To do this I need to GAIN
an electron. Who can help me?
Cl
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Ionic Bonding Revision
Here comes my friend again, Sophie
Sodium
Cl
Na
Hey Johnny. I’m in Group 1 so I have
one electron in my outer shell. Unlike
Harry, this electron is far away from
the nucleus so I’m quite happy to get
rid of it. Do you want it?
Okay
+
Cl
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Na
Now we’ve both got full outer shells
and we’ve both gained a charge.
We’ve formed an IONIC bond.
Covalent Bonding
Cl
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Here comes another one of my
friends, Harry Hydrogen
Hey Johnny. I’ve only got one
electron but it’s really close to my
nucleus so I don’t want to lose it.
Fancy sharing?
Cl
H
Now we’re both really stable.
We’ve formed a covalent bond.
H
Covalent bonding
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Consider an atom of hydrogen:
Notice that hydrogen has just __ electron in its outer
shell. A full (inner) shell would have __ electrons, so two
hydrogen atoms get together and “_____” their electrons:
Now they both have a ____ outer shell and are
more _____. The formula for this molecule is H2.
When two or more atoms bond by sharing electrons we
call it ____________ BONDING. This type of bonding
normally occurs between _______ atoms. It causes the
atoms in a molecule to be held together very strongly
but there are ____ forces between individual molecules.
This is why covalently-bonded molecules have low melting
and boiling points (i.e. they are usually ____ or ______).
Words – gas, covalent, non-metal, 1, 2, liquid, share, full, weak, stable
Dot and Cross Diagrams
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Water, H2O:
H
O
H
Dot and Cross Diagrams
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Oxygen, O2:
O
O
Dot and cross diagrams
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Water, H2O:
Step 1: Draw the atoms with
their outer shell:
H
Step 2: Put the atoms together and
check they all have a full outer shell:
O
H
O
H
H
Oxygen, O2:
O
O
O
O
Dot and cross diagrams
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Nitrogen, N2:
Methane CH4:
H
N
N
H
C
H
H
Ammonia NH3:
H
Carbon dioxide, CO2:
N
H
H
O
C
O
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Other ways of drawing covalent bonds
Consider ammonia (NH3):
H
N
H
H
H
N
H
H
H
N
H
H
Group 1 – The alkali metals
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Li
Na
K
Rb
Cs
Fr
Group 1 – The alkali metals
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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:
Potassium + water
2K(s)
+
2H2O(l)
potassium hydroxide + hydrogen
2KOH(aq)
+
H2(g)
Words – down, one, shell, hydrogen, nucleus, decreases
Trends in Group 1
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Consider a sodium atom:
Take away
one of the
electrons
(oxidation)
+
Sodium
ion
Now consider a potassium atom:
+
Take away
one of the
electrons
(oxidation)
Potassium
ion
Potassium loses its electron more easily because its
further away – potassium is MORE REACTIVE
Flame tests
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Compounds containing lithium, sodium, potassium, calcium and
barium can be recognised by burning the compound and
observing the colours produced:
Lithium
Sodium
Potassium
Red
Yellow
Lilac
Group 0 – The Noble gases
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He
Ne
Ar
Kr
Xe
Rn
Group 0 – The Noble gases
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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
4) Helium is ________ then air and is used in balloons and
airships (as well as for talking in a silly voice)
5) 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
Group 7 – The halogens
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F
Cl
Br
I
At
Group 7 – The Halogens
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1) Reactivity DECREASES
as you go down the group
Decreasing
reactivity
Some facts…
(This is because the electrons are further away from the
nucleus and so any extra electrons aren’t attracted as much).
2) They exist as
diatomic molecules (so
that they both have a
full outer shell):
Cl
Cl
3) Because of this fluorine and chlorine are liquid at room
temperature and bromine is a gas
The halogens – some reactions
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1) Halogen + metal:
+
+
Na
Cl
Halogen + metal
Cl
Na
ionic salt
2) Halogen + non-metal:
H
+
Cl
Halogen + non-metal
Cl
H
covalent molecule
Properties
Element
Melting Point (OC) Boiling Point (OC)
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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?
??
Trends in Group 7
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Consider a flourine atom:
Add an
electron
(reduction)
-
Flouride
ion
Now consider a chlorine atom:
Add an
electron
(reduction)
Chloride
ion
Chlorine doesn’t gain an electron as easily as flourine so it
is LESS REACTIVE
Electrolysis
Positive
electrode
(anode)
Solution
containing
copper ions
(cations) and
chloride ions
(anions)
+
+
+
+
Cu2+
Cl-
Cl-
Cl-
Cu2+
Cu2+
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-
Negative
electrode
(cathode)
Electrolysis
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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!!!
= chloride ion
= copper ion
Electrolysis equations
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We need to be able to write “half equations” to show what
happens during electrolysis (e.g. for copper chloride):
At the negative electrode the
positive ions GAIN electrons to
become neutral copper ATOMS. The
half equation is:
Cu2+ + 2 e-
Cu
At the positive electrode the
negative ions LOSE electrons to
become neutral chlorine
MOLECULES. The half equation is:
2 Cl- - 2 e-
Cl2
Electrolysis of sulfuric acid
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Sufuric acid is an electrolyte – it contains cations (H+) and anions (OH-)
Oxygen gas (O2)
Anode
Hydrogen gas (H2)
Cathode
2 H+(aq) + 2 e-
Half equations:
4OH-(aq) - 4 e-
H2(g)
2 H2O(l) + O2(g)
Testing for Hydrogen
“POP”
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Testing for Oxygen
Oxygen will relight a glowing splint
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Extracting Aluminium
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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
Electrolysis of Aluminium Oxide
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Overall:
Aluminium oxide
2Al2O3(l)
At the cathode:
Al3+(l) + 3e-
Al(l)
aluminium + oxygen
4Al(l)
+
3O2(g)
At the anode:
2O2-(l) - 4e-
O2(g)
The Transition Metals
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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
Thermal decomposition
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Thermal Decomposition is when a substance breaks down into a
simpler substance through the action of heat. For example,
consider copper carbonate:
Copper carbonate
(green) turns into
copper oxide (black)
Limewater
Limewater goes
cloudy due to carbon
dioxide being made
Copper carbonate
copper oxide + carbon dioxide
Metal ions and precipitates
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Some metal ions form precipitates, i.e. an insoluble solid that
is formed when sodium hydroxide is added to them. Consider
calcium chloride:
Ca2+(aq)
Metal ion
Calcium Ca2+
Aluminium Al3+
Magnesium Mg2+
Copper(II) Cu2+
Iron(II) Fe2+
Iron(III) Fe3+
+ 2OH-
Ca(OH)2 (s)
Precipitate formed
Calcium hydroxide: Ca2+(aq) + OH-(aq)
Colour
Ca(OH)2 (s)
White
Metals
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Metal atoms are very closely packed together in a
regular arrangement. The atoms are held together by
metallic bonds.
A closer look at metals
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Metals are defined as elements that readily
lose electrons to form positive ions. There
are a number of ways of drawing them:
+
-
+
-
+
+
+
-
+
+
+
+
+
-
-
-
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
Delocalised electrons
Properties of metals
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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
don’t (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
Superconductors
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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.