GCSE Carlam Cymru GCSE Session 1 – Autumn 2023
Session 1- Atomic Structure
and the Periodic Table
Sessions�1) Atomic Structure and the Periodic Table��2) Elements, Compounds and Formulas Balancing Equations��3) Group 1, 7 and 0 chemistry��4) Calculations
Double Award
USEFUL TO HAVE WITH YOU!!!!
The atom: check it out!
nucleus
electron
Which of the particles in the nucleus is the proton/neutron
Contains protons and neutrrons
Properties of sub-atomic particles
particle | charge | Mass | Position |
Proton | | | |
Neutron | | | |
electron | | | |
0
+1
-1
a.m.u
1
1
0
nucleus
nucleus
shells
negligible
The atom: check it out!
nucleus
neutron
proton
electron
Which of the particles in the nucleus is the proton/neutron
Atoms do not have charge!!�Why is this
Atomic number
Atomic mass
15
31
15p + 16N
The number of protons
Sum of protons + neutrons
Atomic number tells us the number of protons
The number of electrons should be the same
Atomic mass – to work out the number of neutrons, take away the atomic number
Neutrons = big –small!!!
Protons = 11
Electrons = 11
Neutrons = 12
(23-11)
Putting electrons into shells
2,8,8,2
p+ =
e- =
n0 =
20
20
20
Putting electrons into shells
p+ =
e- =
n0 =
11
11
12
Try magnesium
Atomic number =12
So 12 protons �AND 12 electrons
Atomic mass 24
Atomic number 12
Neutrons = atomic mass– atomic number
24 - 12 = 12 neutrons
Isotopes
Atoms with the same number of protons ( so are atoms of the same element) but with differing numbers of neutrons
All three atoms have an atomic number of
1
(all contain 1 proton in the nucleus)
With an atomic number of 1, these are all atoms of the element
HYDROGEN
These atoms represent the different isotopes of hydrogen
All of the atoms contain one proton but one has no neutrons, one has a single neutron and one has two neutrons
Notice the isotopes all have the same symbol and atomic number BUT have differing atomic masses (atomic mass = protons + neutrons)
Which Element?
Triple: Session 4 will look at working out the relative atomic mass value for isotopes
Metals – conduct
shiny
malleable
usually high mpt/bpt
Non -metals
Low mpt/bpt
Brittle solids
insulators
Properties of metals and non-metals
High melting point
Low melting point
malleable
Brittle when solid
Conduct heat and electricity
Insulators of heat and electricity
High density
Low density
Now do questions 6 and 7 on page 2
metalloids
The elements marked in red are called metalloids – they display some properties of metals and some of non-metals eg carbon (graphite is a brittle dull black solid (non-metal proerties), but is able to conduct electricity (a metallic property).
SILICON
Brittle and poor conductor of electricity
A quick exercise on groups and periods
You will need a periodic table – use page 142 of your planner to fill in the gaps on the next page
Group Chemistry
Remember:
Group is a column in the periodic table
Elements in a group display similar chemical properties (react in the same way/have the same balanced equation) and show a general trend in physical/chemical properties as you go down the group e.g. melting points increase, become more reactive, get darker etc
Trends in Group 1:
Reactivity increases
down group
Melting point DECREASES
down group
Density increases down group
Trends in Group 7:
Reactivity DECREASES
down group
Melting point INCREASES
down group
Density increases down group
They become darker in colour down the group
element
group
period
2
3
magnesium
iodine
7
5
4
1
potassium
Argon
0
3
If your period is one less than the answer- you have forgotten to count the first period with hydrogen in it.
Sessions�1) Atomic Structure and the Periodic Table��2) Elements, Compounds and Formulas Balancing Equations��3) Group 1, 7 and 0 chemistry��4) Calculations
element
Materials can be classed as elements, mixtures and compounds. Can you remember the definition of each?
mixture
compound
A material made up of only one type of atom
A material made up of two or more different types of atom, chemically joined together, the elements can only be separated through chemical means e.g. electrolysis
A material made up of atoms or molecules that are not chemically joined together so can be separated from each other by techniques like filtering, distillation etc
Element or compound?
Can you see any individual atoms in this picture
What name do we give to the particles you can see circled in red now
This is an example of a molecule – a molecule is what you get when two or more atoms join together
Molecules can be elements or compounds – is this molecule an example of an element or compound (see previous slides if not sure)
This molecule is a compound as it contains two different types of atom joined together
So does this picture represent an element, mixture or compound
This picture represents a mixture - you can see more than one type of substance that are not joined together
This is an element – there is only one type of atom
This is a compound – there are two different types of atom joined together
This is an element
I know, it does look like a compound but it is not – this substance is made up of only type of atom
This is an element
Again I know, it does look like a compound but it is not – these molecules are made up of only type of atom
And finally – yup you got it – this is a mixture
In fact it is a mixture of two elements and a compound
In the next slides we will look at formulas of molecules
The formula of a substance tells us what atoms are in the molecule and how many of them there are
In this molecule there are 2 oxygen atoms joined to one carbon atom
Formula = CO2
Not CO2 or CO2
The 2 goes below
Now see if you can work out the formulas of the substances in the next few slides – you may need a periodic table
N2
CH4
SO2
SULPHUR DIOXIDE
H2SO4
Calculating Mr
Mr stands for relative molecular mass
It tells you how heavy a molecule is
To calculate the Mr of a molecule
We will use water as an example
H2O
1) Look at the formula of the molecule you want to work out the Mr for
Hydrogen atoms 2x 1 = 2
Oxygen atoms 1 x 16 = 16
2) Now look up the relative atomic mass of each element and multiply it by the number of atoms for that element in the formula
3) Add the values you get together to obtain the Mr
2+16 =18
Mr (H2O) =18
Some more examples
H2SO4
element | Number of atoms in the molecule | Ar of element | Total mass of the element in the molecule |
| | | |
| | | |
| | | |
hydrogen
sulphur
oxygen
2
1
4
1
32
16
2 X 1 = 2
1 x 32 = 32
4 X 16 = 64
Mr H2SO4 = 2 + 32 + 64
= 98
What about formulas with a bracket
e.g. Calcium nitrate
Ca(NO3)2
element | Number of atoms in the molecule | Ar of element | Total mass of the element in the molecule |
Calcium | | | |
Nitrogen | | | |
Oxygen | | | |
Same as before but every element in the brackets is multiplied twice more (because of the two that you can see with the bracket)
1
2
6
40
2 x14 = 28
6 X 16 = 96
1 X 40 = 40
14
16
Mr Ca(NO3)2 = 40 + 28 + 96 164
= 164
Another example with brackets
Ammonium sulphate (NH4)2SO4
element | Number of atoms in the molecule | Ar of element | Total mass of the element in the molecule |
nitrogen | | | |
hydrogen | | | |
sulphur | | | |
Oxygen | | | |
2
8
1
4
14
1
32
16
2 X 14 =28
8 X 1 = 8
1 x 32 = 32
4 x 16 = 64
Mr = 28 + 8 + 32 + 64
= 132
Naming compounds
If ONLY two elements have combined the substances name ends in IDE
e.g. Sodium and chlorine join to make sodium chloride
MgCl2
Here we can see the symbols for the elements magnesium and chlorine
This compound must be called magnesium chloride
If a compound contains two elements AND oxygen it names end in ATE
Which elements can you see in the formula below
Calcium x 1
Carbon x 1
Oxygen x 3
This compound is called
Calcium
carbon
ATE
What is this compound called
FeSO4
Iron x 1
Sulphur x 1
Oxygen x 4
iron
sulph
ate
Working out the formula of a compound from its constituent ions!!
A large number of compounds are made up of IONS
IONS are basically atoms or molecules which have a positive or negative charge
Remember atoms DO NOT have charges as they contain EQUAL NUMBERS OF POSITIVE PROTONS AND NEGATIVE ELECTRONS. We look at ions more in year 11 but we also saw ions in electrolysis, this year.
A BIT OF BACKGROUND, BEFORE WE BEGIN
YOU WILL BE GIVEN A SHEET TELLING YOU THE CHARGES OF IONS IN YOUR EXAM BOOK, IT LOOKS LIKE THIS
As stated earlier, many compounds are made up of positive and negative charged ions
When the ions join together, their opposite charges MUST cancel each other
To do this, you may need more than one of the ions, if more are needed, we show this in the formula of the compound
Lets see it being done!!
What is the formula of sodium chloride
Na+1
Cl-1
The charges cancel, we only need one of each, so the formula is
NaCl
What is the formula of magnesium chloride
Mg2+
Cl-1
This time the charges DO NOT cancel. To cancel the +2 charge of the magnesium we need another Cl-1
Cl-1
We show the fact, that two chloride ions are needed in the formula, so the formula is written as
MgCl
2
Formulas of compounds with molecular ions
What is the formula for potassium carbonate
K+1
CO3-2
This is the carbonate ion- look at its formula and you will see that this ion is a molecule, if you need more of these, we need to put the formula of the ion in brackets
In this case we only need one carbonate ion but we do need two potassium ions to cancel out the -2 charge of the carbonate ion, so the formula is
K2CO3
In this example we will see the need for brackets
What is the formula for Iron (III) hydroxide
Iron can have different charges on its ions, either +2 or +3
You are TOLD the charge of the iron in the name of the compound, with the Roman numerals
So the iron must have a + 3 charge
Fe3+
OH-1
Look at the formula of hydroxide, this is also a molecular ion. In this example we need 3 of them to cancel the +3 charge on the iron.
OH-1
OH-1
Because the hydroxide is a molecular ion and we need 3 of them, we have to use brackets around the OH
Fe(OH)3
Ammonium sulphate, a favourite of examiners
NH4+
SO42-
The sulphate ion has a -2 charge, so we need two ammonium ions, to cancel the charge
(NH4)2SO4
NH4+
Group Chemistry
Remember:
Group is a column in the periodic table
Elements in a group display similar chemical properties (react in the same way/have the same balanced equation) and show a general trend in physical/chemical properties as you go down the group e.g. melting points increase, become more reactive, get darker etc
Group 1 – The Alkali Metals
Properties of group typical of metals - conduct electricity
malleable (way too much!)
shiny lustre when freshly cut
Properties of group NOT typical - low melting points (Cs melts of metals in the hand)
- low density (Li/Na/K float on water)
- incredibly soft
- very reactive
Trends as you go down the group
As we go down the group (from Li to Cs) their melting points decrease
As we go down the group their densities increase
Water has a density of 1gcm-3, so Rb/Cs sink in water as their density is higher
As we go down the group theyt become easier to cut
As we go down the group THEY BECOME MORE REACTIVE!!
Lithium reacting with water
Caesium in water
The reaction with water
As they are in a group, they effectively react the same way with water, ie produce the same products and follow the same word and balanced symbol equation. We will use sodium for now.
SODIUM + WATER
SODIUM
HYDROXIDE
+
HYDROGEN
Hydroxides are alkalis. This explains why universal indicator goes purple showing pH 14 (strong alkali).
Below sodium, enough heat is generated in the reaction to set the hydrogen on fire but with lithium and sodium not enough heat is produced, hence no flame/explosion, instead we observe fizzing.
You also need to know the balanced equation for the reaction
Na
+
NaOH
H2
H2O
+
Ions sheet: sodium = Na+1
hydroxide = OH-1
Hence sodium hydroxide = NaOH
2
2
2
You need to be able to write this equation for the whole of the group. Just learn this one and then simply replace the symbol for sodium with the symbol of any other element from GROUP 1, e.g. potassium
POTASSIUM + WATER
POTASSIUM
K
K
Reaction with water (contd..)
2) the reaction not producing as much heat as sodium’s
Reactivity of group 1 HIGHER ONLY
You should remember that as we go down group 1, the alkali metals become MORE reactive. You need to know why!!
How many outer electrons do group one have
How will these atoms become stable
If they are becoming more reactive as we go down the group it must be easier for them to lose their outer electron!!
Why is it easier to lose an electron further down the group
Answer: As you go down a group, you add a shell of electrons to an atom, making it easier to remove an electron. This is because EACH shells provide SHIELDING between the attractive pull of the positive nucleus towards the negative electron you are trying to remove. Therefore, as we go down group 1 there are more shells of electrons between the outer electron and the nucleus, so the electron receives more shielding making it easier to remove and so the element is more reactive.
one
By losing their one outer electron
This is the e- removed when Li reacts. The electron only receives shielding from the positive charge of the nucleus from one shell of electrons
The outer electron removed from sodium has an extra shell of electrons between it and the positive nucleus, compared to lithium. So despite sodium having more protons in its nucleus, the electron can be removed more easily due to the outer electron benefitting from increased shielding.
Represents shielding effect a shell of electrons gives an outer electron from the attractive pull of the positive nucleus
Group 1 metals and oxygen
When exposed to the air the group 1 metal rapidly tarnish (go dull) due to the formation of an oxide of the metal forming on its surface. As you down the group the surfaces tarnish more rapidly
Word equation:
Sodium + Oxygen
Sodium oxide
Na
+
O2
Na2O
Ions sheet sodium = Na+
oxygen = O2-
Hence sodium oxide = Na2O
Obviously the equation needs balancing. I’ll deal with the problem of oxygen first, then the Na atoms
4
2
As before the reaction of the group 1 metals is the same with oxygen, so the Na symbol can be swapped with any other group 1 metal’s symbol
K
K
It is worth noting that if BURNT in oxygen, we will observe the characteristic flame colour associated with the metal
Lithium =
Sodium =
Potassium =
Red
Yellow/Orange
lilac
The reaction of the Alkali Metals with Group 7 – The Halogens
As stated before, the reactions become more vigorous as we descend the group
Again as they burn we will see the flame colour associated with the metal
Lithium =
Sodium =
Potassium =
Red
Yellow/Orange
lilac
Lithium in chlorine
potassium in chlorine
Sodium in chlorine
Word:
Sodium + chlorine
Sodium chloride
Ions sheet
Sodium =Na+1
Chloride = Cl-1
Hence: sodium chloride = NaCl
Na
+
Cl2
NaCl
All that is left to do now is balance the chlorines and then balance the sodium atoms
2
2
As before we can replace the symbol for Na with the symbol of any other group one element e.g.
HEY!! We can also replace the chlorine with any other symbol from group 7. The only difference in the reaction of the group 7 elements is that they become less reactive as we go down the group e.g.
Cs
Cs
Br
Br
bromine