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Periodicity:
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The periodic table is arranged by proton number
All the elements along a period have the same number of shells
All elements down the group have the same number of electrons in the outer shell
Elements are classified into blocks:
S-block - groups 1 and 2
P-block - groups 3 to 8/0
D-block - transition metals
F-block - radioactive elements (lanthanides and actinides)
The different electron configurations are linked to other trends

Atomic Radius:
Along a period: atomic radius decreases
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Nuclear charge increases (with the same number of shells)
The outer electrons are pulled closer to the nucleus
This is due to the increased charge that produces a greater attraction
This leads to the decrease of the atomic radius

Down a group: atomic radius increases
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Number of electron shells increase
This increases the distance between the outer electrons and nucleus
The power of attraction is reduced
More shells leads to an increase in electron shielding
The inner shells create a 'barrier' that blocks the forces
Therefore, the nuclear attraction is reduced
So the atomic radius increases

Ionisation Energy:
Along a period: ionisation energy increases
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Atomic radius decreases
Nuclear charge increases
The outer electrons are held more strongly
More energy is needed to remove the outer electron (and so ionise the atoms)

Down a group: ionisation energy decreases
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The nuclear attraction between the nucleus and outer electrons decreases
Large amounts of shielding
Less energy is needed to remove the outer electron

Melting points of Period 3:
Increasing melting point then decreasing melting point
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Sodium, magnesium and aluminium have metallic bonding

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Melting point increases due to more positive charged ions
This means more electrons are released as free electrons
So the attractive electrostatic forces increase
Silicon is macromolecular
So it has very strong covalent structure
The covalent bonds need a lot of energy to break
These means it has a high melting point
Phosphorus, sulphur and chlorine are simple molecules
They are held with weak van der waals forces
The IMF don’t need a lot of energy to overcome
Therefore these molecular have low melting points
Argon is a noble gas
So it exists has an individual atom, and has an outer shell of electrons
This means the atom is stable, and the van der waals forces are weak
These leads to a low melting point, as well as it existing as a gas at room temperature

Group 2 - the alkali metals
When group 2 metals react, they lose two electrons to form 2+ ions, this is so they can achieve a full
outer shell
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This is because the force has to act
over a greater distance

Reactions with water:
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The metals react with water in a redox reaction
This produces a metal hydroxide and hydrogen
The metal hydroxide is formed as an alkaline solution

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Mg + 2H2O ---> Mg(OH)2 + H2
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Magnesium reacts slowly with liquid water
However it does react faster with steam
This is because it provides the reaction with more energy
When steam is used, the magnesium burns with a bright, white flame
It the forms hydrogen and magnesium oxide (a white powder)

Solubility of hydroxides:
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The solubility of hydroxides varies
Which means each compound has a different use
Solubility increases down the group
This means that magnesium hydroxide is the least soluble, and barium hydroxide is the most
soluble

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This means magnesium hydroxide is used in medicine as an antacid
This is because it is alkaline and can neutralise acids

Solubility of sulfates:
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Group 2 sulfates decrease down the group
This means magnesium sulfate is the most soluble and barium sulfate is the least soluble
The insolubility of barium sulfate means it can be used as barium meals in medicine
This is a medical tracer that allows internal tissue/organs to be imaged
Barium sulfate is toxic but is also insoluble and cannot be absorbed into the blood, making it
safe to use
Barium chloride is used a test for sulfate ions
This is because it reacts to form barium sulfate
It forms as a white precipitate when there are sulfate ions are present

Metal extraction:
Magnesium is used to extract titanium from titanium chlorine through a displacement reaction
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This forms calcium sulfite and water:
CaO + 2H2O + SO2 ---> CaSO3 + 2H2O
Group 7 - The Halogens
The group 7 elements are very reactive non-metals, and need to gain one electron to form a 1- ion
and achieve a full outer shell
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Atomic radius increases down the group, this is due to additional electron shells
Reactivity decreases down the group, this is because as atomic radius increases, causing the
attraction between the electrons and the nucleus to be weakened due to more shielding
First ionisation energy decreases as you go down the group, this is due to a greater atomic
radius and increased shielding
Boiling point increases down the group, this is because all group 2 elements are simple
covalent molecules with van der waals forces
Oxidising power decreases down the group, their ability to attract electrons decreases due to
shielding and a greater atomic radius
The relative oxidising strengths means that a halogen will displace any halogen beneath it in
the periodic table

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Cl2 will displace Br- and I- ions
Testing for ANIONS

Halide ions:
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The negative ions of halogens are halide ions
These are good reducing agents as they donate electrons to the species being reduced
Their reducing power increases down the group
This is because electrons are easily lost from larger ions due to shielding and a larger atomic
radius
The greater the reducing power, the longer the reaction
As the halide is powerful enough to reduce more species

Silver Nitrate:
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Acidified silver nitrate is used to test for halide ions
Silver nitrate is acidified to remove any impurities that could form a precipitate
It reacts to form different coloured precipitates depending on the ion
Sometimes its not clear, so it can be tested further using ammonia
ClAgNO3

Br-

I-

White ppt (AgCl)

Cream ppt (AgBr)

Yellow ppt (AgI)

Dilute NH3

Ppt dissolves

No change

No change

Conc NH3

Ppt dissolves

Ppt dissolves

No change

Chlorine and chlorate (I) ions:
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Chlorine reacts with cold water to produce chlorate ions (ClO-) and chloride ions

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Cl2 + H2O ---> ClO- + Cl- + 2H+
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This is a disproportionation reaction
As chlorine is oxidised and reduced
The oxidation goes from 0 to +1 and -1
In the presence of UV light, chlorine decomposed water to produce hydrochloric acid and
oxygen

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2Cl2 + 2H2O --UV--> 4HCl + O2
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Chlorine is used in small quantities to kill bacteria when treating water
This does create some risks as chlorine can be toxic
Chlorine can also be mixed with cold, aqueous sodium hydroxide to produce sodium chlorate
(I)

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2NaOH + Cl2 --> NaClO + NaCl + H2O
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Sulfates (SO42-) are used for testing BaCl2, which forms a white ppt
Hydroxides (OH-) are used to indicate if a substance is alkaline
Litmus paper is used, and turns from red to blue
Carbonates (CO32-) react with HCl, and will fizz as well produce CO2 gas

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The gas can then be collected and bubbled through limewater, which would turn cloudy if its
carbon dioxide

Testing for CATIONS
Flame tests for group 2:
Calcium (Ca2+)

Brick Red

Strontium (Sr2+)

Red

Barium (Ba2+)

Pale Green

Ammonium (NH4+):
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If ammonium ions are present, ammonia gas is given off
The presence of ammonium ions can be tested by holding red litmus paper over a petri dish of
the substance being tested
As it is a base, it would turn blue if they are present
They can also be tested in the same way but with NaOH
This produces the ammonia gas faster



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