Chemistry unit 3 notes AQA

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C3 ­ Development of the periodic table
Describe the law of octaves
The law of octaves stated that similar properties were repeated every eighth element
Explain why Newland's table was ignored in 1864
He placed some non-metals and metals in the same group
He had no gaps for currently undiscovered elements
Explain why Mendeleev's table was accepted by scientists in 1869
He left gaps for undiscovered elements and correctly predicted their properties
He arranged the elements in atomic mass
Describe how the modern periodic table is arranged
The modern periodic table is arranged on atomic number. Elements in a group have the same
number of electrons on the outer shell and have similar chemical properties. Elements in a
period have the same number of energy levels.
Explain why Group 1 metals become more reactive as you move down the group
As you go down the group, they are more reactive because the atom gets larger so
there are more inner energy levels to shield the positive charge of the nucleus and
the outer electron is further away from the positive charge of the nucleus.
The outer electron is less attracted to the positive charge of nucleus and is easier to
lose
Explain why Group 7 non-metals become less reactive as you move down the group
As you move down the group, they are less reactive because the atom gets larger so
there are more inner energy levels to shield the positive charge of the nucleus and
the extra electron is further away from the positive charge of the nucleus.
The extra electron is less attracted to the positive charge of nucleus and is harder to
gain
Describe the properties of Group 1 metals, the alkali metals
They all have one electron in their outer shell so only form ionic compounds in which
their ions have a single positive charge
They have low densities so float on water
They react readily with water to produce a metal hydroxide and hydrogen (floats on
water and fizzes)
They react with halogens to form white/colourless salts which dissolve in water to
form

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As you go down the group, they get more reactive and the boiling/melting points
decrease
Describe the reaction between water and potassium
Describe the reaction between chlorine and lithium
Describe the properties of Group 7 non-metals, the halogens
They exist as diatomic molecules
They form covalent structures with non-metals but ionic structures with metals,
forming a ion with a single negative charge
They have low melting/boiling points
They have displacement reactions
As you go down the group, they get less reactive and the boiling/melting points…read more

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Describe a titration
A set volume of alkali is measured using a pipette and added to a conical flask
Two drops of indicator are added to the conical flask
Acid is added to a burette
Acid is added to the conical flask drop wise, whilst swirling
...…read more

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When water comes into contact with rocks, the Magnesium/Calcium salts may dissolve into
the water.
Explain how scum is formed
The dissolved Magnesium/Calcium salts in hard water react with soap to form stearate salts,
which are precipitates known as scum.
Explain how scale is formed
The dissolved Magnesium/Calcium salts in hard water decompose when heated to form
scale.…read more

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Carbon water filters reduce the level of chlorine, pesticides and other organic
impurities
Ion-exchange ions remove ions from magnesium and calcium to aluminium and
copper
Silver filter cartridges discourage the growth of bacteria in the filter
Describe how pure water can be produced
Distillation can be used where water is boiled and then condensed into a separate beaker.
De-ionisation may be used where an ion-exchange column removes all ions except OH- and
H+ from water.…read more

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This method can be used for reactions of solids with water or for neutralisation
reactions
Evaluate the consequences of using fuel…read more

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