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AS-Level Chemistry : Paper 1
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AS-Level Chemistry : Paper 1
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AS-Level Chemistry : Paper 1Arranged in periods (rows) and groups (columns) by atomic (proton)
number - ANS✔✔How is the periodic table arranged
Have the same number of electrons shells, even if they are not all parts of
the s or p sub-shells - ANS✔✔All elements within a period ...
Have the same number of electrons in their outer shell, meaning that they
all have similar properties - ANS✔✔All elements within a group ...
Periodicity - ANS✔✔The trends in the physical and chemical properties of
elements as you go across the periodic table.
Atomic radius across period 3 - ANS✔✔Atomic radius across period 3 goes
as follows:
1) As the number of protons increases the further down a period you go,
the positive charge of the nucleus increases
2) And though the amount of electrons increases across a period, they are
added to the outer energy level - So their isn't any extra shielding
3) This means that the electrons are pulled closer to the nucleus, causing
the atomic radius to decrease
4) Therefore, that overall the atomic radius of an atom decreases across
period 3 with the largest radius being the first element, Na, and the smallest
being the last element, Ar
Melting points across a period 3 - ANS✔✔The melting point across period
3 goes as follows:
1) At the start with sodium, magnesium and aluminium their melting points
increase. This is because they are metals and have strong electrostatic
forces to overcome - The bonds get stronger by the time you reach Al due
to having and more positively charged nucleus, increased number of
delocalised electrons and a decreasing radius
2) From Al to Silicon, the melting point increases further as Si is a
macromolecular substance which has very strong covalent bonds that take
a lot of energy to break
,3) However, the melting point then drops due to phosphorus, sulfur,
chlorine and argon all being molecular substances. The issue with being
that kind of substance is that to break the bonds apart all you need to do is
to overcome the weak Van der Waals forces - A very easy task
4) The difference in melting points between P, S, Cl and Ar is that some
molecules are bigger than others which leads to slightly greater Van der
Waals forces
First ionisation energy across period 3 - ANS✔✔First ionisation energy
across period 3 goes as follows:
1) As you mover across the period, the general trend is for the ionisation
energy to increase - This is due to an increase in number of protons within
an atom as you go across the period which leads to a stronger nuclear
attraction
2) The electrons do not counter this increase in protons due to the
electrons remaining in roughly the same energy level which means their is
little shielding affect or extra distance to lessen the attraction from the
nucleus - Though there is a dip between elements in Mg and Al, P and S
3) The issue between Mg and Al is that Al has a 3p outer orbital rather than
the 3s on Mg. Because of this the outer most electron in Al is further away
from the nucleus and has an extra layer of shielding in the form of a 3s
4) As for the drop from P to S, this is because, though the ionised electron
come out of the same sub-shell for both P and S. However, in P case the
electron is being removed from a single occupied shell whereas is is being
removed from an orbital containing two in S. The repulsion between the two
electrons means that the electrons are easier to remove from shared orbital
Increases as you go down the group due to extra electron shells as you go
down the group - ANS✔✔Atomic radius across group 2
First Ionisation Energy down Group 2 Alkali Metals - ANS✔✔First ionisation
energy down Group 2 Alkali Metals goes as follows:
1) The ionisation energy decreases as you go down the group
2) This is due to their being extra shielding for the outermost electrons the
further down the group you go as well as the further distance between the
outer electrons
3) These two occurrences out weigh the power of the increasing positively
charged nucleus as you go down the group
How does reactivity change in group 2 elements - ANS✔✔Some of the
ways that reactivity changes in group 2 elements are as follows:
1) Their is an increase as you go down the group
,2) This is because the ionisation energy needed to carry out a reaction is
lower the further down the group you go - This means you don't have to put
in much energy for a reaction to take place if the element you select is one
of the obese further down this group
Melting point of group 2 metals - ANS✔✔The melting points of group 2
metals goes as follows:
1) Overall the melting points of these metals decrease as you go down the
group
2) This is because, thought the metal ions get bigger, the number of
delocalised electrons and the charge on the ion doesn't change to keep
thing equivalent
3) This larger ionic radius therefore causes the distance between the ions
and the electrons to increase as their are not as many electrons that are
able to get just as close a previously
4) This means that it takes less energy to break the bonds, which means
that the melting point generally decrease as you go down the group -
Though this is not the case for Mg where it melting point is really lower in
comparison to those around them
5) The reason for Mg being different is that the arrangement of the metallic
ions change
How do group 2 metals react with water? - ANS✔✔The way that group 2
metals react with water goes as follows:
1) When group 2 metals react, they are oxidised from a state of 0 to +2
2) This means that when they react with water, a metal hydroxide and
hydrogen gas is produced
3) This reaction happens more rapidly as you go down the group due to the
ionisation energy decreasing
4) However, it is important to remember that Beryllium does not react with
water as its ionisation energy is to high
Solubility of group 2 metals - ANS✔✔The solubility of group 2 metals goes
as follows:
1) This heavily depend on the anion the group 2 metal is attached to
2) If they are connected to OH-, solubility increases down the group as they
are connected to a singly charged negative ion
3) If they are connected to SO4^2- solubility decreases as you go down the
group as they are connected to a doubly charged negative ion
barium sulfate - ANS✔✔What group 2 metal sulfate is insoluble in water
Test for sulfate ions - ANS✔✔To test for sulfate ions you do as follows:
1) Pour you solution containing sulfate ions into a test tube
, 2) Use a pipette to add hydrochloric acid and barium chloride to the
solution
3) If sulfate ions are present a barium sulfate white precipitate will form
Use of group 2 metals - ANS✔✔Some of the uses of group 2 metals are:
1) Barium meals
2) Extraction of titanium
3) Removal of sulfur dioxide from flue gases
4) Acid neutralisers
Barium meals - ANS✔✔Barium meals goes as follows:
1) When using X-rays, a doctor can use the machine to detect for where
bones are and whether they are broken or not
2) However, this is not beneficial however should you be looking for soft
tissues as they do not show up
3) Therefore 'barium meals', made up of suspended barium sulfate, are
given to the patient to help diagnose problems with the oesophagus,
stomach or intestines by showing the outlines of these tissues
4) You could only use barium sulfate for this task due to other solutions
being poisonous
Extraction of titanium - ANS✔✔The extraction of titanium goes as follows:
1) Magnesium is used as part of the process of extracting the titanium from
its impure ore
2) First the ore, TiO2 is converted to titanium(IV) chloride, TiCl4 by heating
it with carbon in a steam of chlorine gas
3) The TiCl4 is then purified through fractional distillation before being
reduced by Mg in a furnace at almost 1000 'C
Removal of sulfur dioxide from flue gases - ANS✔✔The removal of sulfur
dioxide from flue gas is important when burning fossil fuels to produce
electricity as sulfur dioxide pollutes the atmosphere. The system works as
follows:
1) A slurry of calcium carbonate and water is produced
2) When Sulfur dioxide react with this, calcium sulfite is produced which
cannot pollute the atomsophere
Group 2 metals and neutralising acids - ANS✔✔Groups 2 metals can
neutralise acids due to the following:
1) Due to being an alkaline earth metal, the elements can be used to
neutralise acids
2) An example of this is calcium hydroxide which neutralises acidic soils
3) Another example of this is Magnesium hydroxide which is used as an
antacid to neutralise stomach acid
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