AQA GCSE Chemistry Unit 2 Revision Notes

HideShow resource information
  • Created by: Yash
  • Created on: 23-01-13 19:55
Preview of AQA GCSE Chemistry Unit 2 Revision Notes

First 336 words of the document:

Chemistry C2 Revision Notes
C2.1.1 Structure and bonding
a) Compounds are substances in which atoms of two or more elements
are chemically combined.
b) Chemical bonding involves either transferring or sharing electrons
in the highest occupied energy levels (shells) of atoms in order to
achieve the electronic structure of a noble gas.
c) When atoms form chemical bonds by transferring electrons, they
form ions. Atoms that lose electrons become positively charged ions.
Atoms that gain electrons become negatively charged ions. Ions have
the electronic structure of a noble gas (Group 0).
d) The elements in Group 1 of the periodic table, the alkali metals, all
react with non-metal elements to form ionic compounds in which the
metal ion has a single positive charge.
e) The elements in Group 7 of the periodic table, the halogens, all react
with the alkali metals to form ionic compounds in which the halide ions
have a single negative charge.
f) An ionic compound is a giant structure of ions. Ionic compounds are
held together by strong electrostatic forces of attraction between
oppositely charged ions.
These forces act in all directions in the lattice and this is called ionic
bonding.
g) When atoms share pairs of electrons, they form covalent bonds.
These bonds between atoms are strong. Some covalently bonded
substances consist of simple molecules such as H2, Cl2, O2, HCl, H2O,
NH3 and CH4. Others have giant covalent structures (macromolecules),
such as diamond and silicon dioxide.
h) Metals consist of giant structures of atoms arranged in a regular
pattern.
The electrons in the highest occupied energy levels (outer shell) of
metal atoms are delocalised and so free to move through the whole
structure. This corresponds to a structure of positive ions with
electrons between the ions holding them together by strong
electrostatic attractions.
By Yash Lallchand

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

Chemistry C2 Revision Notes
C2.2.1 Molecules
a) Substances that consist of simple molecules are gases, liquids or
solids that have relatively low melting points and boiling points.
b) Substances that consist of simple molecules have only weak
forces between the molecules (intermolecular forces). It is these
intermolecular forces that are overcome, not the covalent bonds,
when the substance melts or boils.
c) Substances that consist of simple molecules do not conduct
electricity because the molecules do not have an overall electric
charge.
C2.2.…read more

Page 3

Preview of page 3

Here's a taster:

Chemistry C2 Revision Notes
d) In graphite, one electron from each carbon atom is delocalised.
These delocalised electrons allow graphite to conduct heat and
electricity.
e) Carbon can also form fullerenes with different numbers of
carbon atoms. Fullerenes can be used for drug delivery into the
body, in lubricants, as catalysts, and in nanotubes for reinforcing
materials, e.g. in tennis rackets.
C2.2.4 Metals
a) Metals conduct heat and electricity because of the delocalised
electrons in their structures.…read more

Page 4

Preview of page 4

Here's a taster:

Chemistry C2 Revision Notes
C2.2.6 Nanoscience
a) Nanoscience refers to structures that are 1­100 nm in size, of the
order of a few hundred atoms. Nanoparticles show different
properties to the same materials in bulk and have a high surface
area to volume ratio, which may lead to the development of new
computers, new catalysts, new coatings, highly selective sensors,
stronger and lighter construction materials, and new cosmetics
such as sun tan creams and deodorants.
C2.3.…read more

Page 5

Preview of page 5

Here's a taster:

Chemistry C2 Revision Notes
g) The relative formula mass of a substance, in grams, is known as one
mole of that substance.
C2.3.2 Analysing substances
a) Elements and compounds can be detected and identified using
instrumental methods. Instrumental methods are accurate, sensitive
and rapid and are particularly useful when the amount of a sample is
very small.
b) Chemical analysis can be used to identify additives in foods. Artificial
colours can be detected and identified by paper chromatography.…read more

Page 6

Preview of page 6

Here's a taster:

Chemistry C2 Revision Notes
The reaction may not go to completion because it is reversible
Some of the product may be lost when it is separated from the
reaction mixture
Some of the reactants may react in ways different from the
expected reaction.
e) The amount of a product obtained is known as the yield. When
compared with the maximum theoretical amount as a percentage, it is
called the percentage yield.…read more

Page 7

Preview of page 7

Here's a taster:

Chemistry C2 Revision Notes
e) Increasing the concentration of reactants in solutions increases the
frequency of collisions and so increases the rate of reaction.
f) Increasing the surface area of solid reactants increases the
frequency of collisions and so increases the rate of reaction.
g) Catalysts change the rate of chemical reactions but are not used up
during the reaction. Different reactions need different catalysts.
h) Catalysts are important in increasing the rates of chemical reactions
used in industrial processes to reduce costs.
C2.5.…read more

Page 8

Preview of page 8

Here's a taster:

Chemistry C2 Revision Notes
C2.6.1 Making salts
a) The state symbols in equations are (s), ( l ) , (g) and (aq).…read more

Page 9

Preview of page 9

Here's a taster:

Chemistry C2 Revision Notes
d) Hydrogen ions, H+(aq), make solutions acidic and hydroxide ions,
OH­(aq), make solutions alkaline. The pH scale is a measure of the
acidity or alkalinity of a solution.
e) In neutralisation reactions, hydrogen ions react with hydroxide ions
to produce water. This reaction can be represented by the equation:
C2.7.1 Electrolysis
a) When an ionic substance is melted or dissolved in water, the ions are
free to move about within the liquid or solution.…read more

Page 10

Preview of page 10

Here's a taster:

Chemistry C2 Revision Notes
h) Aluminium is manufactured by the electrolysis of a molten mixture
of aluminium oxide and cryolite.
Aluminium forms at the negative electrode and oxygen at the positive
electrode. The positive electrode is made of carbon, which reacts with
the oxygen to produce carbon dioxide.
i) The electrolysis of sodium chloride solution produces hydrogen and
chlorine. Sodium hydroxide solution is also produced. These are
important reagents for the chemical industry, e.g.…read more

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »