Chemistry unit 2 revision notes gcse higher tear

Chemistry unit 2 revision notes gcse higher tear

HideShow resource information
  • Created by: d
  • Created on: 12-08-12 18:51
Preview of Chemistry unit 2 revision notes gcse higher tear

First 209 words of the document:

Structures and Bonding
The Atomic Structure
Contains the same amount of protons and electrons, making the charge 0.
Protons +1
Neutrons 0
Electrons 1
The Arrangement of electrons in atoms
Each shell represents a different energy level. Lowest energy level is shown by
the shell which is nearest to the nucleus. Electrons in the outer shells have
more energy than those closer to the nucleus.
First shell can only hold 2 electrons
2nd shell onwards can only hold 8 electrons
Electronic structure of carbon written as 2, 4 2 electrons on the inner shell
and 4 on the outer shell
PERIODIC TABLE horizontal rows called periods vertical columns called
groups
As we move across a period each element has one more electron in its outer
shell than the element before it.
All elements in group 1 have one electron in their outer shell. The noble gases,
except helium, have 8 electrons in their outer shell.
Chemical Bonding
When an atom has a full outer shell, it is stable and unreactive. When atoms
react they take part in changes which give them a stable arrangement of
electrons
Sharing electrons covalent bonding
Transferring electrons ionic bonding

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

By gaining electrons the element turns negative. By releasing electrons the
element turns positive.…read more

Page 3

Preview of page 3

Here's a taster:

Higher ­ Metals are another example of giant structures. Metal = lattice of
metal ions (positively charged ions)
The electrons in the outer shell can easily move from one atom to the
next. The electrons which have the highest energy levels form a sea
of free electrons surrounding the positively charged metal ions. Strong
electrostatic forces between the electrons (negatively charged) and the
ions (positively charged) glue the metal ions together.…read more

Page 4

Preview of page 4

Here's a taster:

Ions free to move ­
will conduct electricity
Simple Molecules
Covalent Bonds ­ when atoms of nonmetal elements react to form
compounds ­ share electrons in outer shells ­ each atoms gets a
full outer shell.
Substances with this kind of bond tend to have low boiling and melting points.
This means that many substances with simple molecules are liquids and gases
at room temperature. Others that are solids also have quite low melting points.
Higher ­ Covalent bonds are very strong.…read more

Page 5

Preview of page 5

Here's a taster:

This spare electron
becomes delocalised among the layers of the carbon atoms.
Fullerenes ­ there are other different molecules that carbon can produce. In
these structures carbon atoms join together to make large cages
which can have all sorts of weird shapes.
Giant Metallic Structures
Metals are malleable because of the layers of atoms in elements can slide over
each other easily
Higher ­ The atoms in a metal structure are held together by a sea of
delocalised electrons.…read more

Page 6

Preview of page 6

Here's a taster:

For practical purposes the masses of the
electrons isn't worth bothering about.
Relative Formula Mass ( Mr ) ­ The relative atomic mass is used the work
out the relative formula mass. E.g. Sodium Chloride
(NaCl)
(Ar) Na + (Ar) Cl = (Mr) NaCl
23 + 35.5 = 58.5
Moles ­ Writing Ar and Mr may seem clumsy ­ shorthand = moles. 1 mole =
Ar/Mr in grams. A mole of any substance always contains the same
number of particles.…read more

Page 7

Preview of page 7

Here's a taster:

The percentage mass of carbon in the
strychnine. Not the same ­ not strychnine
334
Higher Working out the formula of a compound from it percentage
composition
Empirical Formula ­ Tells us the ratio of elements in a compound.
Molecular Formula ­ Sometimes the same as the actual number of atoms in
one molecule ­ not always the case
If 9g of aluminium react with 35.…read more

Page 8

Preview of page 8

Here's a taster:

The following formula can be used to find out how much of two
chemicals are used to react together. Sodium hydroxide reacts with
chlorine gas to make bleach.
2NaOH + Cl2 NaOCl + NaCl + H2O
So mass of 1 mole of...
NaOH Cl2
Ar of Hydrogen = 1...
= 23 + 16 + 1 = 40 = 35.5 x 2 = 71
Ar of Oxygen = 16...
Ar of Sodium = 23...
Ar of Chlorine = 35.5...…read more

Page 9

Preview of page 9

Here's a taster:

Percentage yield
Very few chemicals have a yield of 100% because:
The reaction could be reversible
Some reactants may react to give an unexpected product
Some of the reactants could be left behind on the apparatus
The reactants may not be completely pure
Some chemical reactions produce more than one product and it may
be difficult to separate the useful product from the mixture
Atom Economy
Chemical companies use chemical reactions to make products which they sell.…read more

Page 10

Preview of page 10

Here's a taster:

A+B (Eventually the rates of forward and reverse
reactions are the same
In a system that is closed, no reactants or products can get in or out. In a
closed system, as more and more products are made in a reversible reaction
the rate at which these get converted back into reactants increases.
As the rate of the backward reaction increases, the rate of the forward reaction
decreases until they are both the same.…read more

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »