AQA Chemistry Unit 3

HideShow resource information
  • Created by: Hope
  • Created on: 19-05-13 11:14
Preview of AQA Chemistry Unit 3

First 493 words of the document:

THE PERIODIC TABLE
The Early Periodic Table
Newlands and Mendeleev attempted to classify the elements by arranging them in order of their atomic
weights. The list can be arranged in a table so that elements with similar properties are columns, known as
groups. The table is called a periodic table because similar properties occur at regular intervals.
The early periodic tables were incomplete and some elements were placed in inappropriate groups if the
strict order of atomic weights was followed. Mendeleev overcame some of the problems by leaving gaps
for elements that he thought had not yet been discovered.
The Modern Periodic Table
When electrons, protons and neutrons were discovered early in the 20th century, the periodic table was
arranged in order of atomic (proton) numbers. When this was done, all elements were placed in appropriate
groups.
The modern periodic table can be seen as an arrangement of the elements in terms of their electronic
structures. Elements in the same group have the same number of electrons in their highest occupied energy
level (outer shell).
Group 1
The elements in Group 1 of the periodic table are known as the Alkali Metals. These have a low density
(lithium, sodium and potassium are less dense than water) and are soft enough to be cut with a knife.
Properties of alkali metals are:
- Shiny
- Low Boiling Point
- Low Melting Point
- Low Density
- Good Conductor Of Heat And Electricity
- Soft
They react with non-metals to form ionic compounds in which the metals to form ionic compounds, in which
the metal ion carries a charge of +1 (the metal loses an electron). This is because they have one electron in
their outer shell, so they easily obtain a full outer shell by losing on electron. They are stored in oil to stop
them reacting with oxygen in the air. They react with water and release hydrogen, as well as forming
hydroxides that dissolve in water to give alkaline solutions. The further down Group 1 an element is: the
more reactive it is and the lower the boiling/melting point as well as being denser.
The reactivity increases because the size of the element's atom and the number of full electron shells
increases down the group. This means that the electron in the outer shell gets further away from the nucleus
and is shielded by more electron shells. The further away an electron is from the positive attraction of the
nucleus, the easier it can be lost in reactions.
Alkali metals react with oxygen in the air to form metal oxides. This produces a dull layer on the surface of the
metal called tarnish. The speed at which tarnish is produced increases down the group. Oxidation reaction:

Other pages in this set

Page 2

Preview of page 2

Here's a taster:

ALKALI SPEED WORD EQUATION SYMBOL EQUATION
METAL
Lithium Slow lithium + oxygen --> lithium oxide
Sodium Quick sodium + oxygen --> sodium oxide
potassiu Very Quick potassium + oxygen --> potassium oxide
m
Alkali metals react vigorously with water. It is an exothermic reaction as it releases a lot of heat. This reaction
creates alkaline hydroxide ions.…read more

Page 3

Preview of page 3

Here's a taster:

Halogen-metal compounds are salts. Further down the group they become less
reactive, have a higher melting /boiling point and become darker in colour. Properties of the halogens are:
- Poisonous And Smelly
- Non-Metals
- Poor Conductor Of Heat And Electricity
- Brittle And Crumbly When Solid
Bromine and iodine are volatile. When heated iodine sublimes, which means it goes straight from a solid to a
gas.…read more

Page 4

Preview of page 4

Here's a taster:

Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels
of dissolved salts and microbes. Water of the correct quality is produced by :
- Choosing an appropriate source
- Passing the water through filter beds to remove any solids
- Sterilising with chlorine
Water filters containing carbon, silver and ion exchange resins can remove some dissolved substances from
tap water to improve the taste and quality.…read more

Page 5

Preview of page 5

Here's a taster:

Energy released from forming new bonds > energy needed to break existing bonds
In an endothermic reaction:
Energy released from forming new bonds < energy needed to break existing bonds
Catalysts provide a different pathway for a chemical reaction that has a lower activation energy.
Hydrogen can be burned as a fuel in combustion engines, it can also be used in fuel cells that produce
electricity to power vehicles.…read more

Page 6

Preview of page 6

Here's a taster:

Measure the known volume of the solution of alkali into a conical flask using a pipette (fill the pipette
until the bottom of the meniscus coincides with the mark).
2. Now add an indication solution (universal) into the solution in the flask.
3. Put a solution of the acid into the flask using a burette (use the bottom of the meniscus to read the
scale).
4.…read more

Page 7

Preview of page 7

Here's a taster:

RAISED Decreases Increases
TEMPERATURE
LOWERED Increases Decreases
TEMPERATURE
In gaseous reactions, an increase in pressure will favour the reaction that produces the least number of
molecules as shown by the symbol equation for that reaction. These factors, together with reaction rates,
are important when determining the optimum conditions in industrial processes including the Haber process.
ALCOHOLS, CARBOXYLIC ACIDS & ESTERS
Alcohols
Alcohols contain the functional group ­OH. Methanol, ethanol are the first three numbers of a homologous
series of alcohols.…read more

Page 8

Preview of page 8

Here's a taster:

Many esters have pleasant smells- often quite sweet and fruity. They're also volatile. This makes
them ideal for perfumes (the evaporated molecules can be detected by smell receptors in the nose).
2) However, many esters are flammable (or even highly flammable). So their volatility also makes them
potentially dangerous.
3) Esters don't mix well with water. (They're not nearly as soluble as alcohols or carboxylic acids.)
4) But esters do mix well with alcohols and other organic solvents.…read more

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »