GCSE AQA Chemistry - Atomic structure and the periodic table

Does not contain everything on the topic, just the stuff I was unsure of

Size of an atom in metres

1×10^-10m

Size of an atom in nanometres

0.1nm

What fraction of the diameter of an atom is the diameter of a nucleus?

1/10,000

Relative masses of protons, neutrons and electrons

1, 1, relatively 0

What is the top number on a nuclear symbol?

Mass number

What does mass number tell you?

The total number of protons and neutrons in the nucleus.

What is the bottom number on a nuclear symbol?

Atomic number

What does the atomic number tell you?

The number of protons.

Isotopes

Forms of the same element with different numbers of neutrons.

relative atomic mass =

sum of (isotope abundance x isotope mass number) / sum of abundance of all the isotopes

Compounds

Combined atoms formed from chemical reactions.

How should the filter paper be prepared for chromatography?

Draw a line near the bottom of the paper, and add a spot of the ink to the paper.

Why is pencil used instead of ink in chromatography?

Pencil marks are insoluble.

Describe chromatography practical

• Place the sheet in a beaker of solvent

• The solvent will seep up the paper and carry the ink with it

• The dyes will move up the paper at different rates and separate

Why do we need to make sure the ink initially isn’t touching the solvent in chromatography practical?

So the ink doesn’t dissolve in it.

Filtration

Separates an insoluble solid from a liquid reaction mixture.

What are two ways to separate soluble solids from a solutions?

Evaporation and crystallisation.

Simple distillation

Separates out a liquid from a solution if there are large difference in boiling points of the substances.

Simple distillation process

• The solution is heated

• The part of the solution with the lowest boiling point evaporates first

• The vapour is cooled, condenses in the condensor and is collected

Fractional distillation process

• The liquid with the lowest boiling point will evaporate first

• It will reach the top of the fractionating column when the top reaches it’s boiling point and can be collected

How does the fractionating column help fractional distillation?

It is cooler towards the top, so liquids with higher boiling points than the one being collected will only get part way up the column before condensing and running back down.

How did John Dalton describe atoms?

As solid spheres that made up different elements

JJ Thomson’s plum pudding model

A ball of positive charge with negative electrons embedded inside it.

Gold foil experiment

Positively charged alpha particles were fired at a thin sheet of gold foil

What did the fact that most of the alpha particles went straight through show?

Most of the atom is empty space.

What did the fact that some alpha particles were deflected show?

The atom’s mass and positive charge is concentrated in the central nucleus

What did Bohr propose?

Electrons orbit the nucleus at fixed shells.

What did James Chadwick discover?

Neutrons

What is the function of neutrons?

Separate protons to prevent them from repelling.

What were elements originally arranged in order of?

Atomic weight

What was the problem with the early periodic tables?

They were incomplete and some elements were placed in inappropriate groups because of the strict order by atomic weight

How did Mendeleev overcome the problems with the early periodic tables?

• He left gaps for undiscovered elements

• He swapped around the order of some elements to match properties

What explains the fact it was not always possible to order by atomic weight?

The discovery of isotopes

Group 1 properties (3)

• Soft

• Low melting points

• Low densities

Group 1 trends down the group (2)

• Higher reactivity

• Lower melting point

Explain the increasing reactivity down group 1

• The outer shell electron is further away from the nucleus

• So there is less attraction and it is more easily lost

Reaction of alkali metals in water

Metal reacts with water to produce a metal hydroxide and hydrogen

Observations of reaction between alkali metal and water

• Bubbles of hydrogen gas produced

• The metal floats

• The metal dissolves/disappears

Chlorine at room temperature

Pale green gas

Bromine at room temperature

Brown liquid

Iodine at room temperature

purple/black solid

Trends of group 7 down the group

• Lower reactivity

• Higher melting point

Group 1 reaction with chlorine

React vigorously in chlorine gas to form white metal chloride salts

Why does boiling point increase down group 0?

Because there is an increased number of electrons in each atom, there are greater intermolecular forces which need to be overcome.

Why are group 0 elements unreactive?

Their outer shell is already stable, so they don’t need to gain or lose any electrons to become more stable.

Malleable

Able to be bent or battered into different shapes.

Reactivity of transition metals compared to group 1

Transition metals are less reactive

Properties of transition metals compared to group 1 (density, strength, hardness, melting point)

• Transition metals more dense, strong and hard

• Transition metals have a high melting point