AQA GCSE Chemistry (Atomic structure and the periodic table)

What is an element?

A substance that contains only one type of atom.

What is a compound?

2 or more elements chemically bonded together.

What is a mixture?

2 or more elements or compounds which are not chemically bonded together.

What is filtration?

Separate insoluble solids from a liquid

What is crystallisation?

Separation of a soluble solid from a liquid

What is simple distillation?

Used to separate a liquid from a solid when we want to keep the liquid.

What is fractional distillation?

Used to separate liquids with different boiling points.

What is a molecule?

Any elements chemically combined, even if they are the same element.

What is chromotography?

A method used to separate a mixture of dyes

What is a solvent?

A liquid that will dissolve a solute.

What is a solute?

A substance that is dissolved.

What is the stationary phase in chromatography?

The paper

What is the mobile phase is chromatography?

The solvent

What will a pure chemical produce in chromatography?

A single spot

What will chemicals in a mixture produce during chromatography?

Separate spots (depending on solvent used)

Why do we draw to starting line in pencil for chromatography?

If we drew the line in pen, the pen ink would move up the paper with the solvent.

What did the plum pudding model suggest?

That an atom is a ball of positive charge, with negative electrons imbedded in it.

Who came up with the plum pudding model?

JJ Thomson

Explain the Alpha Scattering Experiment:

Step 1?

The scientist took a piece of gold foil

Why was gold used in the alpha scattering experiment?

Gold can be hammered out into very thin foil (a few atoms thick)

Explain the Alpha Scattering Experiment:

Step 2?

Scientists fired tiny alpha particles at the gold

What is the charge of the alpha particles?

Positive

What happed to most of the alpha particles?

They passed through the gold foil without changing direction.

What happened to some of the alpha particles?

Some alpha particles where deflected.

What happened to very few alpha particles?

They reflected back

What did most alpha particles going through the foil tell scientists?

That atoms are mostly empty space, so the plum pudding model had to be wrong.

What did some alpha particles being deflected tell scientists?

The centre of the atom must have a positive charge. Alpha particles that came close where repelled.

What did the alpha particles being reflected tell scientists?

The centre of the atom must contain a great deal of mass.

Who designed the Alpha Scattering Experiment?

Ernest Rutherford

What did Niels Bohr propose?

Electrons orbit the nucleus at specific distances. The idea of energy levels/shells

What did scientists find after Bohr's proposition?

The nucleus contained small positively charged particles, which they named protons.

What did James Chadwick discover?

The nucleus also contained neutral particles called neutrons.

Why do atoms have no overall charge?

Because the number of protons and electrons are equal, so they cancel out, leaving neutrons.

What is the average radius of an atom?

0.1nm (1x10^-10 m)

What is the radius of the nucleus?

1/10000 of the atom

What is the relative charge of protons, neutrons and electrons?

Proton: +1
Neutrons: 0
Electrons: -1

What is the relative mass of protons, neutrons and electrons?

Proton: 1
Neutron: 1
Electrons: Very small

What does the relative mass number tell?

The number of protons and neutrons together.

What does the atomic number tell?

The number of electrons and protons.

What is an isotope?

Atoms of an element with different numbers of neutrons.

What is an ion?

A charged atom

How is relative atomic mass calculated with isotopes?

The relative atomic mass is the average of the mass number of the different isotopes. It is waited for the abundance of each isotope.

Relative atomic mass of isotopes formula:

What is the maximum amount of electrons each energy level can hold from 1-4?

1st: 2
2nd: 8
3rd: 8
4th: 18

How did Newlands arrange the elements?

In order of atomic weight

What were the issues with arranging elements in order of atomic weights?

Sometimes elements were grouped together when they had totally different properties.

What did Mendeleev do differently to Newland?

• He switched the order of specific elements so that they fitted the pattern.
• He left gaps in the periodic table for elements that hadn't yet been discovered.

How are elements arranged in the modern periodic table?

In order of atomic number (amount of protons)

What was the problem with ordering elements by atomic weight (by Mendeleev)?

Elements can appear in the wrong order due to isotopes.

What is the name of elements in group 0?

Noble gases

Why are noble gases unreactive?

All noble gases have a full outer energy level.

How does the boiling point change in group 0?

It increases as the relative atomic masses increase (going down the group)

Do metals lose or gain electrons?

They lose electrons (becoming positive ions)

What are elements in group 1 called?

Alkali metals

How do group 1 metals react with oxygen?

Rapidly
More rapidly as you move don group 1

How do group 1 metals react with chlorine?

Rapidly. They form metal chloride

In group one, metals get reactive as you move down the group.

More

Why are metals more reactive as you go down group 1?

The outer electrons are further away from the nucleus making them less attracted and easier to lose l.

What are elements in group 7 called?

Halogens

What type of compound do group 7 elements form with other non-metals?

Covalent compounds

What type of compound do group 7 elements form with metal atoms.

Ionic compound

Elements in group 7 get reactive as you move down the group.

Less

Why do elements become less reactive as you move down group 1

• There is a greater distance from the nucleus as you move down meaning less attraction.
• Internal electrons shield the nucleus, reducing attraction.

Explain the displacement reactions of halogens.

A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

What are the properties of alkali metals?

• Soft metals (can be cut with a knife).
• Relatively low melting points.
• Low density.
• React rapidly with water, oxygen and chlorine.
• Form positive ions.

What are the properties of transition elements?

• Hard and strong (e.g. iron)
• High melting points
• Much less reactive than group 1 metals.
• Can form ions with different charges.
• Form coloured compounds.
• Can be used as catalysts.