C1: atomic structure and the periodic table

What is an element? What is a molecule?

A substance made up of one type of atom. A molecule is atoms bonded together.

What is a compound?

A compound is two or more different atoms chemically bonded together.

How are compounds separated?

By chemical reaction.

What is a mixture?

A mixture is different atoms not chemically bonded.

How are mixtures separated?

Physical separation techniques (e.g. filtration) - these involve no chemical reactions and no new substances are made

Describe filtration.

Filtration is used to separate an insoluble solid from a liquid.

Place filter paper into a funnel. Pour the mixture through this to a conical flask. The filtrate (liquid) will pass through.

Describe crystallisation.

Crystallisation is used to separate a soluble solid from a liquid.

Gently heat your solution to evaporate the liquid. This can be done in an evaporating basin over a bunsen burner - however, heat slowly and carefully to leave crystals.

Describe simple distillation.

Simple distillation is used to separate a soluble solid from a liquid, whilst keeping the liquid.

Place the solution into a flask with a thermometer, which is connected to a continuous glass tube. This has a condenser on it which keeps the glass tube cold.

First, heat the solution to evaporate the liquid, turning it into a vapour. The vapour will pass into the cold condenser and condense back into a liquid, collecting in a beaker. Crystals of solid should be left in the flask.

Describe paper chromatography.

Chromatography is used to separate substances based on different solubilities.

Draw a pencil (pencil as it’s insoluble). line near the bottom of chromatography paper. Put dots of ink along this line. Place the bottom of the paper into a solvent, BELOW the line. A more soluble substance travels further.

Give a brief timeline of the model of an atom.

1. Dalton - tiny indivisible spheres

2. Scientists discovered electrons

3. JJ Thompson - Plum Pudding model - atoms are balls of positive charge with electrons embedded in it

4. Rutherford - alpha scattering experiment

5. Rutherford - Nuclear model - mass of an atom concentrated at a positive nucleus centre, with electrons around the edge of the atom

6. Protons discovered

7. Bohr - electron shell model - electrons orbit the nucleus on electron shells

8. 20 years later, Chadwick discovered neutrons, also contained in nucleus

Describe the alpha scattering experiment

Scientists fired tiny alpha particles (+) at gold foil. Most passed straight through, but sometimes the particle was deflected, and sometimes it bounced off the foil entirely.

What did the alpha scattering experiment show?

• Most went straight through: atoms mainly empty space

• Some were deflected: centre of atom must be positive

• Some bounced straight back: centre of atom must contain most of the mass

How big is an atom and its nucleus?

Radius is 0.1nm (1 × 10^-10m)

Radius of nucleus is less than 1/10000 of the atom (1 × 10^-14m)

What are the relative masses and charges of subatomic particles? What is the charge of an atom?

An atom has no overall charge as the number of electrons is equal to the number of protons.

What is the atomic number and what is the atomic mass of an element?

• Atomic number = number of protons (and therefore electrons)

  • Same if same element

• Atomic mass = number of protons + neutrons in total

• Atomic mass - atomic number = number of neutrons

Define isotope.

Isotopes are atoms of the same element with different numbers of neutrons.

Define ion

Atoms with a charge - due to losing / gaining electrons

How are atoms drawn / electronic configuration?

2, 8, 8 rule - 2 electrons on the first energy level, then 8 on the other energy levels

See symbol of an element for number of electrons.

What do groups and periods show in the periodic table?

• Groups - number of electrons in outer shell, have similar properties

• Periods - number of electron shells

Give a brief timeline of the periodic table.

• Mendeleev - arranged elements in order of atomic weight, but sometimes switched order to fit patterns (as isotopes could mess this up). He also left gaps for undiscovered elements.

• Modern periodic table - elements arranged in order of atomic number, meaning every element is in the correct group

What is the equation for relative atomic mass?

(mass x abundance) + (mass x abundance) /100

Mass is the number, for example, 35 in chlorine-35. The abundance will be a percentage.

Where are the metals found on the periodic table? Which ones are highly reactive?

Metals are found on the left and centre. The metals in groups 1 and 2 are highly reactive.

What happens when metals react?

They lose their outer electrons to achieve a full outer electron shell. They become positive ions.

What are the key characteristics of group 0? (Noble gases)

• Unreactive / do not easily form molecules because they all have a full outer electron shell

• As you go down, boiling point increases

What are the key characteristics of group 1? (Alkali metals)

• All have one electron on their outer shell

• As you go down, reactivity increases

• React rapidly with oxygen and / or chlorine

How do alkali metals react with water? What is produced?

• A metal hydroxide and hydrogen gas is produced

• Effervescence is seen (fizzing / production of a gas)

• For example: sodium + water —> sodium hydroxide + hydrogen

What is electrostatic attraction and how does it affect reactivity?

The more electron shells there are, the more reactive. This is because there is weaker electrostatic attraction between the positive nucleus and negative outermost electron. This means that an outer electron could get lost more easily, causing a chemical reaction.

• In halogens, more electron shells, less reactive as harder to gain an electron

What are the key characteristics of group 7? (Halogens)

• All have 7 electrons in their outer shell

• Every group 7 element forms a molecule consisting of two atoms joined by a covalent bond

• As you go down, melting point and boiling point increases. Reactivity deceases.

• As you go down, relative molecular mass increases (molecule is bigger)

What is formed when group 7 elements react with other non-metal elements?

• Non-metals - covalent compounds. They join so they both have full outer shells.

• Metals - ionic compounds. The halogen atom gains one electron and forms an ion with a -1 charge