Atomic Structure

Atom

Atom

Basic unit of matter

Element

A pure substance made of only one kind of atom

Periodic Table

A chart of the elements showing the repeating pattern of their properties

Group

A vertical column of similar elements in the periodic table

Row

The horizontal lines of elements related via their number of electrons and protons

Where is the 'stepped line'?

Begins before boron and after aluminium

Molecule

two or more atoms held together by covalent bonds

Compound

A substance made up of atoms of two or more different elements joined by chemical bonds

Nucleus

Center of an atom

Electron

A subatomic particle that has a negative charge

Ion

an atom that has become charged by losing or gaining electrons

Isotope

an atom of the same element with a different number of neutrons

isotopes have different ... properties

physical

isotopes have the same ... properties

chemical

electronic strucutre

atom written as its shells, e.g. 2, 8, 1

What does the number of electrons in the outer shell affect?

the element's Group

John Dalton's model of the atom:

tiny, hard, indivisible spheres - each element's atom has a different mass

Who discovered the electron?

JJ Thomson

How did JJ Thomson discover the electron?

cathode ray tube experiment

cathode ray tube

evacuated glass tube in which a stream of electrons emitted by a cathode strikes a fluorescent material, causing it to glow

Cathode ray tube experiment:

JJ Thompson put positively and negatively charged plates around the cathode ray tube and saw that the ray curved towards the positive plate. He deduced that there must be electrons

JJ Thomson's model of the atom

plum pudding model

Who discovered the nucleus?

Ernest Rutherford

How was the nucleus discovered?

Gold foil experiment

Gold foil experiment [4]:

- gold foil placed in the middle of a fluorescent screen
- alpha particles shot at gold foil
- most particles went through
- some were deflected

conclusions from gold foil experiment [3]:

- atom is mostly empty space
- nucleus has a positive charge
- electrons float around nucleus

Ernest Rutherford's model of the atom:

Nuclear/planetary model

Who discovered that electrons are in shells?

Niels Bohr

Who discovered the neutron?

James Chadwick

How was the neutron discovered? [4]

- alpha particles shot at materials
- emitted rays with no charge
- rays with no charge dislodged protons from paraffin
- deduced that they were neutrons

atomic number

number of protons in an atom

mass number

number of protons + number of neutrons

Miscible

Describes two liquids that are soluble in each other

Why is it difficult to get a pure substance with simple distillation?

Some vapour may be given off before the substance reaches boiling point - the boiling points are too close together.

Fractional distillation

Used to separate liquids with similar boiling points using a fractionating column

Fractionating column

a glass tube filled with beads

How does a fractionating column work? [3]

- vapours must pass over the beads to reach the condenser
- the substance with the higher boiling point is more likely to condense lower down, where the temperature is higher
- the substance with the lower boiling point will continue to rise through the tube and reach the condenser

The use of fractional distillation [2]

- Use of ethanol as a biofuel
- In oil refineries, to separate crude oil

Chromatography

A technique that is used to separate the components of a mixture based on the tendency of each component to travel or be drawn across the surface of another material (solubility)

Paper chromatography [4]

- Draw a pencil line on some absorbent chromatography paper to indicate the starting point
- Use a capillary tube to dab small amounts of solution on the line
- Suspend the paper in a small amount of water (up to the line)
- See which solution travels the furthest

Mixture

A combination of two or more substances that are not chemically combined

Ratios (c vs m)

- Compounds have a fixed composition
- Mixtures have no fixed composition

Separation (c vs m)

- Compounds must be separated by chemical reactions
- Mixtures can be separated by physical means, using the properties of each separate substance

Chemical bonds (c vs m)

- Compounds contain different elements chemically bonded
- There are no chemical bonds between atoms of a different substance in a mixture

Filtration

A process used to separate an insoluble substance from a solvent - usually with filter paper and a funnel

Filtering sand [3]

- The sandy water is poured through filter paper
- The sand collected on the paper is rinsed to remove any remaining soluble solvents
- The sand is dried in a warm oven to evaporate off the water

Crystallisation

The formation of crystals by evaporating a solvent from a saturated solution

Crystallisation process [3]

- Heat an evaporating dish containing the saturated solution (either in a water bath or directly on the gauze and tripod)
- Stop heating at the point of crystallisation
- Leave the rest of the solvent to evaporate at room temp

Filtrate

liquid that has passed through a filter

solvent

A liquid substance capable of dissolving other substances

solute

A substance that is dissolved in a solution.

Distillation

A process that separates the substances in a solution based on their boiling points

Simple distillation [4]

- solution is heated over Bunsen burner
- a thermometer is placed so that we can record the gas's temperature
- the gas enters a condenser where it is cooled and again becomes liquid
- the liquid enters another glass

Condenser

A tube with an outer jacket that has water flowing through it, acting as a coolant to condense the vapours inside

Reactants

A starting material in a chemical reaction

Products

The elements or compounds produced by a chemical reaction.

Word equation

an equation in which the reactants and products in a chemical reaction are represented by words

Symbol equation

equation that shows the chemical symbols and formulae of reactants and products

Law of conservation of mass

Matter is not created nor destroyed in any chemical or physical change

State symbols

Symbols to show the state of a substance - solid (s), liquid (l), gas (g) and aqueous (aq)

Aqueous solutions

solutions with water as the solvent

How do you balance equations? [4]

- Write down all the atoms and the numbers of them on the side of the reactants and of the products
- Change one necessary coefficient
- Rewrite/reevaluate the first step
- Repeat until balanced