🧪 C2

Pure substance

Pure substance

One single substance (properties are always the same) e.g. water, gold

Impure substance/mixture

Two or more substances mixed (properties vary) e.g. milk, sand

Element

A pure substance made for only one type of atom

Compound

Two or more different elements chemically bonded together

Mixture

Two or more different elements or compounds that are not chemically bonded together

Molecule

Two or more atoms chemically bonded together

Homogeneous mixture

Has the same composition throughout, and we cannot see the individual substances e.g. salt water, wine, steel

Heterogeneous mixture

Is not the same throughout, and we can see the individual substances e.g. oil and water, salt and pepper

Purification

Removing impurities so we are only left with the pure substance we want

Effect of impurities on melting points

Melting point decreases

Effect of impurities on boiling points

Boiling points increase

Can be used to measure the purity of a substance

Melting and boiling points

Filtration

A simple method used to separate a liquid from an insoluble solid e.g. water from sand

Crystallisation

A method used to separate a soluble solid from a liquid e.g. salt from water

Chromatography

Used to separate coloured dyes that are mixed together.

Chromatography process

A spot of ink is placed near the bottom of a piece of filter paper, the paper is then placed in a suitable solvent (water or ethanol), as the solvent soaks up the paper it carries the mixture with it, different components of the mixture will move at different rates - this separates the mixture out (due to differences in solubility)

Calculating an Rf value

Distance moved by the compound/Distance moved by the solvent

Rf value not

The value has to be less than 1

Simple distillation

A method used to separate a liquid from a soluble solid e.g. water can be separated from salt which is dissolved in the water

Simple distillation method

Leißig condenser cools the steam that is produced when the liquid is heated, this happens rapidly so you retrieve the distillate much quicker.

Fractional distillation

Method used to separate two or more miscible liquids from each other using the differences in their boiling points

Miscible

Liquids mix completely to form a homogeneous mixture

Fractional distillation method

The glass beads in the fractionating column provide a surface for condensation of the vapours to liquids. The liquid with the lower boiling point turns to vapour when it is heated and travels into the water condenser where it turns back to a liquid and is collected in a beaker

Diatomic molecule

A molecule containing only two atoms

Diatomic elements

Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine, Iodine

Hydrogen

H₂ Colourless, gas (at room temperature)

Nitrogen

N₂ Colourless, gas (at room temperature)

Oxygen

O₂ Colourless, gass (at room temperature)

Fluorine

F₂ Pale yellow, gas (at room temperature)

Chlorine

Cl₂ Pale green, gas (at room temperature)

Bromine

Br₂ Red/brown, liquid (at room temperature)

Iodine

I₂ Purple, solid (at room temperature)

The metallic elements

Shiny, dense, high melting point solids which are excellent conductors of heat and electricity. They are highly malleable and ductile. Tend to form positively charged ions. e.g. Lead (Pb), Mercury (Hg)

Ductile

Can be drawn into wires

Malleable

Can be bent and shaped

The non-metals

Non-shiny and volatile with low density. They are poor conductors of heat and electricity and are not malleable or ductile. e.g. Carbon (C), Bromine (Br)

The metalloids (semi-metals)

Difficult to categorise as metals or nonmetals because they show properties of both e.g. Silicon is hard and shiny with some conductivity but is brittle with low density

Group 1

The alkali metals

Group 2

The alkali earth metals

Group 7

The halogens

Group 0 (8)

Noble gases

Between groups 2&3

The transition metals

Number of shells

Period number

Number of electrons in outer shell

Group number

Makeup of an atom

Atoms are made of even smaller particles called subatomic particles

Subatomic particles

Proton, Neutron, Electron

Proton

Positive charge

Neutron

No electrical charge

Electron

Negative charge

Where protons and neutrons are found

Exist in a dense core at the centre of the atom, called the nucleus

Where electrons are found

Spread out around the edge of the atom. They orbit the nucleus in layers called shells.

Relative atomic mass (mass number)

The number of protons and neutrons in the nucleus

Atomic number

The number of protons in the nucleus

Isotope

Atoms of the same element with the same number of protons but a different number of neutrons (same atomic number, different mass number)

pH scale

Tells you how acid or alkali something is

1-6

Acid

8-14

Alkali

7

Neutral

1

Strong acid

6

Weak acid

9

Weak alkali

14

Strong alkali

Alkali metals

Lithium, Sodium, Potassium, Rubidium, Caesium, Francium

Properties of Alkali metals

Softness, density and reactivity increase as you go down the group, all have 1 electron in their valance (outer) shell, the shine will tarnish quickly in air due to the reaction with oxygen, all react vigorously with water

The Halogens

Fluorine, Chlorine, Bromine, Iodine

Properties of Halogens

All have 7 valence electrons, non-metals, diatomic molecules, reactivity and volatility decreases down the group, density and melting points increase down the group

Displacement

When a halogen is added to a solution of a compound containing a less reactive halogen, it reacts with the compound to form a new one

e.g. fluorine + sodium chloride → sodium fluoride + chlorine