GCSE CHEMISTRY - ATOMIC STRUCTURE AND IONS

An element is a substance of only one type of atom

An atom is the smallest part of an element that can exist

Metals and non-metals

Compounds

Two or more elements combined chemically in fixed proportions which can be represented by formulae

No, they have different properties.

A mixture consists of two or more elements or compounds not chemically combined together; it does have the same chemical properties

Filtration, crystallisation, simple distillation, fractional distillation and chromatography; they do not involve chemical reactions

Simple distillation is used to separate liquid from a solution – the liquid boils off and condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contrary to evaporation, we get to keep the liquid.

Evaporation is a technique for separation of a solid dissolved in a solvent from a solvent (e.g. salt from H2O). The solution is heated until all the solvent evaporates; the solids stays in the vessel. Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved). Then, we cool down the solution. As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures. The crystals can be collected and separated from the solvent via filtration.

Fractional distillation is a technique for separation of a mixture of liquids. It works when liquids have different boiling points. The apparatus is similar to the one of simple distillation apparatus, with the additional fractionating column placed on top of the heated flask. The fractionating column contains glass beads. It helps to separate the compounds. In industry, mixtures are repeatedly condensed and vapourised. The column is hot at the bottom and cold at the top. The liquids will condense at different heights of the column.

Filtration is used to separate an insoluble solid is suspended in a liquid. The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper. The filtrate is the substance that comes through the filter paper. Apparatus: filter paper + funnel.

The atom is a ball of positive charge with negative electron embedded in it.

The nuclear model suggests that electrons orbit the nucleus at specific distances (shells) – it came about from the alpha scattering experiments

The existence of neutrons in the nucleus

The atom has a small central nucleus (made up of protons and neutrons) around which there are electrons

Masses: 1, 1, very small Charges: 1, 0 , -1 (respectively)

They have the same number of electrons and protons

0.1 nm

1 x 10-14 m and 1/10000

Atomic number

Protons

Atoms of the same element (same proton number) that have a different number of neutrons. They have the same chemical properties as they have the same electronic structure

Ions are charged particles. They are formed when atoms lose electrons (positive ions) or gain (negative ions) electrons.

An ionic compound (made of positive and negative ions).

A molecular compound containing covalently bonded atoms.

The strict order of atomic weights

Leaving gaps; atomic weights

The alkali metals

All have one electron in their outer shell; have low density; are stored under oil (to prevent reactions with oxygen or water); are soft (can be cut with knife).

They form ionic compounds which are soluble white solids which form colourless solutions – they all have one electron in their outer shell.

They release hydrogen and form hydroxides which dissolve to form alkaline solutions; react vigorously with water fizzing and moving around on the surface of the water.

Reactivity increases as the atoms get larger and the distance between the nucleus and the outer electrons increases and thus attraction from the nucleus decreases, allowing them to more easily lose electrons.

• 7 electrons in outer shell

• Coloured vapours

• Diatomic molecules

• Form ionic salts with metals

• Form molecular compounds with non-metals

• Fluorine, F. F2 is a pale yellow gas.

• Chlorine, Cl. Cl2 is a pale green gas.

• Bromine, Br. Br2 is dark brown liquid

• Iodine, I. I2 is a grey solid.

• Higher relative molecular mass

• Higher melting and boiling point

• Less reactive – less easily gain electrons

Reactivity decreases down the group. As we go down the group, the atoms get larger, so an incoming electron will be less tightly held by the attractive forces from the nucleus. That’s why Cl2 displaces Br– and I–.

Group 1 metals and transition metals are heat and electricity conductors. They are shiny when polished and form ionic compounds with non metals. Transition metals have higher densities and higher melting points than Group 1 metals. They are less reactive and harder than Group 1 metals.

• Ions with different charges

• Coloured compounds

• Catalytic properties

A catalyst is a chemical substance that increases the rate of a chemical reaction. It is not used up over the course of the reaction

Non-metals, gases, low boiling points, unreactive (full outer shell; they don’t easily accept or lose electrons). The boiling point increases down the group, as the atoms get heavier.