ATOMIC STRUCTURE

Elements, compounds and mixtures

elements are found in the periodic table

Compounds contain 2 or more chemically bonded elements

Mixtures have different elements or compounds NOT chemically bonded

Interpreting a chemical formula

In a compound, the atoms of each element are fixed

Filtration and crystallisation

used to separate mixtures

Filtration - used to separate an insoluble solid from a liquid

Crystallisation - used to separate a soluble solid from a liquid

Simple distillation

used to separate a liquid from a solid, where we need to keep the liquid

first we evaporate the liquid by heating and then condense the vapor by cooling

Fractional distillation

separate a mixture of different liquids with different boiling points

You heat the mixture and the one with the lowest boiling point evaporates first and condenses in the fractionating column until the boiling point is reached and then it is collected as it passes through the condensing tube. then, the second liquid is collected when its boiling point is reached.

Chromatography

Allows us to separate substances based on their different solubilities

Draw a pencil line, put the dots of ink on the line and put the bottom of the paper into a solvent and they will be carried up the paper as the solvent goes up the paper.

Alpha scattering experiment

The plum pudding model is a ball of positive charge with electrons scattered inside it

The experiment was that balls of positive charge were fired at gold foil and the first thing that happened was that most passed through but some were deflected. So, it was said that atoms are mainly empty space with a positive and heavy centre, and so the nuclear model was made.

The nuclear model

Niels Bohr said that electrons orbit the nucleus in shells at different distances

Atomic number and mass number

Atomic number = number of protons and neutrons
Mass number = number of protons

Relative atomic mass

Isotopes = atoms of the same element with different numbers of neutrons. so the RAM is the average of the mass numbers

Electron energy levels

Each shell can hold up to 8 electrons but only 2 in the first

Development of table

Was first put in ascending order of atomic mass, but was not accepted as it was not true for al elements and he didn't leave gaps

Now it is arranged according to elements relative atomic masses and there are gaps (Mendeleev)

Group 0

ALL noble gases

ALL have low melting points

Boiling point increases as you go down due to intermolecular bonds

Metals

Every metal conducts electricity. This is due to the metallic bonding found within metal elements. In metallic bonding, the outer electrons are delocalised (free to move). This produces an electrostatic force of attraction between the positively charged metal ions, and the negatively charged delocalised electrons.

Some lose electrons easily

Group 1

Alkali metals: as you go down they are more reactive and have lower melting and boiling points

All have 1 electron in their outer shell so they are very reactive and all have similar properties

Group 7

Halogens with coloured vapours

As you go down they become less reactive and have higher melting and boiling points

Transition elements

good conductors of heat and electricity , dense and strong and shiny, less reactive than group 1, denser and stronger than alkali metals, have higher melting points than alkali metals

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