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
