Glossary:
A neutral particle made up of protons and neutrons in the nucleus, with electrons surrounding the nucleus.
The number of protons in the nucleus, of an atom.
The number of particles in one mole of a substance, which is 6.02 x 1023.
A substance made up of atoms of at least two different elements, chemically joined together.
A subatomic particle with a relative charge of -1. in atoms, electrons are located in shells around the nucleus.
The number of electrons in an atom (or ion) of an element and how they are arranged.
A substance that is made up only of atoms with the same number of protons.
A different atomic form of the same element, which has the same number of protons, but a different number of neutrons.
The total number of protons and neutrons in an atom.
A particle made up of at least two atoms held together by covalent bonds.
A subatomic particle with a relative charge of 0 and a relative mass of 1. neutrons are located in the nucleus of an atom.
A subatomic particle with a relative charge of 1+ and a relative mass of 1. protons are located in the nucleus of an atom.
A table of all known elements, arranged in order of atomic number so that elements with similar chemical properties are in groups.
The average mass of the atoms of an element measured relative to the mass of one atom of carbon-12.
Development of Periodic Table:
Elements arranged in order of atomic weight
Early periodic tables were incomplete, some elements were placed in inappropriate groups if the strict order atomic weights was followed.
Left gaps for elements that hadn’t been discovered yet
Elements with properties predicted by Mendeleev were discovered and filled in the gaps. Knowledge of isotopes explained why order based on atomic weights was not always correct.
C1: Atomic structure and The Periodic Table
The formula for most elements is just its chemical symbol. For example: helium is He.
Electronic shell | Max number of electrons |
1 | 2 |
2 | 8 |
3 | 8 |
4 | 2 |
Central nucleus Contains protons and neutrons |
Electron shells Contains electrons |
Atom:
The Periodic Table:
Trends:
Very reactive with oxygen, water and chlorine: Only have one electron in their outer shell. Form +1 ions.
Reactivity increases down the group. Negative outer electron is further away from the positive nucleus so is more easily lost.
Unreactive, do not form molecules: This is due to having full outer shells of electrons.
Boiling points increase down the group: Increasing atomic number.
Consist of molecules made of a pair of atoms: Have seven electrons in their outer shell. Form -1 ions.
Melting and boiling points increase down the group (gas 🡪 liquid 🡪 solid): Increasing atomic mass number.
Reactivity decreases down the group: Increasing proton number means an electron is more easily gained.
Pre 1900 | | Tiny solid spheres that could not be divided | Before the discovery of the electron, John Dalton said the solid sphere made up the different elements. |
1897 ‘plum pudding’ | | A ball of positive charge with negative electrons embedded in it | JJ Thompson’s experiments showed that showed that an atom must contain small negative charges (discovery of electrons). |
1909 nuclear model | | Positively charge nucleus at the centre surrounded negative electrons | Ernest Rutherford's alpha particle scattering experiment showed that the mass was concentrated at the centre of the atom. |
1913 Bohr model | | Electrons orbit the nucleus at specific distances | Niels Bohr proposed that electrons orbited in fixed shells; this was supported by experimental observations. |
James Chadwick | Provided the evidence to show the existence of neutrons within the nucleus. | ||
Rutherford's scattering experiment: A beam of alpha particles are directed at a very thin gold foil. |
Most of the alpha particles passed right through.
A few (+) alpha particles were deflected by the positive nucleus.
A tiny number of particles reflected back from the nucleus.
Method | Description | Example |
Filtration | Separating an insoluble solid from a liquid | To get sand from a mixture of sand, salt and water. |
Crystallisation | To separate a solid from a solution | To obtain pure crystals of sodium chloride from salt water. |
Simple distillation | To separate a solvent from a solution | To get pure water from salt water. |
Fractional distillation | Separating a mixture of liquids each with different boiling points | To separate the different compounds in crude oil. |
Chromatography | Separating substances that move at different rates through a medium | To separate out the dyes in food colouring. |
The development of the model of the atom:
Separation techniques:
C1: Atomic Structure and The Periodic Table