Atoms, ions and compounds key words/definitions + constructing formulae

Atom - the smallest particle of an element that has properties of that element

Electron - the negative particle that circles the nucleus on electron shells

Neutron - the neutral particle in the nucleus of an atom

Proton - the positive particle in the nucleus of an atom

Nucleus - the tiny positive core of an atom; contains protons and neutrons

Atomic number - the number of protons and electrons in an atom (bottom number on periodic table)

Mass number - the number of protons plus the number of neutrons in an atom (top number on periodic table)

Ions - charged particles which are formed when atoms lose or gain electrons

Isotopes - atoms of the same element with different numbers of neutrons and different masses

Cations - atoms with fewer electrons than protons, so have an overall positive charge

Anions - atoms with more electrons than protons, so have an overall negative charge

Relative atomic mass - the weighted mean mass of an atom of an element relative to 1/12th of the mass of an atom of carbon-12. 

Relative isotopic mass - the mass of an atom of an element relative to 1/12th the mass of an atom of carbon-12

Mass spectrometry - a process by which the atomic mass of an atom is determined

Worked example - constructing a balanced equation - aluminium and oxygen react to form aluminium oxide

Step 1: Work out the formulae

Aluminium oxide contains Al³⁺ and O²⁻ so the formula would be Al₂O₃

Step 2: Write an equation for all reactants and products

Al + ‎O₂ = Al₂O₃

Step 3: Balance the equation by placing numbers on the line, in front of the formulae

4Al + ‎3O₂ = 2Al₂O₃

Step 4: Finally, add state symbols

4Al(s) + 3O₂‎(g) =  2Al₂O₃(s)