What is an atom and what is an element?
An atom is the smallest particle of an element. An element contains only one type of atom. There are ~100 elements in the periodic table.
What is a compound and how do we represent reactions?
A compound contains two or more elements chemically combined. Represent reactions using word and balanced symbol equations. State symbols: (s), (l), (g), (aq).
What are mixtures and how are they separated?
Mixtures are substances not chemically joined. Methods: filtration, crystallisation, simple distillation, fractional distillation, chromatography. Chromatography separates mixtures based on solubility and attraction.
How did the atomic model develop?
Dalton: solid spheres. Thomson: plum pudding (electrons). Rutherford: nuclear model (mass in nucleus). Bohr: electrons in shells. Chadwick: discovered neutrons.
What are the subatomic particles and their properties?
Proton: charge +1, mass 1. Neutron: charge 0, mass 1. Electron: charge –1, mass 1/2000. Electrons orbit in shells.
What do atomic number and mass number mean?
Atomic number (Z): number of protons. Mass number (A): protons + neutrons. Number of neutrons = A − Z.
What are isotopes and how do we calculate Ar?
Isotopes: Atoms of the same element with different numbers of neutrons. Relative atomic mass (Ar): Weighted average of isotopes.
How do ions form?
By gaining or losing electrons. Metals lose electrons → positive ions. Non-metals gain electrons → negative ions.
What is electronic configuration?
The arrangement of electrons in shells. 1st shell: 2, 2nd: 8, 3rd: 8. For elements 1–20 only. Determines reactivity and group number.
What does chromatography show and how do you calculate Rf?
Separates mixtures of dyes. Shows number of colours present. Rf = distance travelled by substance ÷ distance travelled by solvent.
