Particles

Atoms: the smallest part of an element that can exist as a stable entity.

Element: composed of atoms; a substance which cannot be further divided into simpler substances by chemical methods.

Molecule: a group of atoms chemically bonded together

Diatomic molecules (the ones that you need to know from the syllabus): BrINClHOF

  • Bromine (liquid at room temperature)
  • Iodine (solid)
  • Nitrogen (gas)
  • Chlorine (gas)
  • Hydrogen (gas)
  • Oxygen (gas)
  • Fluorine (gas)

Compounds: pure substance which are formed when two or more elements chemically combine together e.g. water

Mixture: Two or more elements physically combined together e.g. sea water

Differences between compound and mixture:

  • Compound can only be separated by chemical means while mixture can be separated by physical means e.g. using a magnet to separate metal mixture
  • Compounds have different properties since they form new substances after reaction

Atomic structure:

Sub-atomic particles: electrons, protons and neutrons

Electrons:

  • negative charge
  • in electron shells
  • held within the atoms by an electrostatic force of attraction

Relative atomic mass: the average mass of an atom of the element compared to an atom of carbon-12

Atomic number: the number of protons in an atom

Nucleon number (mass number/atomic mass): the number of protons and neutrons in an atom

Energy level of electron shells:

  • First level: maximum two electrons
  • Second level: maximum eight electrons
  • Third level: maximum eight electrons
  • Fourth level: maximum 18 electrons

Group number = valence electrons

Period number = number of shells/energy level