STPM Chemistry: Atoms, Molecules and Stoichiometry [Checklist]

• Electron: A subatomic particle that has a very low mass and carries a single negative electric charge.
• Neutron: A subatomic particle that bears no net electric charge. Its mass is slightly greater than a proton’s.
• Proton: A subatomic particle having a single positive electric charge. The mass of a proton is about 1840 times that of an electron.
• Nucleus: The central core of an atom.
• Nucleon number (mass number) Symbol A: The total number of protons and neutrons found in the nucleus of an atom.
• Avogadro’s number (N_A): 6.02 X 10²³; the number of particles in a mole.
• Relative atomic mass, Ar, is defined as the mass of one atom of an element relative to 1/12 of the mass of an atom of carbon-12, which has a mass of 12.00 atomic mass units.
• Relative isotopic mass is like relative atomic mass in that it deals with atoms. The difference is that we are dealing with different forms of the same element.
• Isotopes have the same number of protons, but different numbers of neutrons. Hence, isotopes of an element have different masses.
• Relative molecular mass, Mr, is defined as the mass of one molecule of an element or compound relative to 1/12 of the mass of an atom of carbon-12, which has a mass of 12.00 atomic mass units.
• Relative formula mass is used for substances that do not contain molecules, such as sodium chloride, NaCl, and is the sum of all the relative atomic masses of the atoms present in the formula of the substance.
• It is important to remember that since these are all relative masses, they have no units.
• Mole: The amount of substance which contains 6 × 10²³ atoms, ions or molecules. This number is called
• Avogadro’s constant.
• Empirical formula: A formula showing the simplest ratio of atoms present.
• Molecular formula: A formula showing the actual number of atoms of each element present in one molecule.

SPM Form 4: The Structure of the Atom (Checklist)

• Matter is anything that occupies the space and has a  mass. Matter is made up of tiny and discrete particles that are in constant motion. There are spaces between these particles. The tiny particles may be atoms, molecules and ions.
• An atom is the smallest particles of an element that can take part in a chemical reaction.
• A molecule is  a group of two or more atoms which are chemically bonded together.
• An ion is a positively-charged or negatively-charged particle.
• Matter consists of small particles that always move and collide among each other.
• The kinetic theory of matter stated the particles move freely when energy is absorb and move slowly when is release, then they are cooled. This theory used to explain the change physical state of matter. The energy used used by the particles to move, we called it kinetic energy.
• Diffusion is the movement of a fluid from an area of higher concentration to an area of lower concentration. Diffusion is a result of the kinetic properties of particles of matter. The particles will mix until they are evenly distributed. Diffusion occurs slowest in solids, faster in liquids and the fastest in gases.
• Melting is the process by which a substance changes from the solid phase to the liquid phase. Melting point is the temperature at which a solid and liquid phase may coexist in equilibrium. The term applies to pure liquids and solutions.
• Freezing is the process through which a substance changes from a liquid to a solid. All liquids except helium undergo freezing when the temperature becomes sufficiently cold. The freezing point is the temperature at which a liquid changes to a solid.
• Condensation is change in the state of matter from the gas phase to the liquid phase.
• Boiling is the process of transition from the liquid state to the gas state, usually occurring when a liquid is heated to its boiling point. The boiling point is the temperature at which the vapor pressure of a liquid equals the external pressure surrounding the liquid.
• Sublimation is the transition from the solid phase to the gas phase without passing through an intermediate liquid phase.
• Isotopes are atoms with the same number of protons, but differing numbers of neutrons. In other words, the have different atomic weights.
• For any atom: 

Number of Electrons = Number of Protons

Number of Neutrons = Mass Number - Atomic Number

Number of Protons = Atomic Number of the Element