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 (NA): 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.
