– Matter is made up of discrete particles namely atoms, molecules and ions.
– Atom is the smallest particle of an element that can take part in a chemical reaction.
– A molecule is the smallest part of a substance that can exist independently.
– Atoms are composed of protons, neutrons and electrons.
– Electrons occupy shells surrounding the nucleus which correspond to energy levels lettered, K, L, M, N, etc.
– Atomic number is the number of protons in an atom.
– Mass number is the total number of protons and neutrons in an atom.
– Isotopes are atoms that have the same atomic number but different mass numbers.
– Relative atomic mass is the average mass of atoms in a naturally occurring sample.
– A chemical formula identifies the atoms in a substance using symbols which are one, two or three letters as abbreviations for atoms.
– An empirical formula gives the simplest whole-number ratio of atoms in a substance,
– A molecular formula indicates the actual or exact number of each type of atom in a molecule.
– The mass of an atom is usually expressed in atomic mass units (amu) and is referred to as the atomic mass. An amu is defined as exactly one-twelfth the mass of a carbon -12 atom.
– When atoms, molecules or ions combine to form other substances, a shorthand type of expression called chemical equation is used to describe the reaction.
– The law of conservation of matter states that matter is neither created nor destroyed in a chemical reaction.
– The law of definite proportion states that in a pure chemical substance, the elements are always in definite proportion by mass.
– The law of multiple proportion states that if two elements A and B combine to form more than one chemical compound, then the various masses of one element A, which combines separately with a fixed mass of other element B are in simple multiple ratio.
