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Particulate Nature of Matter

– 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.