QUIZ 3 on RADIOACTIVITY - revision of atomic structure

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(a) The half-life of a radioactive substance is the it takes for the number of original radioactive atoms in a sample to .
(b) It is also the time it takes for the from the original substance to fall to half its level.

(b) Radioactivity occurs as a result of changes in the of an atom. Atoms have a small central nucleus made up of and neutrons around which there are .

(c) The proton has a mass of and an electrical charge of , the has a mass of 1 and charge of and the has a mass of 1/1850 and a charge of .

(d) In an atom, the number of electrons is equal to the of protons in the nucleus and so the atom as a whole, has no overall charge. All atoms of a particular have the same number of protons.

(e) Atoms of different elements have numbers of protons. Protons and neutrons are collectively called . The sum of the protons and neutrons in an atom is called its (nucleon) number.

(f) Atoms of the same element can have different numbers due to having different numbers of in the nucleus, they are called .