Question

1(a)Bromine has two stable isotopes, 79 and 81

(i) By comparing the number of sub-atomic particles of these
isotopes, explain what is meant by the term isotopes.
(ii) Determine the number of electrons of − ion.

Answer 1

(i) Isotopes are forms of an element that have the same number of protons (and therefore the same atomic number) but different numbers of neutrons. This means they have the same position on the periodic table (same element) but different atomic masses. In the case of Bromine, both isotopes have 35 protons (as Bromine's atomic number is 35), but one has 44 neutrons (79-35) and the other has 46 neutrons (81-35).

(ii) The number of electrons in a Bromine ion (Br-) would be 36. This is because when Bromine gains an electron to become an ion, its electron count increases by one from its atomic number (35 protons) to 36.