Q 1. Fill in the
blanks with the best word from the boxes.
All atoms, except hydrogen, are composed of three particles:
electrons, neutrons and protons.
The nucleus contains 
as well as neutrons. These are both much heavier than
.
Thus nearly all the mass of an atom is in the nucleus. Protons are
almost equal in mass to .
The atomic number of an atom equals the number of
in the nucleus, and is also the number of
in a neutral atom.
All atoms of an element have the same number of
in the nucleus but the number of
can vary slightly. These different varieties of the same element are
called isotopes. The relative atomic mass is an average of the mass of
the different isotopes, taking account of the different proportions of
each isotope. Most hydrogen atoms have one proton and one
but no .
Q 2. (a) The
atomic number of iodine is 53. Use the value of 127 for its relative
atomic mass to work out how many electrons, protons and neutrons are
in each atom.
(b) The element before iodine in the Periodic Table is tellurium. It
has seven different isotopes of which the commonest have 74, 76 and 78
neutrons per atom. Work out the total number of particles in the
nucleus of each of these atoms.
Tellurium with 74 neutrons
Tellurium with 76 neutrons
Tellurium with 78 neutrons
Q 3. Why does the
number of protons in the nucleus govern the chemical properties of an
atom such as the formulae of compounds that it forms and the type of
bonding that it takes part in?
Q4. (a)
Potassium is almost entirely composed of two isotopes potassium-39
(93%) and potassium-41 (7%). What is the relative atomic mass of
potassium?
