Q.1: (a) (i) Define the first ionisation energy of a neutral gaseous atom of an element
in its ground state. (5)
(ii) Why do first ionisation energy values show a general increase across the second
period of the periodic table, from Lithium to Neon? (6)
(iii) Explain why the first ionisation energy value of boron (801 kJ mol-1) is (i) lower than
that of beryllium (900 kJ mol-1) and (ii) higher than aluminium (578 kJ mol-1) (6)
(b) The full set of successive ionisation energy values for the electrons in boron, in kJ
mol-1 and in order starting with the first, is {801, 2427, 3660, 25,026, 32827}.
How does this set of numbers provide evidence for
(i) the number of electrons in a boron atom,
(ii) the number of electrons in each main energy level in a boron atom?
(9)
(c) The arrangement of elements in the modern periodic table is now known to be
consistent with their electrons filling into atomic orbitals of increasing energy.
(i) Define atomic orbital.
(ii) Write the electron configuration (s, p, etc.) of the element Chromium (Cr).
(iii) What do the electron configurations of the series of elements from scandium to
zinc have in common? (18)
(d) Distinguish between intermolecular and intramolecular bonding. (6)
Q.2 : Bohr said that the electron in a hydrogen atom could only occupy certain orbits
n = 1, 2, 3, etc, with corresponding energy levels E1, E2, E3, etc.
(i) What term is used to refer to the condition of the hydrogen atom when its
electron occupies the E1 level?
What term is used for the condition of the hydrogen atom when its electron
occupies any of the levels E2, E3, etc?
(iii) What causes the electron to leave the E1 level?
(iv) Why does the electron not remain in any of the levels E2, E3, etc?
(v) The visible lines in the atomic emission spectrum of a sample of hydrogen are
produced when electrons fall to a particular energy level.
Identify this energy level.
Bohr’s theory considered electrons as tiny particles restricted to orbits.
How does modern atomic theory describe the behaviour of electrons?
What are orbitals? (25)