CHAPTER 2 ATOMIC STRUCTURE
Page 50,51 Ex 2.1
1.
D
2.
B
3.
C
4.
A
5.
C
6.
a) electron; b) neutron; c) electron; d) proton; e) electron
7.
8.
a) Atoms that have the same atomic number (number of protons), but a different
number of neutrons (mass number).
b) Mass numbers 10 and 11
c) 10.8
9.
The calcium phosphate, containing traces of the radioisotope, could be mixed into
the soil, in the same proportions for all the plants being tested. The radioactivity
of the leaves of the plants could then be monitored and the rate of increase in
radioactivity, as a result of the radioisotope, compared.
10.
therefore 72.5% 63Cu and 27.5% 65Cu
11.
12.
Please refer to the relevant chapter for more details.
© IBID Press 2007
CHAPTER 2 ATOMIC STRUCTURE
Page 54 Ex 2.2
1.
a) They are bombarded with fast moving electrons.
b) The paths of the moving ions are deflected by a magnetic field.
c) They are collected on a metal plate and the current flowing to neutralise the
charge on the plate is recorded. (A number of other possible correct answers)
2.
A doubly charged germanium-70 would produce a peak at a mass of 35.
4.
Let % of 207Pb and 208Pb = y, ∴% of 206Pb = (100-2y)
206(100-2y) + 207y + 208y = 207.2 x 100
3y = 20720-20600; ∴ y = 120/3 = 40
20% 206Pb, 40% 207Pb and 40% 208Pb.
Page 59 Ex 2.3
1.
C
2.
A
3.
D
4.
C
5.
C
6.
B
7
D
8.
a) 2,2
b) 2,8,3
c) 2,7
d) 2,8,8
e) 2,8,6
9.
a) They are isotopes of the same element.
b) Chemical properties depend primarily on the number of electrons that an atom
has and the nuclear charge affecting these. Both isotopes have the same number
of electrons and the same nuclear charge.
10
a) Because the electrons in the hydrogen atom can only have certain allowed
energies and light emission depends on transitions between these.
b) The different series correspond to transitions to a given level from a higher
level. The transition from the next higher level is the largest component of this,
hence this dictates the spectral region it occurs in.
c) As the allowed electron levels move to higher energy the difference in energy
from the previous level becomes smaller, hence the difference in the frequencies
of the light emitted by successive transitions becomes smaller.
Please refer to the relevant chapter for more details.
© IBID Press 2007
CHAPTER 2 ATOMIC STRUCTURE
Page 67 Ex 12.1
1.
C
2.
C
3.
B
4.
C
5.
B
6.
B
7.
C
8.
D
9.
a) 1s2 2s2 2p6 3s2 3p6 3d5 4s2
b)1s2 2s2 2p6 3s2 3p4
c)1s2 2s2 2p6
d)1s2 2s2 2p6 3s2 3p6 3d5
e)1s2 2s2 2p6 3s2 3p6 3d10 4s1
10.
Na < Li < O < N < Ne
11.
a)
b) Four electrons are lost relatively easily and they can be thought of as being in
the highest energy level. The next eight are rather more difficult to remove and
they may be thought of as being in the intermediate level. The remaining two
electrons are very difficult to remove and can be thought of as forming the lowest
energy level.
c) As successive electrons are removed, the electron–electron repulsion acting on
the remaining electrons, which to some extent counteracts the attractive force of
the nucleus, decreases. This means that as more electrons are removed from an
energy level, (or as more electrons are removed, the remaining electrons are more
attracted to the nucleus) so that the energy required to remove the remaining
electrons increases.
Please refer to the relevant chapter for more details.
© IBID Press 2007
CHAPTER 2 ATOMIC STRUCTURE
12
a) In both cases the effective nuclear charge acting on the outermost electron is
+1. The electron being lost in sodium however is further from the nucleus and so
less strongly held by electrostatic forces than the electron in lithium.
b) In oxygen one of the 2p–orbitals is doubly filled. This means that there is
increased repulsion between the two electrons sharing the orbital. This increased
repulsion more than offsets the effect of the increase in nuclear charge on going
from nitrogen to oxygen.
c) In beryllium the electron lost comes from a 2s energy level, whereas in boron
the electron lost comes from a 2p orbital, which is at a higher energy than the 2s.
This difference in energy of the 2s and 2p orbitals more than offsets the greater
nuclear charge in boron.
13.
a) Vanadium
b) 1s2 2s2 2p6 3s2 3p6 3d3 4s2
c) The electronic structure of the ion could not be that of an atom because the 3d
level contains electrons, but there are no electrons in the 4s level. In neutral
atoms electrons always at least partially fill the 4s before starting to fill the 3d.
14.
a) The element is aluminium. (It must be in group 3 because 3 electrons are easily
lost before a sudden increase in IE, but it cannot be boron because it contains at
least 6 electrons.)
b) About 4.4 (just slightly greater than that for the last electron shown.)
c) They would be greater because even though the two elements have the same
effective nuclear charge, the electrons being lost would be closer to the nucleus
and hence more strongly attracted.
15.
a) B and D
b) A – the first three electrons have much lower ionisation energies than the
fourth.
c) A and D or E and D.
d) C – it has a high first ionisation energy and it must have more than four
electrons in the outer shell as there is no sudden increase in ionisation energy.
Please refer to the relevant chapter for more details.
© IBID Press 2007