Chapter 5 (p.100): 12, 15, 23, 27, 37
12. List the similarities and differences in the three isotopes of hydrogen. Same number
of protons and electrons, different number of neutrons.
15. Write the isotopic notation symbols for each of the following:
65
a) Z=29, A=65
29 Cu
45
b) Z=20, A=45
20 Ca
84
c) Z=36, A=84
36 Kr
23. 68.9257 au is the mass of 60.4% of the atoms of an element with only two naturally
occurring isotopes. The atomic mass of the other isotope is 70.9249. Determine the
average atomic mass of the element. Identify the element.
The abundance of the second isotope is not given, but it is understood that it must be:
100% - 60.4% = 39.6 %.
Thus: (68.9257 x 0.604) + (70.9248 x 0.396) = 69.7
From the periodic table one finds that the above mass corresponds to element Gallium.
27. What experiment evidence supports the statement?
a) The nucleus of an atom is small. Rutherford’s experiment – most a particles
flow through the atom as there is nothing in their path.
b) The atoms consist of both positive and negative charges. Discovery of protons
and electrons and necessity that the atoms is neutral.
c) The nucleus of the atom is positive. The direction the proton moves in an
electric or magnetic field – it is attracted towards the negative pole of a magnet.
37. Complete the following table with the appropriate data for each isotope given (all
neutral atoms).
The answers are in bold, the data given is in normal font.
Element
Symbol Atomic
number
134
Xe
Xenon
54
Silver
Ag
47
Fluorine
F
9
Potassium K
19
Mass
number
134
107
19
41
#protons #neutrons #electrons
54
47
9
19
80
60
10
22
54
47
9
19
Even though only the #protons given in the third row, one finds in the Periodic Table that
Z=9 corresponds to fluorine that has the average mass of 19.00; this means that there is
only one naturally occurring isotope with 10 neutrons.
Chp. 10 (p.220): 13, 19, 33, 39
13. Which elements have these electron configurations:
a) 1s2 2s2 2p6 3s2
Mg
b) 1s2 2s2 2p6 3s2 3p1
Al
c) 1s2 2s2 2p6 3s2 3p6 4s2 3d8
Ni
2
2
6
2
6
2
5
d) 1s 2s 2p 3s 3p 4s 3d
Mn
19. For each of the electron configurations given, write the corresponding orbital
diagrams.
a) F 1s2 2s2 2p5
An s subshell has only a single orbital and can be occupied with two electrons
with opposite spins. The 2p subshell contains three orbitals with equal energy,
and each can hold two electrons with opposite spins. One of the 2p orbitals
(does not mater which) in fluorine has only one electron.
b) S 1s2 2s2 2p6 3s2 3p4
Remember the rules for filling p, d or f subshell: It is more difficult for an
electron to pair up than to occupy a different orbital with identical spins.
Therefore, in phosphorus (1s2 2s2 2p6 3s2 3p3), each of the three 3p electrons
occupies a single shell and they all have identical spins. In sulfur, the additional
(fourth) 3p electron pairs up with one of the electrons with the opposite spin.
c) Co 1s2 2s2 2p6 3s2 3p6 4s2 3d7
d) Kr
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
e) Ru
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d6
33. Pick the electron structures that represent elements in the same chemical family:
a) 1s2 2s1
b) 1s2 2s2 2p4
c) 1s2 2s2 2p2
d) 1s2 2s2 2p6 3s2 3p4
e) 1s2 2s2 2p6 3s2 3p6
f) 1s2 2s2 2p6 3s2 3p6 4s2
g) 1s2 2s2 2p6 3s2 3p6 4s1
h) 1s2 2s2 2p6 3s2 3p6 4s2 3d1
(a) and (g) have one s electron in the outermost shell;
(b) and (d) have four electrons in the p orbital of the outhermost shell.
39. In which period and group does an electron first appear in an f orbital?
Period 6, group 4B. An f orbital fills up in (n+2) shell, after filling a single
electron in the (n-1) d subshell. Thus, 4f orbital fills up in the n=6 shell, after filling two
electrons in 6s subshell and one in 5d subshell.