ANSWERS TO EXERCISES AND REVISION QUESTIONS 433(iv)Al 4 C 3 12H 2 O4Al(OH) 3 3CH 4
(v)3Zn2H 3 PO 4 Zn 3 (PO 4 ) 2 3H 2
(vi)Fe 2 O 3 Na 2 CO 3 2NaFeO 2 CO 2.
2.12 (i)2Zn(s)O 2 (g)2ZnO(s)
(ii)2K(s)2H 2 O(l)2KOH(aq)H 2 (g)
(iii)CO 2 (g)2Mg(s)2MgO(s)C(s).Unit 3
Exercises
3A
Six neutrons and six protons in the nucleus, with six
electrons outside.
3B
(i)1836 times (using exact masses)
(ii)3.97 (about 4).
3C
Isotope Protons Neutrons Electrons
U-235 92 143 92
U-238 92 146 92(^11) H 11 110 11
(^21) H 11 111 11
(^31) H 11 112 11
3D
(i)(a) uranium-238 (b) fluorine (c) hydrogen-3 (tritium)
(d) tritium.
(ii)49.31%.
3E
m(O)[(15.9949 99.759)(16.9991 0.0374)
(17.9992 0.2039)]/10015.9994 u 16.00 u
(to four significant figures).
3F
The intensities add up to 100, and so correspond to
percentage abundances:
m(Ne)[(91 20)(0.3 21)(8.7 22)]/100
20.18 u 20 u
3G
(i)m/evalues are 44, 15, 14 (i.e. 28/2).
(ii)Fragmentation follows ionization:
HF(g)e–HF+(g)e–e–
HF+(g)F+(g)H(g)
m/efor the F+ion is 19, and for HF+is 20.
(iii)The parent ions C 6 H 6 +, C 6 H 5 NO 2 +and C 6 H 5 OH+are
produced in the ionization stage. They then fragment
producing a C 6 H 5 +ion e.g:
C 6 H 5 NO 2 +(g)C 6 H 5 +(g) NO 2 (g)
m/e 77
3H
Be^3 +(g)Be^4 +(g)e–
electrons: 1 0
There are only four electrons in the beryllium atom and
so there is no fifth ionization energy.
3I
Element Atomic Bohr s,p,d,f
and symbol number structure structure
Hydrogen H 111. 1s^1
Helium He 122. 1s^2
Lithium Li 13 2.1 1s^2 2s^1
Beryllium Be 14 2.2 1s^2 2s^2
Boron B 15 2.3 1s^2 2s^2 2p^1
Carbon C 16 2.4 1s^2 2s^2 2p^2
Nitrogen N 17 2.5 1s^2 2s^2 2p^3
Oxygen O 18 2.6 1s^2 2s^2 2p^4
Fluorine F 19 2.7 1s^2 2s^2 2p^5
Neon Ne 10 2.8 1s^2 2s^2 2p^6
Sodium Na 11 2.8.1 1s^2 2s^2 2p^6 3s^1
Magnesium Mg 12 2.8.2 1s^2 2s^2 2p^6 3s^2
Aluminium Al 13 2.8.3 1s^2 2s^2 2p^6 3s^2 3p^1
Silicon Si 14 2.8.4 1s^2 2s^2 2p^6 3s^2 3p^2
Phosphorus P 15 2.8.5 1s^2 2s^2 2p^6 3s^2 3p^3
Sulfur S 16 2.8.6 1s^2 2s^2 2p^6 3s^2 3p^4
Chlorine Cl 17 2.8.7 1s^2 2s^2 2p^6 3s^2 3p^5
Argon Ar 18 2.8.8 1s^2 2s^2 2p^6 3s^2 3p^6
Potassium K 19 2.8.8.1 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1
Calcium Ca 20 2.8.8.2 1s^2 2s^2 2p^6 3s^2 3p^6 4s^2
3J
(i)
Element 1s 2s 2px 2py 2pz s,p,d,f
and symbol structure
Hydrogen H 1s^1
Helium He 1s^2
Lithium Li 1s^2 2s^1
Beryllium Be 1s^2 2s^2
Boron B 1s^2 2s^2 2p^1
Carbon C 1s^2 2s^2 2p^2
Nitrogen N 1s^2 2s^2 2p^3
Oxygen O 1s^2 2s^2 2p^4
Fluorine F 1s^2 2s^2 2p^5
Neon Ne 1s^2 2s^2 2p^6
(ii)
Element 3d 3d 3d 3d 3d 4s s,p,d,f
and symbol structure
Manganese (Mn)[Ar] 3d^5 4s^2
Iron (Fe) [Ar] 3d^6 4s^2
Copper (Cu) [Ar] 3d^10 4s^1
Revision questions
3.1Following are false:
(ii)should be^126 C,
(iv)atoms of isotopes are not identical,
(v)a mass spectrometer does not detect neutral atoms.
3.2
Isotope Number of Number of Number of Abundance/%
neutrons electrons protons
(^32) S 16 16 16 16 95.0
(^33) S 16 17 16 16 90.76
(^34) S 16 18 16 16 94.2
(^36) S 16 20 16 16 90.021
m(S) is given by the equation:
(9532)(0.7633)(4.234)(0.02136)
100
3208.6 100 32 u (to two significant figures)
Sources of approximation are (i)mass numbers have
been used instead of isotopic masses and (ii)some of
the abundances are only given to two significant figures.
(This explains why the total of the percentage
abundances is 99.981%, not 100.000%.)
3.3
Mg(g)e–Mg+(g)e–e–
m/e
24
(2.8.1)
Mg(g)e–Mg^2 +(g)e–e–e–
m/e
12
(2.8)
3.4
(i)
F 2 (g)e–F 2 +(g)e–e–
m/e 38
F 2 +(g)F+(g)F(g) (fragmentation)
m/e 19
(ii)
HCN(g)e–HCN+(g)e–e–
m/e 27
HCN(g)e–HCN^2 +(g)e–e–e–
m/e13.5
and
HCN+(g)CN+(g)H(g) (fragmentation)
m/e 26
(iii)
C 6 H 5 Cl(g)e–C 6 H 5 Cl(g)+e–e–
m/e114 (due to C 6 H 537 Cl+)
and 112 (due to C 6 H 535 Cl+)
C 6 H 5 Cl(g)+C 6 H 5 +(g)Cl(g) (fragmentation)
m/e 77
(iv)N 2 +(g) from air gives a line at m/e28.
(v)
Cl 2 (g)e–Cl 2 +(g)e–e–
m/e70 (due to^35 Cl^35 Cl+)
m/e72 (^35 Cl^37 Cl+)
m/e74 (^37 Cl^37 Cl+)
CH 4 (g)e–CH 4 +(g)e–e–
m/e 16
If some chlorine and methane react:
CH 4 (g)Cl 2 (g)CH 3 Cl(g)HCl
CH 3 Cl(g)e–CH 3 Cl+(g)e–e–
m/e50 (for CH 335 Cl+)
m/e52 (for CH 337 Cl+)
3.5
211 H 2 (g)O 2 (g) 211 H 2 O(l)
212 H 2 (g)O 2 (g) 212 H 2 O(l)
Heavy water (deuterium oxide) will be more dense than
ordinary water.
3.6m(^21 H 2168 O)(2 2.0140)(15.9949)
20.023 u (to five significant figures).
Since 1 u 1.660 54 10 –^24 g,
m(^21 H 2168 O)1.660 54 10 –^24
20.02293.3249 10 –^23 g
or 3.325 10 –^23 g to four significant figures.
m(H 2 O)(2 1.008)(16.00)18.02 u.
m(H 2 O)18.02 1.660 54 10 –^24 g
2.992 10 –^23 g to four significant figures.
3.7See text.
3.8A plot is seen to contain three groups containing
eight electrons (the outer electrons are removed first),
eight more electrons and two more electrons,
respectively.
Sum of ionization energies 1389373kJmol–^1. This
is the energy required to strip all the electrons from the
atom.
3.9For a definition of orbital see the text. The size of a
100% orbital is the size of the universe itself.
3.10 (i)2.8.7 (ii)2.8.8 (iii)2.8.6 (iv) 2
(v)2.8 (vi)[Ar]9.
(ii),(iv), and (v)are electronic structures in which all the
shells are filled.
3.11 (i)1s^2 2s^2 2p^6 3s^2 3p^5
(ii)1s^2 2s^2 2p^6 3s^2 3p^6
(iii)1s^2 2s^2 2p^6 3s^2 3p^4 (iv)1s^2
(v)1s^2 2s^2 2p^6
(vi)[Ar] 3d^9. Using the box notation for (iii):
□□ □□□ □ □□□
1s^2 2s^2 2px^2 2py^2 2pz^2 3s^2 3px^2 3py^1 3pz^1
Unit 4
Exercises
4A
(i) (ii) (iii)
(iv) (v) (vi)
2.7
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