Chemistry, Third edition

REVISION QUESTIONS

It turns out that the second distribution is the correct one – to minimize repulsion,

electrons ‘prefer’ to occupy orbitals singly. This is known as Hund’s rule.

45

3.1.Which of the following is false?

(i)The atoms of an element all have the same atomic number.

(ii)1u one-twelfth of the mass of one atom of^136 C.

(iii)mass number atomic number number of neutrons.

(iv)The atoms of an element are identical, but different from

atoms of other elements.

(v)A mass spectrometer detects both ions and neutral atoms.

3.2.The following table gives information on the four

naturally occurring isotopes of sulfur:

Isotope Number of Number of Number of Natural

neutrons electrons protons abundance

/%

32

16 S 95.0

(^3316) S 0.76
34
16 S4.2
1636 S 0.021
(i)Fill in the second, third and fourth columns of the table.
(ii)Estimate the atomic mass of sulfur to two significant
figures. Why is your answer an estimate?
3.3.Write equations showing the formation of Mgand Mg^2 in
the chamber of a mass spectrometer. What are (i)them/evalues
and(ii)the 2.8.1-type electronic configurations, of these ions?
3.4. Explain the following, writing equations for the
formation of any ions in the mass spectrometer chamber:
(i)The mass spectrum of fluorine gas (F 2 ) contains two peaks,
atm/e19 and 38.
(ii)The mass spectrum of hydrogen cyanide (HCN) contains
peaks at m/e27, 26 and 13.5.
(iii)The mass spectrum of chlorobenzene (C 6 H 5 Cl) contains
peaks at m/e77, 112 and 114.
(iv)A strong line at m/e28 is observed when an attempt
was made to run the mass spectrum of a compound. (Hint
it is suspected that the spectrometer is leaking.)
(v)A mixture of methane (CH 4 ) and chlorine gas (Cl 2 ) yielded
a mass spectrum with peaks at 70, 72, 74, 16, 52 and 50.
3.5.Write equations for the burning of normal hydrogen gas
(^11 H 2 ) and deuterium gas (^21 H 2 ) in oxygen. Would you expect
the density of normal and heavy water to be the same?
3.6.Use Table 3.2 to calculate the exact mass in (i)atomic
mass units, (ii)grams, of (a) a molecule of heavy water
(^21 H 2168 O) and (b)an average water molecule in nature (work
to four significant figures).
3.7.Briefly explain why atomic emission spectra provide
experimental evidence for the existence of electron energy
levels (shells) in atoms.
3.8.The successive ionization energies (in kJ mol^1 ) for argon
are 1521, 2666, 3931, 5771, 7328, 8781, 11 996, 13 842, 40 761,
46 188, 52 003, 59 654, 66 201, 72 920, 82 570, 88 620, 397 710
and 426 910. Plot the log of the ionization energy against the
number of electrons removed (as in Fig. 3.11). Why does your
graph support the electronic structure of argon as being 2.8.8?
What is the total amount of energy (in kJ mol^1 ) required to
remove all 18 electrons from the argon atom?
3.9.What is an orbital? Comment upon the size of an orbital
in which it is certainthat an electron will be found.
3.10.Write down the electronic configuration of (i) Cl,
(ii)Cl(a chlorine atom which has gained an electron),
(iii)Cl,(iv)He,(v)Ne and (vi)Cu^2 , using the 2.8.1
notation. What is special about the electronic configurations
(ii),(iv)and(v)?
3.11.Repeat question 3.10 using the s,p,d,f notation. Write
out the structure for (iii)using the electrons in boxes notation.
Revision questions
Detailed electron configuration of atoms of the elements
By following the pattern for Al, write out (i) the electronic ‘box structures’ for atoms with
atomic numbers 1–10 and (ii) for the transition metals Mn, Fe and Cu.
Exercise 3J
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