Australian School of Abu Dhabi
Worksheets 1
The periodic table
1. When Mendeleev first discovered the periodic table he placed the elements in order of their
atomic weight (now known as atomic mass). Explain why modern periodic tables contain the
elements placed in order of their atomic number.
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2. Explain what is meant by the term periodicity.
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3. In Mendeleev’s first periodic table the elements were arranged into seven separate groups. Explain
why modern periodic tables contain the elements arranged into eighteen separate groups.
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4. What information about the electron configurations of aluminium, silicon, and phosphorus can be
deduced from the fact that all three elements are located in the same period in the periodic table?
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5. What information about the electron configurations of beryllium, magnesium, and calcium can be
deduced from the fact that all three elements are located in the same group in the periodic table?
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6. Potassium, K, is a metal that is located in group 1 in the periodic table. What information about the
electron configuration of potassium can be deduced from this information?
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7. Sulfur, S, is a non-metal that is located in group 16 and in period 3 in the periodic table. Deduce the
atomic number of sulfur using only this information.
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8. Suggest reasons why hydrogen is sometime located:
(a) at the top of group 1 in the periodic table.
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(b) at the top of group 7 in the periodic table.
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(c) on its own at the top of the periodic table.
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(d) together with helium at the top of the periodic table.
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9. Use the periodic table to deduce the full electron configuration of:
(a) Selenium (Z = 34) _____________________________________________________________
(b) The vanadium(III) ion, V3+ ______________________________________________________
(c) The zinc(II) ion, Zn2+ ___________________________________________________________
(d) The As3- ion _________________________________________________________________
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Answers
1. Mendeleev did not know about isotopes. Although for most elements the atomic mass increases
in the same order as atomic number increases this is not always true. For example argon (Z = 18)
has a relative atomic mass of 39.95 whereas potassium (Z = 19) has a relative atomic mass of
39.10. The chemical and physical properties depend on the number (and arrangement) of electrons
which is equal to the number of protons (atomic number) rather than on the mass.
2. Periodicity describes the repeating pattern of physical and chemical properties that can be seen
when the elements are arranged according to their atomic number.
3. None of the noble gases (He – Rn), which make up the eighth group, had been discovered when
Mendeleev first produced his periodic table in 1869. More recently the number pf groups has been
increased from 8 to 18 as the transition metals have their own group numbers.
4. Al, Si and P all have the third outer energy level partially filled.
5. Be, Mg and Ca all contain the same number of electrons in their outer energy level, ns2.
6. K contains one electron in its outer energy level, ns1.
7. Because it is in period 3 and in group 16 it has the electron configuration 1s22s22p63s23p4 or
[Ne]3s23p4.
This means that it contains sixteen electrons. As it is an atom (which is neutral) it must also
contain sixteen protons so the atomic number is 16.
8. (a) (top of group 1) Because it contains one electron in its outer energy level i.e. it has the
configuration 1s1 so it is an s block element.
(b) (top of group 7) Because it requires just one more electron to gain a full outer energy level.
(c) Because it is not a metal (so not group 1) and it does not contain seven electrons in its outer
energy level (so not group 7)
(d) Because hydrogen and helium together make up the first period where the first energy level is
being filled.
9. (a) 1s22s22p63s23p64s23d104p4
(b) 1s22s22p63s23p63d2
(c) 1s22s22p63s23p63d10
(d) 1s22s22p63s23p64s23d104p6
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