Home / iGCSE Chemistry Theory (Extended) : 2.2 Atomic structure and the Periodic Table: Exam Style Questions Paper 4

iGCSE Chemistry Theory (Extended) : 2.2 Atomic structure and the Periodic Table: Exam Style Questions Paper 4

iGCSE Chemistry Theory (Extended) Paper 4 - All Chapters
Question

This question is about atomic structure and the Periodic Table.

(a) Define the term nucleon number.

(b) State the connection between the number of occupied electron shells in an atom and the period number of that element.

(c) Write the electronic configuration of the following atom and ion.

\(^{28}_{14}Si\) 

\(^{37}_{17}Cl^-\) 

(d) Complete Table 2.1.

Table 2.1

(e) A sample of thallium, Tl, contains two isotopes, \(^{203}Tl\) and \(^{205}Tl\).

(i) Define the term isotopes.

(ii) The relative abundance of \(^{203}Tl:^{205}Tl\) is in the ratio 3:7.

Calculate the relative atomic mass of thallium in the sample to one decimal place.

relative atomic mass = ……

(iii) Suggest why these two isotopes have identical chemical properties.

▶️ Answer/Explanation
Solution

(a) The nucleon number is the total number of protons and neutrons in the nucleus of an atom.

(b) The period number of an element equals the number of occupied electron shells in its atom.

(c) For \(^{28}_{14}Si\): 2,8,4
For \(^{37}_{17}Cl^-\): 2,8,8
The silicon atom has 14 electrons arranged in shells as 2 in the first, 8 in the second, and 4 in the third. The chloride ion has gained one extra electron (17+1=18) arranged as 2,8,8.

(d) Completed table:

atom or ionnumber of protonsnumber of neutronsnumber of electrons
\(^{23}_{11}Na\)111211
\(^{19}_{9}F^-\)91010
\(^{69}_{31}Ga^{3+}\)313828

For sodium: neutrons = 23-11 = 12, electrons = protons = 11.
For fluoride ion: neutrons = 19-9 = 10.
The last row is for a gallium ion (Ga³⁺) with 31 protons, 38 neutrons, and 28 electrons (31-3=28).

(e) (i) Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons.
(ii) Relative atomic mass calculation:
(3 × 203) + (7 × 205) = 609 + 1435 = 2044
2044 ÷ 10 = 204.4
(iii) The two isotopes have identical chemical properties because they have the same number and arrangement of electrons, which determines chemical behavior.

Question

(a) Atoms are made of protons, neutrons and electrons. Atoms of the same element are known as isotopes.

(i) Complete the table.

(ii) \(_{12}^{24}\textrm{Mg}\) and \(_{12}^{25}\textrm{Mg}\) are isotopes of magnesium.

Complete the table to show the numbers of electrons, neutrons and protons in these isotopes of magnesium.

(iii) Explain why magnesium ions have a charge of 2+.

(b) Mg2+ ions have the electronic structure 2,8.

Give the formula of the following particles which have the same electronic structure as Mg2+ ions.

    • a cation (positive ion)
    • an anion (negative ion)
    • an atom
▶️ Answer/Explanation
Solution

(a)(i)

The table should be completed as follows:

(a)(ii)

For \(_{12}^{24}\textrm{Mg}\): 12 protons, 12 electrons, 12 neutrons.

For \(_{12}^{25}\textrm{Mg}\): 12 protons, 12 electrons, 13 neutrons.

(a)(iii)

Magnesium loses 2 electrons to achieve a stable electronic configuration, resulting in a 2+ charge.

(b)

Cation: Na+ (sodium ion) or Al3+ (aluminum ion).

Anion: F– (fluoride ion), O2- (oxide ion), or N3- (nitride ion).

Atom: Ne (neon).

Final Answer:

2(a)(i)

2(a)(ii)

2(a)(iii) (they have) 2 more protons than electrons
OR
(they have) 2 fewer electrons than protons
OR
(they have) 12 protons and 10 electrons

2(b) Na+ or Al3+ (1)
F– or O2– or N3– (1)
Ne (1)

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