Fig. 13.1 shows the nuclide notation for two atoms of the same element. The symbol X has been used in place of the chemical symbol. Fig. 13.1 (a) With refer...
Question 1 Report
Fig. 13.1 shows the nuclide notation for two atoms of the same element. The symbol X has been used in place of the chemical symbol.
Fig. 13.1
(a) With reference to these two atoms, explain the meaning of the term isotopes. [2]
(b) Determine the number of neutrons in the atom with nucleon number 35. [1]
(c) Determine the number of neutrons in the atom with nucleon number 37. [1]
(d) State the number of protons in each of these atoms. [1]
(e) Deduce the electronic configuration of an atom of this element. [1]
(f) Use the Periodic Table to name this element. [1]
(g) State whether these two atoms are in the same group of the Periodic Table. [1]
Answer Details
The two boxes both read X with a lower number 17 (the proton number) and an upper number of 35 or 37 (the nucleon number). Same proton number but different nucleon numbers is the definition of isotopes.
(a) Isotopes are atoms of the same element, meaning they have the same proton number (here both have 17 protons) [1], but they have different numbers of neutrons (and so different nucleon numbers, 35 and 37) [1].
(b) Number of neutrons = nucleon number - proton number = \( 35 - 17 = 18 \) [1].
(c) For the second atom: \( 37 - 17 = 20 \) neutrons [1]. The two extra neutrons are exactly what makes this isotope heavier.
(d) The lower number is the proton number, so each atom has 17 protons [1].
(e) A neutral atom with 17 electrons fills the shells as 2, then 8, then 7, giving 2,8,7 [1].
(f) Proton number 17 in the Periodic Table is chlorine [1].
(g) Isotopes have identical proton numbers and identical electron arrangements, so yes, both atoms are in the same group (Group VII) [1]. Chemical properties depend on outer electrons, not on the number of neutrons, which is why isotopes react in the same way.
Exam tip: neutrons = top number minus bottom number; isotopes differ only in neutron count, so they share chemistry and group.
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