Atomic structure and isotopesEdexcel A-Level Chemistry: Subtopic test

1. 1
   Sulfur has several naturally occurring isotopes, including ³²S and ³⁴S (atomic number 16). A technician is studying a sample of sodium sulfide, which contains the sulfide ion ³⁴S²⁻.

   (a)

   How many neutrons are there in one ³⁴S²⁻ ion?

   [1 mark]

   • A16
   • B18
   • C34
   • D36

   (b)

   Which species has the same number of electrons as one ³⁴S²⁻ ion?

   [1 mark]

   • AA neon atom
   • BA chlorine atom
   • CA magnesium ion, Mg²⁺
   • DAn argon atom

   (c)

   Explain why ³²S and ³⁴S have the same chemical properties but different masses.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   A physics teacher describes the sodium ion ²³Na⁺ (atomic number 11) to a class using the relative mass and relative charge of the three sub-atomic particles.

   (a)

   A beam of neutrons passes between two electrically charged plates. What happens to the beam?

   [1 mark]

   • AIt is not deflected, because neutrons have no charge
   • BIt is deflected towards the negative plate, because neutrons are slightly positive
   • CIt is deflected towards the positive plate, because neutrons have a relative charge of −1
   • DIt splits into two beams, because neutrons have two different relative masses

   (b)

   Which statement about the relative mass of the particles in the sodium ion is correct?

   [1 mark]

   • AA proton has a relative mass of 1/1840
   • BA neutron has a relative mass of 0
   • CAn electron has a relative mass of about 1/1840, much smaller than a proton
   • DAn electron, a proton and a neutron all have a relative mass of 1

   (c)

   Deduce the total relative charge of the ²³Na⁺ ion and its approximate relative mass. Explain why the electrons can be ignored when finding the relative mass.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Chlorine exists naturally as two isotopes, ³⁵Cl and ³⁷Cl (atomic number 17). A student studies the chloride ion ³⁷Cl⁻ and a chlorine molecule in which one atom is ³⁵Cl and the other is ³⁷Cl.

   (a)

   State the number of protons, neutrons and electrons in one ³⁷Cl⁻ ion.

   [3 marks]

   (b)

   Deduce the total number of neutrons and the total number of electrons in one ³⁵Cl³⁷Cl molecule. Explain why ³⁵Cl and ³⁷Cl undergo the same chemical reactions.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   Carbon exists as three naturally occurring isotopes, ¹²C, ¹³C and ¹⁴C (atomic number 6). The radioactive isotope ¹⁴C is used in radiocarbon dating. A student makes two claims. Claim 1: 'The isotopes of an element have different numbers of protons.' Claim 2: 'Isotopes of an element react differently because their atoms have different masses.'

   (a)

   Describe the atomic structure of a ¹⁴C atom, giving the relative mass and relative charge of each type of sub-atomic particle, and explain how ¹⁴C differs from ¹²C.

   [6 marks]

   (b)

   Evaluate the two claims made by the student.

   [6 marks]

   Total for question 4: 12 marks

End of questions