Atomic number, mass number and isotopesIB MYP Chemistry: Subtopic test

1. 1
   A student is studying sodium, which is written in notation as $^{23}_{11}\mathrm{Na}$. She is learning what the two numbers in the notation tell her about the particles inside a sodium atom.

   (a)

   What does the atomic number, 11, tell you about a sodium atom?

   [1 mark]

   • AThe number of neutrons
   • BThe number of protons
   • CThe number of protons plus neutrons
   • DThe number of shells

   (b)

   How many neutrons are in this sodium atom?

   [1 mark]

   • A11
   • B23
   • C34
   • D12

   (c)

   Explain why a neutral sodium atom has 11 electrons.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Chemists describe atoms by the numbers of particles they contain. Four atoms are described below. Atom W has 17 protons, 18 neutrons and 17 electrons. Atom X has 18 protons, 18 neutrons and 18 electrons. Atom Y has 17 protons, 20 neutrons and 17 electrons. Atom Z has 19 protons, 20 neutrons and 19 electrons.

   (a)

   What is the mass number of atom W?

   [1 mark]

   • A35
   • B17
   • C18
   • D52

   (b)

   Which two atoms are isotopes of the same element?

   [1 mark]

   • AW and X
   • BX and Y
   • CW and Y
   • DY and Z

   (c)

   Explain why atoms W and Y are the same element but have different masses.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Chlorine has atomic number 17. A typical sample of chlorine contains two isotopes, $^{35}\mathrm{Cl}$ and $^{37}\mathrm{Cl}$. In the sample, 75% of the atoms are $^{35}\mathrm{Cl}$ and 25% of the atoms are $^{37}\mathrm{Cl}$.

   (a)

   State the number of protons, neutrons and electrons in a neutral atom of $^{37}\mathrm{Cl}$.

   [3 marks]

   (b)

   Calculate the relative atomic mass of chlorine in this sample. Show your working.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A hospital nuclear medicine department uses isotopes of iodine, which has atomic number 53. Natural iodine is entirely the stable isotope iodine-127. The department also uses iodine-131, a radioactive isotope made in a nuclear reactor, to treat an overactive thyroid gland. Iodine-131 has the same chemical properties as iodine-127, so the thyroid absorbs it from the blood. The radiation from iodine-131 kills thyroid cells but can also harm healthy tissue nearby, and the radioactive waste from treatment has to be stored securely.

   (a)

   A technician analyses a sample of iodine from the reactor. It contains 60% iodine-127 atoms and 40% iodine-131 atoms. Calculate the number of neutrons in an atom of each isotope, and the relative atomic mass of the sample to 1 decimal place.

   [6 marks]

   (b)

   Discuss and evaluate the use of iodine-131 to treat an overactive thyroid gland.

   [6 marks]

   Total for question 4: 12 marks

End of questions