IonsIB MYP Chemistry: Subtopic test

1. 1
   A sodium atom, with electron arrangement 2,8,1, reacts with a chlorine atom, with electron arrangement 2,8,7, to make sodium chloride. Sodium chloride is an ionic compound made of sodium ions and chloride ions. Chlorine has atomic number 17.

   (a)

   What happens to the sodium atom when it forms a sodium ion?

   [1 mark]

   • AIt gains one electron and forms Na⁻
   • BIt loses one proton and forms Na⁺
   • CIt loses two electrons and forms Na²⁺
   • DIt loses one electron and forms Na⁺

   (b)

   What is the electron arrangement of a chloride ion?

   [1 mark]

   • A2,8,7
   • B2,8,8
   • C2,8,8,1
   • D2,8,6

   (c)

   Explain why a chloride ion has a charge of 1-.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   Magnesium oxide is used to line furnaces because it can withstand very high temperatures. It is an ionic compound made of magnesium ions, Mg²⁺, and oxide ions, O²⁻. Magnesium has atomic number 12 and is in Group 2. Oxygen has atomic number 8 and is in Group 6.

   (a)

   How many electrons are in a magnesium ion, Mg²⁺?

   [1 mark]

   • A12
   • B14
   • C10
   • D2

   (b)

   What is the electron arrangement of an oxide ion, O²⁻?

   [1 mark]

   • A2,8
   • B2,6
   • C2,8,2
   • D2,8,8

   (c)

   Explain, using its group number, why magnesium forms an ion with a charge of 2+.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   Aluminium fluoride is an ionic compound made of aluminium ions, Al³⁺, and fluoride ions, F⁻. Aluminium has atomic number 13 and is in Group 3. Fluorine has atomic number 9, with the electron arrangement 2,7, and is in Group 7.

   (a)

   Describe how an aluminium atom forms an Al³⁺ ion, and state the number of protons and electrons in the ion.

   [3 marks]

   (b)

   Explain how a fluorine atom forms a fluoride ion, and state the electron arrangement of the ion and why it is stable.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A city water company adds fluoride ions, F⁻, to the drinking water supply to help protect people's teeth against decay. A laboratory technician records the number of protons and electrons in five particles found in the treated water. Particle P has 11 protons and 10 electrons. Particle Q has 9 protons and 10 electrons. Particle R has 12 protons and 10 electrons. Particle S has 8 protons and 8 electrons. Particle T has 17 protons and 18 electrons.

   (a)

   Use the data to work out the charge on each particle P to T, and state which particle is an atom rather than an ion. Identify the fluoride ion (fluorine has atomic number 9), and give the electron arrangement that is shared by P, Q and R.

   [6 marks]

   (b)

   Discuss and evaluate the addition of fluoride ions to drinking water.

   [6 marks]

   Total for question 4: 12 marks

End of questions