Periodic trendsIB MYP Chemistry: Subtopic test

1. 1
   A student collects data on the atoms of the period 3 elements. Their approximate atomic radii, in picometres (pm), are: sodium 186, magnesium 160, aluminium 143, silicon 118, phosphorus 110, sulfur 103 and chlorine 99.

   (a)

   Which statement describes the trend in atomic radius from sodium to chlorine?

   [1 mark]

   • AIt increases steadily
   • BIt decreases steadily
   • CIt stays the same
   • DIt decreases and then increases

   (b)

   Which statement best explains this trend?

   [1 mark]

   • AThe number of electron shells increases across the period
   • BThe number of protons decreases across the period
   • CThe number of protons increases while electrons are added to the same shell, so the attraction to the outer electrons is stronger
   • DThe extra electrons repel one another and push the outer shell closer to the nucleus

   (c)

   Describe how metallic character changes across period 3 from sodium to chlorine.

   [2 marks]

   Total for question 1: 4 marks

2. 2
   The elements in Group 4 of the periodic table are carbon, silicon, germanium, tin and lead. Carbon is a brittle non-metal, silicon and germanium are semiconductors, and tin and lead are shiny, malleable metals that conduct electricity well.

   (a)

   Which statement describes the trend in metallic character down Group 4?

   [1 mark]

   • AIt decreases
   • BIt stays the same
   • CIt increases and then decreases
   • DIt increases

   (b)

   Which statement best explains why tin and lead are more metallic than carbon?

   [1 mark]

   • ATheir outer electrons are further from the nucleus and more shielded, so they are lost more easily
   • BThey have more outer electrons than carbon
   • CTheir nuclei contain fewer protons than carbon
   • DThey have fewer electron shells than carbon

   (c)

   Explain why the atomic radius increases down Group 4.

   [2 marks]

   Total for question 2: 4 marks

3. 3
   A student investigates the reactivity of three halogens (Group 7) using displacement reactions. She adds a few drops of each halogen solution to separate solutions of potassium chloride, potassium bromide and potassium iodide, and records a reaction when the mixture changes colour. Chlorine solution changed potassium bromide solution orange and potassium iodide solution brown, but did not change potassium chloride solution. Bromine solution changed potassium iodide solution brown, but did not change potassium chloride or potassium bromide solution. Iodine solution caused no change with any of the three.

   (a)

   Identify the independent variable, the dependent variable and one control variable in this investigation.

   [3 marks]

   (b)

   Analyse the results to describe the trend in reactivity down Group 7 and explain it.

   [4 marks]

   Total for question 3: 7 marks

4. 4
   A school chemistry department is deciding whether to keep its annual demonstration of Group 1 metals reacting with water. A teacher drops a small piece of lithium, then sodium, then potassium into separate troughs of water behind a safety screen while students wear eye protection. Lithium fizzes steadily, sodium melts into a ball and darts across the surface, and potassium ignites with a lilac flame. A colleague suggests replacing the demonstration with a video, which would cost nothing and remove any risk.

   (a)

   Explain, using ideas about electron shells and nuclear attraction, why potassium reacted more vigorously than lithium, and predict how caesium would compare.

   [6 marks]

   (b)

   Discuss and evaluate whether the department should replace the live demonstration with a video.

   [6 marks]

   Total for question 4: 12 marks

End of questions