IB MYP Integrated Sciences e-Assessment : Trends, periods, groups
Exam Style Practice Questions - New Syllabus
Question (10 marks)
Scientists have used their creativity to produce dazzling firework displays. One of the uses of group one elements is to produce bright colours in fireworks.
The flask in the simulation contains chlorine gas. Click on the video in each tab to observe the reaction of each element with chlorine.
Question 3a (2 marks)
Group one elements are highly reactive. Outline the reason for the high reactivity of group one elements.
▶️Answer/Explanation
Answer: Group one elements only have one valence electron. They are able to easily give away this electron and therefore they are able to react easily with elements that need another electron.
Detailed Solution: Group one elements, also known as alkali metals, have a single electron in their outermost shell. This electron is loosely held due to the large atomic radius and low effective nuclear charge. As a result, these elements readily lose their valence electron to achieve a stable noble gas configuration, making them highly reactive.
Question b (3 marks)
Select one reaction from the videos above and write down a balanced chemical equation for this reaction. Include state symbols in your answer.
▶️Answer/Explanation
Answer: 2Na(s) + Cl2(g) → 2NaCl(s)
Detailed Solution: Sodium (Na) reacts with chlorine (Cl2) to form sodium chloride (NaCl). The balanced equation shows that two sodium atoms react with one chlorine molecule to produce two sodium chloride molecules.
Question c (2 marks)
Using your knowledge of periodic trends, compare and contrast the reactions between caesium and chlorine, and lithium and chlorine.
▶️Answer/Explanation
Answer: Caesium and lithium both have one electron in the outer shell of their atoms, so the mole ratio between caesium and chlorine and lithium and chlorine is the same. However, because in the first group, the reactivity of an element increases when the periodic trend goes down, caesium would have higher reactivity than lithium, which would result in a more violent reaction with chlorine.
Detailed Solution: Caesium is larger and has more electron shells than lithium, making its valence electron less tightly held. This makes caesium more reactive than lithium, leading to a more vigorous reaction with chlorine.
Question d (3 marks)
Francium (Fr) is also a group one element. Francium is very rare and it is never found in nature as an uncombined element. Apart from being rare, explain why francium is never found as an uncombined element.
▶️Answer/Explanation
Answer: Francium has an even larger atomic radius than caesium. This means that it is even more reactive with many other elements in nature, because the electrostatic forces are weaker between its nucleus and its valence electrons. Because of this reactivity, it is very likely to react with the things in nature and will therefore not be found as an uncombined element usually.
Detailed Solution: Francium is the most reactive alkali metal due to its large atomic size and weak electrostatic forces between the nucleus and the outermost electron. It reacts immediately with water, oxygen, and other elements, making it impossible to exist in nature as a pure element.