The questions are on the electron arrangement test. Take it under real conditions before reading the mark scheme.
Quick answer: Electrons fill shells from the nucleus outwards, holding 2, 8 and 8 in the first three shells of the first 20 elements. This mark scheme gives the model answers and the marks for the 9 questions of the Chemistry 9-10 test on electron arrangement, from electron arrangements to losing or gaining, with the equivalent answers to accept.
Each model answer is followed by the marking points. Accept any correct equivalent wording, and give credit where the reasoning is clear even if the arrangement is written without commas.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS1-1, HS-PS1-2
Question 2 Group and period (2 marks)
Two outer electrons: Group 2. Four shells: period 4 (calcium).
Marking: 1 mark each.
Question 3 Mendeleev’s table (3 marks)
(a) Increasing relative atomic mass.
(b) Elements with similar properties had to line up in columns, so a space was left where none was known.
(c) Germanium was discovered with properties that matched his predictions for eka-silicon.
Marking: 1 mark each.
Question 4 Atom Y (2 marks)
(a) 5 outer electrons: Group 5.
(b) 2 shells: period 2.
Marking: 1 mark each.
Question 5 Similar elements (2 marks)
Their atoms each have one electron in the outer shell. Chemical reactions depend on the outer electrons, so the elements behave alike.
Marking: 1 mark for one outer electron; 1 mark for reactions depend on outer electrons.
Question 6 Moseley’s contribution (2 marks)
Moseley showed that elements should be ordered by atomic number, not mass. Tellurium (52) comes before iodine (53), which puts iodine in the same group as chlorine, even though iodine has a lower relative atomic mass.
Marking: 1 mark for atomic number; 1 mark for the correct order of the two elements.
Question 7 Noble gases (2 marks)
Neon has the arrangement 2,8, with a full outer shell. This is stable, so its atoms do not lose, gain or share electrons.
Marking: 1 mark for the full outer shell; 1 mark for no need to lose, gain or share electrons.
Question 8 Identify an element (2 marks)
Arrangement 2,8,6: 2 + 8 + 6 = 16 electrons, so atomic number 16.
Atomic number 16, sulfur
Marking: 1 mark for the sum; 1 mark for the element.
Question 9 Losing or gaining (2 marks)
Magnesium loses 2 electrons to reach 2,8. Oxygen gains 2 electrons to reach 2,8.
Mg loses 2; O gains 2
Marking: 1 mark each.
