The method and the results are on the electron arrangement lab. Do the analysis yourself first, then check the answers below.
Quick answer: Electrons fill shells from the nucleus outwards, holding 2, 8 and 8 in the first three shells of the first 20 elements. These answers go with the Chemistry 9-10 lab on electron arrangement: the graph, the calculations, the uncertainties and the conclusion explained, for all 6 analysis questions.
These model answers use the sample card data. Also, they link the pattern in chloride formulas to outer electrons and show why a gap in mass points to missing elements.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS1-1, HS-PS1-2
Question 1 Describe the pattern
The numbers run 1, 2, 3, 4, then return to 1, 2, 3, 4, then 1, 2. So the sequence repeats.The pattern 1, 2, 3, 4 repeats.
Question 2 Find the columns
Firstly, column 1: Li, Na, K. Then column 2: Be, Mg, Ca. Afterwards, column 3: B, Al. Finally, column 4: C, Si.Li, Na, K; Be, Mg, Ca; B, Al; C, Si.
Question 3 Link to electrons
The number of chlorine atoms equals the number of outer electrons for these cards (Li 1, Be 2, B 3, C 4, and so on). Therefore an element with 3 outer electrons would form XCl₃, the same as BCl₃ and AlCl₃.Prediction: XCl₃.
Question 4 Explain the mass gaps
Firstly, C to Na: 23.0 − 12.0 = 11.0. Then Si to K: 39.1 − 28.1 = 11.0. Also, elements 7 to 10 (nitrogen, oxygen, fluorine, neon) lie between carbon and sodium, and elements 15 to 18 (phosphorus, sulfur, chlorine, argon) lie between silicon and potassium.Jumps of 11.0; four elements missing each time.
Question 5 Explain the repeat
Li is 2,1, Na is 2,8,1 and K is 2,8,8,1. Each has one outer electron, so they form similar chlorides. In addition, after a shell fills, the next element starts a new shell with one outer electron, so the pattern repeats.Same outer electrons give the same chemistry.
Question 6 Evaluate and improve
With only ten cards the gaps look like jumps, so the full length of the period is hidden. Rounded masses could also hide the true order. Finally, improvement: use all eighteen cards for atomic numbers 3 to 20 and order them by atomic number.Use a complete set of cards ordered by atomic number.
