Electron Shells and the Shape of the Periodic Table · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Electron shells and the shape of the periodic table

Science · Matter & Materials · ages 14-15
Name ______________________   Date ____________

  1. A group 1 metal atom reacts. What does it do with its outer electron?

    • it splits the electron between two shells
    • it pulls one more in and turns negative
    • it shares the electron with its own nucleus instead
    • it loses the electron and becomes a positive ion

  2. An atom has the arrangement 2,8,5. Which period does it sit in?

    • period 2
    • period 3
    • period 5
    • period 15

  3. Electrons fill the outermost shell before they fill the inner ones.

    Circle one:   True   False

  4. An atom has 7 electrons in total. How many of them sit in its second shell?

    Answer: ______________

  5. Potassium has 19 electrons. Which arrangement is right, and how many shells does it use?

    • 2,8,9 with three shells in use
    • 2,8,8,1 with four shells in use
    • 2,9,8 with three shells in use
    • 2,8,7,2 with four shells in use

  6. Phosphorus has 15 electrons. How many of them sit in its second shell?

    Answer: ______________

  7. Sulfur has the arrangement 2,8,6. What charge will its ion carry?

    • 6+
    • 2-
    • 2+
    • 6-

  8. Priya sees the arrangement 2,8,4 and says the element is in period 4, because 4 is the last number. What has she mixed up?

    • the last number is the outer-shell count, so it gives the group
    • the last number gives the atomic number rather than the period here
    • she should have added the numbers together to find the period
    • periods are counted from the right-hand side of the chart

  9. A non-metal on the right of the chart forms a positive ion when it reacts.

    Circle one:   True   False

  10. One atom is 2,8,2 and another is 2,2. What do the two elements share?

    • their group, because each has two outer electrons
    • their period, because each has two outer electrons
    • their number of shells, since both lists end in 2
    • nothing, because the two lists are different lengths
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Electron shells and the shape of the periodic table W1-mt__Sdcw4RnZF-s1

  1. it loses the electron and becomes a positive ion · A group 1 atom has one outer electron. Losing it leaves a full shell underneath, and the atom is left with one more proton than electron, so it is positive.
  2. period 3 · The period is how many shells are in use. This arrangement lists three numbers, so three shells are occupied and the atom sits in period 3.
  3. False · Filling runs the other way. The shell closest to the nucleus takes its electrons first, and the next one starts only when that is full.
  4. 5 · The first shell takes 2, which leaves 7 - 2 = 5 for the second. The arrangement is 2,5.
  5. 2,8,8,1 with four shells in use · 2 and 8 fill the first two shells. The third takes 8 more, reaching 18, and the last electron opens a fourth shell.
  6. 8 · The first shell takes 2, then the second fills to its limit of 8, leaving 15 - 10 = 5 for the third. The arrangement is 2,8,5.
  7. 2- · Six outer electrons means sulfur is in group 6 and needs 2 more to fill the shell. Gaining 2 electrons makes the ion 2-.
  8. the last number is the outer-shell count, so it gives the group · The last number gives the group, so this element is in group 4. The period comes from how many numbers there are, which is three here.
  9. False · Non-metals have nearly full outer shells, so they gain electrons rather than lose them. Extra electrons make the ion negative.
  10. their group, because each has two outer electrons · Both end in 2, so both have two outer electrons and both sit in group 2. Their periods differ, since one uses three shells and the other two.
Worksheet · LightMySky