Group 1, Group 7 and Group 0: Trends You Can Predict · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Groups 1, 7 and 0: trends you can predict

Science · Matter & Materials · ages 14-16
Name ______________________   Date ____________

  1. Which equation shows potassium reacting with water?

    • K + H₂O → KH + O₂
    • 2K + 2H₂O → 2KOH + H₂
    • 2K + 2H₂O → 2KO + H₂ + O₂
    • K + 2H₂O → KO₂ + 2H₂

  2. Chlorine water is added to a colourless solution of potassium bromide. What happens?

    • nothing changes, because the two are both halogens
    • the solution turns green as chlorine is set free
    • the solution turns orange as bromine is set free
    • the solution turns grey as iodine is set free

  3. Of chlorine, bromine and iodine, which reacts most readily?

    • iodine, because it is the heaviest of the three by far
    • bromine, because it sits in the middle
    • all three react equally, since all are group 7
    • chlorine, because it is the highest of the three

  4. Why is potassium more reactive with water than lithium?

    • potassium has more outer electrons to give away
    • potassium's outer electron is further out and better shielded
    • potassium's nucleus holds fewer protons than lithium's
    • potassium is a heavier metal, so it hits the water surface harder

  5. What does shielding mean in the group 1 explanation?

    • full inner shells sit between the outer electron and the protons
    • the outer electron is protected from the water molecules by the shells
    • neutrons in the nucleus block some of the positive charge
    • the outer shell blocks other atoms from getting close

  6. In 2Na + 2H₂O → 2NaOH + H₂, how many oxygen atoms are on the right-hand side?

    Answer: ______________

  7. In 2Na + 2H₂O → 2NaOH + H₂, how many hydrogen atoms are on the left-hand side?

    Answer: ______________

  8. Sam says group 7 must get more reactive down the column, because group 1 does. What would have to be true for his reasoning to hold?

    • group 7 would have to be on the left-hand side of the chart
    • group 7 would have to react by losing an outer electron too
    • group 7 atoms would have to hold fewer outer electrons than group 1
    • group 7 would have to have no shielding at all in its atoms

  9. Bromine water is added to colourless potassium iodide solution. What is seen, and why?

    • it darkens as iodine is set free, because bromine sits above iodine
    • it stays colourless, because bromine sits below iodine in the column
    • it turns green, because chlorine is set free
    • it stays colourless, because both are group 7 and neither wins

  10. Sodium is 2,8,1 and lithium is 2,1. How many more full shells shield sodium's outer electron than lithium's?

    Answer: ______________

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Answer key

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

Groups 1, 7 and 0: trends you can predict W1-mt_cy1OrVAjIo-s1

  1. 2K + 2H₂O → 2KOH + H₂ · The products are potassium hydroxide and hydrogen, which is the same pattern as sodium. Both sides carry 2 potassium, 4 hydrogen and 2 oxygen.
  2. the solution turns orange as bromine is set free · Chlorine is above bromine, so it displaces bromine from the salt. The bromine set free colours the solution orange.
  3. chlorine, because it is the highest of the three · Group 7 reactivity falls down the column, so the highest of the three is the most reactive. Chlorine sits above bromine, which sits above iodine.
  4. potassium's outer electron is further out and better shielded · Both have exactly one outer electron. Potassium's sits four shells out with more full shells shielding it, so the nucleus holds it more loosely and it comes off more easily.
  5. full inner shells sit between the outer electron and the protons · Shielding is about the inside of the atom. Every full shell between the nucleus and the outer electron weakens the pull the outer electron feels.
  6. 2 · Each NaOH holds one oxygen atom, and there are 2 of them, so 2 oxygen atoms. The H₂ carries none.
  7. 4 · Each water molecule holds 2 hydrogen atoms, and there are 2 of them, so 2 x 2 = 4.
  8. group 7 would have to react by losing an outer electron too · His cause is right: distance and shielding grow down both columns. They make losing an electron easier, so his conclusion would follow only if group 7 reacted by losing one. It reacts by gaining.
  9. it darkens as iodine is set free, because bromine sits above iodine · Bromine is above iodine, so it displaces it: Br₂ + 2KI gives 2KBr + I₂. The iodine set free darkens the solution.
  10. 1 · Sodium's outer electron sits in shell three with two full shells inside it. Lithium's sits in shell two with one full shell inside. 2 - 1 = 1.
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