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11.6Chapter 11: Patterns in the Periodic Table

The periodic table: Group 2 and Group 7/8 Trends — Alhussan Chemistry - Stage 9 Revision Notes & Topical Questions

5 min read 8 parts Lesson 6 of 7 2 quizzes

📚 Alhussan Chemistry - Stage 9 Hub / Topical Revision
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11.6 The periodic table: Group 2 and Group 7/8 Trends — Alhussan International Academy — Chemistry (Stages 7–9) notes: Describe patterns in the physical and chemical properties of Group 2, and the trends in Group 7 and Group 0.Position — Group 2 is the second column of the period…

  • Compared with Group 1
  • With water
  • Prediction
  • Hypothesis
  • Conclusion
  • Limitation

Section 1 of 8Group 2: the alkaline earth metals

Group 2: the alkaline earth metals
Position
  • Group 2 is the second column of the periodic table: beryllium, magnesium, calcium, strontium, barium and radium.
Electrons
  • Electrons atoms of all Group 2 elements have two electrons in the outer shell and form 2+ ions.
  • Their similar configurations give them similar chemical properties.
Compared with Group 1
  • Compared with Group 1 they are harder and denser, have higher melting points and react less vigorously.
Beryllium
  • Beryllium the 18 mirror segments of the James Webb Space Telescope are beryllium coated with gold,
  • because beryllium is strong for its weight and holds its shape over a range of temperatures.

Section 2 of 8Physical properties of Group 2

ElementMelting point (°C)
Beryllium1287
Magnesium650
Calcium842
Strontium777
Barium727
Radium700
Physical properties of Group 2
Trend
  • Trend in general melting point decreases from top to bottom of Group 2.
Exception
  • Exception the melting point of magnesium does not fit the pattern.
Variables
  • Variables the independent variable is the element and the dependent variable is the melting point in °C.

Section 3 of 8Chemical properties of Group 2

Chemical properties of Group 2
With acid
  • With acid all Group 2 elements react with dilute hydrochloric acid to make a solution of a chloride and hydrogen gas.
  • strontium + hydrochloric acid → strontium chloride + hydrogen.
  • calcium + hydrochloric acid → calcium chloride + hydrogen.
With water
  • With water magnesium reacts very slowly with cold water, whereas calcium produces a steady stream of bubbles.
  • calcium + water → calcium hydroxide + hydrogen.
Trend
  • Trend reactivity increases down the group because the outer electrons are further from the nucleus in larger atoms and are lost more easily.
Prediction
  • Prediction strontium would react faster than calcium.

Section 4 of 8Investigating the reactivity of Group 2

Investigating the reactivity of Group 2
Question
  • Question what is the pattern in reactivity of the Group 2 elements with hydrochloric acid?
Hypothesis
  • Hypothesis from top to bottom the outer electrons get further from the nucleus and are easier to give away, so reactions get more vigorous.
Prediction
  • Prediction calcium, which is below magnesium, will react more vigorously.
Method
  • Method add each metal to dilute hydrochloric acid in a test tube, collect the gas, and test it with a lighted splint.
  • The splint goes out with a squeaky pop, which shows the gas is hydrogen.
Conclusion
  • Conclusion calcium reacted more vigorously than magnesium, so for the elements tested the reactions get more vigorous down the group.
Limitation
  • Limitation only two Group 2 elements were tested, and reacting more of them would make the conclusion more certain.

Section 5 of 8Group 7: the halogens

Group 7: the halogens
Properties
  • Properties fluorine, chlorine, bromine and iodine are non-metals with seven outer electrons that exist as diatomic molecules F2, Cl2, Br2 and I2.
Down the group
  • Down the group the colour darkens and the melting point rises.
  • Chlorine is a pale green gas, bromine an orange-brown liquid and iodine a grey-black solid.
Reactivity
  • Reactivity it decreases down the group because a larger atom finds it harder to attract an extra electron into its outer shell.
Displacement
  • Displacement a more reactive halogen displaces a less reactive one from its salt solution.
  • chlorine + potassium bromide → potassium chloride + bromine, and the solution turns orange.
  • chlorine with potassium iodide turns the solution brown as iodine forms, and iodine with potassium chloride gives no change.
Safety
  • Safety halogens are toxic: chlorine irritates the lungs and bromine causes burns, so they are used in a fume cupboard.

Section 6 of 8Group 0: the noble gases

Group 0: the noble gases
Properties
  • Properties helium, neon, argon, krypton and xenon have full outer shells, so they are unreactive and exist as single atoms.
Boiling points
  • Boiling points they increase down the group because bigger atoms have stronger attractions between them.
  • Helium boils at -269 °C, neon at -246 °C and argon at -186 °C.
Uses
  • Uses helium is used in balloons, neon in advertising signs and argon in filament lamps (an inert atmosphere).
    • (low density and non-flammable)
GroupOuter electronsIonReactivity down the group
111+Increases
222+Increases
771-Decreases
08 (2 for He)NoneUnreactive

Section 7 of 8Key terms

TermMeaning
Halogena reactive non-metal in Group 7.
Noble gasan unreactive Group 0 element.
Diatomica molecule with two atoms.
Displacementa more reactive element replacing a less reactive one in a compound.
Alkaline earth metala Group 2 element.
Hypothesisa possible explanation based on evidence that can be tested.

Section 8 of 8Exam technique

1
Saying halogens get more reactive down the group — they get less reactive.
2
Writing a halogen as a single atom — halogens are diatomic molecules.
3
Saying noble gases form ions — their outer shells are full, so they are unreactive.
4
Confusing Group 2 with Group 1 charge — Group 2 forms 2+ ions and Group 1 forms 1+ ions.

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