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1.4Principles of Chemistry

The Periodic Table — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 7 parts Lesson 12 of 25 Unit quiz

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The Periodic Table: Arrangement, Electronic Configuration and Reactivity — EDEXCEL LINEAR – OL (CHEMISTRY) notes: Explain how elements are arranged, write electronic configurations, classify metals and non-metals and relate group number to reactivity and the unreactivity of noble…

  • Worked example 1
  • Worked example 2
  • Worked example 3
  • Worked example 4
  • Outer shell
  • Saying the period number gives the outer electrons — the group does

Part 1 of 5Arrangement of the Periodic Table

Elements are arranged in order of increasing atomic number; each has one more proton than the one before.

Arrangement of the Periodic Table
Groups
Vertical columns are groups and horizontal rows are periods.
The period number is the number of electron shells; the group number is the number of outer-shell electrons (Group 0 or 8 has a full shell).
Group 4 elements have four outer electrons; period 3 elements have three shells.
Elements in the same group have similar chemical properties because they have the same number of outer electrons.
The atomic number is a unique "fingerprint" that does not change in chemical reactions, although the number of electrons can.

Mendeleev's table was arranged by atomic mass with gaps left for undiscovered elements; the modern table uses atomic number, which explains why the properties repeat periodically.

Part 2 of 5Electronic configuration

Electrons occupy shells (energy levels) closest to the nucleus first.

Electronic configuration
The first shell holds 2, the second 8, and in the simplified model used here the third holds 8 for the first 20 elements,
  • then the fourth begins to fill.
Configurations: H 1, He 2, Li 2,1, Be 2,2, B 2,3, C 2,4, N 2,5, O 2,6, F 2,7, Ne 2,8, Na 2,8,1, Mg 2,8,2, Al 2,8,3, Si 2,8,4, P 2,8,5, S 2,8,6, Cl 2,8,7, Ar 2,8,8, K 2,8,8,1, Ca 2,8,8,2.
  • Chlorine has three figures so three shells (Period 3) and a last figure of 7, so it is in Group 7.
  • Ions have configurations tooNa+ is 2,8.

Part 3 of 5Metals and non-metals

PropertyMetalsNon-metals
Outer electrons1 to 34 to 7
BondingMetallic; lose electronsCovalent; share electrons
ConductivityGoodPoor
OxideBasicAcidic (some neutral)
Reaction with acidsMany reactUsually do not
Appearance and structureShiny, malleable, high melting pointDull, brittle, varied states

Metals are on the left and non-metals on the right of a zig-zag line. Elements next to the line, such as silicon, have properties of both and are called metalloids.

Part 4 of 5Reactivity and the noble gases

Group number predicts how an element reacts.

Reactivity and the noble gases
Group 1 metals (lithium, sodium, potassium) all react with Group 7 elements to form ionic compounds; reactivity increases down Group 1 and decreases down Group 7.
  • Noble gases (Group 0) are non-metals, monatomic, colourless and non-flammable.
They have full outer shells (He 2; Ne 2,8; Ar 2,8,8; Kr 2,8,18,8; Xe 2,8,18,18,8),
  • so they do not need to gain, lose or share electrons and are unreactive.
Their uses depend on this inertness.

Predicting propertiesbecause the number of outer electrons controls bonding, an element in Group 2 loses two electrons to form a 2+ ion, an element in Group 6 gains two electrons to form a 2- ion, and a Group 7 element gains one to form a 1- ion.

Reactivity and the noble gases
Use the group number to predict ion charges: groups 1, 2 and 3 form ions 1+, 2+ and 3+; groups 5, 6 and 7 form ions 3-, 2- and 1-.
Metals react by losing electrons,
  • so reactivity of metals increases as outer electrons become easier to lose (down a group),
  • while the reactivity of non-metals depends on how easily they gain electrons,
  • which is greater for fluorine than for iodine.

Part 5 of 5Worked examples

  1. Chlorine is 2,8,7. State its group and period. [2]2 marks

  2. Why do Group 1 elements have similar reactions? [1]1 mark

  3. Explain why neon is unreactive. [2]2 marks

  4. State two differences in properties between metals and non-metals. [2]2 marks

Key terms

TermMeaning
GroupVertical column of the Periodic Table.
PeriodHorizontal row of the Periodic Table.
Noble gasUnreactive Group 0 element with a full outer shell.
MetalloidElement with properties of both metals and non-metals.
Electronic configurationArrangement of electrons in shells.
Outer shellHighest-energy occupied shell.

Avoid these mistakes

1
Saying the period number gives the outer electrons — the group does.
2
Writing the third shell holds 18 at GCSE for calcium.
3
Stating noble gases are reactive.
4
Thinking group number changes when electrons are lost.

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