Chemistry • Year 11 • Module 1 • Lesson 19
Electron Configuration and Chemical Behaviour
Secure the core vocabulary and patterns linking electron configuration to ion charge, group behaviour, and isoelectronic series before moving to applied questions.
1. Term–definition match
The definitions below are shuffled. In the right-hand column write the matching term from this list: valence electrons, octet rule, isoelectronic, cation, anion, oxidation state, noble gas configuration, electron configuration, 4s electrons, variable oxidation state. 10 marks (1 each)
| # | Definition | Matching term |
|---|---|---|
| 1.1 | The electrons in the outermost shell of an atom; these determine the chemical behaviour of an element. | |
| 1.2 | The principle that main-group atoms react to achieve eight electrons in their outermost shell. | |
| 1.3 | Two or more species that have the same number of electrons and the same electron configuration but different nuclear charges. | |
| 1.4 | A positively charged ion formed when a neutral atom loses one or more electrons. | |
| 1.5 | A negatively charged ion formed when a neutral atom gains one or more electrons. | |
| 1.6 | A number indicating the degree of oxidation of an element; reflects how many electrons have been gained, lost or shared. | |
| 1.7 | The electron arrangement of the nearest noble gas; the stable arrangement that main-group ions achieve. | |
| 1.8 | A systematic description of how electrons are distributed across subshells in an atom or ion, written using notation such as 1s²2s²2p&sup6;. | |
| 1.9 | The electrons in the 4s subshell of a transition metal; these are always removed first when the metal forms a cation. | |
| 1.10 | The property of transition metals by which they can form ions with more than one possible charge, due to similar energies of the 3d and 4s subshells. |
2. True or false — with correction
Circle T or F for each statement. If the statement is false, write the corrected version on the line below it. 12 marks (1 T/F + 1 correction each)
2.1 Sodium (Group 1) forms a Na²+ ion because it has two valence electrons to lose. T / F
2.2 Cl− and Ar are isoelectronic because they both have 18 electrons and the same electron configuration. T / F
2.3 When iron (Z = 26) forms Fe³+, the electron configuration of the ion is [Ar]3d³4s². T / F
2.4 Elements in the same group have the same number of valence electrons, which is why they display similar chemical behaviour. T / F
2.5 Anions are always smaller than the neutral atom they formed from, because gaining electrons adds to the nuclear charge. T / F
2.6 Carbon (Group 14) typically forms a C&sup4;+ ion because it has four valence electrons to lose. T / F
3. Fill-in-the-blank paragraph
Use the word bank to complete the passage. Each word is used once. 8 marks (1 per blank)
Word bank:
cation · octet · valence · noble gas · anion · isoelectronic · 4s · group
The chemical behaviour of an element is primarily determined by its ___________ electrons — those in the outermost shell. Main-group elements gain or lose electrons to achieve a ___________ configuration, satisfying the ___________ rule. A metal such as sodium loses its single outer electron to form a ___________, while a non-metal such as chlorine gains an electron to form an ___________. Species that share the same electron configuration are described as ___________ (e.g. Na+, Ne, and F− all have 1s²2s²2p&sup6;). All elements in the same ___________ share the same valence electron arrangement, which is why they react in the same way. For transition metals, when forming ions the ___________ electrons are always removed first.
4. Function recall
Answer each question in 1–2 sentences using precise terms from the lesson. 8 marks (2 each)
4.1 Why do elements in Group 17 form 1− ions rather than 7+ ions?
4.2 What is the electron configuration of Al³+ (Z = 13)? Which noble gas does it match?
4.3 Explain why Group 14 elements (such as carbon and silicon) typically form covalent bonds rather than ions.
4.4 What feature of the d-block electron configuration allows transition metals to form compounds that are often coloured?
5. Build a concept map
Draw labelled arrows between the six terms below to show how they connect. Each arrow must carry a linking phrase (e.g. “determines”, “achieves”, “results in”). Aim for at least 6 labelled arrows. 6 marks (1 per valid labelled arrow)
Supplied terms: valence electrons · octet rule · ion charge · group number · noble gas configuration · chemical behaviour.
6. Complete the ion formation table
For each element, write the expected ion formed, its electron configuration, and the noble gas it is isoelectronic with. The first row is completed as an example. 10 marks (1 per blank cell)
| Element (Z) | Group | Ion formed | Ion electron configuration | Isoelectronic noble gas |
|---|---|---|---|---|
| Na (Z = 11) | 1 | Na+ | 1s²2s²2p&sup6; | Ne |
| Mg (Z = 12) | 2 | |||
| Al (Z = 13) | 13 | |||
| S (Z = 16) | 16 | |||
| Cl (Z = 17) | 17 |
Q1 — Term–definition match
1.1 valence electrons • 1.2 octet rule • 1.3 isoelectronic • 1.4 cation • 1.5 anion • 1.6 oxidation state • 1.7 noble gas configuration • 1.8 electron configuration • 1.9 4s electrons • 1.10 variable oxidation state.
Q2 — True / false with correction
2.1 False. Sodium is in Group 1 and has one valence electron. It loses that one electron to form Na+ (not Na²+), achieving the [Ne] noble gas configuration with 10 electrons.
2.2 True. Cl− (Z = 17, gained 1 e− = 18 e−) and Ar (Z = 18, 18 e−) both have the configuration 1s²2s²2p&sup6;3s²3p&sup6;. They are isoelectronic.
2.3 False. When Fe (Z = 26, [Ar]3d&sup6;4s²) forms Fe³+, both 4s electrons are removed first, then one 3d electron. Fe³+ configuration is [Ar]3d&sup5;, not [Ar]3d³4s².
2.4 True.
2.5 False. Anions are larger than the neutral atom, not smaller. Gaining electrons adds electron–electron repulsion, expanding the electron cloud. The nuclear charge is unchanged but now attracts more electrons, so the effective pull per electron is weaker, increasing the radius.
2.6 False. Carbon (Group 14) has four valence electrons and typically forms covalent bonds by sharing all four electrons, not ionic C&sup4;+ ions. The energy required to remove four electrons (cumulative ionisation energies) is enormous and would never be compensated by lattice energy under normal conditions.
Q3 — Cloze paragraph
In order: valence / noble gas / octet / cation / anion / isoelectronic / group / 4s.
Q4.1 — Why Group 17 forms 1− ions
Group 17 elements have seven valence electrons (ns²np&sup5;) and are only one electron away from a full octet. Gaining one electron to reach ns²np&sup6; (noble gas configuration) requires far less energy than removing seven electrons. The energetics strongly favour gain over loss.
Q4.2 — Al³+ configuration
Al (Z = 13): 1s²2s²2p&sup6;3s²3p¹. Losing three valence electrons gives Al³+: 1s²2s²2p&sup6; (10 electrons). This matches the configuration of Ne (Z = 10).
Q4.3 — Why Group 14 prefers covalent bonding
Group 14 elements have four valence electrons — the mid-point between gaining four and losing four. Removing four electrons (huge cumulative ionisation energy) or gaining four (enormous electron affinity energy) would both be energetically prohibitive. Sharing four electrons in covalent bonds provides stability at a much lower energy cost.
Q4.4 — Colour from partial d-filling
Transition metal compounds are coloured because a partially filled d subshell allows electrons to absorb specific wavelengths of visible light by jumping between d orbitals of different energy (d–d transitions). The complementary colour to what is absorbed is observed. Compounds with fully filled d¹&sup0; (e.g. Zn²+) or empty d&sup0; (e.g. Sc³+) subshells are colourless because no d–d transitions are possible.
Q5 — Sample concept map
Correct maps should include arrows such as:
- group number — determines → valence electrons
- valence electrons — determines → chemical behaviour
- valence electrons — number lost/gained to satisfy → octet rule
- octet rule — drives atoms toward → noble gas configuration
- ion charge — equals electrons lost/gained to reach → noble gas configuration
- valence electrons — sets → ion charge
Award 1 mark per valid labelled arrow (minimum 6, maximum 6 marked).
Q6 — Ion formation table
Mg (Z = 12): Mg²+ | 1s²2s²2p&sup6; | Ne. Al (Z = 13): Al³+ | 1s²2s²2p&sup6; | Ne. S (Z = 16): S²− | 1s²2s²2p&sup6;3s²3p&sup6; | Ar. Cl (Z = 17): Cl− | 1s²2s²2p&sup6;3s²3p&sup6; | Ar.