1.4.4Unit 1. Structure, Bonding and Introduction to Organic Chemistry
Electronic Configurations and Chemical Properties — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions
5 min read 6 parts Lesson 14 of 36 Unit quiz
Curriculum Equation Key معادلة تفاعل تكوين الإستر (الأسترة) - Esterification Reaction EquationFast Exam Solution
R-COOH + R2-OH ⇌ (conc. H₂SO₄) R-COO-R2 + H₂O
Word Equation & Conditions: حمض كربوكسيلي + كحول (في وجود حمض الكبريتيك المركز كعامل حفاز ونازع للماء) ⇌ إستر + ماء
Location & Specifications: الكيمياء العضوية للثانوية العامة والتحصيلي و Edexcel Chemistry.
Section 1 of 6Ionisation Energy as Evidence
Ionisation energy data give direct experimental evidence for how electrons are arranged in shells.
First ionisation energy
- First ionisation energy The energy needed to remove one mole of electrons from one mole of gaseous atoms,
- giving one mole of gaseous 1+ ions, measured in kJ mol⁻¹.
Equation for IE₁
- Equation for IE₁ Write it with state symbols, for example Ca(g) → Ca⁺(g) + e⁻, and the enthalpy change is always endothermic and positive.
Successive ionisation energies
- Successive ionisation energies Each further electron removed is harder to take away because the remaining electrons feel the same nuclear charge with less repulsion.
Large jumps
- Large jumps A sudden big rise between two successive values shows that the next electron comes from an inner shell closer to the nucleus.
Factors affecting IE
- Factors affecting IE Nuclear charge, the distance of the outer electron from the nucleus and shielding by inner electrons all control how large the value is.
Section 2 of 6Shells, Subshells and Orbitals
Shells, Subshells and Orbitals
Shells
- Shells Principal quantum shells numbered 1, 2, 3 and so on hold up to 2n² electrons, so the third shell holds a maximum of eighteen.
s subshell
- s subshell One orbital that is spherical in shape, holding a maximum of two electrons, and present in every shell.
p subshell
- p subshell Three dumbbell-shaped orbitals lying along the x, y and z axes at right angles, holding up to six electrons in total.
d subshell
- d subshell Five orbitals holding up to ten electrons, first appearing in the third shell and filled after 4s in the fourth period.
Orbital rule
- Orbital rule An orbital is a region of space holding at most two electrons, and these two must have opposite spins.
Section 3 of 6Building a Configuration
1
Fill subshells in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, noting that 4s fills before 3d.
2
Place electrons singly into each orbital of a subshell first, with parallel spins, and only then pair them up.
3
Write the result with superscripts for electron numbers, for example sulfur is 1s² 2s² 2p⁶ 3s² 3p⁴, or [Ne] 3s² 3p⁴.
4
Treat chromium and copper as special cases: Cr is [Ar] 3d⁵ 4s¹ and Cu is [Ar] 3d¹⁰ 4s¹ because half-full and full 3d are more stable.
5
To form positive ions remove electrons from the 4s subshell first, so Fe²⁺ is [Ar] 3d⁶ and not [Ar] 3d⁴ 4s².
6
To form negative ions add electrons into the next available orbital, so Cl⁻ is 1s² 2s² 2p⁶ 3s² 3p⁶.
Section 4 of 6Configuration and Chemical Behaviour
Configuration and Chemical Behaviour
Blocks
- Blocks Elements are labelled s, p or d block according to the subshell that holds their highest-energy electron.
Group number link
- Group number link For s and p block elements the group number tells you how many outer shell electrons are present,
- which fixes the ion usually formed.
Metals
- Metals Atoms with few outer electrons, such as Na and Mg, lose them easily to form positive ions with a noble gas configuration.
Non-metals
- Non-metals Atoms with nearly full outer shells, such as O and Cl, gain electrons to form negative ions with a noble gas configuration.
d block
- d block Transition elements lose 4s electrons first and can form ions of different charges, giving variable oxidation states.
| Species | Electronic configuration |
|---|---|
| Mg | 1s² 2s² 2p⁶ 3s² |
| Mg²⁺ | 1s² 2s² 2p⁶ |
| Fe | [Ar] 3d⁶ 4s² |
| Fe³⁺ | [Ar] 3d⁵ |
Section 5 of 6Worked Example
Question Write the electronic configuration of an iron atom and of an Fe³⁺ ion.
- Iron has atomic number 26, so the atom has 26 electrons.
- Fill in order1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁶, which totals 26.
- Fe³⁺ has 23 electrons, so remove the two 4s electrons first and then one 3d electron.
Answer Fe is [Ar] 3d⁶ 4s² and Fe³⁺ is [Ar] 3d⁵.
Section 6 of 6Exam Checklist & Tips
1.4.4 – Key Points for the Exam
- Ionisation energy The energy required to remove one mole of electrons from one mole of gaseous atoms or ions.
- Orbital A region of space around the nucleus that can hold a maximum of two electrons with opposite spins.
- Subshell A group of orbitals of the same type within a shell, labelled s, p, d or f.
- Shielding The repulsion of outer electrons by inner-shell electrons, which reduces the pull felt from the nucleus.
- Block The region of the Periodic Table named for the subshell receiving the last electron.
Common Mistakes
- Removing 3d electrons before 4s when making transition metal ions; the 4s electrons leave first.
- Writing Cr as [Ar] 3d⁴ 4s² or Cu as [Ar] 3d⁹ 4s²; both are exceptions with an extra 3d electron.
- Leaving out state symbols or the minus charge on the electron in an ionisation energy equation.
- Saying an orbital and a shell are the same; a shell contains subshells, which contain orbitals.
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