1.4Unit 1. Structure, Bonding and Introduction to Organic Chemistry
Electrons and ions: predicting chemical behaviour — IAL Edexcel Linear (Chemistry) Revision Notes & Topical Questions
5 min read 9 parts Lesson 5 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.
Lesson summary
1.4 Electrons and ions: predicting chemical behaviour — IAL EDEXCEL LINEAR (CHEMISTRY) notes: Write electron configurations of atoms and ions and use them, with periodic position, to predict bonding, ion formation and the low reactivity of noble gases.Atomic number — the number o…
- Full configuration
- Shorthand configuration
- Exceptions
- Degenerate orbitals
- Atomic number — the number of protons, which equals the number of electrons in a neutral atom
- Blocks are named by the subshell holding the outermost electron: s, p, d or f
Part 1 of 7Blocks, shells and subshell energies
Atomic number
- Atomic number the number of protons, which equals the number of electrons in a neutral atom.
Blocks are named by the subshell holding the outermost electron: s, p, d or f.
Energy order
- Shell energy rises with the principal quantum number (n = 4 is above n = 2).
- Subshell energy rises s < p < d < f.
- Exception3d is slightly higher than 4s, so 4s fills before 3d.
Orbitals in one subshell have the same energy (degenerate), e.g. px, py and pz.
Subshells are filled in order of increasing energy.
Part 2 of 7Writing configurations of atoms
Full configuration
- Full configuration lists every subshell from 1s upwards.
- Potassium (19 electrons) is 1s2 2s2 2p6 3s2 3p6 4s1.
Shorthand configuration
- Shorthand configuration uses the nearest preceding noble gas in square brackets.
- Argon accounts for 18 electrons, so potassium is [Ar] 4s1.
Calcium is [Ar] 4s2.
Gallium (31 electrons) is [Ar] 3d10 4s2 4p1, with 3d written before 4s in numerical order.
Part 3 of 7Writing configurations of ions
Positive ions form by removing electrons from the outer subshell; negative ions form by adding electrons to it.
Transition metals fill 4s before 3d but lose their 4s electrons first.
Ca2+ is 1s2 2s2 2p6 3s2 3p6, identical to argon.
Exceptions
- Exceptions a half-filled or full 3d subshell is more stable.
- Cr is [Ar] 3d5 4s1, not 3d4 4s2.
- Cu is [Ar] 3d10 4s1, not 3d9 4s2.
Part 4 of 7Orbital box notation
1
Each box represents one orbital, boxes are ordered by increasing energy and arrows show electron spin.
2
Electrons occupy separate orbitals of a subshell first, all with the same spin direction, to minimise repulsion.
3
Three p electrons occupy px, py and pz one each.
4
A fourth p electron pairs up in px with opposite spin.
5
Electrons pair only when no empty orbital remains in the subshell, and then with opposite spins.
Part 5 of 7Using configuration to predict chemical behaviour
1
How an element reacts with other elements is determined mainly by the electronic configuration of its atoms.
2
The Periodic Table is arranged in periods and groups.
- Elements in the same period have the same number of shells.
- Elements in the same group have the same number of outer electrons, so they react similarly.
3
Trends in chemical and physical properties across periods and down groups can be explained by atomic number and electron arrangement.
4
Reactions involve losing, gaining or sharing outer electrons,
- so position in the Periodic Table and the occupied subshells predict the ions formed and the bonding.
Part 6 of 7Noble gases
Noble gases
Helium, neon and argon have full outer shells (subshells) and high ionisation energies.
This electron arrangement is very stable, so they have little tendency to gain, lose or share electrons.
As a result they rarely react with other substances.
Part 7 of 7More from the specification
Quantized electronic excitation energy levels
- Quantized electronic excitation energy levels absorbing discrete photons promotes electrons to excited states across strictly quantized molecular orbital energy levels.
First Ionisation Energy
- The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of singly charged gaseous positive ions (X(g) → X⁺(g) + e⁻).
Successive Ionisation Energies
- Each successive ionisation requires more energy as electrons are removed from increasingly positive ions with stronger electrostatic attraction to the nucleus.
Identifying Valence Electrons and Shell Structure
- A huge jump in successive ionisation energies occurs after all valence electrons are removed, indicating the next electron comes from an inner principal shell closer to the nucleus.
Spin-Pair Repulsion and Orbital Shape
- Electrons in the same p orbital experience electrostatic spin-pair repulsion,
- making it easier to remove one paired valence electron than an unpaired electron in an equivalent orbital shape.
First Ionisation Energy
- The energy required to remove one mole of electrons from one mole of gaseous atoms to form one mole of singly charged gaseous positive ions (X(g) → X⁺(g) + e⁻).
Successive Ionisation Energies
- Each successive ionisation requires more energy as electrons are removed from increasingly positive ions with stronger electrostatic attraction to the nucleus.
Identifying Valence Electrons and Shell Structure
- A huge jump in successive ionisation energies occurs after all valence electrons are removed, indicating the next electron comes from an inner principal shell closer to the nucleus.
Spin-Pair Repulsion and Orbital Shape
- Electrons in the same p orbital experience electrostatic spin-pair repulsion,
- making it easier to remove one paired valence electron than an unpaired electron in an equivalent orbital shape.
Nucleus
- Central part of an atom with protons and neutrons.
Valence electron
- An electron in the outermost shell of an atom.
Spin-pair repulsion
- Repulsion between two electrons paired in one orbital, making one easier to remove.
Energy level
- A main shell of fixed energy labelled by principal quantum number n.
Key terms
| Term | Meaning |
|---|---|
| Subshell | A group of orbitals of one type (s, p, d or f) within a shell. |
| Degenerate orbitals | Orbitals in the same subshell with equal energy. |
| Shorthand configuration | A configuration written with the preceding noble-gas symbol in square brackets. |
| Noble gas | A Group 0 element with a full outer shell and very low reactivity. |
| Block | A region of the Periodic Table named for the subshell of the outermost electron. |
Avoid these mistakes
1
Filling 3d before 4s — 4s fills first.
2
Removing 3d electrons first when forming transition-metal ions — 4s electrons are lost first.
3
Writing Cr as [Ar] 3d4 4s2 or Cu as [Ar] 3d9 4s2 — they are [Ar] 3d5 4s1 and [Ar] 3d10 4s1.
4
Pairing electrons in a p subshell before each orbital has one electron — fill singly first.
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