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1cPrinciples of Chemistry

Atomic structure — Edexcel Modular - OL (Chemistry) Revision Notes & Topical Questions

5 min read 7 parts Lesson 3 of 9 2 quizzes

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Lesson summary

Atomic structure Edexcel O Level Modular Chemistry notes: know what is meant by the terms atom and moleculeCr is [Ar]3d⁵4s¹ and Cu is [Ar]3d¹⁰4s¹.Successive IEs show big jumps when a new shell is entered.Isotopes have the same chemical properties but different physical properties…

  • Atomic structure Edexcel O Level Modular Chemistry: what to do next
  • Ionisation energy
  • Electron configuration
  • Give / State / Name
  • Evaluate / Assess
  • Keywords the mark scheme looks for in this lesson

Part 1 of 6Key ideas

Key ideas
Cr is [Ar]3d⁵4s¹ and Cu is [Ar]3d¹⁰4s¹.
Successive IEs show big jumps when a new shell is entered.
Isotopes have the same chemical properties but different physical properties.

Part 2 of 6Syllabus points

Syllabus points
know what is meant by the terms atom and molecule
know the structure of an atom in terms of the positions, relative masses and relative charges of sub-atomic particles
know what is meant by the terms atomic number, mass number, isotopes and relative atomic mass (Ar) be able to calculate the relative atomic mass of an element (Ar) from isotopic abundances

Part 3 of 6Process & sequence

  • 1s
  • 2s
  • 2p
  • 3s
  • 3p
  • 4s
  • 3d
  • 4p
1
First IE: remove outer electron from gaseous atom.
2
Across a period: IE increases (more protons, same shielding).
3
Down a group: IE decreases (bigger radius, more shielding).
4
Dips: Group 2→3 (p electron higher energy), Group 5→6 (paired p electrons repel).

Part 4 of 6Summary

Summary
Across a period first IE generally increases.
An orbital holds 2 electrons.

Part 5 of 6Keep going

Atomic structure Edexcel O Level Modular Chemistry: what to do next

These Atomic structure Edexcel O Level Modular Chemistry notes covered the key ideas, worked examples and exam technique for this topic. Check your Atomic structure Edexcel O Level Modular Chemistry understanding with the practice questions below, then reread any Atomic structure Edexcel O Level Modular Chemistry point you were unsure about before moving on.

1
Practice: Atomic structure Edexcel O Level Modular Chemistry practice questions
2
Previous lesson: 1b Elements, compounds and mixtures — Notes
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Next lesson: 1d The Periodic Table — Notes
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Course: Edexcel Modular – OL (chemistry) — all units
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Official syllabus: Pearson Edexcel International GCSEs

Atomic structure Edexcel O Level Modular Chemistry revision notes

Part 6 of 6Compare: Compare

Subatomic particles and subshells
Particle / subshellRelative mass / capacityCharge / orbitalsLocation / shapeBehaviour in electric fieldNote
Proton1+1NucleusDeflected to − plate (small angle)Defines element
Neutron10NucleusNot deflectedIsotopes differ
Electron1/1836−1OrbitalsDeflected to + plate (large angle)Chemistry depends on them
s subshell2 electrons1 orbitalSpherical—Filled first in each shell
p subshell6 electrons3 orbitalsDumb-bell—px, py, pz
d subshell10 electrons5 orbitals——4s fills before 3d; 4s empties first

Key terms

Command terms

Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.

Exam technique

Keywords the mark scheme looks for in this lesson

Keywords the mark scheme looks for in this lesson
Proton · Neutron · Electron · Isotopes · Orbital · Ionisation energy · Electron configuration · Shielding
Learn each definition in the Key words tab exactly; a missing keyword in a definition usually loses the mark.

How to get full marks (examiner guidance)

How to get full marks (examiner guidance)
Use specification keywords exactly (e.g. electronegativity, nucleophile, dynamic equilibrium, activation energy).
Link ideas
Link ideas for “explain” each marking point is usually a cause → consequence step; unlinked facts often score nothing.
Use the information in the question
“discuss/evaluate” answers must use the data provided and match the number of marks.
Convert units carefully (mg → g, cm³ → dm³) and show working for calculations.
Avoid vague words
“it”, “stuff”, “things”, “goes up”, “energy is made”. Name the substance and the process.
Do not extrapolate a graph line beyond the data or to zero unless asked.
Six-mark extended responses are marked on content AND a logical, linked line of reasoning.

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