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1.1Structure of Matter

Atomic structure — EST 2 Chemistry Revision Notes & Topical Questions

5 min read 8 parts Lesson 1 of 5 1 quiz

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Lesson summary

Atomic structure EST Chemistry notes: Describe subatomic particles.Average atomic mass is weighted by isotope abundance.Ions form when atoms gain or lose electrons; the proton number never changes.Emission spectra show electrons dropping between energy levels.Higher frequency lig…

  • Higher frequency light has higher energy
  • Noble-gas shorthand
  • Wavelength and frequency are inversely related
  • Chlorine is 75% Cl-35 and 25% Cl-37. Find the average atomic mass
  • Write the configuration of sulfur (Z = 16)
  • Atomic structure EST Chemistry: what to do next

Part 1 of 8Key ideas

Key ideas
Average atomic mass is weighted by isotope abundance.
Ions form when atoms gain or lose electrons; the proton number never changes.
Emission spectra show electrons dropping between energy levels.
Higher frequency light has higher energy
E = hν.
Rutherford's gold-foil experiment showed a small, dense, positive nucleus.

Part 2 of 8Learning objectives

Learning objectives
Describe subatomic particles.
Calculate average atomic mass.
Write electron configurations.

Part 3 of 8Essential knowledge

Essential knowledge
Cu and Cr are common configuration exceptions.
Noble-gas shorthand
Na = [Ne]3s1.
Cations lose the highest-n electrons first (4s before 3d).
Wavelength and frequency are inversely related
Wavelength and frequency are inversely related c = λν.
Thomson discovered the electron using cathode rays.

Part 4 of 8Process & sequence

1
Atomic number gives the number of protons.
2
In a neutral atom, electrons = protons.
3
Neutrons = mass number − atomic number.
4
Fill orbitals in order 1s 2s 2p 3s 3p 4s 3d 4p.
5
The outermost (valence) electrons control chemical behaviour.

Building an atomwrite these steps in this order; each step is a marking point.

1
Protons fix identity
2
Neutrons add mass
3
Electrons balance charge
4
Fill lowest orbitals
5
Valence electrons react

Part 5 of 8Worked examples

1Chlorine is 75% Cl-35 and 25% Cl-37. Find the average atomic mass.
  • 0.75 × 35 + 0.25 × 37 = 35.5.
2Write the configuration of sulfur (Z
16).
  • 1s2 2s2 2p6 3s2 3p4.

Part 6 of 8Summary

Summary
Z = protons; A = protons + neutrons.
Isotopes differ in neutrons.
Fill orbitals by Aufbau, Hund, Pauli.

Part 7 of 8Keep going

Atomic structure EST Chemistry: what to do next

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

1
Practice: Atomic structure EST Chemistry practice questions
2
Next lesson: 1.2 The periodic table
3
Course: EST 2 Chemistry — all units
4
Official syllabus: OpenStax free science textbooks

Atomic structure EST Chemistry revision notes

Part 8 of 8Compare: Compare

Subatomic particles
ParticleChargeRelative massLocation
Proton+11Nucleus
Neutron01Nucleus
Electron−11/1840Orbitals
Sublevel capacity
SublevelOrbitalsMax electrons
s12
p36
d510
f714

Key terms

Command terms

Command terms
Identify / Describe (FRQ)
A short, specific statement; describing requires relevant characteristics, not a single word.
Explain / Justify (FRQ)
Give the cause-and-effect reasoning or evidence; a restated fact does not score.
Calculate
Show setup, substitution and the answer with units.
Predict
State the expected outcome; add a reason only if asked to justify.
MCQ technique
Read every option; eliminate distractors that are true statements but do not answer the question; watch for NOT/EXCEPT.

Exam technique

Keywords the mark scheme looks for in this lesson

Keywords the mark scheme looks for in this lesson
Proton · Neutron · Electron · Mass number (A) · Isotopes · Orbital · Aufbau principle · Hund's rule · Pauli exclusion principle
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)

1
Answer exactly what is asked; extra correct material does not earn credit, and contradictory statements can cancel credit (AP FRQ).
2
Use precise vocabulary (e.g. “active site”, “concentration gradient”, “allele”), never “it/stuff/things”.
3
Show units and working in calculations.
4
In MCQs, predict the answer before reading the options, then eliminate.

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