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Chemistry · 1. Particles, atoms and the Periodic Table

Particle model, atoms and ions

Build from particles to electrons, ions and spectral evidence.

40 minutesContent version: 2.1
Start the interactive pathwayOpen the virtual experiment

Driving question

How do observable properties connect to invisible particle structure?

Curriculum coverage

Vietnam science/Chemistry 10; IGCSE states of matter, atoms, elements and compounds.

Model scope and limitations

The shell model is for school-level reasoning; flame colour is a screening test, not unique identification for every ion.

Learning objectives

  • Describe atoms using protons, neutrons and electrons.
  • Infer ion charge from proton and electron counts.
  • Distinguish elements, compounds and mixtures.

Prerequisite knowledge

  • Positive, negative and neutral charge.
  • Basic chemical symbols.

Core knowledge

Atomic number

Z equals proton number; a neutral atom has Z electrons.

Ions

Electron loss forms cations; gain forms anions. The nucleus does not change in chemical reactions.

Flame colour

Excited electrons emit characteristic photons as they fall to lower energy levels.

Worked example

Mg has 12 protons and Mg²⁺ has 10 electrons: 12 positive and 10 negative charges give +2 overall.

Misconceptions to avoid

  • A positive ion forms by losing electrons, not by gaining protons.
  • Mixtures do not have fixed atomic ratios like compounds.

Virtual experiment procedure: Flame tests

  1. Test one metal ion at a time using the same sampling method.
  2. Record the observed colour, then compare with a reference table.
  3. Test an unknown and state confidence and possible interference.

Safety and cautions

  • Real work requires eye protection, clean loops and teacher-controlled flames; use only approved low-hazard salts.

Evidence to collect

  • A table of ion, observed colour, reference colour and unknown conclusion.
Open the virtual experiment

Diagnostic check

1. Atomic number gives the number of which particle?

  1. Protons
  2. Neutrons
  3. All particles
Show answer and explanation

Correct answer: Protons

An element is defined by its proton number.

2. A chlorine atom gains one electron. Which ion forms?

  1. Cl⁻
  2. Cl⁺
  3. Cl²⁺
Show answer and explanation

Correct answer: Cl⁻

Gaining one negative charge gives −1 overall.

3. What is air?

  1. A mixture
  2. An element
  3. A pure compound
Show answer and explanation

Correct answer: A mixture

Air gases are not chemically combined in a fixed ratio.

Application practice

1. An ion has 13 protons and 10 electrons. Its charge is?

  1. 3+
  2. 3−
  3. 0
Show answer and explanation

Correct answer: 3+

13 − 10 = +3.

2. Isotopes of one element differ mainly in which number?

  1. Neutrons
  2. Protons
  3. Nuclear charge
Show answer and explanation

Correct answer: Neutrons

They share proton number but differ in neutrons.

3. Why clean the flame-test loop between samples?

  1. Avoid ion contamination
  2. Make ions heavier
  3. Increase proton number
Show answer and explanation

Correct answer: Avoid ion contamination

A trace of the previous ion can dominate the next colour.

Academic references

  1. OpenStax Chemistry 2e — peer-reviewed general chemistry
  2. IUPAC Gold Book — authoritative chemical terminology
  3. BIPM — SI Brochure, 9th edition

This lesson is maintained against the cited sources below. Simulations are learning models and do not replace supervised physical-laboratory safety procedures.

Content publisher
WebLab STEM
Technical maintainer
Đức Tiến — Control & Automation Engineer