IB Chemistry - Atomic Theory

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Atoms are the smallest building blocks of matter. There are about 100 naturally occurring types of atom. This chapter explains the ways in which atoms differ from one another.

Syllabus reference

Structure 1.2.1 - Atoms contain a positively charged, dense nucleus composed of protons and neutrons (nucleons). Negatively charged electrons occupy the space outside the nucleus.

  • Use the nuclear symbol ZXA to deduce the number of protons, neutrons and electrons in atoms and ions.


  • Relative masses and charges of the subatomic particles should be known; actual values are given in the data booklet. The mass of the electron can be considered negligible.

Tools and links

  • Structure 1.3 - What determines the different chemical properties of atoms?
  • Structure 3.1 - How does the atomic number relate to the position of an element in the periodic table?

In Chapter 1.1