IB Chemistry - Atomic Theory

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Syllabus ref: 2.1

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.

Nature of science:

Evidence and improvements in instrumentation - alpha particles were used in the development of the nuclear model of the atom that was first proposed by Rutherford.

Paradigm shifts - the subatomic particle theory of matter represents a paradigm shift in science that occurred in the late 1800s


Atoms contain a positively charged dense nucleus composed of protons and neutrons (nucleons).

Negatively charged electrons occupy the space outside the nucleus.

The mass spectrometer is used to determine the relative atomic mass of an element from its isotopic composition.

Applications and skills

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

Calculations involving non-integer relative atomic masses and abundance of isotopes from given data, including mass spectra.

In Chapter 1.1