Atomic Structure
10th Grade Science · 8 lessons
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Lessons in this unit
- 1Protons, Neutrons and ElectronsAn atom has a tiny dense nucleus of protons and neutrons, surrounded by electrons. Protons carry +1 charge, electrons −1, and neutrons none. Almost all the mass sits in the nucleus, while almost all the volume is the electron cloud.Experiment
- 2Atomic Number, Mass Number and IsotopesThe atomic number is the proton count and fixes which element an atom is. The mass number is protons plus neutrons. Isotopes are atoms of the same element with different neutron counts — chlorine-35 and chlorine-37 behave identically in reactions.Lesson
- 3Electron Shells and ConfigurationElectrons occupy shells of increasing energy, holding up to 2, 8 and 8 for the first three. The outermost electrons — the valence electrons — decide chemical behaviour: a full valence shell means an unreactive noble gas, and one electron short or over means high reactivity.Experiment
- 4How the Periodic Table Is OrganisedElements are ordered by increasing atomic number. A group is a column sharing outer-shell electron count and therefore similar reactions; a period is a row across which one shell fills. Mendeleev's power was leaving gaps for elements not yet found.Lesson
- 5Group 1: the Alkali MetalsGroup 1 metals have one outer electron, which they lose readily to form +1 ions. They are soft, low-density and stored under oil. Reactivity increases down the group because the outer electron sits further from the nucleus and is lost more easily.Experiment
- 6Group 7: the HalogensHalogens have seven outer electrons and gain one to form −1 ions. Down the group they get darker and less reactive, because the incoming electron is added further from the nucleus. A more reactive halogen displaces a less reactive one from its salt.Experiment
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