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In an atom, a cloud of electrons surround a central nucleus. The electrons carry a negative electric charge. The nucleus is positively charged as it contains a mixture of positively charged protons and neutral neutrons. The arrangement of electron shells in a chlorine atom is revealed.
This clip is from:
First broadcast:
20 March 2008

Classroom Ideas

Introduce students to the three subatomic particles, each with a specific charge, mass and position within the atom. As they watch the clip, students should note down the differences between protons, neutrons and electrons.
Consolidate understanding of the link between the number of protons and the atomic number, between protons and neutrons and the mass number and the balance of protons and electrons that results in atoms being neutral. Students could use beads, sweets, balls or themselves to build models of the positions of particles in the atoms of different elements.
Discuss the link between reactivity and valency and get students to explore how reactivity relates to the period and group an element is in.