C2 - topic 1

C2 - topic 1

1. ATOMS.

   • STRUCTURE OF THE ATOM.
     • The nucleus - it's in the middle of the atom and it contains protons and neutrons. The nucleus has an overall positive charge because protons are positively charged and neutrons have no charge. Almost the whole mass of the atom is concentrated in the nucleus. However, size wise it is tiny compared to the atom as a whole.
     • The electrons - they move around the nucleus and they have a negative charge (electrons and protons have equal but opposite charges). They are tiny compared to the nucleus but as they move around, they cover a lot of space. The size of their orbit determines hwo big they are and they have virtually no mass. They occupy shells (energy levels) around the nucleus.
     • NUMBER OF PROTONS = NUMBER OF ELECTRONS.
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