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2.4.3Atoms, Elements and Compounds

Electric Charge — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 25 of 26 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Part 1 of 5Charge in Atoms

2.4.3 Electric Charge

Every atom is made of charged and uncharged particles, and a neutral atom has no overall charge.

Electron
  • A negatively charged particle, and the only particle that moves when objects are charged by friction.
Proton
  • A positively charged particle in the nucleus that balances the negative charge of the electrons in a neutral atom.
Neutron
  • A particle in the nucleus with no charge, which adds to the mass of the atom but not to its charge.
Neutral atom
  • An atom has equal numbers of electrons and protons, so the positive and negative charges cancel to give zero.

Part 2 of 5Forces Between Charges

Forces Between Charges
Opposite charges
  • Objects with opposite charges attract each other, so they are pulled closer together.
Like charges
  • Objects with the same charge repel each other, so they are pushed further apart.
Non-contact force
  • Electrostatic attraction and repulsion act across a gap, without the objects needing to touch.
Distance
  • The electrostatic force is stronger when the two charged objects are closer together.
Charge of object 1Charge of object 2Attract or repel?
PositivePositiveRepel
PositiveNegativeAttract
NegativePositiveAttract
NegativeNegativeRepel

Part 3 of 5Gaining and Losing Charge

1
An object becomes negatively charged when it gains electrons from another material during rubbing.
2
The material that loses electrons becomes positively charged, because it now has more protons than electrons.
3
Only electrons move in this process, so the total charge of the pair remains the same before and after rubbing.
4
A gain of negative charge on one object is always matched by an equal loss on the other object.

Part 4 of 5Worked Example

Question

  • A neutral object gains 4 electrons.
  • What is its overall charge, taking the charge of one electron as –1?

  1. Start from a neutral object, which has a charge of 0.
  2. Each gained electron adds –1, so the total change is 4 × (–1) = –4.
  3. Add this to the starting charge0 + (–4) = –4.

Answer The object has an overall charge of –4, so it is negatively charged.

Part 5 of 5Exam Checklist & Tips

2.4.3 – Key Points for the Exam

  • Electron A negatively charged particle that orbits the nucleus and is the only charge that moves in friction charging.
  • Proton A positively charged particle found in the nucleus of an atom.
  • Electrostatic force A non-contact force between charged objects, which attracts unlike charges and repels like charges.
  • Non-contact force A force that acts between objects that are not physically touching.
  • Neutral Having no overall electric charge, because the positive and negative charges are equal.

Common Mistakes

  • Saying a positively charged object has gained protons;
    • it has lost electrons, because protons are fixed in the nucleus.
  • Stating that like charges attract each other; like charges repel.
  • Forgetting that the electrostatic force becomes stronger as the charged objects move closer together.
  • Describing a positive object as having an excess of protons, when it actually has fewer electrons than protons.

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