Inside the Atom
Take an atom apart. Meet its three particles and their charges, count them with atomic and mass numbers, sort out isotopes, and follow how the model of the atom was rebuilt as evidence arrived.
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Take an atom apart
Everything around you is made of atoms, and every atom is built from three subatomic particles. Protons and neutrons sit in a tiny central nucleus, and electrons move around it in shells. The nucleus holds almost all the mass, but the atom is mostly empty space.
Label the atom
Drag each label onto the right part of the atom: the red particle and the grey particle in the centre, the small particle on the ring, and the ring itself.
Charge and mass
Each subatomic particle has a relative charge and a relative mass.
Match each particle
- Proton
- Neutron
- Electron
- Charge +1 and a relative mass of 1
- Charge 0 and a relative mass of 1
- Charge -1 and almost no mass
The uncharged one
Which subatomic particle has no electric charge?
- The neutron
- The proton
- The electron
- The nucleus
Two numbers that count
Two numbers describe an atom. The atomic number is the number of protons, and it decides which element the atom is. The mass number is the number of protons plus neutrons. So the number of neutrons = mass number - atomic number. In a neutral atom, the number of electrons equals the number of protons.
How many neutrons?
An atom of sodium has a mass number of 23 and an atomic number of 11. How many neutrons does it have? Subtract the atomic number from the mass number.
What makes an element?
What decides which element an atom is?
- Its number of protons, the atomic number
- Its number of neutrons
- Its number of electrons
- Its mass number
The words that count
Four ideas run through the rest of this module:
True of isotopes
Select the TWO statements that are true of isotopes of the same element.
- They have the same number of protons
- They have different numbers of neutrons
- They have different numbers of protons
- They are completely different elements
Match each model
- Dalton
- Thomson
- Rutherford
- Bohr
- Atoms are tiny solid spheres
- A ball of positive charge with electrons dotted through it
- A small, dense, positive nucleus in mostly empty space
- Electrons orbit the nucleus in fixed shells
Order the models
Put the models of the atom in the order they were proposed, earliest first.
- Dalton: a solid sphere
- Thomson: the plum-pudding model
- Rutherford: the nuclear atom
- Bohr: electrons in shells
Atoms and isotopes
Tap the TWO statements that are TRUE.
- The atomic number is the number of protons, and it defines the element.
- Isotopes of an element have the same protons but different neutrons.
- An electron has a charge of +1.
- The mass number is the number of protons minus the neutrons.
- Most of the space in an atom is taken up by the nucleus.
Read the evidence
Rutherford fired positive alpha particles at thin gold foil. Interpret each result. Choose each time.
- Most of the alpha particles passed straight through the foil. What does that suggest?
- A few alpha particles were deflected straight back the way they came. What does that suggest?
- Which older model did this experiment disprove?
How the model changed
Explain how the alpha-scattering experiment changed the model of the atom, from the plum-pudding model to the nuclear model.
- Describe the plum-pudding model
- State what most alpha particles did and what that showed
- State what a few alpha particles did and what that showed
- Explain what the new nuclear model looked like