Atoms

Atoms

Atoms are incredibly small
1. They have a radius of 0.1 nanometers (1*10^-10m)
2. A 50p piece contains about 77,400,000,000,000,000,000,000 of them
All substances are made of atoms
Parts of an atom
1. Electrons
  1. Move around the nucleus in electron cells
  2. Negatively charged and tiny, but cover a lot of space
  3. Volume of orbit determines size of atom
  4. Have virtually no mass
  5. Relative mass: Very small Charge: -1
2. Nucleus
  1. Protons
    1. Positively charged and heavy
    2. Relative mass: 1 Charge = +1
  2. Neutrons
    1. Relative mass: 1 Charge = 0
    2. Neutral charge and heavy
  3. In the middle of the atom
  4. Contains protons and neutrons
  5. Has a radius of around 1*10^-14m (about 1/10,000 of the radius of an atom
  6. Postive charge because of the protons
  7. Almost all the mass of the atom is concentrated in the nucleus
Number of protons = number of electrons
1. Atoms have no positive charge overall and are neutral (unlike ions)
  1. Because they have the same number of protons and electrons
  2. Charge on electrons is even to charge on protons but opposite, so they cancel out
2. In an ion, number of protons doesn't equal the number of electrons, resulting in an overall charge
  1. For example: an ion with a -2 charge has two more electrons than protons
Atomic number and mass number describe an atom
1. Nuclear symbol tells you the atomic (proton) number and mass number
2. Atomic number (bottom): How many protons there are
3. Mass number (top): Total number of protons and neutrons in the atom
4. To get the number of neutrons, just subtract the atomic number from the mass number

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