Structure Of The Atom

Nucleus & Shells

• An atom has a central Nucleus. This is surrounded by Electrons arranged in shells.
• The Nucleus is tiny compared to the atom as a whole:
• The radius of an atom is about 0.1nm (1 × 10-10 m)
• The radius of a nucleus (1 × 10-14 m) is less than 1/10,000 of the radius of an atom
• For comparison, the radius of a typical bacterium is 1 × 10-6 m and the radius of a human hair is about 1 × 10-4 m.For comparison, the radius of a typical bacterium is 1 × 10-6 m and the radius of a human hair is about 1 × 10-4 m.

Subatomic Particles

• The nuclei of all atoms contain subatomic particles called Protons. The nuclei of most atoms also contain Neutrons.
• The masses of subatomic particles are very tiny. Instead of writing their actual masses in kilograms, we often use their relative masses. The relative mass of a proton is 1, and a particle with a relative mass smaller than 1 has less mass.
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• Caption: The Structure Of A Carbon Atom (Not Drawn To Scale).

Subatomic Particles

• The masses of subatomic particles are very tiny. Instead of writing their actual masses in kilograms, we often use their relative masses. The relative mass of a proton is 1, and a particle with a relative mass smaller than 1 has less mass.
• The mass of an electron is very small compared to a proton or a neutron. Since the nucleus contains protons and neutrons, most of the mass of an atom is concentrated in its nucleus.
• Protons and electrons have electrical charges that are equal and opposite.
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• Caption: Key Fact: Remember that Protons are Positive, and Neutrons are Neutral.