How do particles in matter change when a substance becomes hotter, cool down, or changes state?

When heat is added to a substance, the molecules and atoms vibrate faster. As atoms vibrate faster, the space between atoms increases. The motion and spacing of the particles determines the state of matter of the substance. The end result of increased molecular motion is that the object expands and takes up more space.

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radioactive decay occurs in unstable atomic nuclei – that is, ones that don't have enough binding energy to hold

the nucleus together due to an excess of either protons or neutrons.

metric time was an attempt to create a standard unit of time based off of 10, but it never took off an is not included in the metric system (si)