Inside an Atom

In the picture

1. 1The dense central clump: the nucleus, made of protons and neutrons.
2. 2The blue sphere on the inner hoop: an electron in the shell nearest the nucleus.
3. 3The silver band of the outer hoop: a shell, a fixed distance and energy level an electron can occupy.
4. 4The blue sphere on the outer hoop: an electron further out, carrying more energy.

Examples

• A helium party balloon: each helium atom has two electrons filling its single shell, so the gas hardly reacts with anything.
• Copper wire: copper’s outermost electrons are held loosely, so they drift through the metal and carry the current.

Quiz: Inside an Atom (Age 15)

1. 1

   Compared with the atom as a whole, what is the nucleus like?

   • It holds almost all of the atom’s mass in a tiny part of its volume.
   • It holds about half of the atom’s mass and takes up about half of its volume.
   • It holds very little mass but fills most of the atom’s volume.
2. 2

   An atom’s electrons fill its shells in a set order. Which shell fills first?

   • The shell furthest from the nucleus.
   • Electrons spread out evenly, one into each shell in turn.
   • The shell closest to the nucleus.
3. 3

   An atom has one electron in an inner shell and one in an outer shell. Which electron has more energy?

   • The inner electron, because it is held closer to the nucleus.
   • The outer electron, because shells further out are higher energy levels.
   • Neither: every electron in an atom carries the same energy.

The answers, each with its explanation, are in the app. This lesson has left the free week, so its quiz is part of the subscription.