Build Your First Atom

Why it matters

Imagine zooming into a speck of dust until it looks like a solar system. You will find a tiny, heavy sun surrounded by a vast, empty space where electrons race.

Predict first

If an atom is mostly empty space, why does a solid wall feel hard and solid to your hand?

The 'solidity' comes from electromagnetic repulsion between electron clouds, not physical contact of solid spheres.

• The atoms are packed so tightly there is no space between them
• The electron clouds repel each other strongly when pushed close — correct
• The nucleus is large and blocks the path
• Gravity holds the atoms together rigidly

What you do

Build a neutral carbon-12 atom — drag in 6 protons and 6 neutrons, then place 6 electrons in the shells.

Check yourself

In the atom builder, if you add one more proton to the nucleus without adding an electron, what happens to the atom?

The number of protons (atomic number) defines the element. Carbon (6p) becomes Nitrogen (7p).

Where is most of the atom's mass located?

Protons and neutrons in the nucleus are ~1836 times heavier than electrons, concentrating almost all mass in the center.

• It becomes a different element — correct
• It becomes a heavier isotope
• It becomes a negative ion
• It becomes unstable and explodes
• Evenly distributed throughout the electron cloud
• In the tiny, dense nucleus — correct
• In the electrons orbiting the nucleus
• There is no mass, only energy