What Are Atoms?

What do you think would happen if you took a piece of paper and kept cutting it in half over and over again? Could you do that forever? Or would you eventually reach a point where the paper was so tiny that you couldn’t cut it anymore because it wouldn’t really be paper anymore?

Scientists have wondered about that too! Through experiments, they discovered that everything around us is made of super tiny building blocks called atoms. An atom is the smallest piece of a substance that still acts like that substance. For example, one gold atom still has the same properties as a big piece of gold.

Atoms are made of even smaller parts called subatomic particles — protons, neutrons, and electrons.

• Protons have a positive charge.

• Neutrons have no charge (they’re neutral).

• Electrons have a negative charge.

Protons and neutrons are packed tightly together in the center of the atom, called the nucleus. The electrons move around the nucleus in areas called orbitals.

Elements and the Periodic Table

The number of protons in an atom decides what kind of atom it is. All atoms with the same number of protons belong to the same element. For example, every hydrogen atom has 1 proton, and every oxygen atom has 8 protons. The number of protons in an atom is called its atomic number.

A Russian scientist named Dmitri Mendeleev discovered that if you arrange the elements by their number of protons, they form patterns based on their properties. This arrangement is known as the periodic table.

• The rows are called periods.

• The columns are called groups, and elements in the same group have similar chemical properties.

Valence Electrons and Bonding

Electrons are found outside the nucleus, and the ones farthest away are called valence electrons. These valence electrons are important because they’re the ones that connect, or bond, with other atoms. When atoms bond together, they form molecules.

In the Happy Atoms models, the plastic sphere represents the nucleus, and the arms represent the valence electrons. Even though real atoms have many more electrons, the model only shows the valence electrons since they’re the ones involved in bonding.

For example, a sulfur atom actually has 16 electrons, but only 6 of them are valence electrons—so the Happy Atom model for sulfur only has 6 arms.

The letters on the nucleus stand for the element’s chemical symbol (like “O” for oxygen or “S” for sulfur).

In Summary

• Everything is made of atoms.

• Atoms are made of protons, neutrons, and electrons.

• The number of protons tells you which element it is.

• Valence electrons help atoms bond to make molecules.

• The periodic table organizes all the elements by their atomic number.