Atom

• Atom, tiny basic building block of matter.

• All the material on Earth is composed of various combinations of atoms.

• Atoms are the smallest particles of a chemical element that still exhibit all the chemical properties unique to that element.

• A row of 100 million atoms would be only about a centimeter long.Understanding atoms is key to understanding the physical world.

• More than 100 different elements exist in nature, each with its own unique atomic makeup.

• The atoms of these elements react with one another and combine in different ways to form a virtually unlimited number of chemical compounds.

• When two or more atoms combine, they form a molecule.

• For example, two atoms of the element hydrogen (abbreviated H) combine with one atom of the element oxygen (O) to form a molecule of water (H₂0).

• Throughout history, people have sought to explain the world in terms of its most basic parts.

• Ancient Greek philosophers conceived of the idea of the atom, which they defined as the smallest possible piece of a substance.

• The word atom comes from the Greek word meaning “not divisible.”

• The ancient Greeks also believed this fundamental particle was indestructible. Scientists have since learned that atoms are not indivisible but made of smaller particles, and atoms of different elements contain different numbers of each type of these smaller particles.