2.3 Chemical Properties and Reactions

The Structure of the Atom

Atoms are the building blocks of matter. Atomsare the smallest unit of matter that cannot be broken down into particles by chemical means.

Atoms have a dense nucleus. In the nucleus are two types of particles: protons and neutrons. Protons have a positive (+) charge. Neutronsare neutral; they have no electric charge. Surrounding the nucleus are electrons. These have much less mass than protons and neutrons. They also have a negative (–) charge.

In a particular element, there are the same number of protons and electrons, so an atom of the element is neither positive nor negative in charge. For example, one atom of the element carbon contains six protons and six electrons, and its charge is neutral.

The number of protons in the nucleus of an element is called its atomic number. Each element has a unique atomic number. The higher the atomic number, the heavier the element. Carbon’s atomic number is 6.

Atoms have a lot of empty space. Most of the mass of an atom is in its nucleus, which is very small compared to the atom as a whole. Electrons move around the nucleus at high speed. Because of this speed, an atom behaves as if is solid. It is similar to the rotating blades of a fan. The blades appear solid and repel other matter, even though there is much empty space between them.