Introduction to Atoms and Elements

What you’ll learn to do: Define atoms and elements

You’re probably familiar with the concept of atoms. They are the fundamental unit of matter—everything is made up of atoms, which come together in unique ways to form different things. Before you can understand chemical reactions, you must first understand the way that atoms work.

Over the years, scientists have used different models to visualize atoms as our understanding has changed. You may be familiar with a few of the models in Figure 1. In this course, we largely use the Bohr model.

Four atomic models. The Thomson model features a positive mass with smaller negative particle scattered inside it. The Rutherford model has a positive nucleus, with electrons orbiting around the nucleus on defined paths. The Bohr model is made up of concentric circles; the center is the positive nucleus, and electrons are located in different circles, which represent orbitals. The Heisenberg/Schrödinger model is the most abstract, with the positive and negative elements not specifically represented. Instead the model is shaped like a flower, with six ‘petals,’ which are made up of three intersecting orbital paths (P 1s, P 2s, and P 3s)

Figure 1. The evolution of atomic models over the years. As our understanding of atoms has evolved, the models we use to depict them have changed. The first model is the Thomson model, followed by the Rutherford model, the Bohr model, and the Heisenberg/Schrödinger model.