Section 1 Structure of the Atom

Essential Questions What are the names and symbols of common elements? What is the structure of the atom? How do scientists study quarks? What is the electron cloud model of the atom?

Review Vocabulary element: substance with atoms that are all alike

New Vocabulary atom quark nucleus electron cloud proton neutron

Scientific Shorthand Scientists also use abbreviations. In fact, scientists have developed their own shorthand for naming the elements.

Subatomic Particles An element is matter that is composed of only one type of atom. An atom is the smallest particle of an element that retains the element’s properties. For example, the element iron is composed of only iron atoms and the element hydrogen is composed of only hydrogen atoms. Atoms are composed of even smaller particles—subatomic particles—called protons, neutrons, and electrons, as shown below.

Models—Tools for Scientists Scientists and engineers use models to represent objects or ideas that are difficult to visualize or to picture in your mind. You might have seen models or blueprints of buildings, planetary models of the solar system, or even a model airplane. These are scaled-down models. Scaled-down models allow you to see something that is too large to visualize all at once or something that has not yet been built.

Assessment 1. How many outermost electrons do lithium and potassium have? 1 A CORRECT 2 B 3 C 4 D

Assessment 2. Which of the following is NOT found in the nucleus of an atom? proton A neutron B electron C CORRECT quark D