Chapter 11, Problem 38A

Summary Introduction

To describe:

The structure of an atom

Introduction:

Matter is anything that has mass and takes up space. It is made up of small units called atoms. In 1803, a scientist called Dalton gave an atomic theory to describe the structure of an atom. The atomic theory states that all matter is made of atoms. Since Dalton’s time many scientists have created different models to describe atoms and sub- atomic particles.

Answer to Problem 38A

An atom has a nucleus made of protons and neutrons, and electrons revolving around the nucleus in fixed orbits. Protons are positively charged particles and electrons are negatively charged particles. Neutrons do not have any charge. An atom is neutral since number of protons is equal to number of electrons. The force of attraction between protons and electrons hold them together.

Explanation of Solution

Atoms are building blocks of matter. It is made up of still smaller particles called electrons, protons and neutrons. The nucleus is in the center of the atom and electrons are outside the nucleus. In a neutral atom, protons are positively charged and electrons are negatively charged. Neutrons are particles that have no charge. Electrons revolve around an atom’s nucleus in different energy levels or orbits. The basic structure of an atom is due to attraction between protons and electrons.

The number of protons in the nucleus of an element is called atomic number. In a neutral atom, the atomic number is also equal to the number of electrons because the overall charge in an atom is 0, so the number of protons is equal to the number of electrons.