Ann Ladnier
DCMS

Section 1. Introduction to atoms
STRUCTURE OF AN ATOM
WHAT IS THE STRUCTURE
OF AN ATOM?
Atoms are made of even smaller particles called protons, neutrons, and electrons
WHAT ARE THE PARTICLES
IN ATOMS?
The nucleus is the very small center core of an atom
Protons have a positive electric charge +
Neutrons have no charge
Electrons move rapidly around the nucleus and have a negative electric charge e-

Section 1. Introduction to atoms
STRUCTURE OF AN ATOM
WHAT IS AN ELECTRON
CLOUD?
Electrons move within a sphere shaped region surrounding the nucleus—they may be anywhere within this sphere
WHAT ARE THE PARTICLE
MASSES?
Electrons occupy most of the volume of an atom, but do not have much mass (1/2,000 amu)
Protons and neutrons are about equal in mass (1 amu)
Protons and neutrons together make up nearly all the mass of an atom
Measured in amu (atomic mass units)

Section 1. Introduction to atoms
STRUCTURE OF AN ATOM
ATOMS AND ELEMENTS An element can be identified by the number of protons in the nucleus of its atoms
WHAT IS THE ATOMIC
NUMBER?
Each element has a unique atomic number-the number of protons in its nucleus

Section 1. Introduction to atoms
STRUCTURE OF AN ATOM
WHAT IS AN ISOTOPE?
Atoms with the same number of protons and a different number of neutrons are called isotopes
The mass number is the sum of the protons and neutrons in the nucleus of an atom
The most common carbon isotope has a mass number of
12. Six protons + 6 neutrons= 12

Section 1. Introduction to atoms
STRUCTURE OF AN ATOM
MODELING ATOMS
HOW DO YOU MODEL
ATOMS?
Because atoms are so small, scientists create models to describe them.
Models may be a diagram, mental picture, mathematical statement, or an object that helps explain ideas about the natural world