Chapter 4 Elements and the Periodic Table

Section 1:Introduction to Atoms

How did atomic theory develop and change?

What is the modern model of the atom?

Chapter 4 Elements and the Periodic Table

Imagine you have a piece of

aluminum foil, and you cut it

in half. If each of these pieces is

cut in half a second, third, and

fourth time, the pieces become

smaller but are still aluminum.

How small must a piece be so

that at the next cut it will no

longer be aluminum?

How is the periodic table organized?

Chapter 4 Elements and the Periodic Table

Atomic Theory and Models

Dalton thought that atoms were like smooth, hard spheres that could not be broken into smaller pieces.

Chapter 4 Elements and the Periodic Table

Modern Model of an AtomThis model of a carbon atom consists of positively charged protons and neutral neutrons in a nucleus that is surrounded by a cloud of negatively charged electrons.

Chapter 4 Elements and the Periodic Table

Modern Model of an AtomThis model of an atom shows electrons in a frozen position that can be used to learn about chemistry.

The nucleus contains protons and neutrons that make up the mass of the atom.

The tiny electrons are

arranged in different energy

levels around the nucleus.

Chapter 4 Elements and the Periodic Table

Particles in an AtomAn atom is composed of positively charged protons, neutral neutrons, and negatively charged electrons. Protons and neutrons are about equal in mass. An electron has about 1/2,000 the mass of a proton or neutron.

Chapter 4 Elements and the Periodic Table

Atomic Number # protons Top # in Periodic Table Identifies the name of the

element

# protons (+) = 6

Atomic # = 6Element Name:

Carbon

Example:

Chapter 4 Elements and the Periodic Table

Isotopes & Mass Number

Isotopes are atoms with the same number of protons and electrons but differerent number of neutrons.

Mass number = total particles in the nucleus (protons + neutrons)

Chapter 4 Elements and the Periodic Table

End of Section:Introduction to Atoms