Atomic structure

OBJECTIVES:

• Classify subatomic particles.

• Describe the structure of an atom according to modern theory.

• Describe how the atomic model has changed over time.

Atomic Structure

• Now, don’t let that big word scare you! It is just a fancy name for what makes up an Atom. Remember, Atoms are the tiniest particles that still contain all of the properties of an element.

Three particles of an Atom…

A tom ic S tru c tu re

P ro ton sTyp e t it le h e re

N eu tron sTyp e t it le h e re

E lec tron sTyp e t it le h e re

A tom s

What are Protons?

• They are smaller (subatomic particles) than the atom.

• They are positively (+) charged.

• You can find them in the center of an atom.

The Nucleus

+ +

Helium

** Protons and Neutrons make up the nucleus of an Atom. The Nucleus is found in the center (core) of an Atom.

** The number of protons located in the nucleus of an atom is called the atomic number.

Neutrons

As we learned in the previous slide, you can find these subatomic particles in the Nucleus of an Atom.

They are slightly larger (more mass) than the protons.

Neutrons have no charge

The chart below shows you some common elements, their atomic numbers and mass numbers. To find the mass number you must first find

the sum of the protons and neutrons located in the nucleus of the atom.

Name Atomic Number Mass Number

Hydrogen 1 1

Oxygen 8 16

Gold 79 197

Atomic Models

In the last few frames we have learned a great deal about the most modern theory of the atomic model. This theory was formed over thousands of years of scientific research. Talk about needing to be patient. Most of these models were built on indirect evidence because until recently, you couldn’t even see an atom. That means they came up with mental pictures of what they thought an atom looked like. Now we are going to learn about some of these other theories.

The Greek Model

• Democritus started looking for a description of matter over 2000 years ago. After many years Democritus concluded that matter could not be cut apart forever. It would eventually be cut into the smallest piece possible. He actually gave this piece a name. Can you guess what that name was? If you said an Atom, you were right. The word atom comes from the Greek word “atomos’. It means “not to be cut”.

Dalton’s Model

• Dalton’s theory was the combination of his own studies as well as what others had learned. He proposed the following theory in 1803:

• Everything is made up of Atoms.

• Atoms are indivisible and indestructible.

• Atoms of the same elements are alike.

• The joining of atoms of two or more elements are a compound.

Thomson’s Model

• Thomson’s model proved that Dalton’s theory was not entirely correct. An atom was divisible.

• Thomson’s model states that the atom is made up of positively charged pudding like substances that contain electrons that are negatively charged scattered throughout it. Kind of like how raisins are scattered throughout rice pudding.

Rutherford’s Model

• Rutherford concluded that there was a nucleus in an atom that contained the positively charged particles. He also stated that the electrons which were scattered around the nucleus were negatively charged.

The Bohr Model

• Bohr’s model improved on the Rutherford model. Bohr put the electrons in a specific place called energy levels. His model states that electrons travel around the nucleus in a definite pattern called energy levels. These levels are located at a certain point from the nucleus. Kind of like the planets circling the sun.

The Wave model

• This is the modern atomic model.

• It states that an atom has a small nucleus that is positively charged surrounded by enough electrons to make the atom neutral. The area around the nucleus that contains the electrons is large in comparison to the nucleus of the atom.

Discussion Questions:

• What are the three main subatomic particles that make up an atom?

• What are protons?

• Where can you find the nucleus of an atom?

• What are neutrons?

• What are electrons?

• How has the model of the atom changed over time?

• What atomic particle did J.J. Thomson discover?

• How does the wave model differ from Bohr’s model?

Bibliography

**Prentice Hall Science

Matter

Engle wood Cliffs, New Jersey

**More about Atomic Anatomy

Blackboard Electricity and Magnetism

Online course.