ca-inspire-chemistry-sampler

(t)lynx/iconotec.com/Glow Images, (b)NASA

The Atom

Many experiments since Dalton’s time have proven that

atoms do exist. So what exactly is the definition of an

atom? To answer this question, consider a gold ring.

Suppose you decide to grind the ring down into a pile

of gold dust. Each fragment of gold dust still retains all

of the properties of gold. If it were possible—which it is

not without special equipment—you could continue to

divide the gold dust particles into still smaller particles.

Eventually, you would encounter a particle that could not

be divided any further and still retain the properties of

gold. This smallest particle of matter that retains the

properties of the element is called an

atom.

To get an idea of its size, consider the population of the

world, which was about 6.5

in 2006. By comparison, a

typical solid-copper penny contains 2.9

atoms, almost

five trillion times the world population! The diameter of a

single copper atom is 1.28

m. Placing 6.5

copper atoms side by side would result in a line of copper

atoms less than 1 m long.

Figure 4

illustrates another way to

visualize the size of an atom. Imagine that you increase the

size of an atom to be as big as an orange. To keep the propor-

tions between the real sizes of the atom and the orange, you

would have to increase the size of the orange and make it as

big as Earth. This illustrates how small atoms are. It was

because of this that scientists could not see the atom they

were attempting to model.

Figure 4

Imagine that you could increase the size

of an atom to make it as big as an orange. At this

new scale, an orange would be as big as Earth.

Disciplinary Core Ideas

Crosscutting Concepts

Science & Engineering Practices

3D THINKING

COLLECT EVIDENCE

Use your Science Journal to

record the evidence you collect as

you complete the readings and

activities in this lesson.

INVESTIGATE

GO ONLINE

to find these activities and more resources.

Applying Practices:

Modeling Electrostatic Forces–The Early Atom

HS-PS2-4.

Use mathematical representations of

Newton’s Law of Gravitation and

Coulomb’s Law

to describe and predict the gravitational and electrostatic forces between

objects.

Revisit the Encounter the Phenomenon Question

What information from this lesson can help you answer the module question?

FOCUS QUESTION

What does an atom look like?

LESSON 2

DEFINING THE ATOM

Module 3 • The Structure of the Atom