Introduction to the Atomic Model Advanced Chemistry Ms. Grobsky.

Introduction to the Atomic ModelAdvanced ChemistryMs. Grobsky

Exploring the Black Box

Imagine you’ve received a present that you are not allowed to open. You REALLY want to know what’s inside!

What might you do to figure out the contents?

Exploring the Black Box

In your group, try to figure out the contents and internal structure your present WITHOUT opening it

Note: Do NOT shake the box too violently as the contents may fall out!

As a group, be sure to answer the questions on the hand-out!

So What is a Black Box?

A black box refers to any system that has inner workings that cannot be directly observed because it is not possible or feasible

Can you think of any other black box examples?

The Black Box and Science

An atom is an example of a black box

The Atomic Model and the Nature of Science

When scientists wanted to determine the structure of an atom, they were not able to actually see inside of the atom

They had to rely on empirical evidence, indirect evidence, observation, and inference when developing their ideas-just as you did when determining the contents of your present!

The Atomic Model and the Nature of Science

Scientists then developed a model to express their new ideas

The understanding of the structure of the atom has changed many times over the course of centuries

As new evidence emerged, the ideas of the atomic model changed

Lecturing about the scientists of the atomic model isn’t quite as fun and interesting as understanding:

HOW was the atomic model developed?WHY has the atomic model changed over the years?

The “What” of the Atomic ModelA Brief History

DemocritusThis is the Greek philosopher Democritus who began the search for a description of matter more than 2400 years ago

He asked: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided?

400 BC

Atomos

His theory: Matter could not be divided into smaller and smaller pieces forever, eventually the smallest possible piece would be obtained

This piece would be indivisible

He named the smallest piece of matter “atomos,” meaning “not to be cut”

Atomos To Democritus,

atoms were small, hard particles that were all made of the same material but were different shapes and sizes

Atoms were infinite in number, always moving and capable of joining together

Democritus vs. The Philosophers

The eminent philosophers of the time, Aristotle and Plato, had a more respected, (and ultimately wrong) theory

Aristotle and Plato favored the earth, fire, air and water approach to the nature of matter

Their ideas held sway because of their eminence as philosophers

The atomos idea was buried for approximately 2000 years

Then Along Came Dalton’s Model

In the early 1800s, the English chemist John Dalton performed a number of experiments that eventually led to the acceptance of the idea of atoms

Dalton’s Atomic ModelAll elements are composed of atoms

Atoms are invisible and indestructible particles

Dalton’s Atomic Model Continued

Atoms of the same element are exactly alike

H H

Dalton’s Atomic Model Continued

Atoms of different elements are different

O H

Dalton’s Atomic Model Continued

Compounds are formed by the joining of atoms of two or more elements

H H

O

Dalton’s Atomic Model

This theory became one of the foundations of modern chemistry

BUT it needed work

Thomson’s Plum Pudding Model

In 1897, the work of an English scientist J. J. Thompson provided the first hint that atoms were made up of even smaller particles

Thomson Model

Thomson studied the passage of an electric current through a gas

As the current passed through the gas, it gave off rays of negatively charged particles

Thomson Model

This surprised Thomson, because the atoms of the gas were uncharged

Where had the negative charges come from?

Where did they come from?

• Thomson concluded that the negative charges came from within the atom

• A particle smaller than an atom had to exist

• The atom was divisible!

• Thomson called the negatively charged “corpuscles,” today known as electrons

• Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom

• But he could never find them

And...Thomson thought the positive (+) and negative (-) particles were s p r e a d o u t in atoms like:

p p u l d u d m i s n

(plums in puddin’)

And Then There was Rutherford…

In 1908, the English physicist Ernest Rutherford was hard at work on an experiment that seemed to have little to do with unraveling the mysteries of the atomic structure

You will explore the methods performed in Ernest Rutherford’s experiments and help “develop” a model for an unseen object!