3.2

Question: What is inside the sealed box?Without breaking the seal, make all

observations you can by carefully shaking, tilting or otherwise moving the box.

How might we describe the contents?Next, let’s invent new movements for the

box to determine the size shape, and other physical properties of the objects inside the box.

What do you observe?

Take a guess at the contents

About 450BC Matter is composed of four ‘elements’

EarthAirFireWater

Each element is a mixture of two properties. Ex. Fire is a mixture of hotness and dryness

400BC Democritus suggests matter is made of

tiny particles Atomos, meaning ‘indivisible’ His ideas were never widely accepted

AD 500 – 1600 Alchemists (a combination of

philosophers, mystic, magician, and chemists)

Believed metals grow like plants, ripening into gold.

Devised chemical symbols for substances we now recognize as elements and compounds

(No one ever turned lead into gold)

 1650 An Englishmen, Robert Boyle, didn’t

believe in the four elements model. Redefined the term element, which lead

to the modern definition of an element: a pure substance that cannot be chemically broken down to a simpler substance.

Boyle believed that air was not an element, but rather a mixture.

Late 1700s Joseph Priestly isolated oxygen but

he did not believe it was an element. Antoine Lavoisier concluded that air

was a mixture of at least two gases, one of which was oxygen.

Henry Cavendish discovered hydrogen and found that it would burn in oxygen and produce water.

Until this time, scholars had believed that water was an element.

1808: English chemist, John Dalton, published a new theory of the atomic model.

All matter is made of atoms, which are particles too small to see.

Each element has its own kind of atom, with its own particular mass.

Compounds are created when atoms of different elements link to form molecules.

Atoms cannot be created, destroyed, or subdivided in chemical changes.

1800s: matter is able to develop positive and

negative charges—quantities of electricity. In 1831, Michael Faraday found atoms

could gain electric charges and formed charged atoms called ions. Dalton’s Model modified:

Matter must contain positive and negative charges.

Opposite charges attract and like charges repel.

Atoms combine to form molecules because of electrical attractions between atoms.

1904 J.J. Thomson revised the atomic model

further. It became known as the “raisin bun” model:

Atoms contain particles called electrons. Electrons have a small mass and a

negative charge. The rest of the atom is a sphere of

positive charge. The electrons are embedded in this

sphere, so that the resulting atoms are neutral or uncharged.

H. Nagaoka (Japan) modeled the atom as a large positive sphere surrounded by a ring of negative electrons.

1911 Ernest Rutherford (Montreal) came up

with the Nuclear Model while testing Thomson’s and Nagaoka’s models.

An atom has a tiny, dense, positive core called a nucleus (which deflected the alpha particles and contains protons).

The nucleus is surrounded mostly by empty space, containing rapidly moving negative electrons (through which the alpha particles passed unhindered).

Create a timeline that shows the evolution of the atomic model.

Use text pages 82 – 85 Your timeline should include 10

important years. For each year, include 2-3 important

points as well as an image. Your timeline should be coloured. Use

the white paper provided.