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’  Earth  Air  Fire  Water  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.