1. Grade 9 Science Chemistry Unit: The Study of Matter

2. Outline the development of scientific thought as it relates to matter and the atomic structure. Define element and understand its relationship to the concept of matter. Describe the understanding of the structure of the atom. Key Words Elementatompure substance Hypothesisalchemistplum pudding model Subatomicneutralelectron proton

3. Developing Models of Matter

4. Hypothezised matter was tiny particles in constant motion. Cannot be broken apart – solid. Eternal (unable to create or destroy) Surrounded by an empty space. *called particles atomos – meaning “indivisible” - ATOM Democritus (400 BCE)

5. Aristotle(350 BCE) Ancient Greek philosopher. Believed matter was made of four elements. His theory was accepted by all.

6. Concerned with metallurgy (study of properties of metals). Goals - turn common metals into gold or silver. - find a substance to give eternal life. (the key to both is called the Philosopher’s Stone) Developed observation, experimentation, measurement and classification – first “scientists.” Called “alchemists” Alchemy and the Middle Ages (500 – 1600 CE)

7. 13 known substances – gold, copper, arsenic, bismuth, antimony, iron, mercury, carbon, lead, silver, sulphur, tin, zinc. Performed experiments to show water and air were mixtures of elements. Defined the term ELEMENT - a fundamental pure substance that cannot be broken down into simpler parts. Discovered 23 more elements. Lavoisier (1750)

8. FIRST ATOMIC THEORY all matter is made of indivisible particles - atoms. Atoms of each element are unique (differ by mass). Compounds are combinations of different elemental atoms. Atoms cannot be created or destroyed. (Law of conservation of matter) Dalton (1800)

9. Hypothesized (guessed) first subatomic particles – electron. Electrons have a small mass and negative electric charge. Atom is sphere with equal number of positive charges mixed with negative electrons - Plum pudding model. Overall atom is neutral electrically. Thomson (1890)

10. Conducted “Gold Foil Experiment.” Discovered the atomic nucleus. Nucleus is a small, dense (heavy), positively charged core. Positive charges due to another subatomic particle - protons Hypothesized atom composed of mostly space with a centre nucleus and small electrons floating around. Rutherford (1910)

12. discovered the neutron in the nucleus Neutrons have no charge and are the size of protons. THREE subatomic particles: - dense positive nucleus (protons and neutrons). - negative electrons floated around. Chadwick (1932)

13. Dalton - each element has its own kind of atom - compounds are formed when elements link together - atoms cannot be created or destroyed - billiard ball model Thomson - discovered negatively charged electrons - hypothesized equal positive and negative particles - plum pudding model Rutherford - discovered nucleus (gold foil) and positive protons - hypothesized atoms were mostly empty space - beehive model

15. The Atom Contains 3 subatomic particles: The dense center (nucleus) of the atom contains: Neutron - a particle with no charge. Proton - a particle with a positive charge. Electrons are tiny particles that move around the nucleus. - negative electrical charge. - same # of positive and negative charges = neutral.