Grade 9 Science

Chemistry Unit:The Study of Matter

• 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 Element atom pure substanceHypothesis alchemist plum pudding modelSubatomic neutral electronproton

Developing Models of Matter

• 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)

Aristotle(350 BCE)  

• Ancient Greek philosopher.• Believed matter was made of four elements.• His theory was accepted by all.

• 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)

• 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)

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)

• 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)

• 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)

• 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)

• 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

The AtomContains 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.