grade 9 science chemistry unit: the study of matter
TRANSCRIPT
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.