Atoms and Elements - Grade 9 Science - Home€¦ · Atoms and Elements A- History of the Atomic...
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Grade 9 Chemistry Booklet.notebook 1 April 06, 2020 Apr 2310:26 AM Atoms and Elements Grade 9 Science Unit 2
Transcript of Atoms and Elements - Grade 9 Science - Home€¦ · Atoms and Elements A- History of the Atomic...
Grade 9 Chemistry Booklet.notebook
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Atoms and Elements
Grade 9 Science
Unit 2
Grade 9 Chemistry Booklet.notebook
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Atoms and Elements
A- History of the Atomic Model
B- Atoms and Elements
C- The Periodic Classification of Elements
D- Compounds
E- Properties of Substances
F- Chemical Changes
G- Lab Safety
FINAL UNIT TEST
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A: History of the atomic model
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HISTORICAL IDEAS ABOUT THE NATURE OF MATTERAncient Greek Philosophers
• The ancient Greek philosophers wondered why matter behaves as it does and manipulated ideas in their minds but did almost no experimentation.
Empedocles
• 450 BCE• Proposed that matter was composed of four elements: Earth,
Water, Air, Fire.
Democritus
• 400 BCE• Suggested matter was made of tiny particles that could not be broken down any further.• He called them “atomos” which means indivisible.
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Alchemists
• 500 – 1600 AD• First people to perform handson experiments.• Part philosopher, mystic, and magician (magic = not
real).• Three main beliefs:1. Some elements can be changed into others. (They
were trying to change base metals into gold). This led them to discover new elements and learn more about existing ones.
2. There was a substance that would give them eternal life.
3. There was a universal solvent that would dissolve all substances.
Aristotle
• 350 BCE• After Democritus died, Aristotle rejected the atomos model
and returned to the 4 element model.This model influenced and dominated scientific thinking for almost ~2000 years.
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Modern Chemists
• 1600 – present• Use the scientific method and experimentation to determine properties of pure
substances and explain their composition.
Sir Francis Bacon (1600s)
• One of the first scientists to develop new knowledge as a result of experimentation.
Robert Boyle (1650)
• Believed the Greek philosophers’ fourelement theory could be improved. • Helped lay the foundation for the concepts of elements and compounds.• Recognized that elements can be combined to form compoundBelieved that air was not an element, but a mixture of elements
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Joseph Priestley (late 1700s)
• First person to scientifically isolate oxygen, but did not know oxygen was an element.
Antoine de Lavoisier (late 1700s)
• Defined the term “ELEMENT” as a pure substance that could not be broken down into simpler substances.
• Discovered & identified 23 elements. • Investigations were based on careful measurement and
observations.• Recognized that mixtures exist, and identified air as a mixture of
oxygen and some other gas.
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Henry Cavendish (late 1700s)
• Experimented with mixing metal with acid, which produced a flammable gas called hydrogen.
• Discovered that hydrogen would burn in oxygen and create water. • Until this time, water was thought to be an element.
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MODELS OF ATOMIC STRUCTURE
John Dalton’s Model of the Atom (early 1800s)
• “Billard Ball” model • All matter is made up of atoms which are too small to see.• Each element has its own kind of atom.• Atoms of different elements are different.• Atoms of different elements can join to form compounds. • Elements were classified according to their mass.
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Joseph Thomson (1904)
• “Plum Pudding” model• An atom is a sphere of positive charges with negative
charges scattered through it.
Ernest Rutherford (1911)
• Most of an atom is empty space.• Discovered a tiny, very dense nucleus that contains
neutrons and positive protons.• Surrounding the nucleus is a region of fast moving,
negative electrons.
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Niels Bohr (1913)
• Planetary model• Expanded Rutherford’s model to include electrons have different
amounts of energy which allows them to move in different orbits with different energy levels.
• orbits are at different distances from the nucleus (like planets and the sun)
