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Atoms and Elements
The Atomic Theory
Difficult to identify objects that you can’t see.
Democritus—400 b.c.—matter is made up of
tiny particles
Aristotle—matter is not made of particles
Dalton’s Atomic Theory = all matter is made up
of tiny particles called atoms.
Structure of an Atom
5 million atoms could be lined up on a period.
Atoms are made up of even smaller particles called
subatomic particles.
Nucleus = the tiny center of an atom made of protons and
neutrons
Proton = subatomic particle with a positive (+) charge.
Neutron = subatomic particles with no charge.
Electron = subatomic particle with a negative (-) charge.
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Electrons make up the rest of the atom and surround the nucleus.
The Structure of an Atom
Niels Bohr suggested a model of the structure of an atom in
1913.
Electrons circle the nucleus in a paths called orbits or energy
levels.
 Low-energy = orbit close to nucleus
 High-energy = orbit father away.
Most of an atoms mass is in the nucleus; protons and neutrons
have the same mass; electrons as about 1/2000 of a proton
Proton and electron charges are the same strength
 More protons than electrons = positive charge.
 More electrons than protons = negative charge.
 Same number of protons and electrons = neutral atom.
Elements
Element = a substance made up of only one kind of atom.
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Types of elements: Gold, Copper, Iron.
Atom = smallest unit of an element that has all properties
of that element.
Every element has its own atomic number or the number
of protons in one atom of that element.
Only a few kinds of elements are in most matter
Molecule = two or more atoms linked together.
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A pure state is when atoms are linked to other atoms of the same
kind.
Metals
Elements are classified by their properties.
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¼ Non-metals; the rest are Metals
Properties of metals
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luster, or shininess
malleable
ductile
conduct or transfer electricity
insulators Metals conduct heat
conduct heat
Non-pure elements are alloys.
Other metals are pure elements