Unit 1: Chemistry [Grade 9]
History of Matter
Major Beliefs/Contributions:
Empedocles:
- Proposed that matter was composed of four elements
- Earth, water, air, fire
Democritus:
- Suggest matter was made of tiny particles that could not be broken down further
- “Atomos” = indivisible
Aristotle/Socrates:
- Rejected Democritus’s atomic model and adopted Empedocles “four element”
model
Alchemists:
- 1st to perform hands-on experimentation
- Part philosopher, mystic, magician, and chemist
- Believes that some elements could be changed into other
- Turn base metals into valuable ones like gold
- Believed they could find a substance for immortality
- Believed they could produce a universal solvent for all solutions
Lavoisier defined “element” as a pure substance that could not be chemically broken
down into 2 simpler substances. He discovered 23 elements.
Models of the Atom
Major Descriptions:
Democritus:
- Came up with the idea of an atom
- “atomos”
Dalton:
- Proposed Atomic Theory of Matter
a. Atoms could not be created, destroyed or divided
b. All atoms of the same element are identical in size and mass
- This idea was later disproved by Chadwick due to the discovery of
neutrons
c. Atoms are tiny particles too small to see: like a billiard ball
, d. Compounds are made by atoms linked together in fixed amounts
Thomson:
- Discovered the electron
- Electrons have small mass & negative charge
- Rest of atom is a sphere of positive charge
- Atom = “plum pudding”
- Electrons are embedded in this sphere so that the resulting atoms are neutral or
uncharged (opposite of what is true)
Rutherford:
- Discovered nucleus and proton
- Nucleus = tiny, dense, positive core
- Proton = positive charge inside nucleus
- Nucleus is surrounded mostly by empty space containing rapidly moving negative
electrons
- Created the nuclear model
Bohr:
- Concluded that the planetary model best described the atom
- Small positive nucleus (with protons) are surrounded by negative electrons
- Electrons revolve in orbitals and are at specific locations from the nucleus, each
one holding a max. # of electrons
Chadwick:
- Discovered the neutron
- Disproved one of Dalton’s ideas - neutrons had a neutral charge which added to
the atomic mass
Quantum:
- Theory of orbitals has been replaced by an electron cloud located based on the
amount of energy the electrons have
- Most accurate model so far
- Model we accept today, but Bohr model is used to show the basic way that an
atom is arranged
Subatomic Particles:
History of Matter
Major Beliefs/Contributions:
Empedocles:
- Proposed that matter was composed of four elements
- Earth, water, air, fire
Democritus:
- Suggest matter was made of tiny particles that could not be broken down further
- “Atomos” = indivisible
Aristotle/Socrates:
- Rejected Democritus’s atomic model and adopted Empedocles “four element”
model
Alchemists:
- 1st to perform hands-on experimentation
- Part philosopher, mystic, magician, and chemist
- Believes that some elements could be changed into other
- Turn base metals into valuable ones like gold
- Believed they could find a substance for immortality
- Believed they could produce a universal solvent for all solutions
Lavoisier defined “element” as a pure substance that could not be chemically broken
down into 2 simpler substances. He discovered 23 elements.
Models of the Atom
Major Descriptions:
Democritus:
- Came up with the idea of an atom
- “atomos”
Dalton:
- Proposed Atomic Theory of Matter
a. Atoms could not be created, destroyed or divided
b. All atoms of the same element are identical in size and mass
- This idea was later disproved by Chadwick due to the discovery of
neutrons
c. Atoms are tiny particles too small to see: like a billiard ball
, d. Compounds are made by atoms linked together in fixed amounts
Thomson:
- Discovered the electron
- Electrons have small mass & negative charge
- Rest of atom is a sphere of positive charge
- Atom = “plum pudding”
- Electrons are embedded in this sphere so that the resulting atoms are neutral or
uncharged (opposite of what is true)
Rutherford:
- Discovered nucleus and proton
- Nucleus = tiny, dense, positive core
- Proton = positive charge inside nucleus
- Nucleus is surrounded mostly by empty space containing rapidly moving negative
electrons
- Created the nuclear model
Bohr:
- Concluded that the planetary model best described the atom
- Small positive nucleus (with protons) are surrounded by negative electrons
- Electrons revolve in orbitals and are at specific locations from the nucleus, each
one holding a max. # of electrons
Chadwick:
- Discovered the neutron
- Disproved one of Dalton’s ideas - neutrons had a neutral charge which added to
the atomic mass
Quantum:
- Theory of orbitals has been replaced by an electron cloud located based on the
amount of energy the electrons have
- Most accurate model so far
- Model we accept today, but Bohr model is used to show the basic way that an
atom is arranged
Subatomic Particles:
