SCH3U
Welcome to Grade 11 Chemistry!!
Are you ready?
• What do you remember from the Grade 10
Chemistry Unit?
Are you ready?
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Elements and compounds
Atomic Theory
Periodic table and layout
Naming
Reactions
Early Greek Theories
Aristotle (350 B.C.)
• 4 Elements
Democritus (400 B.C)
• Matter: atoms and a void (empty
space)
• Atoms are indivisible
Dalton’s Billiard Ball Model (1805)
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All matter is made of atoms.
Atoms of an element are identical.
Each element has different atoms.
Atoms of different elements combine in
constant ratios to form compounds.
• Atoms are rearranged in reactions, but are
not created nor destroyed.
Thomson’s Raisin Bun Model (1897)
• Cathode Ray experiment: Sent electricity through a gas,
producing negatively charged particles “cathode rays”
• Discovered the electron: a negatively charged particle
with a small mass
• Atoms consisted of a positively charged sphere embedded
with negative electrons
Cathode ray animation
Rutherford’s Gold Foil Experiment (1910)
• Alpha particles (positively charged helium ions)
were fired toward a very thin gold foil.
• Most alpha particles passed
through.
• Some positive -particles deflected
or bounced back!
• Conclusion – Rutherford’s
model: Atoms are mostly empty
space. Most of the mass of an atom
is concentrated in a positive core
with protons, called the atomic
nucleus.
• Rutherford animation
Shortfalls of Rutherford’s Model
• Orbiting electrons should emit light, losing
energy in the process
• This energy loss should cause the electrons
to collapse into the nucleus
• However, matter is very stable, this does
not happen
Bohr’s Planetary Model (1913)
• Electrons orbit the nucleus in energy “shells”
• Electrons in these shells have a specific and
constant amount of energy, without losing
energy in the shell
• The greater the distance between the nucleus
and the energy level, the greater the energy level
• An electron changes energy levels by emitting or
absorbing a specific quantity (quantum) of
energy in the form of light (photons)
• Electrons at their lowest possible energy state
are in their ground state
• If light or heat is directed at an atom, electrons
can absorb the energy, and move to a higher
energy shell
• When the electron returns to a lower energy
state the energy is released in the form of a
photon, which we see as visible light
• The energy of the photon determines its
wavelength or colour
• Each element has its own frequencies of color
Summary of Atomic Models
1) Dalton’s “Billiard ball” model (1800-1900)
Atoms are solid and indivisible.
2) Thomson’s “Raisin bun” model (1900)
Negative electrons in a positive framework.
3) Rutherford’s “Nuclear” model (~1910)
Atoms are mostly empty space.
Negative electrons orbit a positive nucleus.
4) Bohr’s “Planetary” model (~1920)
Negative electrons orbit a positive nucleus.
Quantized energy shells
Homework - Practice
• Draw a series of at least four diagrams to
represent changing models of the atom
• P. 39 # 4