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Food Chemistry
• Various physical & chemical
techniques have been used to
enhance and preserve our food.
• The most common way food
goes bad (spoils) is when bad
bacteria occur in too large a
number.
Methods for Preserving Food
–Heating and Freezing
• Heating (cooking)- temporarily sterilizes
food (kills the bacteria)
• Freezing (storage) – halts the growth of
bacteria
–Salting (beef jerky)
• Salt removes water, by osmosis, from the
food and the bacteria in it. This changes the
taste of the food but kills the bacteria.
Methods for Preserving Food
– Fermentation – This
process uses beneficial
bacteria (lactobacilli) to
create a natural
preservative (lactic acid).
• Sauerkraut was made
because it lasted long and
had vitamin C to fight off
Scurvy.
• Alcoholic beverages are also
made this way.
-Smoking – smoking your bacon or fish
introduces antioxidants that help control
the number of bacteria.
The science of producing and using metals
Copper age- made tools out of copper
-Annealing (heating before being
hammered) made Cu easy to
manipulate and strengthened it.
Stronger tools and Weapons.
-Smelting – separating a metal from
other compounds using heating. Most
Copper is mixed with other compounds
and was until this time unusable.
Bronze age – Bronze is made from copper &
tin. It is called an alloy (mixture of metals).
Iron Age – started smelting Iron in 1200 B.C.
◦ Later figured out how to add carbon to make steel.
Note: Copper to Bronze to Iron was a
progression to making stronger metals that
enabled better tools (farming) and weapons.
People could change matter, but did not
understand it.
Early Descriptions of Matter
Aristotle
◦ All matter was comprised of fire,
earth, water, & air.
Early Descriptions of Matter
Aristotle
◦ There was no smallest part of
matter. In other words you could
cut an element in half forever &
still have a piece of that element.
◦ Democritus challenged Aristotle on
this last point saying that there were
particles called atoms that were
indivisible. (Aristotle was in the in
crowd so no one listened to
Democritus and set back science for
2000 years give or take.)
http://communicationtheory.org/aristotle%E2%80%99scommunication-model/
Alchemy
Alchemy – branch of early
science that wanted to change
one substance into another.
(ideally lead into gold. WE
can do this now actually just
not cost effective)
◦ Although not successful they
improved lab equipment and
produced many useful
compounds.
Early Scientists
Robert Boyle – tiny particles make
up gases
Antoine Lavoisier -experimentally
came up with the Law of Conservation of
Mass. (Mass of reactants = Mass of
Products)
Matter is made from
Atoms, which look
like small spheres
John Dalton
(1766 - 1844)
 Atoms are tiny, indivisible particles of elements.
 All elements are composed of atoms.
 Atoms of the same element are identical.
 Atoms combine in fixed ratios to form compounds.
His “Billiard Ball” model
 Chemical reactions occur by a rearrangement of
lasted for over 100 years,
atoms.
until later technology
showed that atoms or not indivisible!
(1856 – 1940)
Hooked up materials in a cathode
ray tube & found electrons are
ejected.
Plum pudding model of the atom
electrons evenly scattered
throughout the atom
Thomson’s
Model was
labelled the
“Raisin Bun”
In Thomson’s Model, the atom was made up of a positively charged
sphere (protons) with negative particles embedded in it (electrons).
Net charge = 0.
(1871 – 1937)
• Found majority of an atoms mass is in the
center.
• The center is made
up of positive
gold foil
He expected…
particles (known as
the nucleus).
high-speed particles
• Electrons fly around
the outside (in orbit).
• He used a bee hive
model.
What ACTUALLY happened…
gold foil
high-speed particles
Rutherford was surprised
when all the particles did not
go straight through the gold
foil. Some bounced back and
others were sharply deflected.
He then realized that each
atom must have a dense core
of positive charge.
He called the dense centre the nucleus.
Rutherford redefined the Model of the atom,
by making a tiny positively charged nucleus,
surrounded by electrons. Rutherford calculated
the size of the nucleus to be about 1/10 000 of the size of the atom.
(1885 – 1962)
*Found that different electrons have different
amounts of energy using spectral analysis.
*Bohr model of the atom shows orbits representing
different energy levels.
◦ Energy exists in small units called quanta
◦ Electrons circle the nucleus in orbit at a fixed
distance having a fixed amount of energy
F
Li
Lithium atom
Fluorine atom
◦ Bohr concluded that:
 Electrons surround the nucleus at specific energy levels
(2,8,8,18)
 Since electrons can’t fall below that lowest energy level,
negatively charged electrons don’t merge with the
positively charged nucleus.
Line Spectra
• When atoms are heated, bright lines appear called
line spectra.
• An electron absorbs energy to “jump” to a higher
energy level.
– When an electron falls to a lower energy level,
energy is emitted.
• Electrons are clouds of negative charge
occupying the whole space at once at
different energy levels.
TODAY’S MODEL
Electrons are thought of as a
“cloud” of negative charge,
instead of a tiny negative
particle.
The idea of electron
movement is abandoned.
Instead, electrons
“occupy” the whole space
all at once at different
energy levels (cloud).
The electron cloud surrounds a
nucleus containing 2 types of
particles called nucleons:
PROTONS and NEUTRONS
Protons have a positive electrical
charge, and Neutrons have no
electrical charge.
•Do p.27 of the Notepack using your
notes and textbook.
•Do #1-8 & 11 (pg.25) (Textbook).
•Do # 2, 3, 5-13, 15-17 (pg. 27)
(Textbook).
•Quiz on Section 1 – coming soon…