Download Name: Date: ______ Atoms: The Building Blocks of Matter Do Now

Name: ______________________
Date: _________
Atoms: The Building Blocks of Matter
Do Now
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What is a theory?
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What is a model?
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How do you make inferences about things you can not see?
Atom
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From Greek, meaning “indivisible”
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Atomic theory (from 400 BCE) = atoms are the _____________________
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There wasn’t any evidence for nearly 2000 years.
Atomic Size
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At sea level, one cubic centimeter of air (size of a sugar cube, or marble) will
have 45 billion billion atoms within it. 45,000,000,000,000,000,000
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How many atoms would it take to fill a universe?
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If you tried to count to 45,000,000,000,000,000,000 it would take you
400,000 years
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Fill Rye COMPLETELY with 45,000,000,000,000,000,000 marbles.
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To see the atoms in a drop of water, you would need to enlarge the drop
until…
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it is 24 kilometers wide!
Think of a line 1 millimeter long. If this line were blown up to the size of the
empire state building, an atom would be… a tenth the thickness of a sheet
of paper.
Some History
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Democritus
– 460-371 B.C.
– ancient Greek philosopher
– believed all matter consisted of extremely small particles that could
not be divided
– atoms, from Greek word atomos, means “uncut” or “_____________”
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Aristotle
– believed all matter came from only four elements—earth, air, fire and
water
Some Scientific Laws
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The Law of ____________________________
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The Law of ____________________________
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The Law of ____________________________
Law of Definite Proportions
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Two samples of a chemical compound contain the same elements in _______
______________________________________________ regardless of
the size of the sample or source of the compound.
– NaCl = 39.3% sodium 60.7% chlorine
– H2O = 11.2% hydrogen 88.8% oxygen
– C2H6O2 = 38.7% carbon, 9.7% hydrogen, 51.6% oxygen
Law of Conservation of Mass
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_________________________________________________________
during ordinary chemical reactions or physical changes
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Thus, the mass of the reactants _____________ the mass of the products
Law of Multiple Proportions
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If two or more different compounds are composed of the same two
elements, then the ratio of the masses of the second element combined with
a certain mass of the first element is always a ratio of _______________.
– NO and NO2 = 1:2
– H2O and H2O2 = 1:2
– SO2 and SO3 = 2:3
Dalton’s Atomic Theory
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Dalton proposed an explanation for the law of conservation of mass, the law
of definite proportion, and the law of multiple proportions.
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He reasoned that elements are composed of one kind of atom and that only
whole numbers of two or more kinds of atoms can combine to form
compounds.
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He proposed the ___________________________________
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All matter is composed of extremely small particles called atoms, which
cannot be subdivided, created, or destroyed.
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Atoms of a given element are identical in _________________ (size/mass)
and _________________ properties.
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Atoms of different elements differ in physical (size/mass) and chemical
properties.
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Atoms of different elements combine in simple, _____________________
to form chemical compounds.
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In chemical reactions, atoms are combined, separated, or rearranged, but
_________________________________________________________.
Modern Atomic Theory
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Atoms are divisible into even smaller particles. These smaller parts of the
atom are called ________________________________
– Electrons
– Protons
– Neutrons
Discovering Electrons
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In 1897, J.J. Thomson used a ____________________ (passes electricity
through a glass tube with little pressure) to deduce the presence of a
negatively charged particle.
J.J. Thomson’s cathode ray tube
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He knew that rays must have come from the atoms of the cathode because
most of the atoms in the air had been pumped out of the tube. Because the
cathode ray came from the negatively charged cathode, Thompson reasoned
that the ray was ____________________.
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He observed that when a small paddle wheel was placed in the path of the
rays, the wheel would turn. This observation suggested that the cathode ray
consisted on tiny particles that were hitting the paddles of the wheel.
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His experiments showed the cathode ray consists of particles that have
mass and a negative charge. These were called ______________________.
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He proposed the _______________________________.
Discovering the Nucleus
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In the 1900s, Ernest Rutherford performed his gold foil experiments
– He directed small, positively charged alpha particles (that are helium
nuclei) at a thin gold foil.
– Particle hits on the detecting screen (film) were recorded and
deflected angles were measured.
Rutherford’s gold foil experiments
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Most of the alpha particles are only slightly deflected, as expected, but
occasionally one is deflected back towards the source
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His experiments showed that the nucleus is ________________________
___________________________________.
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He also hypothesized that the mass of the nucleus must be larger than the
mass of the alpha particles, otherwise the alpha particles would have
knocked the nucleus out of the way.
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He also argued that most of the alpha particles were not deflected, because
most of the atom was ______________________________.
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He proposed a ______________________ or nuclear model
Try it Yourself!
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In the following pictures, there is a target hidden by a cloud. To figure out
the shape of the target, we shot some beams into the cloud and recorded
where the beams came out. Can you figure out the shape of the target?