Download iClicker Participation - Canvas by Instructure

2/1/2015

Today:

◦
◦
◦
◦
◦
◦
Periodic Table
Conservation of Matter
Law of Definite Proportions
Law of Multiple Proportions
Avogadro’s Law
Dalton’s Atomic Theory &
Relative Masses
◦ Atomic Structure:
Wednesday:
◦ Intro. Survey for 5 bonus pts. DUE
◦ Lecture Quiz 1 in Lab: check out
study guide on website
◦ Before coming to lecture, read
McMurry, Chp. 1: Sections 1.61.11, pp. 39-54
 Electrons
 Nucleus: Protons & Neutrons
Dimensional Analysis using Density
A neutron star has a density of about 100 million tons per
teaspoon (ton/tsp). What volume of a neutron star (in
cm3) would have the same mass as a Boeing 747, which
weighs 358,000 lbs.?
Given: 1 ton = 2000 lbs. & 1 tsp ≈ 4.92 cm3
iClicker Participation:
Using Dimensional Analysis in Unit Conversions
Which of the dimensional analysis unit conversions below
is set up correctly?
A.
B.
C.
D. ALL of these unit conversions are correct.
E. NONE of these unit conversions above are correct
1
2/1/2015
ATOMISM:
“If, in some cataclysm, all of scientific knowledge were to be
destroyed, and only one sentence passed on to the next
generation of creatures, what statement would contain the
most information in the fewest words? I believe it is
the atomic hypothesis (or the atomic fact, or whatever you
wish to call it) that all things are made of atoms — little
particles that move around in perpetual motion,
attracting each other when they are a little distance apart,
but repelling upon being squeezed into one another. In
that one sentence, you will see, there is an enormous amount
of information about the world, if just a little imagination and
thinking are applied.”
—Richard Feynman
Lecture on Physics, 1964
All of Matter is Composed of Microscopic Particles
Atoms: They’re just really tiny legos
2
2/1/2015
The Periodic Table:
118 Elements divided into 7 Periods & 18 Groups
Brownian Motion as Evidence of Atoms
Does a compound always have the same composition of
elements?
OR
Do these elemental proportions vary, depending on the
exact origin or method of preparation?
Carbon Dioxide is ALWAYS composed of
27 % Carbon & 73% Oxygen BY MASS (3 to 8 mass ratio)
Law of Definite Proportions:
Different samples of a pure chemical compound
always contain the same proportion of elements
by mass.
3
2/1/2015
Law of Definite Proportions:
Different samples of a pure chemical compound
always contain the same proportion of elements
by mass.
Ammonia (NH3): 18% hydrogen, 78% nitrogen
Sodium Chloride (NaCl): 39% sodium, 61% chlorine
Sulfur Dioxide (SO2): 50% oxygen, 50% sulfur
Sulfur Trioxide (SO3): 60% oxygen, 40% sulfur
Sometimes two elements form several different compounds:
Substance
Mass of Sulfur (g)
Mass of Oxygen (g)
Sulfur Trioxide
Sulfur Dioxide
1.0
1.0
1.5
1.0
SO3 has 3 oxygen atoms per sulfur atom
3
SO2 has 2 oxygen atoms per sulfur atom
2
=
1.5
1.0
Law of Multiple Proportions:
J
If two elements form more than one compound
between them:
THEN (given a fixed mass of the first element)…
the ratios of the masses of the second element can
always be expressed as a ratio of small whole
numbers.
Law of Multiple Proportions:
J
If two elements form more than one compound between them:
THEN (given a fixed mass of the first element)…
the ratios of the masses of the second element can always be
expressed as a ratio of small whole numbers.
Substance
Carbon Dioxide (CO2)
Unknown Substance
Mass of Carbon (g) Mass of Oxygen (g)
3.0
4.5
8.0
6.0
Based on this data, what is a likely formula for the unknown?
Compound 1 Element Mass Ratio (O/C)
Compound 2 Element Mass Ratio (O/C)
=
(8.0/3.0)
(6.0/4.5)
=
2
1
Given the same amount of carbon, carbon dioxide has TWICE as
many oxygen atoms as the unknown substance.
4
2/1/2015
iClicker Participation:
Applying the Law of Multiple Proportions
Reported below is the mass composition data of two substances,
both containing nitrogen and oxygen. Based on the Law of Multiple
Proportions, which pair of formulas is consistent with this data?
A. 1: N2O 2: N2O5
Substance
Mass of
Nitrogen (g)
Mass of
Oxygen (g)
B. 1: N2O 2: NO2
Unknown 1
3.5
2.0
C. 1: N2O 2: NO
Unknown 2
7.0
8.0
D. ALL of these options are consistent with the data.
E. NONE of these options are consistent with the data.
Nitrogen Oxides: A series of compounds illustrating
the Law of Multiple Proportions
Compound
Mass of
Nitrogen (g)
Mass of
Oxygen (g)
N2O
1.00
0.571
NO
1.00
1.41
NO2
1.00
2.28
NO4
1.00
4.57
The Law of Definite Proportions still applies here, but
each compound has INCREMENTALLY different
proportions of oxygen by mass. The INCREMENTAL
JUMPS are evidence for the existence of atoms.
iClicker Participation:
Applying the Law of Multiple Proportions
Reported below are nitrogen and oxygen masses for two different
substances. Based on the Law of Multiple Proportions, which pair of
formulas is consistent with this data?
Mass of
Mass of
Nitrogen (g) Oxygen (g)
A. 1: HNO2 2: HNO3
Substance
B. 1: N2O 2: N2O5
Unknown 1
1.00
2.28
C. 1: NO2 2: N2O5
Unknown 2
1.00
3.42
D. ALL of these options are consistent with the data.
E. NONE of these options are consistent with the data.
5
2/1/2015
Composition of Water:
1 g Hydrogen : 8 g Oxygen
Composition of Hydrochloric Acid:
1 gram Hydrogen : 35 g Chlorine
Relative Masses
Father of Atomic Theory, John Dalton used the data above
to conclude:
Oxygen atoms are 8 X heavier than Hydrogen atoms
Chlorine atoms are 35 X heavier than Hydrogen atoms
Chlorine atoms are OVER 4X heavier than Oxygen atoms
What does this assume? What is wrong
with this line of reasoning?
Gay-Lussac Experiment:
Experimenting with Gas Phase Reactions
Makes Hydrochloric Acid
Makes Water
Avogadro’s Hypothesis: EQUAL VOLUMES of different
gases contain EQUAL NUMBERS of gas particles.
Water Electrolysis:
Using Electricity to Break Water into its Component Elements
6
2/1/2015
Avogadro’s Hypothesis Applied to Relative Masses:
Determining the relative masses of Oxygen & Hydrogen
Composition of Water:
• 1 g Hydrogen : 8 g Oxygen
• 2 Hydrogen atoms : 1 Oxygen atom
If…
𝟏 𝒈 𝑯𝒚𝒅𝒓𝒐𝒈𝒆𝒏 𝟐 𝒂𝒕𝒐𝒎𝒔 𝑯𝒚𝒅𝒓𝒐𝒈𝒆𝒏
=
𝟖 𝒈 𝑶𝒙𝒚𝒈𝒆𝒏
𝟏 𝒂𝒕𝒐𝒎 𝑶𝒙𝒚𝒈𝒆𝒏
Then:
𝟏 𝒈 𝑯𝒚𝒅𝒓𝒐𝒈𝒆𝒏 𝟏 𝒂𝒕𝒐𝒎 𝑯𝒚𝒅𝒓𝒐𝒈𝒆𝒏
=
𝟏𝟔 𝒈 𝑶𝒙𝒚𝒈𝒆𝒏
𝟏 𝒂𝒕𝒐𝒎 𝑶𝒙𝒚𝒈𝒆𝒏
These experiments provide a way of establishing the
relative masses of elements.
Periodic Table:
• Historically, Dimitri Mendeleev first organized the elements in
the periodic table by increasing relative masses (circa 1869).
• Vertical columns (Groups) consisted of elements with similar
physical and chemical properties.
iClicker Participation:
Understanding Avogadro’s Hypothesis and Relative Masses
A substance is composed of 5.0 grams hydrogen and 35
grams of an unknown element (X). If this substance
decomposes into 6.3 L hydrogen gas and 3.2 L of the gaseous
X, what is a possible identity & relative mass of element X?
A. Oxygen, relative mass = 16
B. Nitrogen, relative mass = 14
C. Carbon, relative mass ≈ 12
D. Lithium, relative mass ≈ 7
E. None of these
choices are possible
identities for X.
7
2/1/2015
Dalton’s Atomic Theory
1) All matter is composed of atoms, which are tiny, indivisible
particles.
2) A compound is a combination of atoms of two or more
elements in specific ratios (Law of Definite Proportions & Law
of Multiple Proportions).
3) A chemical reaction is a rearrangement of atoms to form
different compounds. Atoms are neither created nor
destroyed in a chemical reaction (the law of conservation of
mass).
4) Atoms of one element cannot be converted into another
element. Atoms of an element are identical in mass and other
properties, and are different from every other element.
The Discovery of the Electron
The Discovery of the Nucleus
8
2/1/2015
The Discovery of the Nucleus
Expected Result:
Actual Result:
Size of the Atom Vs. Size of the Nucleus
If a single ATOM were the
size of a football field…
NUCLEUS (center of atom)
In an atom: The majority of the
space is taken up by electrons
ELECTRON CLOUD
The NUCLEUS would be
the approximate size of a
FLEA on the 50 yard line
Mass Comparisons
(Neutral)
The electron is about 1800 times LESS massive than the proton (or neutron).
Electrons orbit the nucleus in orbital clouds; the degree to
which they spread out determines the overall size of the
atom.
The nucleus is composed of:
PROTONS
NEUTRONS
9
2/1/2015
Volume Comparison
Mass Comparison
If the atom were the size of a
football field, the nucleus would be
the size of a flea on the 50 yard line
If the nucleus was as heavy as a
bowling ball, the electrons would
be as light as a penny.
The space occupied by the electrons
determines the size of the atom
10