The Scientific Method
The Atomic Theory
Classification of Matter
Dr. Yau
(loosely based on Chap. 1.4, 1.5, 1.6
in Jespersen, Brady & Hyslop, 6th edition)
1
What is meant by the
“Scientific Method?”
The scientific method is a way to solve a
problem or answer a question in science.
One simplistic way to view this method is to
think of it as being in 4 steps:
1. Observe
2. Hypothesize
3. Test
2
4. Form Theory
The Scientific Method
1. Observe (looking for a pattern in the
observations) Note: Observations could
be from someone else’s experiments.
2. Form a hypothesis (which is an
educated guess to explain the pattern)
3. Test the hypothesis
a) Design a test that would provide
evidence that the hypothesis is correct. It
MUST be reproducible.
b) Run the test and analyze the results.
4. If proven correct, hypothesis becomes
theory.
If not, it must be revised, re-tested or
3
discarded.
Scientific Theory
A scientific theory is not “absolute.”
With improvement in instrumentation and
new discoveries, additional experimental
data can render a theory to become
questionable.
We can never be absolutely sure that a
theory is correct.
Scientists MUST keep an open mind.
4
The Scientific Method is Cyclical
Fig 1.2 p. 4 Observations suggest explanations,
which suggest new experiments, which suggest
new explanations, and so on.
5
What is a Scientific Law?
It is a generalized summary of a large quantity of data
and observations for which there is no exception.
It differs from a hypothesis or a theory in that it does
not attempt to explain the phenomenon.
e.g. The scientist, Boyle, noticed that when a sample
of gas is allowed to expand, its pressure decreases
proportionally if the temperature is kept constant. He
states that the pressure (P) of a gas is inversely
proportional to its volume (V) at constant
temperature (T):
There is no attempt to
explain why.
6
Theory vs. Scientific Law
Boyle’s Law (previous slide) alone did not bring us to
the theory, but together with other laws such as
Charles’ Law, Gay-Lussac’s Law and Avogadro’s
Law, scientists came up with the Kinetic Molecular
Theory to explain the behavior of gases.
A sample of gases is made of small particles that are
very far apart and are in constant random motion. It
is the collision of these particles on the walls of the
container that creates pressure.
When the V is small, there would be more collisions
with the walls, and thus P is larger.
When V is increased, the particles have more room to
move and there are less collisions with the walls and
7
P decreases.
Learning Check:
Whenever we put a burning match to a piece of
paper it will burn. Classify this statement. It is…
1.
2.
3.
4.
5.
6.
a hypothesis
a theory
a test
an observation
a scientific law
a conclusion
Answer: #4 Why is it not a hypothesis or theory?
8
Dalton’s Atomic Theory
Dalton’s Atomic Theory is based on
three scientific laws:
• Law of Conservation of Mass
• Law of Definite Proportions
• Law of Multiple Proportions
(These comprise the “observations” in
the Scientific Method, leading to the
“hypothesis” and ultimately, the
“theory.”
9
Dalton’s Atomic Theory
1. Matter is made of tiny indivisible particles
called atoms. (from Greek word “atomos”
meaning indivisible).
2. Atoms of an element are identical in mass &
other properties. Atoms of different elements
have different properties.
3. Compounds are made of atoms of different
elements combined in a fixed ratio of small
whole numbers.
4. In reactions, atoms are not destroyed or
created but merely rearrange to form new
cmpds. Why are some words in red????
10
What Is An Element?
• Elements - substances that cannot be
decomposed into simpler substances.
• shown on the periodic table as symbols:
“K” for potassium and “Na” for sodium
There are around 118 known elements.
around 92 are natural occurring
around 26 are man-made
11
Models Helps Us Visualize Matter
Elements are made of
identical atoms, either
singly or in groups.
12
Allotropes of Carbon
a) diamond
b) graphite
c) lonsdaleite
(diamond formed
when C meteorites
hit the earth)
e
To keep it simple, we just write C for
carbon as if it were monatomic.
d)
e)
f)
g)
h)
buckyball
C540 (nested bucky)
C70
amorphous C
single-walled
carbon
nanotube or
bucky tube
13
Chemical Symbols for Elements
Chemical Symbol
– One or two letter symbol for each element name
– First letter capitalized, second letter lower case
Ex. C = carbon
Ca = calcium
Br = bromine
Cl = chlorine
S = sulfur
Ar = argon
H = hydrogen
O = oxygen
• Used to represent elements in chemical formulas
Ex. Water = H2O
Carbon dioxide = CO2
– Most based on English name
– Some based on Latin or German names
14
Chemical Symbols for Elements
Some are given a single letter (always
capitalized): H, B, C, N etc.
Some are given two letters (first letter is always
capitalized, and the second letter is always in
lower case): He, Li, Be etc.
If you write two letters with both upper case you
would be implying a compound (made of two
elements).
e.g. HF is the compound, hydrogen fluoride.
and Hf is the element, hafnium.
15
e.g. Co is the element, cobalt.
and CO is the compound, carbon monoxide.
It is essential you learn not to capitalize both
letters if you had meant to refer to an
element.
In giving the name of an element, do not
capitalize the name unless it is at the
beginning of a sentence.
The name of an element is NOT a proper
noun.
16
Examples of elements:
C, Fe, Al, O2, N2, P4
Examples of compounds:
CO2, C12H22O11, NaCl
What do the subscripts mean?
First we must examine the concept of
"atoms."
An atom is the smallest particle of an
element.
(Note: It can be broken down further but it
would become a different element.)
17
HOMEWORK: Learn the names and symbols
of elements. Quiz next period includes this
type of question.
Example: Give the name or symbol of the
following:
Note: It is not sulphur, but
= ________ sulfur.
= ________ titanium, not Titanium
S
Ti
___ = potassium not P! What is P?
___ = sodium not S!
Note that there are symbols in the periodic table
with more than 2 letters. Which ones??
These are elements not yet named.
Elements are usually named by the scientists who
discovered/made them.
Sometimes it is difficult to prove who discovered
them first.
Meanwhile they are given 3 letters:
Uuu = unununium (Latin for 111)
now named roentgenium (symbol = Rg)
Uub = ununbium (Latin for 112)
now named copernicium (symbol = Cn)
Uut = ununtrium (Latin for 113) not formally
named.
19
Some chemical names originated from Latin or German
English Name Chemical Symbol
Sodium
Na
Potassium
K
Iron
Fe
Copper
Cu
Latin Name
Natrium
Kalium
Ferrum
Cuprum
Silver
Gold
Mercury
Antimony
Ag
Au
Hg
Sb
Argentum
Aurum
Hydrargyrum
Stibium
Tin
Lead
Sn
Pb
Stannium
Plumbum
Tungsten
W
Wolfram
(German)
20
Elements
diamond = carbon
gold
sulfur
Getting bored? Have some fun?
Click here:
http://www.privatehand.com/flash/elements.html
21
Elements
You should have already learned (and still remember!)
the names and chemical symbols for many of these
elements.
This semester you will be learning a few more.
If you took CHEM 107 on the Catonsville Campus you
would be familiar with the Nomenclature Tutorial for
Prep Chem.
This semester you will be using the one designated for
Gen Chem. There will be frequent quizzes on
sections of this Nomenclature Tutorial. Check the
Assignment page for what the quizzes will cover.
They will always be cumulative and may contain
material other than nomenclature.
22
What are Compounds?
Compounds are substances made of more
than one element combined in a fixed ratio.
Mixtures can also be substances made of
more than one element.
e.g. Brass = Cu + Zn
e.g. Bronze = Cu + Sn
Why are these not “compounds?”
There is more than one answer to this. Try
to think up as many as you can.
23
What Is A Compound?
• Compounds - formed from two or more
atoms of different elements combined in
a fixed proportion
• Have different characteristics than the
elements that compose them
• Can be broken down into elements by
some chemical changes
24
Fixed Ratios in Compounds
Hydrogen peroxide
Water is composed of H and O in a fixed ratio of 2 to 1,
(1:8 by mass).
Hydrogen peroxide is composed of H and O in a ratio of 1:1,
(1:16 by mass).
25
Fixed Ratios in Compounds
Methane
Methane is composed of C and H in a fixed
ratio of 1 to 4.
26
Fixed Ratios in Compounds: Oleic Acid from Cow’s Milk
C17H34O2
What does this tell you about Dalton’s Atomic Theory?
27
Classification of Matter
Matter is either a pure substance or a mixture
Mixtures may be separated into pure substances
using physical means such as distillation,
filtration, chromatography (You did all this in CH108!)
28
Separation by physical means:
They are based on the difference in physical
properties of the components.
e.g. Filtration of sand from water
(Difference in solubility)
e.g. Distillation of water from salt water
(Difference in boiling point)
e.g. Distillation of crude oil into useful
fractions. (Difference in boiling point)
At the oil refineries, crude oil is heated and
various fractions are collected at different
temperatures based on their boiling points.
29
Distillation Tower at the Oil Refinery
Gases (methane, ethane, propane,
butane)
C1 to C4 hydrocarbons
BP below 20C
gas
Gasoline (naphthas) (C5 to C12)
BP 20-200C
Kerosene (C12 to C15)
BP 175-275C
Crude Oil is
vaporized
liquid
Fuel Oil (Diesel) (C15 to C18)
BP 250-400C
Lubricating Oil (C18 to C20)
BP above 350C
Residue (asphalt) (more than C20)
Heat
Source
Distillation is separation by physical means.
solid
30
Classification of Matter
Mixtures can be classified as homogeneous
mixtures or heterogeneous mixtures.
31
Homogeneous Mixtures
Homogeneous mixtures have the same
properties throughout the sample.
Solutions are homogeneous mixtures.
e.g. salt water, coffee (without the grind)
e.g. Rubbing alcohol is a solution of isopropyl
alcohol and water. It can be purchased as a 90%
or 70% solution.
Alloys are homogeneous mixtures of metals.
e.g. Brass is a homog. mix of Cu and Zn
e.g. Bronze is a homog. mix of Cu and Sn.
We can have different % of Zn in brass, giving it a
whiter or more orange color. But, within one
sample, the percentage is the same.
32
Homogeneous Mixtures
• Same properties throughout sample
• Solution
– Thoroughly stirred homogeneous mixture
Ex.
– Liquid solution
• Sugar in water
– Gas solution
• Air
– Contains nitrogen, oxygen, carbon
dioxide & other gases
– Solid solution
• US 5¢ coin – Metal Alloy
– Contains copper & nickel metals
33
Heterogeneous Mixtures
Heterogeneous mixtures…
• do not have a uniform composition within a
sample
• components often not of the same
physical state
• components are not miscible (do not mix)
e.g. oil and water
e.g. mixed nuts
e.g. sand and sugar
34
Heterogeneous Mixtures
• 2 or more regions of different properties
• Solution with multiple phases
• Separate layers
Ex.
– Salad dressing
• Oil & vinegar
– Ice & water
• Same composition
• 2 different physical states
35
Mixtures
• mixtures consist of varying
amounts of two or more
elements or compounds
• Homogeneous mixtures or
“solutions”- have the same
properties throughout the
sample
– Brass, tap water
• Heterogeneous mixturesconsist of two or more phases
– Salad dressing, CocaCola ™
36
Learning Check: Pure or Mixture?
• Brass is pure.
• True
• False
• Natural peanut butter made only by
crushing peanuts is pure.
• True
• False
• Because blood cells can be
• True
distinguished from plasma under a
• False
microscope, blood is a heterogeneous
mixture.
37
Elements and Compounds
Pure substances are classified as elements or
compounds.
Compounds can be separated into elements only by
chemical means and not physical means, such as
electrolysis, thermal decomposition.
38
Separation by Chemical Means
Compounds can be separated into
elements by chemical menas:
Decomposition by electrolysis:
– Chemical reaction where 1 substance is broken
down into 2 or more simpler substances by
passing an electric current thru the sample.
Ex.
Molten
sodium
chloride
2 NaCl (s)
Electric
current
Sodium metal
+
chlorine gas
2 Na (s) + Cl2 (g)
39
Separation by Chemical Means
2 H2O (s)
Electric
Current
2 H2 (s) + O2 (g)
Do not confuse this with the what happens
when you boil water!
Write the equation for what happens when
you boil water:
40
Learning Check: Classification
Hot Aluminum Ice
White
Foil
Cocoa
(H2O) Flour
Pure
Substance
Element
Compound
Molecule
Table
Salt
(NaCl)
X
X
X
X
X
X
Heterogeneous
X
Mixture
Homogeneous
Mixture
Why is NaCl not a molecule?
X
41
Metals, Nonmetals, And Metalloids
42
Why it matters whether an element is
METAL or NONMETAL
KNOW THIS WELL!
Nonmetal + Nonmetal = Molecular cmpd
(covalent bonds)
Metal + Nonmetal
= Ionic cmpd
(ionic bonds)
Metal + Metal
= Alloy (homog.mixt.)
So why table salt not made of molecules?
43
Learning Check
How is table sugar classified? Table sugar is
sucrose from sugar cane with the formula
C12H22O11
A. element
B. molecule
C. compound
D. ionic compound
E. homogeneous mixture.
F. heterogeneous mixture.
G. pure substance
Ans. B, C, G
44
Learning Check
How is S8 classified?
A. element
B. molecule
C. compound
D. ionic compound
E. homogeneous mixture
F. heterogeneous mixture
G. pure substance
Ans. A, B, G
45
Learning Check
How is chalk classified?
Assume it is calcium carbonate.
A. element
B. molecule
C. compound
D. ionic compound
E. homogeneous mixture.
F. heterogeneous mixture.
G. pure substance
Ans. C, D, G
46
Learning Check
Which of the following is/are molecular
compounds?
A. P2O5 (in match heads)
B. SO2 (air pollutant from factories)
C. Fool’s gold (pyrite: FeS2)
Fool’s Gold
D. H2S (gas produced from acid on fool’s
gold, smells like rotten eggs)
E. I2
Ans. A, B, D, E
47
We can now extend
the Classification of
Matter further.
48
MATTER
Pure Substance
Element
Compound
Mixture
Homogen. Heterogen.
Mixture
Mixture
atom molecule
molecular ionic
compound compound
49