The Scientific Method The Atomic Theory Classification of Matter

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The Scientific MethodThe Atomic
TheoryClassification of Matter

• Dr. Yau
• (loosely based on Chap. 1.4, 1.5, 1.6
• in Jespersen, Brady Hyslop, 6th edition)

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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
• Observe
• Hypothesize
• Test
• Form Theory

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The Scientific Method

• Observe (looking for a pattern in the
  observations) Note Observations could be from
  someone elses experiments.
• Form a hypothesis (which is an educated guess to
  explain the pattern)
• 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.
• If proven correct, hypothesis becomes theory.
• If not, it must be revised, re-tested or
  discarded.

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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.

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The Scientific Method is Cyclical
Fig 1.2 p. 4 Observations suggest explanations,
which suggest new experiments, which suggest new
explanations, and so on.
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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.
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Theory vs. Scientific Law

• Boyles Law (previous slide) alone did not bring
  us to the theory, but together with other laws
  such as Charles Law, Gay-Lussacs Law and
  Avogadros 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 P decreases.

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Learning Check

• Whenever we put a burning match to a piece of
  paper it will burn. Classify this statement. It
  is

1. a hypothesis
2. a theory
3. a test
4. an observation
5. a scientific law
6. a conclusion

Answer 4 Why is it not a hypothesis or theory?
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Daltons Atomic Theory

• Daltons 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.

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Daltons 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????
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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

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Models Helps Us Visualize Matter
Elements are made of identical atoms, either
singly or in groups.
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Allotropes of Carbon

• diamond
• graphite
• lonsdaleite
• (diamond formed when C meteorites hit the
  earth)
• buckyball
• C540 (nested bucky)
• C70
• amorphous C
• single-walled carbon nanotube or bucky tube

To keep it simple, we just write C for carbon as
if it were monatomic.
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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 S sulfur
• Ca calcium Ar argon
• Br bromine H hydrogen
• Cl chlorine 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

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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.
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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.
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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.)
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• 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
• S ________
• Ti ________
• ___ potassium
• ___ sodium

Note It is not sulphur, but sulfur.
titanium, not Titanium
not P! What is P?
not S!
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• 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.

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Some chemical names originated from Latin or
German
English Name Chemical Symbol Latin Name
Sodium Na Natrium
Potassium K Kalium
Iron Fe Ferrum
Copper Cu Cuprum
Silver Ag Argentum
Gold Au Aurum
Mercury Hg Hydrargyrum
Antimony Sb Stibium
Tin Sn Stannium
Lead Pb Plumbum
Tungsten W Wolfram (German)
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Elements

• Getting bored? Have some fun?
• Click here http//www.privatehand.com/flash/eleme
  nts.html

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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.

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What are Compounds?

• Compounds are substances made of more than one
  element combined
• 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.

in a fixed ratio.
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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

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Fixed Ratios in Compounds
Water is composed of H and O in a fixed ratio of
2 to 1, (18 by mass). Hydrogen peroxide is
composed of H and O in a ratio of 11, (116 by
mass).
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Fixed Ratios in Compounds

• Methane

Methane is composed of C and H in a fixed ratio
of 1 to 4.
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Fixed Ratios in Compounds Oleic Acid from Cows
Milk
C17H34O2
What does this tell you about Daltons Atomic
Theory?
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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!)

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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.
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Distillation Tower at the Oil Refinery
Gases (methane, ethane, propane, butane) C1 to C4
hydrocarbons BP below 20?C
Gasoline (naphthas) (C5 to C12) BP 20?-200?C
Kerosene (C12 to C15) BP 175-275?C
Crude Oil is vaporized
Fuel Oil (Diesel) (C15 to C18) BP 250-400?C
Lubricating Oil (C18 to C20) BP above 350?C
Residue (asphalt) (more than C20)
solid
Heat Source
Distillation is separation by physical means.
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Classification of Matter

• Mixtures can be classified as homogeneous
  mixtures or heterogeneous mixtures.

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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.

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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

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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

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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

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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 mixtures- consist of two or more
  phases
• Salad dressing, Coca-Cola

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Learning Check Pure or Mixture?

• True
• False
• True
• False
• True
• False

• Brass is pure.
• Natural peanut butter made only by crushing
  peanuts is pure.
• Because blood cells can be distinguished from
  plasma under a microscope, blood is a
  heterogeneous mixture.

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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.

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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.

2 NaCl (s) 2 Na (s) Cl2 (g)
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Separation by Chemical Means

• Electric
• Current

2 H2O (s) 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
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Learning Check Classification
Hot Cocoa Aluminum Foil Ice (H2O) White Flour Table Salt (NaCl)
Pure Substance
Element
Compound
Molecule
Heterogeneous Mixture
Homogeneous Mixture
X
X
X
X
X
X
X
X
Why is NaCl not a molecule?
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Metals, Nonmetals, And Metalloids
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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?
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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
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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
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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
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Learning Check

• Which of the following is/are molecular
  compounds?
• A. P2O5 (in match heads)
• B. SO2 (air pollutant from factories)
• C. Fools gold (pyrite FeS2)
  Fools Gold
• D. H2S (gas produced from acid on fools gold,
  smells like rotten eggs)
• E. I2

Ans. A, B, D, E
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• We can now extend the Classification of Matter
  further.

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• MATTER
• Pure Substance
  Mixture
• Element Compound Homogen. Heterogen.
• 
  Mixture Mixture
• atom molecule
• molecular ionic
• compound compound