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Chapter 3 - Atoms: the building blocks of matter
Taken from Modern Chemistry written by Davis, Metcalfe, Williams
& Castka
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Section 3.1 – The Atom: from philosophical idea to scientific theory
Objectives
Students will be able to :• Explain the laws of
Conservation of massDefinite proportionMultiple proportion
• Summarize the 5 essential points of Dalton’s atomic theory
• Explain the relationship between the 5 essential points and the above mentioned laws
HW – Notes on section 3.1 pgs 65-67
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Section 3.1 – The Atom: from philosophical idea to scientific theory
Foundations of Atomic Theory
As early as 400 B.C.E. particle theory of matter was supported – the particle was called an atom based on the Greek for “indivisible”.
Supported by DemocritusAristotle did not believe this theory
and his opinion lasted for 2 000 years. Felt all matter was continuous.
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Section 3.1 – The Atom: from philosophical idea to scientific theory
Foundations of Atomic Theory (continued)
By 1700s accepted idea that an element could not be broken down further. Back
The transformation of substance or substances into one or more new substances was known as a chemical reaction.
By the 1790s there was a new emphasis on quantitative analysis of chemical reactions
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Section 3.1 – The Atom: from philosophical idea to scientific theory
Foundations of Atomic Theory (continued)
This work lead to the discovery of several laws. . .
Law of Conservation of matter which states that mass is neither destroyed or created during ordinary chemical or physical reactions.
Antoine LavoisierBack
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Section 3.1 – The Atom: from philosophical idea to scientific theory
Foundations of Atomic Theory (continued)
The law of definite proportions, sometimes called Proust's Law, states that a chemical compound always contains exactly the same proportion of elements by mass.
Book example: salt is always 39.34% Na (sodium) and 60.66% Cl (Chlorine) by mass
Joseph Proust
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Section 3.1 – The Atom: from philosophical idea to scientific theory
Foundations of Atomic Theory (continued)
The law of multiple proportions, statement that when two elements combine with each other to form more than one compound, the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.
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Section 3.1 – The Atom: from philosophical idea to scientific theory
Dalton’s Atomic Theory1.All matter is made of extremely small particles called atoms. Relationship
2.All atoms of the same element are identical in size, mass & other properties. Relationship
3.Atoms cannot be subdivided, created or destroyed. Relationship
4.Atoms of different elements combine in WHOLE-number ratios to form compounds.
5.In chemical reactions atoms are combined, separated or rearranged. Relationship
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Section 3.1 – The Atom: from philosophical idea to scientific theory
Modern Atomic TheoryDalton turned idea’s (of ancient Greeks) into scientific theory
Today we know that atoms can be divided, but the law of conservation of matter holds true still.
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Section 3.1 – The Atom: from philosophical idea to scientific theory
Quiz Break
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Section 3.2 – The Structure of the Atom
Objectives
Students will be able to :• Summarize the observed properties of cathode rays that led to the discovery of the electron.• Summarize the experiment carried out by Rutherford and his co-workers that led to the discovery of the nucleus.• List the properties of protons, neutron and electrons•Define atom.
HW – Notes on section 3.2 pgs 70-74
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Section 3.2 – The Structure of the Atom
Discovery of the Electron
1st discovery of a subatomic particle resulted from investigations into the relationship between electricity and matter.
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Section 3.2 – The Structure of the AtomDiscovery of the Electron - Cathode Rays and Electrons
Hypothesized that the glow was caused by a stream of particles which they called a cathode ray.
Tested and found that1.An object placed between the cathode ray and the opposite end casts a shadow.2.A paddle wheel placed on rail
s rolled toward the anode from the cathode
.
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Section 3.2 – The Structure of the AtomDiscovery of the Electron - Cathode Rays and Electrons (continued) This supported the idea of a cathode ray. . .
Further testing found that1.Cathode rays were deflected by a magnetic field.2.Deflected away from negatively charged objects.
Thompson hypothesized that the ray was a particle, a negative one – later named electrons.
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Section 3.2 – The Structure of the AtomCharge and Mass of the electrons Thompson’s work showed that the electron has a very large charge for its tiny mass
R. A. Millikan (right) showed the mass to be
9.109 x 10-31 kg
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Section 3.2 – The Structure of the AtomCharge and Mass of the electrons – (continued) Based on that information two more inferences were made about atomic structure.
1.Atoms are electrically neutral so there must be positively charged particles to balance out the negative electron.
2.Because electrons have so much less mass than atoms, atoms must contain other particles which account for most of their mass.
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Section 3.2 – The Structure of the Atom
Discovery of the Atomic Nucleus
Ernest Rutherford & associates bombarded a thin gold foil with alpha particles (+ charge & 4 x mass of H atom)
Expected most particles to pass through with slight deflection – shocked to find that 1 in 8 000 were redirected back toward source.
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Section 3.2 – The Structure of the Atom
Discovery of the Atomic Nucleus – (continued)
Rutherford reasoned that the bounce back was from a densely packed bundle with a positively bundle he called the nucleus.
If the nucleus were the size of a marble the atom would be the size of a football field
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Section 3.2 – The Structure of the Atom
Composition of the Atomic Nucleus
Except for the simplest type of hydrogen all atomic nuclei are made of two types of particles, protonsprotons and neutronsneutrons.
Protons have a (+) charge which balances out the charge of the electrons.
Mass = 1.673 x 10-27 kg
Neutrons have a no charge and amass = 1.675 x 10-27 kg
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Section 3.2 – The Structure of the Atom
Composition of the Atomic Nucleus – (continued)
Nuclei of atoms of different elements differ in the # of protonsprotons they contain and therefore in the amount of positive charge.
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Section 3.2 – The Structure of the Atom
Properties Summarized
Particle SymbolsRelative electric charge
Mass number
Relative Mass (amu*)
Actual mass (kg)
Electron e-, -1 0 0.000 5486 9.109 x 10-31
Proton p+, +1 1 1.007 276 1.673 x 10-27
Neutron no, 0 1 1.008 665 1.675 x 10-27
e0-1
1 0
n
1 1
H
* 1 amu (atomic mass unit) = 1.660 540 x 10-27 kg
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Section 3.2 – The Structure of the AtomComposition of the Atomic Nucleus - Forces in the Nucleus
Like forces generally repel one another however when two protons are extremely close there is a strong attractions
These short-range proton-neutron, proton-proton, and neutron-neutron forces hold the particles together and a referred to as nuclear forces.nuclear forces.
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Section 3.2 – The Structure of the Atom
The sizes of Atoms
Atomic radii range from 40 to 270 pm (picometers)
Where as the nuclei of atoms have a much smaller radiiAbout 0.001 pm
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Section 3.3(A) – Counting Atoms
Objectives
Students will be able to :• Explain what isotopes are.• Define atomic number and mass number, and describe how they apply to isotopes.• Given the identity nuclide, determine its number of protons, neutrons and electrons.
HW – Notes on section 3.3 pgs 75-80
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Section 3.3(A) – Counting AtomsAtomic NumberThe atomic numberatomic number of an element is the number of protons in the nucleus of each atom of that element
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Section 3.3(A) – Counting Atoms
IsotopesIsotopes Isotopes are atoms of the same element that have different masses.
All hydrogen contain the same number of protons but may contain different number of neutrons.
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Section 3.3(A) – Counting Atoms
Mass Number
The mass number mass number is the total number of protons and neutrons in the nucleus of an isotope.
Mass Number 1 2 3
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Section 3.3(A) – Counting Atoms
Isotopes - pogil
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Section 3.3(A) – Counting Atoms
Isotopes – Pennium Lab
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Section 3.3(A) – Counting Atoms
Designating IsotopesNuclide Nuclide is a general term for any isotope of any element.
Nuclear Symbol
Sab
S = element’s symbola = protons + neutronsb = protons
3580
BrBromine has
Protons = ______
Neutrons = _______
Electrons = ________ Practice Practice Key
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Section 3.3(A) – Counting Atoms
Relative Atomic MassesThe standard used by scientist to govern units of atomic mass is the carbon-12 nuclide. One atomic mass atomic mass unit unit , or amu is exactly 1/12th the mass of a carbon-12 atom, or 1.660 540 x 10-27 kg
Although isotopes may have different masses, they do not differ significantly in their chemical behavior.
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Section 3.3(A) – Counting Atoms
Average Atomic Masses of Elements
AverageAverage atomic mass atomic mass is the weighted average of the atomic masses of the naturally occurring elements.
Example with marbles (100 total)
25 marbles x 2.00 g = 50 g75 marbles x 3.00 g = 225 g
Adding the masses gives
50 g + 225 g = 275 g
Divide this by the total number of marbles and you get an average marble mass of 2.75 g
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Section 3.3(A) – Counting AtomsAverage Atomic Masses of Elements –(continued)
AverageAverage atomic massatomic massHow are the masses on the periodic table determined?How are the masses on the periodic table determined?
(KEY)
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Section 3.3(B) – Counting Atoms
Objectives
Students will be able to :•Define mole in terms of Avogadro’s number, and define molar mass.•Solve problems involving mass in grams, amount in moles and number of atoms of an element.
HW – Notes on section 3.3 pgs 80-85
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms - the Mole
A mole mole (abbreviated mol)is the amount of a substance that contains as many particles as there are atoms in exactly 12 g of carbon-12.
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – Avogadro’s number
The number of particles in a mole has been experimentally determined in a number of ways.
Avogadro’s number Avogadro’s number 6.011 1367 x 1023 – is the number of particles in exactly one mole of a pure substance.
For ours (and most purposes) Avogadro’s number is rounded to 6.022 x 1023
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – Molar Mass
The alternative definition of mole is the amount of substance that contains avogadro’s number of particles.
The mass of one mole of a pure substance is called the molar mass molar mass of that substance. Usually written in units of g/mol.
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – Gram/Mole Conversions
There are 3 mole equalities. They are:
1 mol = 6.02 x 1023 particles1 mol = g-formula-mass
(periodic table)1 mol = 22.4 L for a gas at
STP*
* STP = 0° C & 1 atm Pressure
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – Conversions
There are 3 mole equalities. They are:
1 mol = 6.02 x 1023 particles1 mol = g-formula-mass (periodic table)
1 mol = 22.4 L for a gas at STP*
These become. . .
[-------------] or [-------------] 1 mol
6.02 x 1023 particles 1 mol 6.02 x 1023 particles
[-------------] or [-------------] 1 mol g-formula-mass (periodic table) 1 mol
g-formula-mass (periodic table)
[----] OR [----] 1 mol 22.4 L 1 mol
22.4 L
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Reference Sheet
There are 3 mole equalities. They are:
1 mol = 6.02 x 1023 particles1 mol = g-formula-mass (periodic table)
1 mol = 22.4 L for a gas at STP*
These become. . .
[-------------] or [-------------] 1 mol
6.02 x 1023 particles 1 mol 6.02 x 1023 particles
[-------------] or [-------------] 1 mol g-formula-mass (periodic table) 1 mol
g-formula-mass (periodic table)
[----] OR [----] 1 mol 22.4 L 1 mol
22.4 L
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Section 3.3(A) – Counting AtomsRelating Mass to Numbers of Atoms – What does it mean?
g-formula-mass (periodic table)
For a single element it is simply the atomic mass found on the periodic chart
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Section 3.3(A) – Counting AtomsRelating Mass to Numbers of Atoms – Examples
g-formula-mass (periodic table)
N
Ca
Ag
Ba
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Section 3.3(A) – Counting AtomsRelating Mass to Numbers of Atoms – What does it mean?
g-formula-mass (periodic table)
For a COMPOUNDCOMPOUND you will need to calculate using atomic mass found on the periodic chart
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – EXAMPLE
g-formula-mass (periodic table)
COMPOUNDSCOMPOUNDS
Table Salt
NaCl
Water
H2O
Sugar(glucose)
C6H12O6
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – EXAMPLE
g-formula-mass (periodic table)COMPOUNDSCOMPOUNDS
inorganic salt(soil fertilizer)
(NH4)2SO4
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – MOLE PRACTICES
Practice 1
Practice 2 Practice 2 (Key)
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – FUN WITH MOLES
Given : 2.860 m ceiling height9.630 m room depth10.620 m room width
Atmosphere composition:
Nitrogen - 78.084%Oxygen - 20.95%
1 000 L = 1 m3
How many mols of O2 and N2 are present in this room?
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – FUN WITH MOLES
Atmosphere composition:
Nitrogen - 78.084%Oxygen - 20.95%
How many particles of O2 and N2 are taken in with each breath?
Average lung volumes in healthy adults[7]
VolumeValue (litres)
In men In womenInspiratory
reserve volume 3.3 1.9
Tidal volume 0.5 0.5Expiratory
reserve volume 1.0 0.7
Residual volume 1.2 1.1
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – suggestions
1. Relax 2. Look for things you recognize3. Estimate size of final answer
(with this comes do I remember using any of these before)4. Set up and work out5. Double check with estimate and
your sig figs
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – MORE MOLE PRACTICES
Practice 3 Practice 3 (KEY)
TAKE-HOME QUIZ (KEY)
TAKE-HOME QUIZ
Practice 4 Practice 4 (KEY)
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Section 3.3(B) – Counting AtomsRelating Mass to Numbers of Atoms – Q - #4
100 atoms Ar 1 x 102 atoms Ar
1 x 102 atoms Ar-------------------------
1X -------------------------
Want to get to Mols...
6.02 x 1023 particles
1 mol
0.166 x 10-21 particles , which is equal to 1.66 x 10-1 x 10-21
Or more properly written as 1.66 x 10-22 mols Ar