Download Unit 5 Notes

Unit 5 (Ch.3 & 21) Guided Notes
I.
5.1: Democritus and Dalton
A.
The Atom: A Philosophical Idea
1.
The idea of __________________ is very old.
2.
Democritus (Greek, 400 BC) - said that things were made up of tiny, indivisible particles (atoms)
– only an idea
3.
Aristotle - disagreed with Democritus’ idea – his opinion was more ___________________, so
the concept of atoms was lost until John Dalton.
4.
B.
No evidence to support either idea.
Three Fundamental Laws of Chemistry
1.
Law of Conservation of Mass (1789):
a)
In ordinary chemical reactions, mass is neither ______________ nor
___________________.
b)
2.
Mass of the reactants equals the mass of the products (as does # of atoms).
Law of Definite Proportions (1797):
a)
A chemical compound contains the same elements in exactly the same proportions
regardless of the size of the sample or source of the compound.
b)
3.
Example: water – hydrogen to oxygen ratio is always _____________.
Law of Multiple Proportions (1803):
a)
If two or more different compounds are composed of the same two elements, then the
proportions can be expressed as simple, whole-number ratios.
b)
Example:
(1)
Carbon and Oxygen
(a)
Carbon monoxide - CO
(b)
Carbon dioxide – CO2
C.
John Dalton (1808)
1.
English __________________ __________________________, wanted to explain the laws of
conservation of mass, definite proportions and multiple proportions.
2.
His model is called Dalton’s Atomic Theory.
3.
Postulates of his theory
a)
All matter is composed of extremely small particles called __________.
b)
Atoms of a given element are identical in size, mass, and other properties; atoms of
different elements differ in size, mass, and other properties.
c)
Atoms cannot be subdivided, created, or destroyed.
d)
Atoms of different elements combine in simple whole-number ___________ to form
chemical compounds (molar ratios).
e)
4.
II.
In chemical reactions, atoms are combined, separated, or rearranged.
Some aspects of Dalton’s atomic theory have been revised. We now know that:
a)
Atoms are divisible into even smaller particles.
b)
A given element can have atoms with different _____________.
5.2: Models of the Atom
A.
Warm up: Friday, September 27
1.
Create a drawing that illustrates Dalton’s view of an atom.
2.
Based on what you learned about atoms in other science classes, create a diagram that
represents the structure of an atom.
3.
Explain how your two drawings are different.
B.
JJ Thomson – 1897
1.
He discovered that within atoms there are negatively charged particles
2.
He called these particles ____________________.
a)
Thomson performed experiments that involved passing electric current through gases at
low pressure.
b)
3.
The result was a glowing beam called a _______________ _________.
A cathode ray is deflected by electrically charged plates.
4.
Thomson concluded that a cathode ray is a stream of electrons. Electrons are parts of the atoms
of all elements.
5.
From his findings, Thomson developed the “Plum pudding” model.
a)
The atom was filled with positively charged material and the electrons were evenly
distributed throughout.
C.
Ernest Rutherford - 1911
1.
Gold foil experiment
2.
He directed a narrow beam of alpha particles at a very thin sheet of gold foil.
3.
Alpha particles are positively charged particles that are released by certain radioactive elements
as they decay.
4.
Rutherford’s Gold-Foil Experiment
a)
Alpha particles scatter from the gold foil.
b)
The Rutherford Atomic Model
(1)
Rutherford concluded that the atom is mostly _____________ __________.
(2)
All the positive charge and almost all of the mass are concentrated in a small
region in the center of the atom.
(3)
He called this tiny core the _________________.
D.
III.
Niels Bohr- 1913
1.
Planetary Model
1.
Electron is found only in specific circular paths, or ________________, around the nucleus.
5.3 Modern Atomic Theory
A.
Warm Up: Decide whether each of the following statements concerning atoms is true (T) or false (F).
1.
All of the particles in the
nucleus of an atom are charged.
2.
The atom is best described as
a uniform sphere of matter in which
electrons are embedded.
3.
The mass of the nucleus is
only a very small fraction of the
mass of the entire atom.
4.
The size of the nucleus is only
a very small fraction of the total size
of the atom.
5.
The number of neutrons in
an atom must equal the number of
electrons.
B.
Modern Atomic Theory
a)
1.
Atom – smallest unit of an element that retains the ________________ of that element.
Atoms are composed of two regions and three subatomic particles.
a)
Nucleus – positively charged region located at the center of the atom.
(1)
Very small compared to the total size of the atom. (marble = size of nucleus /
football field = size of atom)
(2)
b)
Composed of two particles
(a)
Proton = ______________ particle
(b)
Neutron = ______________ particle
(3)
Almost all mass is located in nucleus (extremely dense)
(4)
Nucleus held together by strong nuclear forces.
Electron Cloud –
(1)
Mostly ________________ space
2.
3.
4.
(2)
Gives atom its size
(3)
Contains tiny negatively charged particles called ____________.
Atoms are very small in size.
a)
So small we use picometers (1x10-12m)
b)
Atomic radii range from 40 to 270 pm
Atoms have very small masses.
a)
Example: mass of oxygen atom 2.6 x 10-23g.
b)
atomic mass unit (amu)
c)
1 amu = 1.66 x 10-27g = 1/12 the mass of a carbon-12 atom.
d)
atoms have masses from 1-300 amu’s
Atoms are electrically neutral.
a)
Although an atom contains charged particles, the atom overall is
____________________.
C.
A proton and an electron have the same amount of charge just opposite in sign.
c)
NUMBER OF PROTONS = NUMBER OF ELECTRONS.
Atomic Number and Mass Number
1.
2.
D.
b)
Atomic Number (Z) –
a)
number of _________________in the nucleus of atom of a particular element.
b)
whole number listed on the periodic table.
Mass Number (A) –
a)
number of protons and neutrons in nucleus of an atom.
b)
do not confuse with decimal number listed on periodic table (that’s avg. atomic mass).
Representing Atoms
1.
There are two different ways to represent atoms.
a)
Symbol Notation –
b)
Hyphen-Notation
(1)
Consists of name of element and a number.
(a)
Example: chlorine – 37
(b)
Number after name is the mass number.
c)
Sample Problem: Determine the number of protons, neutrons, and electrons for a
bromine-80 atom.
IV.
5.4 Isotopes
A.
As techniques for finding the masses of atoms has improved, we have learned that not all atoms of the
same element are identical.
B.
C.
D.
Isotopes –
1.
atoms of the same element that have different masses
2.
vary in the number of _______________ they contain in the nucleus
3.
almost all elements have more than one isotope.
4.
Chemically, isotopes _________ exactly the same.
Average Atomic Mass
1.
Decimal number listed on periodic table.
2.
Weighted average of all the naturally occurring _____________ of that element.
3.
No atom has this exact mass.
Think About It
1.
Hydrogen has two natural isotopes hydrogen-1 and hydrogen-2. The atomic mass for hydrogen
is 1.007 amu. Explain why the atomic mass is not 1.50.
2.
Chlorine has two naturally occurring isotopes, chlorine-37 and chlorine-35. Which isotope is
more abundant? How do you know?
E.
Counting Atoms and the Mole
1.
SI unit for amount of substance is called mole.
a)
A mole measures the number of particles within a substance.
b)
A mole refers to a specific number of ____________________. (Counting Unit like a
dozen)
c)
1 mole = 6.02 x 1023 particles
d)
6.02 x 1023 is also known as Avogadro’s Number
e)
1 mole magnesium = ___________________ Mg atoms
2.
f)
1 mole zinc
= 6.02 x 1023 Zn atoms
g)
1 mole lead
= ___________________ Pb atoms
Molar Mass
a)
Although 1 mole always contains the same number of particles, the
_________________ of one mole varies depending on the substance.
3.
Molar Mass – mass of one mole of a substance.
a)
Mass of one mole of an element is equal to its _______________ ________________
expressed in grams.
V.
b)
1 mole of magnesium = 24.31 grams
c)
1 mole of zinc
d)
1 mole of lead
= 65.39 grams
= 207.2 grams
5.5 Calculations Involving Moles
A.
Warm Up: A student has a 1 mole sample of silver and a 1 mole sample of gold.
1.
Which sample contains the greatest number of atoms? How many atoms are in each sample?
2.
Which sample has the greatest mass? What is the mass of each sample?
3.
The current price of gold is $42.37 per gram. How much is the gold sample worth?
B.
Many times in chemistry, you will need to express a measurement in a unit different from the one given
or measured initially.
C.
A ___________________________ is a ratio of equivalent measurements used to convert from one unit
to another. They are written in the form of a ___________________.
Label
Mole
Atoms
Grams (mass)
D.
Number Used in Conversion Factor
Example Problems:
1.
A chemist produced 11.25 g of magnesium, Mg. How many moles of magnesium were
produced?
2.
Determine the number of silver atoms that are contained in 0.650 mol Ag?
3.
E.
Calculate the mass, in grams, of 3.07 x 1024 atoms of sulfur (S).
What Do You Think?
1.
Determine the number of moles that are contained in 2.65 g of fluorine (F).
2.
How many atoms are found in 6.53 mol chlorine (Cl)?
3.
Determine the mass, in grams, of 8.29 x 1022 atoms of cobalt (Co).
4.
Calculate the number of moles found in 8.49 x 1024 atoms oxygen (O).
5.
Calculate the mass, in grams, of 0.0845 mol argon (Ar).
6.
How many atoms are contained in 17.63 g of aluminum (Al)?
VI.
5.6: History of the Periodic Table
A.
Warm Up
1.
Using the periodic table, determine the number of protons and electrons in a chlorine atom.
2.
Identify which group and period chlorine is located on the periodic table.
3.
Is chlorine considered a metal, nonmetal, or metalloid?
a)
4.
Explain your choice.
What is the mass of one mole of chlorine atoms?
5.
Name two other elements that would have similar chemical properties as chlorine. Explain your
choices.
B.
History of the Periodic Table
1.
Russian chemist Dmitri Mendeleev (1869) wanted to organize known elements by properties.
2.
When he arranged elements by increasing ______________ ________________, he noticed
that similar elements occurred at regular intervals.
C.
Mendeleev’s Periodic Table
1.
He called his chart the “________________” table.
2.
In order for similar elements to line up, Mendeleev left gaps in his chart.
3.
Mendeleev stated these were undiscovered elements. He made ________________________
about these undiscovered elements based on the other elements in the same row.
a)
By 1886, these elements (scandium, gallium, and germanium) were discovered and their
properties closely matched his predictions.
D.
Mendeleev has Unresolved Issues
1.
With the discovery of Mendeleev’s predicted elements, most chemists were persuaded to
accept his table. However, there were two issues unresolved by his table.
a)
What caused elements to have similar properties?
b)
Why were there certain cases when a heavier element had to be placed in front of a
light element so properties would line up (Te and I)?
E.
Moseley and the Periodic Table
1.
Henry Moseley (1911) – discovered technique to determine nuclear charge of atom.
a)
2.
He called this the ________________ __________________.
Every element had its own unique atomic number.
3.
When Moseley arranged elements by increasing atomic number, the inconsistencies of
Mendeleev’s table disappeared.
F.
Modern Periodic Table
1.
Periodic Law – when elements are arranged by increasing ______________
__________________, elements with similar chemical and physical properties occur at regular intervals.
2.
Today the periodic table arranges elements by ________________ and
_____________________.
a)
Group – vertical column of elements
(1)
also known as families
b)
G.
Period – horizontal row of elements
Changes in the Periodic Table
1.
There have been significant changes to the periodic table since Mendeleev created his chart.
a)
Noble Gases – elements that make up group 18. Include He, Ne, Ar, Kr, Xe, and Rn.
(1)
Extremely unreactive gases
(1)
Very stable elements that __________ ____________ combine with other
atoms in nature.
b)
c)
Lanthanide series – elements 58-71
(1)
Also called rare earth elements since they are hard to identify and separate.
(2)
These elements are part of period 6.
Actinide series – elements 90-103
(1)
Most are ___________________ and all are radioactive.
(2)
These elements are part of period 7.
Nuclear Chemistry
VI.
5.7 Nuclear Radiation
A.
Changes in Matter
1.
Matter can undergo three types of changes.
a)
Physical Change – change in __________________________ but not identity.
b)
Chemical Change – production of ___________ _______________________ with
different properties – same elements just rearranged – usually involves valence electrons.
c)
Nuclear Change – forms different ____________________ from what you started with.
(1)
Nuclear changes involve changes in the nucleus of an atom.
B.
Radioactivity – spontaneous emission of __________ or ________________________ from certain
elements (like uranium).
1.
also known as radioactive decay
2.
rays and particles emitted from a radioactive source are called nuclear
_____________________.
C.
Radioactivity is an example of a nuclear reaction.
1.
Purpose of radioactive decay is for an _______________________ _____________________to
become stable.
2.
Nuclear reactions begin with unstable isotopes known as radioisotopes.
3.
Atoms become stable when changes occur in the ______________________.
4.
These changes are always accompanied by the emission of large amounts of energy.
5.
Unlike chemical reactions, nuclear reactions are not affected by changes in temperature,
pressure, or the presence of catalysts.
6.
Nuclear reactions of given radioisotope cannot be slowed down, sped up, or stopped.
7.
Radioactive decay is a ________________________ process.
8.
If the product of a nuclear reaction is unstable, it will decay __________________.
9.
The process continues until unstable isotopes of one element are changed, or transformed, into
stable isotopes of a different element.
10.
These stable isotopes are not radioactive.
11.
Nuclear _____________________ is emitted during radioactive decay.
12.
There are three main types of nuclear radiation: ______________ radiation, ___________
radiation, and __________________radiation.
D.
Types of Radiation
1.
Alpha Radiation
a)
An alpha particle (α) is two protons and two neutrons bound together and is emitted
from the nucleus during some kinds of radioactive decay (also referred to a as a helium nucleus).
b)
Alpha particles have a ________________ charge
c)
In nuclear equations, an alpha particle is written as:
(1)
Example:
(2)
When an atom loses an alpha particle, the atomic number of the product is
lowered by two and the mass number decreases by four.
d)
In balanced nuclear equations, the sum of the _________ numbers on the right must
equal the sum on the left.
e)
This is also true for the _______________ numbers.
f)
Alpha particles are the least penetrating type of radiation.
(1)
2.
Sheet of paper or the surface of your skin can stop them.
Beta Radiation
a)
A beta particle (β) is an electron emitted from the nucleus during some kinds of
radioactive decay.
b)
A beta particle is formed when a neutron breaks apart into a proton and an electron.
c)
The proton remains in the nucleus while the _________________ is ejected.
d)
The -1 refers to the charge of the electron and the 0 refers to the mass (essentially
zero).
(1)
Example:
(2)
When an atom loses a beta particle, the atomic number of the product is
increased by one; however, the mass number remains the same.
e)
Since a beta particle has less charge and much less mass than an alpha particle, beta
particles are __________ _________________________ than alpha particles.
(1)
Beta particles can pass through paper but are stopped by aluminum foil or thin
pieces of wood.
3.
Gamma Radiation
a)
Gamma rays () are high-energy waves emitted from a nucleus as it decays.
b)
Gamma rays have no mass and no electrical charge. Therefore, gamma radiation does
not alter the atomic number or mass number of an atom.
c)
Nuclei often emit gamma rays along with ______________ or _____________ particles.
d)
Gamma rays are the _____________ penetrating type of nuclear radiation.
(1)
Easily pass through paper, wood, and human body (extremely dangerous).
(2)
They can be stopped, although not completely, by several meters of concrete or
several centimeters of lead.
E.
Nuclear Equations Sample problems
1.
Radium-226 is a radioactive isotope that decays by releasing an alpha particle. Write a nuclear
equation for the radioactive decay of radium-226.
2.
Potassium-40 decays by releasing a beta particle. Write a nuclear equation that represents the
radioactive decay of potassium-40.
VIII.
5.8: Nuclear Stability and Half-Life
A.
More than 1500 different isotopes are known. Of those, only _____________ are stable and do not
decay over time.
B.
1.
One factor that affects the stability of nucleus is the ratio of neutrons to protons.
2.
Too many or too few neutrons relative to the number of protons makes the nucleus unstable.
3.
A neutron vs proton plot of stable nuclei form a pattern called the band of stability.
Band of Stability
1.
For elements with atomic numbers 20 or less, this ratio is about 1:1. Above atomic number 20,
stable nuclei have ____________ neutrons than protons.
2.
The band of stability can be explained by the relationship between the nuclear force and the
electrostatic forces between protons.
a)
As the number of protons in a nucleus increases, the _____________________
electrostatic force between protons increases faster than the nuclear force.
b)
More neutrons are required to increase the nuclear force and stabilize the nucleus.
c)
Beyond the atomic number 83, bismuth, the repulsive force of the protons is so great
that ________ stable isotopes exist.
C.
Half-Life
1.
Every radioisotope has a characteristic rate of decay, which is measured by its half-life.
2.
Half-life is the time required for one-half of the nuclei in a radioisotope sample to decay.
3.
During each half-life, half of the remaining radioactive atoms decay into atoms of a
___________ __________________.
4.
Each radioactive nuclide has its own half-life. Half-lives can be a short as a fraction of a second
or as long as billions of years.
a)
One isotope that has a long half-life is uranium-238.
(1)
4.5 billion years
(2)
Decays through a complex series of unstable isotopes to the stable isotope of
lead-206.
5.
The following equation can be used to calculate how much of an isotope will remain after a
given number of half-lives.
(1)
A = Ao x (1/2)n
(a)
A stands for the amount remaining, Ao for the initial amount, and n for
the number of half-lives.
D.
Half-Life Sample Problem
1.
Phosphorus-32 has a half-life of 14.3 days.
a)
How long is four half-lives?
b)
If you started with 24.0 g of phosphorus-32, how many grams of the isotope remain at
the end four half-lives?
E.
IX.
Reflection
5.9: Fission and Fusion
A.
Nuclear Fission
1.
What happens in a nuclear chain reaction?
a)
When the nuclei of certain isotopes are bombarded with neutrons, they undergo
_________________, the splitting of a nucleus into smaller fragments.
b)
In a chain reaction, some of the neutrons produced react with other fissionable atoms,
producing more neutrons which react with still more fissionable atoms.
2.
Nuclear fission can release enormous amounts of ____________________.
a)
The fission of 1 kg of uranium-235 yields an amount of energy equal to that produced
when 20,000 tons of dynamite explode.
b)
Nuclear reactors used _________________________ fission to produce useful energy.
c)
Reaction takes place within uranium-235 or plutonium-239 fuel rods.
d)
Much of the energy produced is in the form of heat.
e)
A fluid, usually liquid sodium or water, removes heat from the core (coolant).
f)
The heated fluid is used to change water into ___________________, which drives a
turbine that generates electricity.
g)
B.
Nuclear Reactors
1.
The control of fission in a nuclear reactor involves two steps, neutron moderation and neutron
absorption.
a)
Neutron Moderation is a process that ____________ ________________ neutrons so
the reactor fuel (uranium-235 or plutonium-239) captures them to continue the chain reaction
(water or graphite serves as moderators).
2.
Neutron Absorption is a process that decreases the number of slow-moving neutrons. Control
rods, made of a material such as cadmium, are used to absorb neutrons.
C.
Nuclear Waste
1.
Fuel rods from nuclear power plants are one major source of nuclear waste.
a)
Why are spent fuel rods from a nuclear reaction stored in water?
(1)
Water cools the spent rods, and also acts as a radiation shield to
________________ the radiation levels.
D.
Nuclear Fusion
1.
How do fission reactions and fusion reactions differ?
a)
Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar
fusion, hydrogen nuclei (protons) fuse to make helium nuclei and two positrons.
2.
Fusion reactions, in which small nuclei combine, release ______________ ______________
_________________ than fission reactions, in which large nuclei split.
3.
The use of controlled fusion as an energy source on Earth is appealing.
a)
The potential fuels are inexpensive and readily available.
b)
Reaction of hydrogen-2 nucleus and hydrogen-3 combine to form a helium nucleus.
c)
The problems with fusion lie in achieving the high temperatures necessary to start the
reaction and in containing the reaction once it has started.