Download The Atom

Chapter 4
The Structure of the Atom
Section 1
Early Ideas About Matter
Section 1: Early Ideas About Matter
The ancient Greeks tried to explain matter, but the scientific study of the
atom began with John Dalton in the early 1800s.
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The Roots of Atomic Theory
•
Many ancient scholars believed matter was composed of such things as
earth, water, _________, and _______________.
•
Many believed matter could be endlessly _________into smaller and smaller
pieces.
Early Ideas About Matter
Greek Philosophers
•
Democritus (460–370 B.C.) was the first person to propose the idea that
matter was not infinitely divisible, but made up of individual particles called
_____________, from which the English word atom is derived.
•
Aristotle (484–322 B.C.) disagreed with Democritus because he did not
believe ____________space could exist.
•
Aristotle’s views went unchallenged for ______ years until science developed
methods to test the validity of his ideas.
Early Ideas About Matter
Greek Philosophers
Table 1
Ancient Greek Ideas About Matter
Philosopher
Democritus
(460–370 B.C.)
Aristotle
(384–322 B.C.)
Ideas
•
Matter is composed of atoms, which move through empty space.
•
Atoms are solid, homogeneous, indestructible, and indivisible.
•
Different kinds of atoms have different sizes and shapes.
•
Size, shape, and movement of atoms determine the properties
of matter.
•
Empty space cannot exist.
•
Matter is made of earth, fire, air, and water.
Early Ideas About Matter
Dalton’s Atomic Theory
•
John Dalton revived the idea of the atom in the early 1800s based on
numerous ______________reactions.
•
Dalton’s _______theory easily explained conservation of mass in a reaction
as the result of the combination, separation, or rearrangement of atoms.
Table 2
Dalton’s Atomic Theory
Scientist
Dalton
(1766–1844)
Ideas
•
Matter is composed of extremely small particles called atoms.
•
Atoms are indivisible and indestructible.
•
Atoms of a given element are identical in size, mass, and chemical
properties.
•
Atoms of a specific element are different from those of another element.
•
Different atoms combine in simple whole-number ratios to form
compounds.
•
In a chemical reaction, atoms are separated, combined or rearranged.
Early Ideas About Matter
Essential Questions
• What are the similarities and differences of the atomic models of
Democritus, Aristotle, and Dalton?
• How was Dalton’s theory used to explain the conservation of mass?
Early Ideas About Matter
Section 2
Defining the Atom
Section 2: Defining the Atom
An atom is made of a nucleus containing protons and neutrons;
electrons move around the nucleus.
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The Atom
•
The smallest particle of an element that retains the properties of the element
is called an _________________________.
•
An instrument called the scanning tunneling microscope (STM) allows
individual _______to be seen.
Defining the Atom
The Electron
•
When an electric charge is applied, a ray of radiation travels from the cathode
to the anode, called a _______________ray.
•
Cathode rays are a stream of particles carrying a negative charge. The
particles carrying a negative charge are known as _________________.
•
This figure below shows a typical cathode ray tube.
Defining the Atom
The Electron
•
J.J. Thomson measured the effects of both magnetic and electric fields on the
cathode ray to determine the charge-to-mass ratio of a charged particle, then
compared it to known values.
•
The mass of the charged particle was much less than a hydrogen atom, then
the lightest known atom.
•
Thomson received the Nobel Prize in 1906 for identifying the first subatomic
particle—the _________________.
Defining the Atom
The Electron
•
In the early 1910s, Robert Millikan used the oil-drop apparatus shown below
to determine the _____________of an electron.
Defining the Atom
The Electron
•
Charges change in discrete amounts—1.602 × 10–19 coulombs, the charge of
one electron (now equated to a single unit, 1–).
•
With the electron’s charge and charge-to-mass ratio known, Millikan
calculated the mass of a single electron.
the mass of a
hydrogen atom
Defining the Atom
The Electron
•
Matter is ______. You know that matter is neutral from everyday experiences.
You do not receive an electric shock (except under certain conditions) when
you touch an object.
•
If electrons are negative, then how is matter, which is made up of electrons,
neutral?
•
J.J. Thomson proposed a model of the atom to answer this question.
Defining the Atom
The Electron
•
J.J. Thomson's _______________model of the atom states that the atom is a
uniform, positively charged sphere containing _________________.
Defining the Atom
The Nucleus
•
In 1911, Ernest Rutherford studied how positively charged alpha particles
interacted with solid matter.
•
By aiming the particles at a thin sheet of gold _____, Rutherford expected the
paths of the alpha particles to be only slightly altered by a collision with an
electron.
Defining the Atom
The Nucleus
•
Although most of the alpha
particles went through the
gold foil, a few of them
bounced back, some at
large angles.
Defining the Atom
The Nucleus
•
Rutherford concluded that atoms are
mostly empty space.
•
Almost all of the atom's positive
charge and almost all of its mass is
contained in a dense region in the
center of the atom called the
____________.
•
Electrons are held within the atom by
their attraction to the positively
charged nucleus.
•
The __________force between the
positively charged nucleus and
positive alpha particles caused the
deflections.
Defining the Atom
The Nucleus
•
Rutherford refined the model to include positively charged particles in the
nucleus called __________________.
•
James Chadwick received the Nobel Prize in 1935 for discovering the
existence of _______, neutral particles in the nucleus which accounts for
the remainder of an atom’s mass.
Defining the Atom
The Nucleus
•
All atoms are made of _______
fundamental subatomic particles:
the electron, the proton, and the
__________.
•
Atoms are __________shaped.
•
Atoms are mostly _______space,
and electrons travel around the
nucleus held by an attraction to
the positively charged nucleus.
Defining the Atom
The Nucleus
•
Scientists have determined that protons and neutrons are composed of
subatomic particles called ________________.
•
Scientists do not yet understand if or how quarks affect chemical behavior.
•
Chemical behavior can be explained by considering only an atom's
electrons.
Defining the Atom
Electron Cloud Model
Rutherford VS Electron Cloud
• Rutherford model says that whole mass and
positive charge of electron is concentrated at its
________. The electrons move around nucleus in
elliptical orbit in the same way as planets move
around ___________
• Modern electron cloud theory says (in addition to
above theory ) that trajectory of electron is
impossible to determine
History of the Atomic Theory
Atomic Theory Song
Essential Questions
• What is an atom?
• How can the subatomic particles be distinguished in terms of relative
charge and mass?
• Where are the locations of the subatomic particles within the structure
of the atom?
Defining the Atom
Section 3
How Atoms Differ
Section 3: How Atoms Differ
The number of protons and the mass number define the type of atom.
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• How small is an atom?
Atomic Number
•
Each element contains a unique positive charge in their nucleus.
•
The number of protons in the nucleus of an atom identifies the element
and is known as the element’s _________________number.
How Atoms Differ
Subatomic particle
Location
Charge
Key feature
____________
Nucleus
______________
Atomic identity
Neutron
__________
Neutral
_____________
______________
Electron cloud
Negative
Charge
Atomic Number
Use with Example Problem 1.
Problem
Complete the table at right.
How Atoms Differ
Isotopes and Mass Number
•
All atoms of a particular element have the same number of protons and
electrons but the number of neutrons in the nucleus can differ.
•
Atoms with the same number of protons but different numbers of
neutrons are called ____________________.
•
In nature, most elements are found as mixtures of isotopes. Usually,
the relative abundance of each isotope is constant.
– Example: In a banana, 93.26% is potassium-39, 6.73% is potassium-41
and 0.01% is potassium-40. In another banana or in a different source of
potassium, the percentage composition of the potassium isotopes will still
be the same.
•
Isotopes containing more neutrons have a greater mass.
•
Isotopes of an atom have the same chemical behavior.
How Atoms Differ
Atomic #, Mass #, & Isotopes
Isotopes and Mass Number
•
The _____number is the sum of the protons and neutrons in the nucleus.
How Atoms Differ
Mass of Atoms
•
One ____________________(amu) is defined as 1/12th the mass of a
carbon-12 atom.
•
One amu is nearly, but not exactly, equal to one proton and one
neutron.
How Atoms Differ
Mass of Atoms
•
The _______mass of an element is the weighted average mass of the
isotopes of that element.
How Atoms Differ
• Calculating the mass of an element
– The atomic mass is not really a whole number
• The atomic mass is the mass of an atom expressed in
atomic mass units
• Hydrogen has an atomic mass of 1.000797
– Where does this number come from?
• Calculating the Mass of an Element
– The atomic mass is a weighted _________of
the masses of all naturally occurring
isotopes of the element
• Takes into account that not all isotopes
are found equally on earth
• Calculating the mass of an element
– There are two different isotopes of copper
• Copper-63 (69% of earth’s copper is this type)
• Copper-65 (31% of earth’s copper is this type
• Steps
1. Convert percentages into decimals
2. Multiple decimal value by atomic mass
3. Add these amounts together to find the mass
• Calculating the mass of an element
– There are two different isotopes of copper
• Copper-63 (69% of earth’s copper is this type)
• Copper-65 (31% of earth’s copper is this type
• Steps
1. Convert percentages into decimals
• 69%  0.69
• 31%  0.31
• Calculating the mass of an element
– There are two different isotopes of copper
• Copper-63 (69% of earth’s copper is this type)
• Copper-65 (31% of earth’s copper is this type
• Steps
2. Multiple decimal value by atomic mass
• (0.69 x 63) = 43.47
• (0.31 x 65) = 20.15
• Calculating the mass of an element
– There are two different isotopes of copper
• Copper-63 (69% of earth’s copper is this type)
• Copper-65 (31% of earth’s copper is this type
• Steps
3. Add these amounts together to find the mass
• (43.47 + 20.15) = 63.62 amu
• You try!
– There are two different isotopes of chlorine
• Chlorine-35 (76% of earth’s chlorine is this type)
• Chlorine-37 (24% of earth’s chlorine is this type
• Steps
1.
2.
3.
Convert percentages into decimals
Multiple decimal value by atomic mass
Add these amounts together to find the mass
Essential Questions
• How is the atomic number used to determine the identity of an
atom?
• Why are atomic masses not whole numbers?
• Given the mass number and atomic number, how are the
number of electrons, protons, and neutrons in an atom
calculated?
How Atoms Differ
Section 4
How Atoms Differ
Section 4: Unstable Nuclei and Radioactive Decay
Unstable atoms emit radiation to gain stability.
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Radioactivity
•
Nuclear reactions can change one element into another element.
•
In the late 1890s, scientists noticed some substances spontaneously
emitted radiation, a process they called ___________________.
•
The rays and particles emitted are called ______________.
•
A reaction that involves a change in an atom's nucleus is called a
____________________reaction.
Unstable Nuclei and Radioactive Decay
Radioactivity
Radioactive Decay
•
Unstable nuclei lose energy by emitting radiation in a spontaneous
process called radioactive _____________________.
•
Unstable radioactive elements undergo radioactive decay thus forming
stable nonradioactive elements.
•
There are three types of radiation: alpha, _______, and gamma
Unstable Nuclei and Radioactive Decay
Types of Radiation
Alpha Radiation
•
•
•
•
•
______radiation is made up of positively charged particles called alpha
particles.
Each alpha particle contains two protons and two neutrons and has a 2+
charge.
The figure shown below is a nuclear equation showing the radioactive
decay of radium-226 to radon-222.
An alpha particle is equivalent to a helium-4 nucleus and is represented
4
by 2He or α.
Thus, showing mass is conserved in a nuclear equation.
Unstable Nuclei and Radioactive Decay
Types of Radiation
Beta Radiation
•
______radiation is radiation that has a negative charge and emits beta
particles.
•
Each beta particle is an electron with a 1– charge.
•
During Beta decay, a neutron is converted to a proton and an electron.
The electron is emitted and the proton stays in the nucleus.
Unstable Nuclei and Radioactive Decay
Radiation Deflection
Unstable Nuclei and Radioactive Decay
Types of Radiation
Gamma Radiation
•
Gamma _____are high-energy radiation with no mass and are neutral.
•
They usually accompany alpha and beta radiation.
•
Gamma rays account for most of the energy lost during radioactive
decay.
Unstable Nuclei and Radioactive Decay
Types of Radiation
Nuclear Stability
•
Atoms that contain too many or two few neutrons are unstable and lose
energy through radioactive decay to form a stable nucleus.
•
Few exist in nature—most have already ___________to stable forms.
Unstable Nuclei and Radioactive Decay
Essential Questions
• What is the relationship between unstable nuclei and radioactive
decay?
• How are alpha, beta, and gamma radiation characterized in
terms of mass and charge?
Unstable Nuclei and Radioactive Decay