Study Guide for Chapters 38, 39, 40Chapter 38: The Atom and the Quantum

38.1 Models The planetary model in which electrons orbit the nucleus was suggested by the Danish physicist

________________ in 1913. It is still useful for understanding the emission of light. The planetary model has been replaced by a more complex model in which the electrons are represented

as ____________. A useful model of the atom must be consistent with a model for ________. Most of what we know about atoms we learn from the _______ and other radiations they emit. Most light comes from the ________________________________ within the atom. There have been _________ primary models of light: ____________ and _______________ ___________________ believed light was composed of tiny particles. __________________________ believed that light was a wave phenomenon. The wave model was reinforced when ___________________ demonstrated constructive and destructive

interference of light. In 1905, _________________________ resurrected the particle theory of light. Einstein visualized particles of light as _____________________ of electromagnetic energy. _______________ had proposed that atoms do not emit and absorb light continuously, but do so in little

chunks. Each chunk was considered a _____________, or a fundamental unit. One quantum of light energy is now called a ________________.

Quantization:o Matter is quantized, equal to some whole-number multiple of the mass of a single _______. o Electric charge is quantized as a multiple of the charge of a single _________.

38.2 Light Quanta The energy in a light beam is quantized and comes in packets, or quanta; only a whole number of quanta

can exist.o The quanta of electromagnetic radiation are the ___________.o Photons have __________ rest energy. o They move at the speed of _________ so the total energy of a photon is the same as its

_______________ energy. The energy of a photon of light is proportional to its vibrational _______________.

o When the energy E of a photon is divided by its frequency f, the quantity that results is known as ____________________, h.

o This quantity ‘h’ is always the same, no matter what the frequency. o The energy of every photon is therefore ________________.

38.3 The Photoelectric Effect Einstein found support for his quantum theory of light in the photoelectric effect. The photoelectric effect is the ejection of ___________ from certain metals when light falls upon them. These metals are said to be __________________.

Explanation of the Photoelectric EffectEnergy from the light shining on a metal plate gives electrons bound in the metal enough _________ to escape.

• High-frequency light, even from a _____________, is capable of ejecting electrons from a photosensitive metal surface.

• Low-frequency light, even from a very ____________, cannot dislodge electrons. • Since bright light carries more ________ than dim light, it was puzzling that dim blue light could

dislodge electrons when bright red light could not.

Einstein explained the photoelectric effect in terms of _________________.• The absorption of a photon by an atom in the metal surface is an

______________________________ process. • Only one photon is absorbed by each ______________ ejected from the metal. • The number of photons that hit the metal has nothing to do with whether a given electron will

be _____________. • If the energy in the photon is __________________, the electron will be ejected from the

metal.

The intensity of light ________________. From E = hf, the critical factor is the frequency, or color, of the light.• Each blue or violet light photon carries ____________ energy to free an electron from the

metal.• A few photons of blue or violet light can eject a few electrons. Many red or orange photons

_____________ eject a single electron.• Only high-frequency photons have the energy needed to pull loose an electron.

38.4 Waves as ParticlesLight behaves like __________ when it travels in empty space, and like ______________ when it interacts with solid matter.

38.5 Particles as Waves If waves can have particle properties, cannot particles have wave properties? This question was posed by the French physicist Louis _________________ and his answer later won

the Nobel Prize in physics. _______________________ suggested that all matter could be viewed as having ___________

properties.

All particles—______________, ______________, ____________, marbles, and even _____________—have a wavelength:

where h is ____________ constant. The wavelength of a particle is called the __________________________.

o A particle of large mass and ordinary speed has _______________ wavelength to be detected by conventional means.

o A tiny particle—such as an electron—moving at typical speed has a ___________________ wavelength.

The wavelength of electrons is ________________ than the wavelength of visible light but large enough for noticeable ______________.

A beam of electrons can be ________________ and undergoes wave ______________ under the same conditions that light does.

An ___________________ microscope uses the wave nature of electrons. The wavelength of electron beams is typically thousands of times _____________ than the wavelength

of visible light. The electron microscope is able to distinguish details thousands of times smaller than is possible with

_________________ microscopes.

38.6 Electron Waves The planetary model of the atom was useful in explaining the ____________________ of the elements and

why elements emitted only certain frequencies of light.o An electron has different amounts of energy when it is in different _________ around a nucleus. o An electron is in a different __________________ when it is in a different orbit. o Electrons in an atom normally occupy the ____________ energy levels available.

In the Bohr model of the atom, the electron orbits correspond to different __________________________________.

Bohr Model Explanation of Atomic Spectra An electron can be boosted to a ___________ energy level.

o This occurs in gas discharge tubes such as ___________ signs. o Electric current boosts electrons of the gas to higher energy levels. o As the electrons return to lower levels, _______________ are emitted.o The energy of a photon is exactly equal to the ______________ in the energy levels in the

atom. The pattern of lines in the spectrum of an element corresponds to ____________ ________________

between the energy levels of the atoms of that element. Why were electrons at discrete distances from the atomic nucleus? This was resolved by thinking of the electron not as a __________ whirling around the nucleus but as a

__________. According to de Broglie’s theory of matter waves, electron orbits exist only where an electron wave

___________________________ in phase.

De Broglie’s Theory The electron is visualized not as a _____________ located at some point in the atom.

o Its mass and charge are spread throughout a __________ surrounding the nucleus. o The wavelength of the electron wave must fit evenly into the

_________________________________ of the orbits.

a. ________________________________ b. _________________________________

The circumference of the innermost orbit, according to this model, is equal to __________ wavelength of the electron wave.

The second orbit has a circumference of ___________ electron wavelengths, the third _______________, and so on.

Orbit circumferences are __________________ multiples of the electron wavelengths, which differ for the various elements.

This results in ____________ energy levels, which characterize each element. Since the circumferences of electron orbits are discrete, the ____________ of these orbits, and hence the

_________________________, are also ______________.

This explains why electrons do not spiral closer and closer to the __________ when photons are emitted. Since an orbit is described by a wave, the circumference of the smallest orbit can be no smaller than

__________ wavelength. In the modern wave model of the atom, electron waves also move in and out, toward and away from the

nucleus. The electron wave is in three dimensions, an ________________________.

38.7 Relative Sizes of Atoms The radii of the electron orbits in the Bohr model of the atom are determined by the amount of

_____________________________________________________.

The single proton in the hydrogen atom holds _________ negatively charged electron in an orbit at a particular radius.

In helium, the orbiting electron would be pulled into a ___________ orbit with __________ its former radius since the electrical attraction is ______________.

This doesn’t quite happen because the double-positive charge in the nucleus attracts and holds a _____________ electron.

The negative charge of the second electron ____________ the effect of the positive nucleus. This added electron makes the atom electrically _____________. The two electrons assume an orbit characteristic of _______________. In a lithium atom, an additional proton pulls the first two electrons into an even __________ orbit and

holds a third electron in a ___________ orbit.

As the nuclear charge increases, the inner orbits ___________ because of the ___________________ electrical attraction to the nucleus.

This means that the heavier elements are ________________________ in diameter than the lighter elements.

The diameter of the uranium atom, for example, is only about __________ hydrogen diameters, even though it is _________ times more massive.

Each element has a unique arrangement of __________________________. The radii of orbits for the sodium atom are the same for all ___________ atoms, but different from the

radii of orbits for other kinds of atoms. The Bohr model solved the mystery of the ___________________ of the elements. The model accounted for the ______________ properties of the elements and predicted properties of

hafnium, which led to its discovery.

Bohr was quick to point out that his model was to be interpreted as a crude beginning. The picture of electrons whirling like planets about the sun was not to be taken _________________. His discrete orbits were conceptual representations of an atom whose later description involved a

______________________.

a. In the Bohr model, the electrons orbit the nucleus like _________ going around the sun.

b. According to de Broglie’s idea, a ___________ follows along an orbit.c. The wave model—electrons are distributed in a “___________” throughout the volume of the atom.

38.8 Quantum Physics Physicists became convinced that the Newtonian laws that work so well for large objects do not apply

to the ________________________________. In the macro world, the study of motion is called ____________________, or sometimes

__________________________________. The study of the motion of particles in the __________________ of atoms and nuclei is called

____________________________________. The branch of physics that is the general study of the microworld of photons, atoms, and nuclei is

simply called ___________________________________. There are fundamental ________________ in the measurements of the atomic domain. For the measurement of macroscopic quantities, such as the temperature of materials or the speeds of

light and sound, there is no limit to the _______________ with which the experimenter can measure. _________________ measurements, such as the momentum and position of an electron or the mass

of an extremely short-lived particle, are entirely different. In this domain, the uncertainties in many measurements are comparable to the magnitudes of the

______________________ themselves. The subatomic interactions described by quantum mechanics are governed by laws of

__________________, not laws of _______________________.

Chapter 39: The Atomic Nucleus and Radioactivity

39.1 The Atomic Nucleus The nucleus is composed of particles called ______________________—electrically charged

_____________ and electrically neutral _____________. Neutrons and protons have close to the same mass, with the _______________ being slightly greater. Nucleons have nearly ___________ times the mass of electrons. The mass of an atom is practically

equal to the mass of its ______________ alone. The positively charged protons in the nucleus hold the ______________________________________

in their orbits. The number of protons in the nucleus therefore determines the possible ___________

__________________orbits that can occur and the _____________________ of that atom. The number of neutrons has ______________ effect on the electron structure, and hence does not

affect the chemistry of the atom.

The principal role of the neutrons in an atomic nucleus is to act as a sort of nuclear cement to hold the nucleus together.

Nucleons are bound together by an attractive nuclear force appropriately called the _____________________________.• The nuclear force of attraction is strong only over a ____________________ distance.• When two nucleons are just a few nucleon diameters apart, the nuclear force they exert on

each other is _________________.• This means that if nucleons are to be held together by the strong force, they must be held in a

__________________________. • Nuclei are tiny because the nuclear force is very ___________________.

Meanwhile, the electrical force acts as a _________________ force between protons that are not in direct contact with one another.

Stability is due to a tension between the _____________ force’s tendency to hold the nucleus _________________ and the electrical force’s tendency to ___________________.

A nucleus needs a certain balance of neutrons and protons for _________________. For a pair of protons, which repel each other electrically, the nuclear force is

___________________________ enough to keep them together. When neutrons are present, the attractive strong force is _____________ relative to the repulsive

electrical force. The presence of neutrons adds to the nuclear attraction and keeps protons from ____________________. The more protons there are in a nucleus, the more ______________ are needed to hold them together. For light elements, it is sufficient to have about as many ___________ as protons. For heavy elements, __________________________ are required. For elements with more than 83 protons, even the addition of extra neutrons

______________________________________________ the nucleus.

39.2 Radioactive Decay One factor that limits how many stable nuclei can exist is the ________________ of the neutron.

A lone neutron will decay into a ____________________________. About half of a bunch of lone neutrons will decay in __________ minutes. Particles that decay by spontaneously emitting ___________________ and ________________ are said to

be ___________________.

Radioactivity is governed by ____________________ equivalence.• Particles decay spontaneously only when their combined products have

_____________________ after decay than before. • The mass of a neutron is slightly greater than the total mass of a proton plus electron.• When a neutron decays, there is ________________.• Decay will not spontaneously occur for reactions where more mass results. A proton decaying

into a _____________ can occur only with external energy input.• All elements heavier than bismuth (atomic number 83) decay in one way or another, so these

elements are ___________________. • Radiation is the name given to the ___________________________________ emitted by an

unstable nucleus or particle.

The atoms of radioactive elements emit three distinct types of radiation called __________________________________________________________________.• ____________ particles have a ___________ electric charge.• ___________ particles are negative.• ___________ rays are electrically _______________.

An alpha particle is made of ________ protons and __________ neutrons and is identical to the nucleus of a ____________ atom.

A beta particle is simply an _____________ ejected from the nucleus when a neutron is transformed into a _______________.

A gamma ray is _______________________. Like visible light, gamma rays are simply photons, but of ________________________ frequency and energy.

o Visible light is emitted when electrons jump from one atomic orbit to another of ____________ energy.

o Gamma rays are emitted when nucleons do a similar sort of thing inside the _____________. o There are great energy differences in nuclear energy levels, so the photons emitted carry a

______________________ of energy. A gamma ray is simply ________________________________________, much higher in frequency and

energy per photon than __________________________.

39.3 Radiation Penetrating Power There is a great difference in the penetrating power of the three types of radiation.

o Alpha particles are the ______________ to stop. They can be stopped by a ___________________________________________.

o Beta particles go right through paper but are stopped by several sheets of ________________________________.

o Gamma rays are the __________________________ to stop and require __________________ or other heavy shielding to block them.

Alpha Particles:o An alpha particle is easy to stop because it is relatively ___________ and its _____________

interacts with the molecules it encounters along its path. o It slows down as it shakes many of these molecules apart and leaves positive and negative ions

in its wake. o Even when traveling through nothing but air, an alpha particle will come to a stop after only a

few __________________. o It soon grabs up a couple of stray electrons and becomes nothing more than a harmless

______________________.

Beta Particles:o A beta particle normally moves at a _______________ speed than an alpha particle and carries

only a _______________________ charge.o It is able to travel much farther through the air.o Most beta particles lose their energy during the course of a large number of

___________________________ with atomic electrons. o Beta particles slow down until they become a part of the material they are in, like any other

_______________________.

Gamma rays:o Gamma rays are the most penetrating of the three because they have __________________. o A gamma ray photon interacts with the absorbing material only via a direct hit with an

_______________________________________. o Unlike charged particles, a gamma ray photon can be removed from its beam in a single

encounter. o Dense materials such as ___________ are good absorbers mainly because of their high

_______________________________.