Chapter 5.3 Chemistry

before and after collision

Before collision: A photon strikes an electron during an attempt to observe the electron's position. After collision: The impact changes the electron's velocity, making it uncertain.

How does quantum mechanics differ from classical mechanics?

Classical mechanics adequately describes the motions of bodies much larger than atoms, while quantum mechanics describes the motions of subatomic particles and atoms as waves.

To locate an electron, you might strike it with a ________ The electron has such a small mass that striking it with a photon affects _________________________ The very act of measuring the position of the electron changes its

photon. its motion in a way that cannot be predicted accurately. velocity, making its velocity uncertain.

These light quanta are called

photons.

When an electron moves from a higher energy level back down to a lower energy level,

light is emitted.

In the photoelectric effect, electrons are ejected when

light shines on a metal.

In the visible spectrum, red light has the

longest wavelength and the lowest frequency.

electromagnetic spectrum in order

radio waves, radar, microwaves, infrared, visible light, ultraviolet, x-rays, gamma rays (wavelength gets smaller for each one)

order of longest to shortest wavelength

red, orange, yellow, green, blue, violet

German physicist Max Planck (1858-1947) showed

mathematically that the amount of radiant energy (E) of a single quantum absorbed or emitted by a body is proportional to the frequency of radiation (n). E n or E = hn (equation in textbook)

The electromagnetic spectrum consists of radiation

over a broad range of wavelengths.

Albert Einstein used

Planck's quantum theory to explain the photoelectric effect.

three possibilities for the photoelectric effect

-No electrons are ejected because the frequency of the light is below the threshold frequency. -If the light is at or above the threshold frequency, electrons are ejected. -If the frequency is increased, the ejected electrons will travel faster.

what light will cause the photoelectric effect

-Not just any frequency of light will cause the photoelectric effect. -Red light will not cause potassium to eject electrons, no matter how intense the light. -Yet a very weak yellow light shining on potassium begins the effect.

In the ground state, the principal quantum number (n) is

1.

What is the frequency of a photon whose energy is 1.166 10-17 J?

1.760 x 1016 Hz

1 m equals

10 to the 9 nm

What is the energy of a photon of microwave radiation with a frequency of 3.20 × 1011/s?

2.12 x 10-22 J

All electromagnetic waves travel in a vacuum at a speed of

2.998 x 108 m/s.

What is the frequency of a red laser that has a wavelength of 676 nm?

4.43 x 1014 /s

Calculate the wavelength of the yellow light emitted by a sodium lamp if the frequency of the radiation is 5.09 × 1014 Hz (5.09 × 1014/s).

5.89 x 10-7 m

In the hydrogen spectrum, which of the following transitions produces a spectral line of the greatest energy? A. n = 2 to n = 1 B. n = 3 to n = 2 C. n = 4 to n = 3

A

What gives gas-filled lights their colors?

An electric current passing through the gas in each glass tube makes the gas glow with its own characteristic color.

The glass tubes in lighted signs contain helium, neon, argon, krypton, or xenon gas, or a mixture of these gases. Why do the colors of the light depend on the gases that are used?

Each different gas has its own characteristic emission spectrum, creating different colors of light when excited electrons return to the ground state.

includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays.

Electromagnetic radiation

what raises the atom to an excited state

Excitation of the electron by absorbing energy raises the atom to an excited state with n = 2, 3, 4, 5, or 6, and so forth.

Given that light behaves as waves and particles, can particles of matter behave as waves?

Louis de Broglie referred to the wavelike behavior of particles as matter waves. His reasoning led him to a mathematical expression for the wavelength of a moving particle.

The constant (h), which has a value of 6.626 10-34 J·s (J is the joule, the SI unit of energy), is called

Planck's constant.

states that it is impossible to know both the velocity and the position of a particle at the same time.

The Heisenberg uncertainty principle

why are properties of beams of electrons useful in viewing objects that cannot be viewed with an optical microscope?

The electrons in an electron microscope have much smaller wavelengths than visible light. These smaller wavelengths allow a much clearer enlarged image of a very small object, such as this pollen grain, than is possible with an ordinary microscope.

represented by v (the Greek letter nu), is the number of wave cycles to pass a given point per unit of time.

The frequency,

How are the frequencies of light emitted by an atom related to changes of electron energies?

The light emitted by an electron moving from a higher to a lower energy level has a frequency directly proportional to the energy change of the electron.

________________________equals a constant (c), the speed of light.

The product of frequency and wavelength c = ln

represented by k (the Greek letter lambda), is the distance between the crests.

The wavelength,

How did Einstein explain the photoelectric effect?

To explain the photoelectric effect, Einstein proposed that light could be described as quanta of energy that behave as if they were particles.

What causes atomic emission spectra?

When atoms absorb energy, their electrons move to higher energy levels. These electrons lose energy by emitting light when they return to lower energy levels.

White light produces

a rainbow of colors.

Electrons can________________ to move from one energy level to a higher energy level

absorb energy

of a wave is the wave's height from zero to the crest.

amplitude

The wavelengths of the spectral lines are characteristic of the element, and they make up the___________________________ of the element.

atomic emission spectrum

The photoelectric effect could not be explained by ___________________ What did it correctly describe?

classical physics. Classical physics correctly described light as a form of energy.

By the year 1900, there was enough experimental evidence to

convince scientists that light consisted of waves.

Light from a helium lamp produces

discrete lines.

According to the wave model, light consists of

electromagnetic waves.

it assumed that under weak light of any wavelength, an

electron in a metal should eventually collect enough energy to be ejected.

No two elements have the same

emission spectrum

When an electron has its lowest possible energy, the atom is in its

ground state.

The SI unit of cycles per second is called the

hertz (Hz).

The three groups of lines in the hydrogen spectrum correspond to the transition of electrons from

higher energy levels to lower energy levels.

The frequency () and wavelength () of light are

inversely proportional to each other. As the wavelength increases, the frequency decreases.

J is the

joule, the SI unit of energy

the greek letter for wavelength is known as

lambda

the heisenberg uncertainty principle is true for _________________ but not for

small particles such as electrons. for ordinary-sized objects such as cars or airplanes.

When sunlight passes through a prism, the different wavelengths separate into a _______________of colors.

spectrum

A prism separates light into

the colors it contains.

A quantum of energy in the form of light is emitted when

the electron drops back to a lower energy level.

Einstein's theory that light behaves as a stream of particles explains

the photoelectric effect and many other observations.

The energy absorbed by an electron for it to move from its current energy level to a higher energy level is identical

to the energy of the light emitted by the electron as it drops back to its original energy level.

The Heisenberg uncertainty principle states that it is impossible to simultaneously know which two attributes of a particle?

velocity and position

Today, the wavelike properties of beams of electrons are useful in

viewing objects that cannot be viewed with an optical microscope.

Light behaves as __________in other situations; we must consider that light possesses both

waves; wavelike and particle-like properties.

The sun and incandescent light bulbs emit

white light, which consists of light with a continuous range of wavelengths and frequencies.