Quantum-Mechanical model of an atom

Question 1

What is the quantum mechanical mode of an atom

Answer 1

It’s a model that explains the strange behavoir of electrons. It focuses on the description of electrons as they exist within atoms

Question 2

Describe the wave particle duality of light

Answer 2

• The wave nature of light: Light is electromagnetic radiation: a type of energy embodied in oscillating electric and magnetic field.
• Particle nature of light: was supported by the photoelectric effect.

Question 3

What is the photo electric effect

Answer 3

(The observation that many metals emit electrons when light shines upon them).

(a) When sufficiently energetic light shines on a metal surface, the surface emits electrons.
(b) The emitted electrons can be measured as an electrical current.

Question 4

Describe the two types of interference.

Answer 4

• For example, if two waves are in phase when they interact—that is, they align with overlapping crests—a wave with twice the amplitude results. This is called constructive interference.
• If, however, two waves are completely out of phase when they interact—that is, they align so that the crest from one overlaps with the trough from the other—the waves cancel by destructive interference.

Question 5

Describe the electromagnetic spectrum and how wave length affects the energy of a wave, and the order of waves on the electromagnetic spectrum.

Answer 5

ranging in wavelength from 10-15m (gamma rays) to 105m (radio waves). Short-wavelength, high-frequency radiation is on the right, and long-wavelength, low-frequency radiation on the left. As you can see, visible light constitutes only a small region in the middle.

Note: short wavelength = more energy, like gamma rays

Order: Radio < Microwaves < infrared< visible < Ultraviolet < X-ray < Gamma ray

Question 6

binding energy of an electron in a metal

Answer 6

the energy with which the electron is bound to the metal

Question 7

threshold frequency.

Answer 7

Electrons are only ejected when the energy of a photon exceeds the energy with which an electron is held to the metal. The frequency at this time is the threshold frequency.

Notice that increasing the intensity of the light does not change the threshold frequency.

Question 8

What is an emission spectrum.

Answer 8

The emission spectrum of a particular element is always the same—it consists of the same bright lines at a black background—and we can use it to identify the element.

Question 9

The Bohr Model of Emission Spectra, and it’sproblems

Answer 9

Each line in an emission spectrum corresponds
to a transition between orbits.

The energy of the atom is quantatized: the could have only a very specific amount of energy

Electrons travel in orbits that are at a fixed distance from the nucleus, so they energy of the electron is directly proportional to the distance the orbit was from the necleus.

Problems:
- It only explains the spectrum of hydrogen. It is not able to explain the spectra of atoms with multiple electrons

Question 10

What is an absorption spectrum and it’s different from emission spectrum.

Answer 10

consists of dark lines on a bright background

Question 11

The heisenberg’s uncertainty Principle

Answer 11

an electron is observed as either a particle or a wave, but never both at once.

Heisenberg stated that the product of the uncertainties in both the position and velocity of a particle was inversely proportional to its mass

This means that the more accurately you know the position of a small particle, such as an electron, the less you knowabout its speed, and vice versa.

Question 12

Indeterminacy and Probability Distribution Maps

Answer 12

In quantum mechanics, trajectory is replaced by probability distribution maps; we cannot know the position and velocity of an electron, therefore we can’t know it’s trajectory, and this violates the laws of newton.

Indeterminacy: If an electron were thrown from the pitcher’s mound to home plate, it would land in a different place every time, even if it were thrown in exactly the same way.

Question 13

Einstein’s adoption of Planck’s quantum hypothesis

Answer 13

Light is considered to consist of a stream of packets of energy, called photons.

The energy carried by a photon is E=hv

Question 14

The central idea of quantum theory, proposed by Max Planck

Answer 14

is that light energy is absorbed or emitted in discrete packets called, quanta

Question 15

Modern Quantum theory

Answer 15

Modern quantum theory retains the concept of quantization and discrete energy states.

But does not use the concept of electron moving in circular orbits.

Instead, electron is considered to have wave like properties

Question 16

Louis de Broglie Hypothesis and why it is suitable for microscopic particles

Answer 16

an electron confined in its orbit about the nucleus sets up a standing wave of specific wavelength, energy and frequency.

microscopic particles can have wave-like character

De broglies relation: wavelength = (h/ mv)
(mv) is linear momentum. This relation is suitable to any microscopic particle not macroscopic. (NB: mass is in KG bcs the planks const uses kg)

this is bcs every particle behaves like a wave, but the wave character becomes significant only when mass is very small.

Question 17

Schrödinger Equation

Answer 17

Schrödinger’s equation allows us to calculate the
probability of finding an electron’s location in an atom

Note: Schrodinger’s equation can only be solved for one electron atom/ions (Example: hydrogen atom) !!

Question 18

the Bohr model of the atom

Answer 18

• energy of an atom is quantitized. the amount of energy in an atom is related to the electrons position in the atom.
• Electrons in orbits that are at a fixed distance from the nucleus.
• Electrons emit energy when they jump from an orbit of higher energy to an orbit of lower energy.

NOTE: The Bohr model of electron orbiting around the nucleus gives satisfactory explanation of line spectra for only one electron atoms or ions.

Question 19

What is an orbital

Answer 19

An orbital is a probability distribution map of a region where the electron is likely to be found.

Question 20

What does the wavelength and amplitude determine

Answer 20

• the wavelength determines the color

- the amplitude determines the brightness or intensity.

Question 21

Why do some substances appear colored.

Answer 21

When an object absorbs some of the wavelengths of white light and reflects others, it appears colored; the observed color is predominantly the colors reflected.

Question 22

Failure of classical mechanics

Answer 22

• Black body radiation
• Photoelectric effect
• Stability of an atom

Question 23

Nodes in the shapes of s-orbital

Answer 23

• Where the probabilty of finding an electron drops go zero