CHEM 121: Chapter 6; "Electronic structure of atoms"

Exam 2

Electronic structure

The number of electrons in the atom as well as their distribution around the nucleus and their energies

Quantum mechanics (3 major descriptions)

1. The most fundamental theory to understand the properties of matter

2. The most incomprehensible theory

3. The theory that shows clearly the limit of human knowledge and understand of the universe

Bohr v. Einstein

Bohr proposed that entities such as electrons had only probabilities if they weren’t observed; Einstein argued that they had an independent reality (“God does not play dice”).

Richard Philips Feyman contributed to what?

quantum mechanics

Who was a major contributor to quantum mechanics?

Richard Philips Feyman

Most behaviors of atoms depend on the ______

electrons

Attraction between _______ and _______ explains all the differences among different elements

electrons, nuclei

Virtually everything we know about matter comes from the interaction between ______ with ________ _________

matter, electromagnetic radiation

Commonality of all scientific conducts:

Tools + subject

Electromagnetic energy =

Radiant energy

All electromagnetic radiation travels at the same _______, that being _______: the speed of light

velocity, 3.0 × 10^8 m/s

Who did the “Double slit” experiment?

Thomas Young

Describe the double slit experiment and what is demonstrates

A light source hits a place illuminated by two parallel slits; the wave nature of light causes the light waves passing through the slits to interfere with one another, resulting in light and dark bands; this establishes light as both a particle and a wave.

How do different variations of the double slit experiment establish one of light’s identity’s as a photon?

Some variations of the experiment revealed that each photon passed through one slit individually rather than two, establishing the independency of the photon as a particle

How else is light demonstrate having a photon nature? (not the double slit experiment)

Einstein Photoelectric Effect theory: when photons hit a metal surface with energy (hv), electrons are emitted from the surface by the energy of the photons. This “ejection” of electrons from the surface occurs because photons transfer their energy to the electrons, allowing them to overcome their attraction to the surface

Wavelength

The distance between adjacent peaks or troughs

Frequency

The number of complete wavelengths passing a given point per unit of time

For waves traveling at the same velocity, the longer the wavelength, the ______ the frequency

smaller

Range of wavelength (longest to shortest)

1. Radio

2. Microwave

3. Infrared

4. Visible

5. Ultraviolet

6. X-ray

7. Gamme

Black body

An idealized opaque, non-reflective body; does not necessarily have to be black; a perfect absorber and emitter of radiation

Planks constant (h)

h = 6.626 × 10^-34 J/s

Light interacting with electric oscillations in matter can be described in this equation:

E = hv

Planks constant in words can be summarized as:

light interacting with electric oscillations in matter

Wien Displacement Law

States that the black body radiation curve will peak at different wavelengths and are inversely proportional to the temperature

Continuous v. Quantized

Continuous: potential energy increases uniformly, can take on any value within its range

Quantized: potential energy increases stepwise; only has specific values

Planks constant argues for a _______ form of potential energy

quantized

What fundamental theory in physics labels energy as quantized at the atomic level?

Quantum mechanics

The photoelectric effect

Light striking a surface can cause electrons to be emitted

Photoelectric effect experiment

A beam of light (which carries energy) hits a piece of metal. This causes some electrons to eject into the photoelectron detector, allowing one to calculate the speed of the electrons ejected.

Neil Bohr’s atomic model adopted ________ assumption

Planks

Bohr Model (3 assumptions):

1. Electrons in an atoms can only occupy certain orbits

2. Electrons in certain orbits have allowed/stationary energies that they do not radiate

3. Energy is only absorbed or emitted in such as way as to move an electron from one energy state to another

3 Limitations of Bohr’s model

1. Not applicable to other atoms

2. Does not address why electrons do not fall into the positively charge nucleus

3. Fixed radiuses (radii)

In the Bohr model, energy is defined as

E = hv

Two important (notable) determinations from Bohr’s model

1. Electrons only exist in certain discrete energy level

2. Energy is involved in the transition of an electron between energy levels

Rydberg constant

2.18 × 10^-18

mv is called:

momentum

De Broglie’s hypothesis

If waves can behave like particles, then particles can behave like waves; the wavelength of matter is inversely proportional to its momentum

De Broglie’s hypothesis as an equation

wavelength = h/mv

X-ray diffraction/crystallography

Many materials are made up of tiny crystals, in which different phases of these crystals give off different patterns when exposed to x-ray beams. Due to these varying patterns, wavelengths can interfere with one another, which can help to reveal the internal structure of the material.

Electron diffraction

Similar to x-ray diffraction except it measures the change in direction of electron beams

Can we know the exact position of a wave?

no

Heisenberg’s uncertainty principle

It is impossible to know simultaneously the exact momentum of an electron and its exact location in space

What set the stage for a more applicable theory of atomic structure?

De Broglie’s hypothesis and Heisenberg’s uncertainty principle

(Wavefunction)² determines:

probability

High dot density v. Low dot density

1. High dot: High (Wavefunction)² value; high probability of finding electrons

2. Low dot: Low (Wavefunction)² value; low probability of finding electrons

Solving the Schrodinger Equation gives 3 quantum numbers:

n, l, m

Quantum number n:

1. Principle quantum number

2. Determines energy level/shell

3. As n increases, the orbital gets larger

4. n = 1,2,3,…

Quantum number l:

1. Angular momentum quantum number

2. Determines shape of orbital/subshells

3. l = 0,1,2,…(n-1)

Quantum number m:

1. Magnetic quantum number

2. (z-component of l)

3. m = -l, -(l - 1), l, (l -1)

During an electron transmission, what has to happen for there to be an emission of light?

Electron goes from a higher energy level to a lower energy level

During an electron transmission, what has to happen for for light to be absorbed?

The electron shifts from a lower energy level to a higher energy level

Paul exclusion principle

1. No two electrons in an atom can have the same set of four quantum numbers n, l, m

2. An orbital can have a maximum of two electrons and they must have opposite spins

Aufbau Principle

Electrons first fill subshells of the lowest available energy

Hund’s rule

Within a subshell, electrons will individual occupy each orbital before any orbital is doubly occupied