energy levels and orbitals an investigation into electrons and their location and behavior within...
TRANSCRIPT
Energy Levels and Orbitals
An investigation into electrons and their location and behavior within the atom
Learning Targets:A. Describe the process of excitation and
emission of energy by an electron.B. Write electron configurations for
elements or ions (incl. noble gas config.)
C. Draw orbital energy diagrams for elements or ions.
Emission Spectroscopy
● The spectra that were shown through emission spectroscopy led Niels Bohr to question the structure of the atom.
Electromagnetic Spectrum With white light, all of the colors of the visible
spectrum are shown.
Emission Spectroscopy
● Since that was NOT what the spectra of elements looked like, Bohr began to look at why only certain wavelengths of color appeared.
Wavelengths and Energy
E = hc λ
Energy hc = two constants wavelength(Planck’s and speed of light)
This equation shows that larger wavelengths indicate lower amounts of energy and smaller wavelengths indicate higher amounts of energy... an inverse relationship.
Bohr realized that the specific wavelengths revealed specific amounts of energy.
The Bohr Model
According to Niels Bohr, an electron can circle the nucleus in orbits of only certain distances from the nucleus. Bohr called these orbits, or energy levels.
An electron cannot be in-between energy levels (i.e. it is either on the first level or the second).
Therefore, energy is quantized.
Exciting electrons...
Niels Bohr realized that the spectra were being created as electrons moved between these energy levels:
● If an electron absorbs energy, it may jump to a higher energy level.
● When an electron is at a higher energy level we say that the electron is in its “excited” state.
● When the electron releases energy in the form of radiation, we say that the electron has returned to its “ground” state.
● The type of radiation that is emitted depends on the amount of energy released (more on that in a moment)
The Bohr Model (excitation)
Nucleus
1st Energy Level
3rd Energy Level2nd Energy Level
4th Energy Level
Energy Coming In!
The Bohr Model (emission)
Nucleus
1st Energy Level
3rd Energy Level2nd Energy Level
4th Energy Level
Energy emitted (infrared)
Energy emitted (red light)
Energy emitted (ultraviolet light)
The Bohr Model (alternate emission)
Nucleus
1st Energy Level
3rd Energy Level2nd Energy Level
4th Energy Level
Energy emitted (blue/green light)
Energy emitted (ultraviolet light)
Types of RadiationThe following are types of electromagnetic radiation, listed
from highest energy to the lowest:
● Gamma rays: cosmic radiation, very high energy
● Ultraviolet rays (UV): solar radiation, high energy
● Infrared rays (IR): thermal radiation, remote controls, low energy
● Visible Light (more to follow)
● Microwave rays: microwave oven, very low energy
● Radio: lowest energy waves
Types of Radiation
● Bohr saw visible light: wavelength is in the
range of 400 to 700 nanometers (4 x 10-7 meters)
ROY G. BIV White light is made of all
the colors of light
Energy Levels and Spectra
2 --> 1 Ultraviolet3 --> 1 Ultraviolet4 --> 1 Ultraviolet3 --> 2 Visible Red4 --> 2 Visible Blue/Green5 --> 2 Visible Blue4 --> 3 Infrared
Energy LevelChange
Spectra Emission
Electrons release certain types of electromagnetic radiation as they fall to specific energy levels
Quantum Theory
● Energy emission and absorption from elements like hydrogen led to scientists attempting to explain why…
Quantum Mechanical Model
● In addition to knowing that there were energy levels in the atom, three scientists began to notice other things...
Heisenberg – impossible to know the exact position and exact speed of an electron at the same time
De Broglie – electrons have wave-like properties, as in they move in wave patterns
Schroedinger – developed probability of finding each electron in a given location
Using the Quantum Mechanical Model
● Quantum mechanics is a mathematical way of describing where electrons are located.
● It is based on the probability of finding an electron in the space outside the nucleus.
Why Quantum Numbers?
● The quantum numbers are like an address:
State City Street House Number
● Each piece of information is needed to describe the location, and each one tells more specific information about where the electron is located.
First Quantum NumberEnergy level (n)
• Each energy level is farther away from the nucleus.
• Electrons are attracted to the nucleus, so they will fill the lower energy levels first!
nucleus
E1
E2
E3
E4
E5
Second Quantum Number Subshell (l)
As the energy levels increase, so do the number of subshells that are needed to cover all the space around the atom.
The first energy level (n=1) has 1 subshell (s)
The second energy level (n=2) has 2 subshells (s & p)
The third energy level (n=3) has 3 subshells (s, p, & d)
The fourth energy level (n=4) has 4 subshells (s, p, d, & f)
Extension…
● How many subshells would be present in energy level 5?
Answer: 5! s, p, d, f, and g
● How many subshells would be present in energy level 6?
Answer: 6! s, p, d, f, g, and h
Subshells
● s orbital = sphere
● p orbital = peanut
● d orbital = double peanut
● f orbital = flower
Quantum Mechanical Model
● To recap: Energy level 1 = 1 subshell (s) Energy level 2 = 2 subshells (s and p) Energy level 3 = 3 subshells (s, p, and d) Energy level 4 = 4 subshells (s, p, d, and f) etc.
● Why are more subshells present? Each energy level is larger than the
previous. As a result, there are more possible locations for where an electron could reside.
Nucleus
1s subshell
2s subshell
2p subshell
3s subshell3p subshell
3d subshell
4s subshell
Third Quantum Number
Atomic Orbitals ( ml )
•The atomic orbital essentially describes how many of that shape of subshell are needed to cover all the space around the nucleus.
•The more complicated the shape, the more orbitals are needed to cover all the space.
Third Quantum Number
Atomic Orbitals ( ml )
•“s” has 1 orbital (just 1 type of s)
•“d” has 5 orbitals (dxy
, dxz
, dyz
, dz
2, dx
2-y
2)
•“p” has 3 orbitals (px, p
y, p
z)
•“f” has 7 orbitals (etc., etc.,)
There is 1 s orbital
There are 3 p orbitals
There are 5 d orbitals
There are 7 f orbitals
Fourth Quantum NumberElectron Spin
( ms )Each electron can be spin up (+1/2) or spin down (-1/2)
No two electrons in the same orbital orientation can have the same spin.
With only one spin up and one spin down, the maximum number of electrons that can fit into any given orbital orientation is two.
This is called the Pauli Exclusion Principle.
Energy LevelPossible
SubshellsAtomic Orbitals
Number of Electrons in
Each Subshell
Maximum Possible
Electrons in Energy Level
1 s 1 2 2
2sp
13
26
8
3spd
135
26
1018
4
spdf
1357
26
1014
32
Aufbau Principle / Hunds’ Rule
Aufbau:Fill from the ground up
Hund’s Rule:When choosing between equivalent orbitals, fill the empty orbitals first