Lesson 1 Flashcards
What is the Bohr Model?
Electrons travel around the nucleus in specific energy levels.
What happens when electrons are in their stationary state in the Bohr Model?
Atoms do not emit energy in their stationary state.
How do electrons move to higher energy levels in the Bohr Model?
Electrons can be excited by absorbing a certain amount of energy and jumping to a higher energy level.
What occurs when electrons drop back to their lower stationary state in the Bohr Model?
They release energy in the form of light (photon).
Bohr’s main energy levels consists of:
scientists later found that Bohr’s main energy levels/shells consisted of subshells or sublevels
1st shell - 1 subshell
2nd shell - 2 subshells
3rd shell - 3 subshells
What does the Quantum Mechanics Model describe?
The statistical probability of finding the electron in a region of space (orbital) in an atom.
How do electrons move between different orbitals according to the Quantum Mechanics Model?
By absorbing or emitting a specific quanta of energy (energy is quantized).
What does the Heisenberg uncertainty principle state about electrons?
It is impossible to simultaneously know the speed and exact location of an electron.
Why do we rely on probability when dealing with electrons in the Quantum Mechanics Model?
Electrons are too small and too fast, making it impossible to precisely determine their speed and location.
Quantum Numbers and Atomic Orbitals
There are various types of atomic orbitals. Each type of orbital has a set of 4 numbers called quantum numbers, which describe various properties of the orbital
Analogy –> Specify the “address” of each electron in an atom
What are the quantum numbers?
4 Quantum Numbers describe the distribution and behaviour of electrons in orbitals
n - describes orbitals energy level and relative size
l - orbital shape
ml - orientation in space
ms - describes the spin of an electron in an orbital
What does the Principal Quantum Number (n) indicate?
Energy level/shell and size of an orbital for each element
What is the range of n in the Principal Quantum Number?
From 1 to ∞ (only positive integers)
How does n affect the energy required to occupy the orbital?
Increases as n increases for a given atom
What does n2 represent in relation to the Principal Quantum Number?
Number of orbitals in the energy level
quantum number n and shells
All orbitals that have the same n are said to be in the same shell
What is the secondary quantum number (l) also known as?
Azimuthal quantum number
What does the secondary quantum number (l) determine?
Shape of the orbital
What are the allowed values of l dependent on?
The value of n
What is the range of allowed values for the secondary quantum number (l)?
From 0 to n - 1
What does l = 0 correspond to in terms of orbital shape?
s orbital
What does l = 1 correspond to in terms of orbital shape?
p orbital
What does l = 2 correspond to in terms of orbital shape?
d orbital
What does l = 3 correspond to in terms of orbital shape?
f orbital
If n = 2, what are the possible values for l?
0 and 1
L quantum vaue and the energy subshells
All the ‘l’ quantum values represent different subshells or sublevels within each principal energy level
Example:
when n= 2; there are 2 values for ‘l’ (0 and 1) indicating two subshells in the second energy level
Saturn and the atom (A Cross Section of an Atom)
From a distance the rings look solid. When viewed more closely, we notice the rings are made of smaller rings.
We can think about the Bohr model of an atom - where the second ring is actually made of two smaller (closely together) rings; the third ring is made of three closely grouped rings, etc…
What does the Magnetic Quantum Number (ml) determine?
Number of orbitals in a subshell
How does the Magnetic Quantum Number (ml) relate to the orientation of an orbital in space?
Specifies the orientation in space of the orbital; different orientations have different energies
What are the possible values of the Magnetic Quantum Number (ml)?
-l to +l; e.g., if l = 2, ml can be -2, -1, 0, 1, 2
How many values of ml are there for any given value of l?
(2l + 1) values; ie. # of orbitals for the l value
perpendicular axis and quantum number ml
Called px, py, pz (the 3d axis is x,y,z)
Shells
The SHELL is the main energy level
the shell number is given by the principal quantum number, n
It also corresponds to the period number on the periodic table
Subshells
The SUBSHELLS/SUBLEVELS are orbitals of different shapes and energies
as given by the secondary quantum number, l
most often referred to as s, p, d, f.
Quantum Numbers Summary
Taken together the three quantum numbers specific the orbital the electron occupies. Namely:the energy of the orbital, the shape of the orbital, and the orientation of the orbital
writing 3 quantum numbers to indicate every possible orbital an electron can occupy is cumbersome; instead do we do the following:
retain the numeric value of the principal quantum number and we use a letter to indicate the secondary quantum number:
l = 0 🡺 s; l = 1🡺 p; l = 2 🡺 d; l = 3 🡺 f
When combined, they indicate a specific orbital e.g. 1s orbital; 2s orbital; 2p orbital
Electron Probabilities and the 1s Orbital
The 1s orbital looks very much like a fuzzy ball, that is, the orbital has spherical symmetry (the probability of finding an electron is the same in every direction)
The electrons are more concentrated near the center
The Three p Orbitals
There are 3 p orbital; each orbital is cylindrically symmetrical with respect to rotation around one of the 3 axes, x, y, or zEach ‘p’ orbital has two lobes of high probability density separated by a node (region of zero probability)
Electrons are not found in the middle (the node of the orbitals)
s, p, and d-orbitals - how many electrons do they hold?
s orbitals: Hold 2 electrons (outer orbitals of Groups 1 and 2)
p orbitals: Each of 3 pairs of lobes holds 2 electrons = 6 electrons (outer orbitals of Groups 13 to 18)
d orbitals: Each of 5 sets of lobes holds 2 electrons= 10 electrons (found in elements with atomic no. of 21 and higher)
4) Spin Quantum Number(ms)
The spin quantum number explains some of the finer features of atomic emission spectra
The spin refers to a magnetic field induced by the moving electric charge of the electron as it spins
An orbital can hold 2 electrons that spin in opposite directions
Only possible values = +1/2 and -1/2
(clockwise or counterclockwise)
*Only worry about up or down on tests!
Pauli Exclusion Principle
No two electrons in an atom can have the same 4 quantum numbers.
Each electron has a unique “address”:
Principal # → Energy level
- Secondary # → Sublevel s,p,d,f
- Magnetic # → orbital
- Spin # → electron spin
photon
a particle representing a quantum of light or other electromagnetic radiation. A photon carries energy proportional to the radiation frequency but has zero rest mass
