2A2 Electron Configuration Flashcards
Explain the current atomic model, the quantum mechanical model, and the experimental basis for both models.
Define:
electron configuration
A representation of the unique arrangement of electrons in an atom.
It is numerical expression of a 3D space around an atom’s nucleus.
It follows specific rules and principles to minimize energy.
Define:
shells
A region around the nucleus that represents a specific energy level.
These regions are often depicted as circles around a nucleus, with energy increasing the further a shell is from the nucleus. The shells are where electrons can be found, and the specific shell determines the energy level.
Define:
orbitals
Precise 3D regions around the nucleus that mathematically describe where an electron is most likely to be found.
They differ in their shapes and sizes, electron capacity, and quantum numbers. They are much more specific than a shell, as they define a location within a shell.
What is the difference between shells and orbitals?
A shell refers to a specific energy level, while an orbital refers to a specific 3D region.
Shells can contain different shapes of orbitals. For instance, the second shell (n=2), there are 2s and 2p orbitals.
What is the significance of electron configuration?
It helps predict:
- Bonding behavior
- Reactivity of elements
Elements with full configurations, like noble gases, do not bond easily.
What is the purpose of quantum numbers in atomic structure?
They provide a unique location for each electron in an atom.
They define an electron’s energy, position, and spin, ensuring no two electrons are identical. This is important when trying to compare and contrast electrons within an atomic structure.
List the four quantum numbers.
- n: principal quantum number
- l: orbital angular momentum
- ml: magnetic quantum number
- ms: spin quantum number
Each number describes different aspects of an electron’s position and behavior.
What does the principal quantum number (n) indicate?
The energy level or shell that the electron is located on.
Possible values for n are nonzero integers: 1, 2, 3, etc.
The shell located closest to the nucelus is labeled as n=1, increasing as the shells become further from the nucleus.
It can be thought of as the floors of a hotel, where lower values indicate lower energy.
What is the significance of the quantum number l?
It denotes the orbital angular momentum and indicates the subshell.
Possible values of l range from 0 to n-1, corresponding to s, p, d, and f subshells.
The subshells denote the shapes of the orbitals.
Fill in the blank:
The magnetic quantum number (ml) specifies the __________ of an orbital.
orientation
Values for ml range from -l to l.
Each l value has different subshells.
It determines the orbital’s orientation in space and number of subshells within a given shell.
What does the fourth quantum number (ms) represent?
The spin of an electron, which can either be 1/2 (spin-up) or -1/2 (spin-down).
This quantum number differentiates electrons in the same orbital.
Electrons in the same orbital have opposite spins.
Spin creates a magnetic field for the electron.
List the three main rules that define electron positions within an atom.
- Hund’s Rule
- The Pauli Exclusion Principle
- The Aufbau Principle
These rules are fundamental in quantum physics and the arrangement of electrons.
What is the Aufbau Principle?
Electrons fill lower energy levels before higher ones.
“Aufbau” means “building up” in German.
This principle governs the order of filling atomic orbitals.
Define:
Pauli Exclusion Principle
- No more than two electrons can occupy a single orbital.
- The two electrons in an orbital must have opposite spins.
This ensures unique quantum numbers for each electron.
Define:
degenerate orbitals
Two or more orbitals that have the same energy level.
Define:
Hund’s Rule
Electrons fill degenerate orbitals singly before pairing.
This minimizes electron-electron repulsion.
Degenerate orbitals are orbitals with equal energy.
Atoms with unpaired electrons are paramagnetic, while those with all paired electrons are diamagnetic.
True or False:
All orbitals in the same sub-level have equal energy.
True
Orbitals in the same sub-level are degenerate (a.k.a. have the same energy level) until influenced by external factors.
For example, the three p orbitals (px, py, pz) are degenerate.
Define:
electron pair
Two electrons occupying the same orbital with opposite spins.
Electron pairs are essential in bonding and stability.
What is the order of orbital filling in the Aufbau diagram?
1s → 2s → 2p → 3s → 3p → 4s → 3d → 4p → 5s → 4d → 5p → 6s → 4f → 5d → 6p → 7s
Electrons fill orbitals in increasing energy order, following the Aufbau principle. Many follow the “diagonal rule” by drawing diagonal lines across energy levels to showcase how the lowest energy orbitals are filled up first.
Define:
subshell
A group of orbitals with same energy level and shape located within a shell.
The number of electrons within a shell is determined by the size and type of subshells within that shell.
What are the four subshells for electrons?
- s orbitals
- p orbitals
- d orbitals
- f orbitals
Each level has a specific electron capacity.
How many orbitals and electrons can the s, p, d, and f subshells hold?
- s: 1 orbital, 2 electrons
- p: 3 orbitals, 6 electrons
- d: 5 orbitals, 10 electrons
- f: 7 orbitals, 14 electrons
These are the capacities of the four subshells.
How many sub-levels are in the second energy level?
Two
These are the s and p sub-levels. The second energy level can hold a total of 8 electrons, 2 in the s sub-level and 6 in the p sub-level.
Explain why 4s is filled before 3d.
4s has lower energy than 3d, so it is filled first according to the Aufbau Principle.
Lower energy levels are filled before higher energy levels. Although it can be confusing, 4s is considered lower in energy than 3d. This is due to the shape of the s orbital, which leads to a stronger attraction to the nucleus and an overall lower energy level.
