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.
True or False:
The f orbital appears in the fourth energy level.
True
The f orbitals start appearing in the fourth principal energy level.
What is the maximum number of electrons in the third energy level?
18
The third energy level has s, p, and d sub-levels.
The number of electrons in the three sublevels is 2, 6, and 10 repectively.
The total number of electrons adds upto 18.
What is the maximum number of electrons in the fourth energy level?
32
The fourth energy level has s, p, d and f sub-levels.
The number of electrons in the four sublevels is 2, 6, 10, and 14 repectively.
The total number of electrons adds upto 32.
List the steps followed when writing an electron configuration.
- Identify the atomic number.
- Follow the Aufbau Principle.
- Apply Hund’s Rule.
- Check Pauli Exclusion Principle.
List three factors influencing electron configuration.
- Energy levels
- Orbital shapes
- Electron repulsion
These factors determine the most stable arrangement.
Fill in the blank:
The electron configuration of oxygen is ______________.
1s² 2s² 2p⁴
Oxygen has eight electrons distributed across two subshells.
What is the electron configuration of sodium?
1s² 2s² 2p⁶ 3s¹
Sodium has 11 electrons distributed across three subshells.
What is the electron configuration of chlorine?
1s² 2s² 2p⁶ 3s² 3p⁵
Chlorine has 17 electrons distributed across three subshells.
Describe the electron configuration for a noble gas.
They have fully filled outermost energy levels.
Example: Helium (2 electrons), neon (10 electrons), and argon (18 electrons).
This configuration gives them chemical stability.
What is the general electron configuration for noble gases?
ns² np⁶
Examples:
- Helium - 1s²
- Neon - 1s² 2s² 2p⁶
- Argon - [Ne] 3s² 3p⁶
- Krypton - [Ar] 4s² 3d¹⁰ 4p⁶
- Xenon - [Kr] 4d¹⁰ 5s² 5p⁶
What is a shorthand electron configuration?
A condensed notation using the noble gas from the previous period.
For example:
- Sodium’s configuration can be written as [Ne] 3s¹.
- Chlorine’s configuration can be written as [Ar] 3s² 3p⁵.
What is the electron configuration of calcium?
1s² 2s² 2p⁶ 3s² 3p⁶ 4s² or [Ar] 4s²
Calcium has 20 electrons distributed across three energy levels.
What is notable about the electron configuration of chromium?
It’s electron configuration is
[Ar] 4s¹ 3d⁵ instead of [Ar] 4s² 3d⁴.
This is due to the repulsion force between electrons being more significant than the energy jump between subshells.
