BackAtomic Structure, Electron Configuration, and Periodic Trends: Study Notes
Study Guide - Smart Notes
Tailored notes based on your materials, expanded with key definitions, examples, and context.
Atomic Structure and Electron Configuration
Ground State Electron Configuration
Electron configuration describes the arrangement of electrons in an atom's orbitals. The ground state configuration is the lowest energy arrangement of electrons.
Full electron configuration: Lists all occupied orbitals in order of increasing energy.
Condensed electron configuration: Uses noble gas notation to simplify the configuration.
Example: For fluorine (F): Full: Condensed: [He]
Box Diagrams (Valence Shell Only)
Box diagrams visually represent electron occupancy in orbitals, showing paired and unpaired electrons.
Each box: Represents an orbital; arrows indicate electrons and their spins.
Example: For F: [He] 2s (two paired electrons), 2p (five electrons: two pairs, one unpaired).
Quantum Numbers and Atomic Orbitals
Quantum Numbers
Quantum numbers describe the properties of atomic orbitals and the electrons in them:
Principal quantum number (n): Energy level (shell)
Angular momentum quantum number (l): Subshell (s, p, d, f)
Magnetic quantum number (ml): Orientation of orbital
Spin quantum number (ms): Electron spin (+1/2 or -1/2)
Orbital Sketches
Orbitals are regions in space where electrons are likely to be found. For a fluorine atom, the 2p orbitals are shown as three perpendicular dumbbell shapes centered on the nucleus.
Each orbital: Assigned quantum numbers (n, l, ml, ms).
Effective Nuclear Charge (Zeff) and Periodic Trends
Effective Nuclear Charge (Zeff)
Zeff is the net positive charge experienced by valence electrons, accounting for shielding by inner electrons.
Formula: Where Z = atomic number, S = number of shielding electrons
Trend: Zeff increases across a period (left to right) and decreases down a group.
Example: For P, Cl, As, Br (all with 2p electrons):
Element
Z
S
Zeff
P
15
2
13
Cl
17
2
15
As
33
2
31
Br
35
2
33
Bromine's 2p electrons feel the largest Zeff.
Atomic Radius Trends
Atomic radius generally decreases across a period due to increasing Zeff, pulling electrons closer to the nucleus. Down a group, radius increases as additional shells are added.
Additional info: The effect of electron repulsion and shielding is more pronounced in elements with more electrons.
Transition Metals and Oxidation States
Variable Oxidation States
Transition metals can exhibit multiple oxidation states due to the similar energies of their s and d orbitals.
Example: Vanadium ([Ar] ) can have +1 or +2 oxidation states by removing electrons from the 4s orbital.
Higher oxidation states: Require removal of electrons from inner shells, which needs much more energy due to higher Zeff.
Ionization Energy and Periodic Trends
Ionization Energy
Ionization energy is the energy required to remove an electron from an atom in the gas phase.
Trend: Increases across a period, decreases down a group.
Example: For Ti, K, Mg, Na:
Element
Electron Configuration
Z
S
Zeff
Ti+
[Ar] 4s1 3d1
22
18
4
K+
[Ne] 3s2 3p6
19
10
9
Mg+
[Ne] 3s2
12
10
2
Na+
[He] 2s2 2p6
11
10
1
It is hardest to remove an additional electron from Na+ due to its higher Zeff and smaller radius.
Excited State Electron Configurations
Excited States
An excited state occurs when an electron absorbs energy and moves to a higher energy orbital.
Example: Sodium with configuration (excited state).
Energy absorption: The electron must absorb energy to move from the 3s to the 3p orbital.
Summary Table: Key Concepts
Concept | Definition | Example/Application |
|---|---|---|
Electron Configuration | Arrangement of electrons in orbitals | [He] for F |
Quantum Numbers | Describe electron properties in orbitals | n=2, l=1, ml=0, ms=+1/2 |
Zeff | Net positive charge felt by valence electrons | |
Ionization Energy | Energy to remove an electron | Highest for Na+ in the given set |
Excited State | Electron in higher energy orbital | Sodium: |
