Electron Configurations Pre Ap

Electron Configurations

Electron Configurations • Electron Configurations – the way electrons are arranged (placed) around the nucleus. nucleus • Guiding Principle: electrons are arranged in a way that gives the lowest energy to the atom. (low energy = high stability)

Rules for Electron Configurations • Aufbau Principle – lowest energy levels fill first. • Pauli Exclusion Principle – no two electrons in an atom can be at the same place at the same time. All atomic orbitals can only hold 2 electrons maximum & they have to be spinning opposite directions. • Hund’s Rule – Don’t pair until you have to. When electrons can go into orbitals of equal energy (ex.3 types of p orbitals) one electron enters each orbital until each has one electron. They all spin the same direction until they pair up. • Each orbital corresponds to a specific section on the periodic table.

How orbitals align on the Periodic Table

Drawing Orbital Box Diagrams

You try a few! • Nitrogen 1s2

2s2

2p3

• Chlorine 1s2

2s2

2p6

3s2

3p5

Write the electron configurations for the following elements: • • • • • • • •

Hydrogen Helium Lithium Beryllium Boron Fluorine Sodium Phosphorus

1s1 1s2 1s22s1 1s22s2 1s22s22p1 1s22s22p5 1s22s22p63s1 1s22s22p63s23p3

Using the “d” orbitals • The transition metals use the “d” orbitals to denote their electron configurations. • “d” orbitals have a higher energy level than “s” orbitals with a larger number. Therefore, the “s” orbital will fill before the “d” orbital. • There are exceptions to the rule within the transition elements.

Examples • Scandium 1s22s22p63s23p64s23d1 • Titanium 1s22s22p63s23p64s23d2 • Vanadium 1s22s22p63s23p64s23d3

You try a few! • Iron • Nickel • Bromine

1s22s22p63s23p64s23d6 1s22s22p63s23p64s23d8 1s22s22p63s23p64s23d104p5

Using the “Core” to shorten things up: • Instead of writing the entire electron configuration, you can use the “core” of the last noble gas. • Example: Phosphorous Regular - 1s22s22p63s23p3 Core - [Ne] 3s23p3

You try! Chlorine

[Ne] 3s23p5

Barium [Xe] 6s2 Iodine [Kr] 5s24d105p5

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