# Day 2 Quantum Numbers and Electron Configurations

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Day 2 Quantum Numbers and Electron Configurations
Bono "The less you know, the more you believe." Chapter 13 Day 2 Quantum Numbers and Electron Configurations

Models of the Atom Dalton Thomson Rutherford Bohr

Neils Bohr model of the Atom:
Electrons can be in 1 of many “principle energy levels”, but cannot be in between any of these energy levels. Each Principle Energy Level (n) is given a number n=1 n=2 n=3 Electrons move around the nucleus like planets move around the sun.

Unfortunately, Bohr’s model of the Hydrogen atom turned out to be incorrect, so a new model was introduced. But, This! Not This!

What are the Quantum Numbers?
Remember – they give the approximate location of electrons in an atom. They are actually represented by letters. N – distance (size of orbital) l – Shape of orbital m – orientation in space of orbital s – spin of the electron

Erwin Schrödinger, using complex mathematics, calculated the probability of where an electron is located. The probability of an electron in the first principle energy level: An orbital is drawn that encloses the region where the electron is found 90% of the time.

First Energy Level (n=1) can contain 1 sublevel orbital
Second Energy Level (n=2) can contain 2 sublevel orbitals Third Energy Level (n=3) can contain 3 sublevel orbitals and so on… There are many types of sublevels:

Shape Name Maximum # of electrons Lowest Energy s 2 Spherical p 6 Highest Energy Dumbell Dumbell

Maximum # of electrons Name Shape Lowest Energy d 10 f Highest Energy 14 f

The next sublevel is g. How many electrons would it hold?
What type of sublevel orbital(s) would be found in the first principle energy level (n=1)? How many electrons will it hold? What type of sublevel orbital(s) would be found in the second principle energy level (n=2)? How many electrons will it hold? What type of sublevel orbital(s) would be found in the third principle energy level (n=3)? How many electrons will it hold?

1s vs 2s vs 3s orbitals

Called the Pauli exclusion principle
Each sublevel orbital can hold 2 electrons, which have opposite magnetic fields. Therefore, we say that each electron has a spin, which is opposite of each other. This is symbolized by: Called the Pauli exclusion principle

Electron Configurations

Electron Configurations
Using quantum numbers to give the arrangement of electrons around the nucleus. There are three rules that must be followed!

Rule #1 AUFBAU principle Electrons fill low energy orbitals first
s,p,d then f Filling order 1s2s2p3s3p4s3d4p5s4d5p6s4f5d6p7s5f6d7p

Rule #2 Pauli Exclusion Principle
Since there are two possible spins for an electron, no more than two electrons may fill an orbital. Remember: s = 1 orbital, p = 3 orbitals, d = 5 orbitals and f = 7 orbitals

Rule # 3 Hund’s Rule When multiple shapes are present, electrons fill orbitals with parallel spins before pairing up. Must follow rule #2! Example 2p

Write the following electron configurations
Li Na Be C Si

Using the Periodic Table
Read from left to right and top to bottom. Stop when you: Reach the end of a row Change color Reach the element of interest Try the following Mg, B, Ne and Cl

Short-Cut Skip back to the previous Noble Gas (core electrons) and start with the element after that. Try: I, U, Fe

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