Electrons in Atoms Electron Configuration Chapter 4 Electrons in Atoms Electron Configuration

Electron Configuration the arrangement of electrons in the atom There are three rules we need to follow when building an atom.

1. Aufbau Principle German for Building Up When we build an atom with its various electrons we start with the lowest energy level and build up. Lowest energy level is closest to the nucleus

Filling Order 7s 7p 7d 7f 7g 7h 7i 6s 6p 6d 6f 6g 6h 5s 5p 5d 5f 5g further away from the nucleus the higher the energy All sublevels beyond the f sublevel is theoretical Lowest Energy Nucleus

The easy way to remember the filling order 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f 1s2 2 electrons

Fill from the bottom up following the arrows 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f 1s2 2s2 4 electrons

Fill from the bottom up following the arrows 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f 1s2 2s2 2p6 3s2 12 electrons

Fill from the bottom up following the arrows 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f 1s2 2s2 2p6 3s2 3p6 4s2 20 electrons

Fill from the bottom up following the arrows 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 38 electrons

Fill from the bottom up following the arrows 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 56 electrons

Fill from the bottom up following the arrows 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 88 electrons

Fill from the bottom up following the arrows 2s 2p 3s 3p 3d 4s 4p 4d 4f 5s 5p 5d 5f 6s 6p 6d 6f 7s 7p 7d 7f 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6 118 electrons No elements with more

Increasing energy 7s 2p 3p 4p 5p 6p 7p 3d 4d 5d 6d 6s 5s 4f 5f 4s 3s

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p 3s 2p

2. Pauli Exclusion Principal No two electrons can have the exact same four quantum numbers! Each orbital has no more than 2 electrons– they must have opposite spins

3. Hund’s Rule When electrons occupy orbitals of equal energy they don’t pair up until each orbital has one electron.

Three ways to write electron configuration Orbital Notation Electron Configuration Notation Noble Gas Notation

Orbital Notation Represents each orbital in the sublevel as a box or a line Each electron is represented by an arrow pointing up (+1/2 spin) or down (-1/2 spin) Ex: phosphorous with 15 electrons

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p The first two electrons go into the 1s orbital Notice the opposite spins only 13 more Lets find the electron configuration for phosphorous with 15 electrons

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p The next electrons go into the 2s orbital only 11 more

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p The next electrons go into the 2p orbital only 5 more

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s 3p The next electrons go into the 3s orbital only 3 more

Increasing energy 7p 6d 5f 7s 6p 5d 6s 4f 5p 4d 5s 4p 3d 4s The last three electrons go into the 3p orbitals. They each go into separate orbitals 3 unpaired electrons

Electron Configuration Notation Represents each sublevel designation from lowest energy to highest Electrons are represented by superscripts Sublevel Maximum # of e- s 2 p 6 d 10 f 14

Electron Configuration Notation 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f14 6d10 7p6

Electron Configuration Notation Ex: Manganese 25 electrons From lowest energy to highest Follow the filling order 1s22s22p63s23p64s23d5

Try these Na F Cl Ca

Answers Na 1s2 2s2 2p6 3s1 F 1s2 2s2 2p5 Cl 1s2 2s2 2p6 3s2 3p5 Ca 1s2 2s2 2p6 3s2 3p6 4s2

3. Noble Gas Configuration Place the noble gas that precedes the element in brackets [ ] this accounts for that number of electrons Continue the electron configuration with the next highest principal energy level (period number) and the s orbital This is a shorthand way of writing electron configuration.

Noble Gas Configuration Ex: Silicon 14 electrons 1s22s22p63s23p2 same as the noble gas Ne Si is in period 3 [Ne] 3s23p2

Exceptions to Electron Configuration There’s always exceptions

Orbitals fill in order Lowest energy to higher energy. Adding electrons can change the energy of the orbital. Filled and half-filled orbitals have a lower energy. Makes them more stable. Changes the filling order of d orbitals

Write these electron configurations Titanium - 22 electrons 1s22s22p63s23p64s23d2 Vanadium - 23 electrons 1s22s22p63s23p64s23d3 Chromium - 24 electrons 1s22s22p63s23p64s23d4 is expected But this is wrong!!

Chromium is actually 1s22s22p63s23p64s13d5 Why? This gives us two half filled orbitals.

Chromium is actually 1s22s22p63s23p63d54s1 Why? This gives us two half filled orbitals.

Chromium is actually 1s22s22p63s23p63d54s1 Why? This gives us two half filled orbitals. Slightly lower in energy. The same principle applies to copper.

Copper’s electron configuration Copper has 29 electrons so we expect 1s22s22p63s23p64s23d9 But the actual configuration is 1s22s22p63s23p64s13d10

Copper’s electron configuration This gives one filled orbital and one half filled orbital. Remember these exceptions s2d4  s1d5 s2d9  s1d10

In each energy level The number of electrons that can fit in each energy level is calculated with maximum e- = 2n2 where n is energy level n = 1 maximum e- = 2 n = 2 maximum e- = 6 n = 3 maximum e- = 18 …