Electron arrangements

What happens to electrons in diff shells

• electrons in different shells have diff amounts of energy- can therefore be represnted on energy level diagram

What are shells called

• shells are called main energy levels(n)- labelled n= 1,2,3(principial quantum number)

How many in 1st , 2nd , 3rd maine energy level etc

• 1st main energy level- 2 electrons

• 2nd main energy level- 8 electrons

• 3rd main energy level-18 electrons

What are the main energy levels divided into

• divided into sub-levels/ diff atomic orbitals : s, p. d, f- all have slightly diff energies

• level 1 has 1 s sub level/shell/orbital

• level 2 has 1 s and 3 p sub-levels- slightly higher energy

• level 3 has 1 s sub level , 3 p sub level , 5 d sub level- slightly higher energy

• then (exception etc with transition) level 4- 1s,3p,5d,(7 f but not needed )

What are atomic orbitals

• diff sub energy levels/shells: s, p, d, f- all have slighlty diff energy levels

• Electron is no longer considered to be a particle but a cloud of negative charge

• Electron fills volume in space calle dit;s atomic orbital

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What is a orbital

• the little box that holds 2 electrons

How many eletrons do each atomic orbitla hold and how much does a single orbital hold

Any single orbital holds 2 electrons

all the orbitals in p, d , f are degenerate in energy(sam energy as e/o)- so electrons fill each orbital singly first and then pairs

• s orbital- 1 orbital- 2 electrons

• p orbital - 3 orbitals- 2 electrons each - 6 electrons

• d orbitals- 5 orbitals - 2 electrons each - 10 electrons

What do electrons have

• electrons have property called spin

What is spin

• 2 electrons in same orbital must have opp spin

• electrons are usually represented by arrows pointing up or down to show diff directions of spin

Key rules of atomic orbitals/ key principles

• Aufbau principle: atomic orbitals of lower energy that is available are filled first - so lower main level is filled first and within level sub-levels of lower enrgy are filled first(i/e s lower energy than p)

• Hund’s rule: degenerate atomic orbital( of same energy) fill singly before pairing starts- b/c this minimises electron-electron repulsion

• Pauli’s exclusion principle:no atomic orbital can hold more than 2 electrons and they must have opposite spin

Important points about 4s and 3d orbitals

• 4s orbital fills before 3d orbital

• electrons are lost from the 4s orbital before 3d orbital

• when populated with electrons 4s jumps in energy to above 3d

• stability is associated with a full and half filled 3d orbital- if 3d4 or 3d9 electron from 4s orbital moves to more stable 3d orbital to make 2d5 or 3d10

How to write notation for electronic configuration

• 1s2,2s2,2p6 etc

• condensed elctronic configuration- noble gas thats closest to it - electrons