Atoms: Electron Configuration An overview

Electron Arrangements The arrangement of electrons in an atom is very important This arrangement determines how an element will react with/bond with other elements We will examine a simple model of the electron arrangement of the atom This model has electrons located in regions around the nucleus called shells

Electron Shells In all there are 7 energy levels or electron shells These are numbered 1 to 7 They are given letters to denote them 1(K) 5 2(L) N 6 3(M) 4(N) 7

Electron Shells Generally, the further the shell is from the nucleus, the higher its energy level The closer the shell from the nucleus the lower its energy level Different shells can hold different numbers of electrons Higher energy shells can hold more electrons than lower energy shells

Capacity of Electron shells Maximum number of electrons per shell = 2n2

Maximum number of electrons per shell Shell number Formula] [2 (n)2] Maximum e- 1 2 x (1)2 2 2 x (2)2 8 3 2 x (3)2 18 4 2 x (4)2 32 5 2 x (5)2 50 6 2 x (6)2 72 7 2 x (7)2 98

Filling of electrons into shells Shells are filled with electrons(e-) in order Lower shells are filled before higher shells BUT The outer shell never holds more than 8 e-, regardless of its maximum capacity (exception is helium whose outer shell can’t hold more that 2 electrons)

Filling of electrons into shells This is referred to as the OCTET rule The outer shell refers to the outer most shell holding electrons It is also referred to as the valence shell Electrons in the outer shell are called valence electrons

Lets look at lithium ( Li ) 7 3 An atom of Lithium has 3 electrons 2 e- fill the first shell Here is its nucleus Here the 2nd shell is the outer shell + o The 3rd e- is in the second shell

Now for potassium ( K) An atom of Potassium has 19 electrons 39 19 An atom of Potassium has 19 electrons But all 9 can’t go here as this would result in an outer shell with > 8 e- The next shell has a maximum capacity of 18 e- 2 e- fill the first shell N:20 P:19 19-2=17 8 e- fill the second shell 1 of these e- will occupy the next shell 17-8=9

Now for potassium ( K) An atom of Potassium has 19 electrons 39 19 An atom of Potassium has 19 electrons 8 e- occupy the 3rd shell 2 e- fill the first shell 9-8=1 P:19 N:20 Outer shell 8 e- fill the second shell 1 e- occupies the 4th shell

Electronic configuration Describes the arrangement of electrons in each shell of an atom Lithium’s electronic configuration is: 2,1

Electronic configuration Potassium’s electronic configuration is: 2,8,8,1

Draw the arrangement of electrons in an atom on Magnesium Atomic number :12

Check your answer Atomic number :12 2,8,2

Check your answer Complete the drawing of the electron arrangements in the table provided Complete the table of electron configurations