Drawing Models of the Atom The Bohr Model

How do Scientists View the Atom Today?  2 models are most widely used  The Bohr Model and the Electron Cloud Model

 Both of these models explain how the electrons are arranged in the electron cloud.  However, the Bohr Model is Much Easier to Draw and Visualize  We will be drawing Bohr models today.

The Bohr Model (Planetary Model)  Electrons are located in specific orbitals (energy levels) = Circles  Only so many electrons will fit into each electron level.  Levels are filled from the innermost working out. Fill inside circles first.

How to do it  Find number of electrons, protons & neutrons from the atomic number and atomic mass.  Draw a little circle for the nucleus and label with number of protons and neutrons.  Draw larger circles for each energy level.  Draw dots for each electron representing the electrons in each orbital on these circles.

OK, now how do you to really do it?  You use the periodic table  Each period represents an electron level: Each row is Each row is 1 circle 1 circle  Each square represents an electron

Thus it is a Numbers Game TTTThe periods (rows) tell you how many circles (electron shells). TTTThe squares will tell you how many electrons on each orbital.

 You will notice that each period has a certain number of squares  This tells you how many electrons can fit in each period Energy Levels Max Electrons 1 st 2 2 nd 8 2 nd 8 3 rd 18 3 rd 18 4 th 32 4 th 32 5 th 50 5 th 50 6 th 6 th 7 th

Sodium Example  Atomic number 11  Atomic mass 23  In period 3  Thus: number of electrons = 11 protons = 11 protons = 11 neutrons = 12 neutrons = 12 orbitals = 3 orbitals = 3

 Place a dot ( ) for each electron on the orbitals  Sodium has  1 st orbital = 2 e -  2 nd orbital = 8 e -  3 rd orbital = 1 e - total = 11e - total = 11e -

Draw a Bohr Model of your atom model Atom Name: Atom Number: p + Number of e - : Number of n 0 : Energy Levels Electrons 1 st 2 2 nd 8 2 nd 8 3 rd __ 3 rd __ 4 th __ 4 th __ 5 th __ 5 th __

Note To Teacher: Let the next slide run by itself to see the model of several atoms.

A Few of the Atoms

Now it is your Turn! Lets try it. Draw Kr in your Powerpoint notes.