Wednesday, May 4, 2011

Bohr Model




The Bohr model is the diagram we use today to visualize what an atom looks like.

image66.gif (5746 bytes)
click to enlarge

Orbitals: the space occupied by electrons, also known as shells

This is what Bohr believed:

  • Electrons have certain energy levels
  • When electrons jump to a different orbital, they release a certain spectrum of light
  • Ground states are the lowest energy states
  • Excited states are when the electrons jump into a higher or lower level
  • Each element gives off a certain spectrum of light when they are heated
We use this to identify what elements are present in distant stars
 

Structure of a Bohr model

Here are the orders of the shells and the maximum electrons they can have

1st shell: 2 electrons
2nd shell: 8 electrons             } octet rule
3rd shell: 8 electrons             }

In the middle of the diagram, we write the atomic number (number of protons) and the number of neutrons
For example:

The atomic number of chlorine is 17. The atomic mass of chlorine is ~35.
To find the number of neutrons we subtract the atomic number from the atomic mass

  35
­-17
 18

So in the middle of the diagram, we write

17p
18n

chlorine atom model

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