Work in groups on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help.
What is the first step that you must do in order to draw the electron dot formula for ammonia, NH3?
The first step in drawing the electron dot formula for ammonia is to determine the number of bonding electrons for each of the atoms. The arabic numeral above the element's column in the periodic table gives you that number.
What are the numbers of bonding electrons for the nitrogen atom and the hydrogen atoms?
The nitrogen atom has 5 electrons and each of the three hydrogen atoms has 1 electron. The total number of electrons for ammonia will therefore be 8 electrons.
Draw a hydrogen atom next to a nitrogen atom and place a pair of electrons between these two atoms.
Now draw a second hydrogen atom next to the nitrogen atom and place a second pair of electrons between these atoms.
Now draw a third hydrogen atom next to the nitrogen atom and place a third pair of electrons between these atoms.
You have now used 6 of the 8 electrons. Place the remaining two electrons on the nitrogen atom. Remember that each hydrogen atom should not have more than 2 electrons and the nitrogen atom should have a total of 8 electrons.
The electron dot formula for ammonia is now complete. Note that the nitrogen atom now has three bonds. This is the normal number of bonds for a nitrogen atom when it does not have a charge.
Click here to see an animated gif of this process...