1. Isotopes
Lewis dot diagrams
and predicting reactions

2. But First, Let’s Review!!
• Name the three
subatomic particles
that an atom is made
of.
• Protons, neutrons,
electrons

3. But First, Let’s Review!!
• How do I calculate the
number of protons?
• It’s the same as the
atomic number!

4. But First, Let’s Review!!
• How do I know how
many neutrons there
are?
• Round the atomic
mass and subtract the
atomic number!

5. But First, Let’s Review!!
• How do I know how
many electrons there
are?
• It’s the same as the
number of protons!
That’s how the charge
of the atom stays
neutral!

6. But First, Let’s Review!!
• Where does most of
the atoms mass come
from? AND what
subatomic particles
does it include?
• The nucleus and it
consists of protons
and neutrons!

7. But First, Let’s Review!!
• How many electrons
are on the first,
second an third shell?
• 2, 8, 8

8. But First, Let’s Review!!
• Who can draw a Bohr
diagram for Sulfur?

9. Great Job!
NOW we can learn more stuff!

10. Isotopes
• Isotopes are another type of atom of the
same chemical element with a different
number of neutrons.
• An isotope of Carbon, is still carbon it just
has different neutrons in the nucleus.
• Having more neutrons does not affect the
atomic number because the number of
protons stays the same.

11. Isotopes
• Some isotopes are radioactive while most
are quite stable.
• C14 is a radioactive form of Carbon, where C13
is a stable isotope.
• C14 still has 6 protons (because the atomic
number has not changed) but has 8 neutrons
instead of 6.

12. Lewis dot Diagrams
• When predicting reactions, valence
electrons are very important!!!
• Valence electrons- electrons that are on
the outermost shell.
• Lewis dot diagrams are similar to Bohr
Diagrams but they only show the outermost
shell.

13. Lewis dot Diagrams
• Bohr Diagram:
F
• Lewis dot Diagram:
F

14. Lewis dot Diagrams
• This diagram allows us to focus only on the
valence electrons- which is all we really
care about when predicting reactions.

15. Lewis dot Diagrams
• One more short-cut: Rather than have to draw a
Bohr diagram first, or do the math to figure out the
number of valence electrons- all you need to do is
look at the number at the top of the column.
• EX: Phosphorus is in group 17, so it has 7 valence
electrons.
• EX: Carbon is in group 14, it has 4 valence electrons
• EX: Hydrogen is in group 1, it has 1 valence electron

16. Predicting Reactions
• RULE 1: Everyone wants to be a noble gas!!
The noble gasses are PERFECT. They have a
full outer shell. All elements want to have a
full outer shell.
• RULE 2: No one plays unless everyone is
happy. All elements reacting must get what
they want or no one reacts.

17. Predicting Reactions
• Atoms are lazy (like you!) and they don’t
want to do too much work. If they only need
to lose 1,2, or 3 electrons, they will do that
rather than search for 5,6, or 7 to fill their
shell.
• Atoms will do the least amount of work to
gain or lose electrons in order to have a full
outer shell.
• Remember 2 on the first shell is full! ! !

18. Predicting Reactions
• If I have Beryllium and Oxygen, how many
atoms of each will I need to satisfy both
rules?
• Beryllium has 2 valence electrons that it wants
to get rid of.
• Oxygen has 6 valence electrons and needs to
gain 2.

19. Predicting Reactions
Be
O
We only need one of each! Beryllium is happy
because it lost the two outer electrons, and
went to its inner full shell. Oxygen is happy
because with Berylliums two electrons it
now has a full outer shell!

20. Predicting Reactions: Lithium
Lithium is atomic number 3
How many protons does Lithium have?
How many Neutrons does it have?
How many electrons does it have?
How many valence electrons does it have?
(What group is it in?)
• What would a Bohr Diagram look like for
Lithium?
•
•
•
•
•

21. Predicting Reactions: Lithium
• Will lithium try to lose it’s 1 electron? Or will
it try to find 7? Which is easier?
• Who is it lost likely to bond with? Who
needs to find an extra electron in order to
be happy?
• What will the charge of it be in the end?