Download combining number

By Chantelle Dickie,
Produced in 2003
As you go through this self-paced tutorial, follow
the instructions carefully.
You will need your periodic table as you work
through the tutorial.
Click on the left mouse button to move to the next
screen or to reveal answers.
Make sure that you try to figure out the answers for
yourself before revealing the correct ones. There’s
no need to hand in anything for this. It’s entirely
for your benefit!
In this tutorial, you will review atomic structure and
Bohr models.
You will also learn how to use your knowledge of
atomic structure to predict what happens…
If you already remember the basics of atomic
structure, click on the icon below to skip the
review.
Atoms are made up of three types of subatomic
particles. Before clicking to see the answers, see
if you can fill in the table below on your own:
Name
1. Protons
2. Neutrons
3. Electrons
Location
Type of charge
In the nucleus
Positive
In the nucleus
No charge
Spinning around the nucleus
Negative
Protons and neutrons
in nucleus
Electrons
7 p+
7n
12 p+
12 n
Nitrogen
Magnesium
Do you need review of Bohr models? Try to predict
what the Bohr models above will look like when
completed. Once you think you know, click once to
reveal the answer.
If you’re already a pro, you may find this
review “Bohr”-ing so click the icon to skip it.
Remember, Bohr’s theory has three main ideas:
Electrons move around the nucleus of the atom
in orbits (sometimes called shells).
Orbits or shells
Electron travels
around the nucleus
(like a runner
around a track)
Nucleus
It may help to think of these
orbits as layers of an onion!
Each orbital is a certain distance away from the
nucleus of the atom and can hold a specific
number of electrons.
1st orbit
2nd orbit
Nucleus
3rd orbit
Maximum
number of
electrons
1st orbit
2nd orbit
3rd orbit
2
8
8
After the orbital closest to the nucleus is full,
electrons start filling the next orbit, and the next.
First, count how many electrons you
have in total (equal to the atomic
number). Let’s say 11 for this
example.
Then you can start filling the
orbitals. Two electrons can
fit in the first orbital.
Next, count how many electrons you still need a
“home” for. We have 9 left, so not all of them will
fit into the second orbital. Put in the eight that do
fit and…
That leaves one to fit into the third orbital.
Here are more practice questions. Make sure you
figure out the answer by yourself before clicking to
see if you got it correct.
8 p+
8n
14 p+
14 n
3 p+
4n
Oxygen
Silicon
Lithium
(Atomic Number = 8,
Atomic Weight = 16)
(Atomic Number = 14,
Atomic Weight = 28)
(Atomic Number = 3,
Atomic Weight = 7)
Still need more help? Go back to your class notes
and review before continuing.
When atoms come towards each other, which of the
subatomic particles do you think will determine
how the atoms will react?
Click on the answer you think is correct.
Protons
Neutrons
Electrons
Remember, protons and neutrons are “hidden”
away in the nucleus so they won’t come into
contact with the other atoms.
Since they don’t “touch” the other atoms, the
protons and neutrons don’t have a say in how the
atoms will react.
Click here to try again.
You’re right! Since the electrons are spinning
around outside the nucleus, they are the subatomic
particles that would “touch” the other atom’s
electrons first.
Now we can use what we know about our Bohr
models to predict just how the atoms will react
with each other.
Atoms want to be happy. Do you know what
makes atoms happy?
They’re pretty easy to please…
All they want is a full outer orbital.
It doesn’t matter to them whether it’s the 1st, 2nd,
3rd or 7th orbital. They just don’t want to have any
orbitals with any space for electrons.
8 p+
8n
Full =
3 p+
4n
14 p+
14 n
Empty =
To get a complete outer orbital, atoms depend on
other atoms. This is why atoms form compounds.
A compound is a combination of 2 or more atoms.
For example, CO2 and H2O
O
C
O
Carbon dioxide
Water
There are two ways that atoms can combine to get
a complete outer shell.
To see if you can figure out the two ways, consider
these situations:
1) You have 20 candies, but only want 18 of them.
Your friend has 8 candies and would like 10. Is
there any way you could you solve this problem?
You could give your friend 2 candies.
2) You have a car (and a license) but your little
brother doesn’t. How can he get to school?
You could give him a ride and SHARE the car.
Atoms use the same ideas that you came up with to
get a full outer shell.
Ionic bonding is the the type of bonding that
happens when atoms decide to give or take
electrons from another atom. It happens between
a metal and a non-metal.
For example, when sodium and chlorine react,
sodium gives one electron to chlorine.
To figure out whether atoms will gain or lose
electrons when they form compounds, we look at
their combining number. The combining number
is usually found on the periodic table in the box for
each element above and to the right of the symbol.
Atomic number
Symbol
Atomic mass
Name
9
F
-1
Combining
number
19.00
Fluorine
If the combining number is positive (+), the
atom will lose electrons.
If it’s negative (-), the atom gains electrons.
See if you can fill in this table before clicking to
reveal the correct answers.
Element
Gains or
loses?
How many?
Magnesium
Combining
Number
+2
Loses
2
Phosphorus
-3
Gains
3
Oxygen
-2
Gains
2
Boron
+3
Loses
3
Zinc
+2
Gains
2
Back to our candy story. How might you solve the
problem if you want 2 pieces of candy but your
friend only has 1 to give away?
I’d find another friend who wants to
give away one candy and take one
from each of them.
Atoms do the same thing. For example, oxygen
wants 2 electrons and magnesium can only give
1 electron.
How many magnesium atoms do you think would
combine with one oxygen?
2 magnesium
Mg2O
1 oxygen
There’s an easy way to figure out how many of
each atom will be in the compound. I’ll tell it to
you (‘cause that’s just the kind of person I am!)
1)Put down the symbols of the ions, add brackets around any
complex ion. Write the positive (metallic) ion first.
e.g. Ca Cl
2) Put combining numbers above each symbol.
e.g. Ca+2Cl-1
3) Cross out the positive and negative, criss-cross the combining
numbers and use them as subscripts.
e.g. Ca+2 Cl-1  Ca1Cl2 = CaCl2
It’s almost that easy! There are just a few more
rules you need to know…
* If an element has a subscript of one, you don’t need to
use it.
i.e. Na1Cl1 = NaCl
* If there are subscripts that can be reduced, you must
reduce them. Remember, they can be reduced if there’s a
smaller number that can divide into both numbers equally.
i.e. Mg2O2 = MgO
C2O4 = CO2
Here are some for you to try. Remember to figure
them out for yourself before you click on the
mouse!
Element #1
Element #2
Formula
Calcium
Fluorine
CaF2
Bromine
Strontium
SrBr2
Magnesium
Sulfur
MgS
Phosphorus
Calcium
Ca3P2
Scandium
Oxygen
Sc2O3
Did you have trouble with any of these?
Yes
No
•Did you remember to write the metallic element
first? Remember that the metallic elements are
found on the left hand side of the periodic table.
•Did you remember to cross out the positive and
negative signs of the combining numbers? The
subscripts shouldn’t have any (+) or (-) in front of
them.
•Did you remember to cross over the subscripts?
•Did you remember to reduce the subscripts?
You are now finished this tutorial. By now, you
should know:
•The structure of atoms
•How to draw Bohr models of atoms
•What an ionic bond is
•How to predict the chemical formulas of
compounds
If you have any questions about the information in
this tutorial, please come and see me!!