Download Introduction to Chemical Bonding

Name _______________________________________
Date _______________________ Hour __________
Introduction to Chemical Bonding
The difference between physical and chemical changes:
Demonstrations:
Description:
Picture:
1. Paper:
What happened?
Physical or Chemical Change?
2. Paper:
Physical or Chemical Change?
3. Magnesium:
Physical or Chemical Change?
4. Magnesium:
Physical or Chemical Change?
5. Calcium:
Physical or Chemical Change?
6. Calcium:
Physical or Chemical Change?
Chemical Reactions:
•
During chemical reactions, elements __________________, ______________________, or
____________________________ with others to form _________________________________.
•
New substances are __________________ when chemical bonds are broken or created.
•
If the characteristics of a substance totally change, it is probably a chemical reaction. Evidence that a
chemical reaction has occurred:
o
o
o
o
o
Compounds are more than one kind of element joined together.
Octet Rule: Describes how chemical bonds happen.
•
Atoms want a full ____________________ (or outer electron energy level).
•
Full valence will mean having _____ valence electrons.
•
To reach full valence, some atoms want (will be more likely) to lose electrons and others want to gain
electrons.
o Atoms with _______________ than 4 valence electrons will bond by _______________ those
electrons.
ƒ
These atoms will become ____________________ charged!
o Atoms with _______________ than 4 valence electrons will bond by _______________ those
electrons (up to eight).
ƒ
These atoms will become ____________________ charged!
o Atoms with 4 valence electrons can _______________ or _______________ electrons. It
depends on the element to which it is bonding.
A chemical bond is created by the sharing or exchange of electrons between elements.
Example: Sodium
Draw a model of a sodium (Na) atom:
Example: Fluorine
Draw a model of a fluorine (F) atom:
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•
How many valence electrons does sodium
have?
•
What would be the easiest way for sodium to
follow the Octet rule?
•
If sodium followed the octet rule, what will its
charge be?
•
How many valence electrons does fluorine
have?
•
What would be the easiest way for fluorine to
follow the Octet rule?
•
If fluorine followed the octet rule, what will its
charge be?
BIG QUESTION: What will happen if Sodium and Fluorine atoms are mixed?
Ions and Ionic Bonding
The bond of Sodium and Fluorine is an example of Ionic bonding: electrons have been transferred in order for
the atoms to have a full outer level. When an atom loses or gains electrons, it becomes what is called an ion.
An ion is no longer neutrally charged because it has different numbers of protons and electrons. Ions of
opposite charges attract and so they stick together. The Oxidation number is the overall charge of an element
once it becomes an ion. Because elements in the same family (column) have the same number of valence
electrons, they will also have the same oxidation number.
In your own words define and answer the following:
Chemical Reaction:
Ion:
Why does an element become an ion?
Neutral Charge:
What causes ions to “stick” or bond together?
Explain the relationship between the valence # and the Oxidation #:
Oxidation Numbers
Family
# of valence electrons
Oxidation Number
1
1
+1
2
2
+2
13
3
+3
14
4
+4 or -4
15
5
-3
16
6
-2
17
7
-1
18
8
0
Write these oxidation numbers over the families in your periodic table.
If an atom loses electrons, it becomes more positive. This positive ion is called a cation.
If an atom gains electrons, it becomes more negative. This negative ion is called an anion.
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Do These Examples:
If an element has 3 valence electrons, it will ( lose / gain ) 3 electrons to become a ( + / - ) 3 ion.
If an element has 7 valence electrons, it will ( lose / gain ) __ electrons to become a ( + / - ) __ ion.
Using your periodic table, find the number of protons and electrons in the following ions: (Remember the
number of protons of elements never change.)
1.) Sr+2
2.) Ca+2
3.) B+3
protons =
protons =
protons =
electrons =
electrons =
electrons =
4.) S-2
5.) C-4
6.) F –1
protons =
protons =
protons =
electrons =
electrons =
electrons =
7.) O -2
8.) K +1
9.) Fe +3
protons =
protons =
protons =
electrons =
electrons =
electrons =
Aluminum:
a.) Draw a model of an Aluminum (Al) atom:
b.) Draw a model of an aluminum ion:
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•
How many valence electrons does aluminum
have?
•
What would be the easiest way for aluminum
to follow the Octet rule?
•
If aluminum followed the octet rule, what will
its charge be?
•
What is the oxidation number of aluminum?
•
Write the symbol for the aluminum ion
(element symbol with oxidation number)?
•
Number of protons in ion =
•
Number of neutrons in ion =
•
Number of electrons in ion =
Combining Ions:
Diagram a Ca+2 ion:
Diagram a S-2 ion:
•
Since calcium forms a positive ion, did the
atom gain or lose electrons?
•
Number of protons in ion =
•
Number of electrons in ion =
•
Since sulfur forms a negative ion, did the atom
gain or lose electrons?
•
Number of protons in ion =
•
Number of electrons in ion =
What will happen if Calcium and Sulfur are mixed?
Begin with the Oxidation number and fill in the other columns:
Element:
Be
How many valence
electrons?
How does this element fulfill
the octet rule?
2
Lose two electrons
What is its new
symbol?
(Write the ion.)
Be+2
What is its oxidation
number?
Is it a cation or
anion?
+2
Cation
Na
Ca
F
P
B
Si
Sodium Chloride: table salt
Draw the outer most level (valence electrons) of Sodium and Chlorine. What will happen when
these two elements are combined?
Na
By transferring its outer level electron to
Chlorine, Sodium can know have its outer level of
electrons full. Cl is happy too! Na and Cl now
have opposite charges and will stick together due
to ionic bonding. This forms the compound NaCl.
Cl
Do you think the elements Na and Ca will combine together? Why or why not? [Start by writing the ions!]
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•
What is the easiest way for potassium (K) to follow the Octet Rule?
•
What is potassium’s oxidation number (or charge once it becomes an ion)?
•
What is the easiest way for nitrogen (N) to follow the Octet Rule?
•
What is nitrogen’s oxidation number?
Draw the outer levels (valence electrons) of these three K and three N atoms. What will happen
when you combine these two elements?
K’s
The K’s all want to lose their one
valence electron to be happy. The N’s
all want to gain three electrons to be
happy. By transferring the electrons
from three K atoms to one N the Octet
rule will be followed. The K’s and N’s
will have opposite charges and stick
together (ionic bonding). This forms
the compound K3N because there is
three K to every one N.
N’s
*Writing the formula for the compound formed:
• The position ion is written first.
• Use subscripts (lowered numbers) to indicate more than one atom within a molecule.
On your own: Just like the above example, with pictures and descriptions complete the following:
•
What is the easiest way for magnesium (Mg) to follow the Octet Rule?
•
What is magnesium’s oxidation number?
•
What is the easiest way for iodine (I) to follow the Octet Rule?
•
What is iodine’s oxidation number?
Draw the outer levels of these three Mg and three I atoms. What will happen when you combine
these two elements?
Mg’s
I’s
Formula for magnesium iodide:
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