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Covalent Bonding
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DIRECTIONS:
We know a lot about atoms. The question is how do two atoms
Bond to become a new compound? Using the space below, please
write a quick explanation of how do two atoms connect or bond?
Write your best explanation of how two atoms bond?
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SHARE OUT TIME
Take a quick look at your answer. In the minutes that follow, your teacher will ask
you to share your answer to the group. Let’s hear about what we know about
bonding.
WORDS I NEED TO KNOW
Directions:
Before we start our discussion about chemical bonding, there
are some important words we need to know. Work with a
partner to define the important terms that we need to know in
order to really understand bonding (turn the page for help).
THE WORD WE NEED
Book Definition
Valence
The Octet Rule
Electronegativity
How do I know how
many electrons are in
the valence layer?
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SOME HELP FOR WORDS I NEED TO KNOW
You can read the section below to help you understand the words you need to know.
Valence
The electrons in the outermost shell of an atom are known as the valence electrons. These
valence electrons are the electrons on an atom that can be gained or lost in a chemical
reaction. Since filled d or f subshells are seldom disturbed in a chemical reaction, we can
define valence electrons as follows: The electrons on an atom that are not present in the
previous rare gas, ignoring filled d or f subshells.
The Octet Rule
The octet rule states that atoms tend to combine in such a way that they each have eight
electrons in their valence shells outer shell, giving them the same electronic configuration
as a noble gas. The rule is applicable to the main-group elements, especially carbon,
nitrogen, oxygen, and the halogens, but also to metals such as sodium or magnesium. In
simple terms, molecules or ions tend to be most stable when the outermost electron shells
of their constituent atoms contain eight electrons.
Electronegativity
Electronegativity, is a chemical property that describes the tendency of an atom or a
functional group to attract electrons (or electron density) towards itself and thus the
tendency to form negative ions. An atom's electronegativity is affected by its atomic
number, the number of positively charged particles, and the distance that its valence
electrons reside from the charged nucleus. The higher the electronegativity number, the
more an element or compound attracts electrons towards it.
Determining the number of Valence Layer electrons
The number of valence layer electrons is easy to determine. The periodic table is
organized by columns. The columns are organized according the number of valence layer
electrons, ascending from left to right.
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Determining Valence Layer Electrons
8 Valence electron
7 Valence electron
6 Valence electron
5 Valence electron
4 Valence electron
3 Valence electron
2 Valence electron
1 Valence electron
To determine the number of valence layer electrons, simply identify what row the atoms
are listed in and your atoms are listed in and identify the valence layer
electrons.
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KHAN ACADEMY NOTES
What did Khan Say?
In the Space below writing down any interesting notes and ideas that you learned from
watching the explanation about bonding from Khan Academy
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Notes from Mr. Ang’s Lecture on Covalent Bonding
What is Covalent Bonding?
What is Polar Bonding?
What is Non-Polar Covalent Bonding?
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Notes from Mr. Ang’s Lecture on Covalent Bonding
Why would some bonds be Polar Covalent, while others are Non-Polar Covalent?
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WHAT WE KNOW NOW!
Directions: In the space below provide a brief explanation of what you know about
Covalent Bonding. The Picture below is picture of two atoms bonded in a covalent bond.
Tell the story of this bond. (1) Explain how they are connected. (2) Describe how the
octet rule helps to explain why this happens? (3) Describe how the valence layer of
electrons has to do with this.
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Image Explanation
Please listen closely as your teacher explains how Bond Energies are associated with the
type of bonds being formed. Take notes using the space below:
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QUICK WRITE
Before we proceed, it is important to identify how well you know the key ideas that
help us understand bonding. Use the space below to explain the following concepts:
(a) What is the octet rule?
(b) What is the valence layer?
(c) What is a Covalent Bond?
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(d) What is the electronegativity of an atom?
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TYPES OF COVALENT BONDS
There are two types of covalent Bonds: (a) Polar Covalent Bonds and (b) Non-Polar
Covalent Bonds. Use the space below to complete the fill-ins as your teacher explains
the difference.
A. Polar Covalent Bonds:
A Pole is something that has opposite charges on opposite sides. Polar
Covalent Bonds are bonds that are called “Polar” because the
electrons spend more time with one of the atoms than with the other.
Because the electrons are _________________, they create charges
on both sides of the molecule. The reason why it is called polar is
because the electrons are shared unevenly so the molecule has poles.
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B. Non – Covalent Bonds
A Non-Polar Covalent bond is a bond where the electrons are shared
___________________. They are called “non-polar” because the
electrons are shared equally, so the molecule does not have poles.
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READ & TRANSLATE
Electronegativity and Covalent Bonding
The example in which two hydrogen atoms bond is simple because both
atoms are the same. Also, each one has a single proton and a single electron,
so the attractions are easy to identify. However, many covalent bonds form
between two different atoms. These atoms often have different attractions
for shared electrons. In such cases, electronegativity values are a useful tool
to predict what kind of bond will form.
Atoms Share Electrons Equally or Unequally
Figure 6 lists the electronegativity values for several elements. In a
molecule such as H2, the values of the two atoms in the bond are equal.
Because each one attracts the bonding electrons with the same force, they
share the electrons equally. A nonpolar covalent bond is a covalent bond in
which the bonding electrons in the molecular orbital are shared equally.
What happens when the electronegativity values are not the same? If
the values differ significantly, the two atoms form a different type of
covalent bond. Think about a carbon atom bonding with an oxygen atom.
The O atom has a higher electronegativity and attracts the bonding electrons
more than the C atom does. As a result, the two atoms share the bonding
electrons, but unequally. This type of bond is a polar covalent bond. In a
polar covalent bond, the shared electrons, which are in a molecular orbital,
are more likely to be found nearer to the atom whose electronegativity is
higher.
If the difference in electronegativity values of the two atoms is great
enough, the atom with the higher value may remove an electron from the
other atom. An ionic bond will form. For example, the electronegativity
difference between magnesium and oxygen is great enough for an O atom to
remove two electrons from a Mg atom. Figure 7 shows a model of how to
classify bonds based on electronegativity differences. Keep in mind that the
boundaries between bond types are arbitrary. This model is just one way that
you can classify bonds. You can also classify bonds by looking at the
characteristics of the substance.
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WHAT THEY ARE REALLY SAYING IS…….
Directions:
Use the space below to describe what they authors were
trying to say in the reading on the page before. Explain
this in your own words.
What they are really saying is…..
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What The?
Directions:
The following picture explains the difference between the
types of covalent bonds. It explains how different types
of bonds have different types of electronegativity. Use
the space below to explain what this image means.
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WHAT DID WE LEARN FROM THE
LEWIS DOT STRUCTURE VIDEO
Directions:
You will watch a short video about Doing Lewis Dot
Structures. While you watch the video, use the
information below to help you complete the fill in the
blank sentences.
The Lewis Dot Structure is a quick and easy way to create a model
of how covalent bonding happens. In Covalent Bonding electrons
want to have __________ in the Valent layer, so they share
electrons with other atoms to make sure they have a total of 8
Valent layer electrons. When you create Lewis dot structures you
move the atoms around and move the electrons around so that
every atom has 8 electrons surrounding them in their Valent layer.
Be careful, there are some exceptions. ______________ only
needs 2 Valent layer electrons and ______________can sometime
form triple bonds with itself that share 6 electrons.
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Lewis Dot Structure Exercise
Directions: In the following activity your will use the past and the pieces of
paper to make Lewis Dot structure. When making a Lewis Dot Structure, the
Pasta represents a single electron. Placing two pasta pieces together make a
bond of two shared electrons. After you make the molecules draw the Lewis
dot structure in the space provided:
Molecule
Lewis Dot Structure
H2
CH3
C6H12O6
C2H2
PBr3
N2H2
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MINI LECTURE
Use the space below to write any notes you are taking from your teacher’s
lecture on Covalent Bonding
BOND CHARACTER =
BOND STRENGTH =
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DIRECTIONS:
Read the text below and translate in into your own words on the following
page.
Polarity is Related to Bond Strength
When examining the electronegativity differences between elements,
you may notice a connection between electronegativity differences, the
polarity of a bond, and the strength of that bond. The greater the
difference between the electronegativity values of two elements joined
by a bond, the greater the polarity of the bond. In addition, greater
electronegativity differences tend to be associated with stronger bonds.
Of the compounds listed in Table 2, H—F has the greatest
electronegativity difference and thus the greatest polarity. Notice that
H—F also requires the largest input of energy to break the bond and
therefore has the strongest bond.
Electronegativity and Bond Types
You have learned that when sodium and chlorine react, and electron is
removed from Na and transferred to Cl to form Na+ and Cl- ions. These
ions form an ionic bond. However, when hydrogen and oxygen gas react,
their atoms form a polar covalent bond by sharing electrons. How do
you know which type of bond the atoms will form? Differences in
electronegativity values provide one model that can tell you.
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DIRECTIONS:
Read the text below and translate in into your own words on the following
page.
Bonds Can Be Classified by Bond Character
Figure 2 on page 16 shows the relationship between electronegativity
differences and the type of bond that forms between two elements. Notice
the general rule that can be used to predict the type of bond that forms. If the
difference in electronegativity is between 0 and 0.5, the bond is probably
nonpolar covalent. If the difference in electronegativity is between 0.5 and
2.1, the bond is considered polar covalent. If the difference is larger than 2.1,
then the bond is usually ionic. Remember that this method of classifying
bonds is just one model. Another general rule states that covalent bonds tend
to form between nonmetals, while a nonmetal and a metal will form an ionic
bond.
You can see how electronegativity differences provide information
about bond character. Think about the bonds that form between the ions
sodium and fluoride and between the ions calcium and oxide. The
electronegativity difference between Na and F is 3.1. Therefore, they form
an ionic bond. The electronegativity difference between Ca and O is 2.4.
They also form an ionic bond. However, the larger electronegativity
difference between Na and F means that the bond between them has a higher
percentage of ionic character.
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WHAT THEY ARE REALLY SAYING IS…….
Directions:
Use the space below to describe what they authors were
trying to say in the reading on the page before. Explain
this in your own words.
What they are really saying is…..
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REVIEW
BOND CHARACTER =
BOND STRENGTH =
POLARITY =
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QUICK READ
Directions: Read the text below
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QUICK READ
Directions: Read the text below
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QUICK READ
Directions: Read the text below
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Paragraph #
PARAGRAPH SUMMARIES
What does it mean to you …. in your words?
1
2
3
4
5
PRACTICE PROBLEMS
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IN MY WORDS LAB PREP
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Directions:
Use the space below to describe each of the steps you
need to complete to the lab.
Chemical Bonding Lab
Chemical compounds are combinations of atoms held together by chemical bonds.
These chemical bonds are of two basic types—ionic and covalent. Ionic bonds result
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when one or more electrons from one atom or group of atoms are transferred to
another atom. Positive and negative ions are created through the transfer. In
covalent compounds no electrons are transferred; instead the bonded atoms share
electrons.
The physical properties of a substance, such as melting point, solubility, and
conductivity, can be used to predict the type of bond that binds the atoms of the
compound. In this experiment, you will test six compounds to determine these
properties. Your compiled data will enable you to classify the substances as either
ionic or covalent compounds.
OBJECTIVES
Compare the melting points of six solids.
Determine the solubility of the solids in water and in ethanol.
Determine the conductivity of water solutions of the soluble solids.
Classify the compounds into groups of ionic and covalent compounds.
Summarize the properties of each group.
MATERIALS
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24-well
microplate
Bunsen burner
Conductivity
tester
Ethanol
iron ring
Ring stand
Thermal gloves
Lab apron
Safety goggles
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Aluminum foil square
Thin-stemmed pipets (2)
CaCl2 (calcium chloride)
KI (potassium iodide)
NaCl (sodium chloride)
C13H18O2 (ibuprofen)
Chttp://en.wikipedia.org/wiki/Chemical_formula8H9NO2
(acetaminophen)
http://en.wikipedia.org/wiki/Chemical_formulaC12H22O11
(sucrose)
Always wear safety goggles, gloves, and a lab apron to protect your
eyes and clothing. If you get a chemical in your eyes, immediately flush the
chemical out at the eyewash station while calling to your teacher. Know the location
of the emergency lab shower and eyewash station and the procedures for using
them.
Do not touch any chemicals. If you get a chemical on your skin or clothing,
wash the chemical off at the sink while calling to your teacher. Make sure you
carefully read the labels and follow the precautions on all containers of chemicals
that you use. If there are no precautions stated on the label, ask your teacher what
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precautions to follow. Do not taste any chemicals or items used in the laboratory.
Never return leftovers to their original container; take only small amounts to avoid
wasting supplies.
Do not heat glassware that is broken, chipped, or cracked. Use tongs or a
hot mitt to handle heated glassware and other equipment because hot glassware
does not always look hot.
When using a flame, confine long hair and loose clothing. If your clothing
catches on fire, WALK to the emergency lab shower and use it to put out the fire.
Procedure
1. Put on safety goggles and a lab apron.
2. Before you begin, write a brief description of each of the six substances in Table
1.
3. Place a folded square of aluminum foil on an iron ring attached to a ring stand.
Position the ring so that it is just above the tip of a Bunsen burner flame, as
shown in Figure 1. Light the burner for a moment to check that you have the
correct height.
4. Place a few crystals of sucrose, sodium chloride, acetaminophen, calcium
chloride, ibuprofen, and potassium iodide in separate locations on the square of
aluminum foil. Do not allow the samples of crystals to touch. Draw and label a
diagram that shows the position of each compound.
Figure 1
5. For this experiment, it is not necessary to have exact values for the melting point.
The foil will continue to get hotter as it is heated, so the order of melting will give
relative melting points. Light the burner and observe. Note the substance that
melts first by writing a 1 in Table 1. Record the order of melting for the other
substances.
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6. After 2 min, record an n in Table 1 for each substance that did not melt.
Extinguish the candle flame. Allow the can lid to cool while you complete the
remainder of the experiment.
7. Put a few crystals of each of the white solids in the top row of your microplate.
Repeat with the second row. Add 10 drops of water to each well in the top row.
Do not stir. Record the solubility of each substance in Table 1.
8. Add 10 drops of ethanol to each well in the second row of the microplate. Do not
stir. Record the solubility of each substance in Table 1.
9. Test the conductivity of each water solution in the top row by dipping both
electrodes into each well of the microplate. Be sure to rinse the electrodes and
dry them with a paper towel after each test. If the bulb of the conductivity
apparatus lights up, the solution conducts electric current. Record your results in
Table 1.
10. Clean the microplate by rinsing it with water into a pan provided by your
teacher. If any wells are difficult to clean, use a cotton swab. Wash your hands
thoroughly before you leave the lab and after all work is finished.
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NAME: _______________________________________
DATE: _________________________ PERIOD: _____
TABLE 1 CHARACTERISTICS OF COMPOUNDS
Compound
Description
Melting
point
Solubility
in H2O
Solubility in
ethanol
Conductivity
Calcium chloride
Ibuprofen
Acetaminophen
Potassium iodide
Sodium chloride
Sucrose
Analysis
1. Organizing Results Group the substances into two groups according to their
properties.
2. Organizing Results List the properties of each group.
Conclusions
1. Inferring Conclusions Use your textbook and your experimental data to
determine which of the groups consists of ionic compounds and which consists
of covalent compounds.
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2. Relating Ideas Write a statement to summarize the properties of ionic
compounds and another statement to summarize the properties of covalent
compounds.
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MINI LECTURE
Directions: In the moments that follow, use the space below to take notes about
what the teacher explains about Resonance Structures.
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SUMMARY OF KEY IDEAS
Directions: In the space below, you will quickly write what you now
understand about bonding. Use the boxes to the right to
explain some of the key ides of Covalent Bonding.
KEY IDEA &
QUESTION
ANSWERS
Valence
Electronegativity
Covalent Bonding
Polar Covalent
Bonds
Bond Energy
Bond Length
Lewis Dot
Structures
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