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Name: ____________________________________
Unit 6: Covalent Bonding
Binary Covalent Formulas: consist of two (2) different NONMETALS; smallest unit is
called a molecule; the lower electronegative element is written first in the formula.
Electrons are shared between bonding atoms to get an octet. This is known as a covalent
bond. One way to name these compounds is using Greek Prefixes with the elements’
names. This is the system you use when you call CO, carbon monoxide and CO 2, carbon
dioxide.
Naming Binary Covalent Formulas: molecules, NM (or metalloids) only, electrons
shared to get 8
A. Naming using Greek prefixes: Greek prefixes equal to how many of each nonmetal
in the formula are used to name the molecule. The Greek prefixes are:
Mono- 1
Di – 2
Tri – 3
tetra – 4
penta - 5
hexa – 6
hepta – 7
octo - 8
nona - 9
dec - 10
** mono- never used with 1st NM in formula
To name binary molecules, the prefix equal to how many of first nonmetal is combined
with the nonmetal’s name and the prefix to how many of second nonmetal is combined
with the nonmetal’s name with the ide ending:
prefix+nonmetal,
prefix +nonmetal + IDE ending
Ex- S2O3 : di + sulfur
tri + ox
+ ide = disulfur trioxide
Ex- CBr4:
carbon
tetra + brom
+ ide = carbon tetrabromide
Name the following using the Greek prefixes:
Formula
Name
Formula
CO
PCl 5
CO 2
CS2
CCl 4
N 2O
NO
NO 2
SO 2
SO 3
Name
Exceptions: As Always..... Since hydrogen as the first element in a formula has only one
charge, prefixes are not used in naming its compounds... HF(g) is hydrogen fluoride, H2S(g) is
hydrogen sulfide (stuff that makes “passed gas” stink). H2O goes by its common name
_________ NH3 goes by its common name ammonia (Note here formula is written backwards...
the more electronegative element is written first: N followed by H)
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I. How can ELECTRONEGATIVITY be used to determine the type of BONDING?
Electronegativity (EN): attraction for electrons in a bond. (found on Reference Table
_______)
Element with the highest EN value is: _____________________
Element with the lowest EN value is: ______________________
a) Use the periodic table to determine type of element (metal or nonmetal)
b) look up the Electronegativity of the element (use the chart that you created or
ref table S)
Element
Type
EN value
Li
N
What type of elements has low values for EN? ________________
What type of elements has high values for EN? _______________
We can use the ElectroNegativity Difference (END) to predict the type of bond, which
forms between two atoms. The “END” is just the difference between the two bonding
atoms’ electronegativity (use the absolute or positive value.)
Example: the END between Li and N:________________________
Using Reference Table S complete the following charts:
Metal
EN value
Nonmetal
EN value
|END|
Li
1.0
O
3.5
3.5-1.0 = 2.5
EN value
|END|
Na
F
K
N
Nonmetal
EN value
Nonmetal
C
O
C
Cl
N
N
When a metal and a nonmetal bond, the “END” is a (LARGE /SMALL) difference. The
electrons are stolen from the metal by the nonmetal and an ______________bond
forms to get an octet (8 valence electrons).
When two nonmetals bond, the “END” is a (LARGE or SMALL) difference. Neither can
steal away the electrons so the nonmetals share electrons to get an octet (or a duet in
the case of hydrogen). This is called __________________bonding. ELECTRONS
_________________
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II. Covalent Bonding: Sharing Electrons is not always FAIR (or equal)
Type of elements, which form covalent bonds: __________________
Two types of sharing:
Sharing equally: _______________________________ bonding.
Sharing unequally: ______________________________ bonding.
We can use a END (ElectroNegativity Difference) Number Line to determine the type of
bond formed. Draw this number line below the periodic table on your reference tables.
In a polar covalent bond, the shared electrons are pulled closer to the ________
electronegative element giving it a slightly negative charge. The other element is left
with a slightly _________charge. We use a funny Greek letter called rho , _____, to
represent a partial or slight charge. The dash between the elements represents one
bond or one pair of electrons being shared. The atoms are still attached, so they are
NOT ions.
example:
H-O
N-Cl
Write the electronegativity over each element. Determine who wins and pulls the
electron closer to itself! Label the ∂ + and ∂ - of the bond.
O-F
I-Cl
P-Cl
N-F
I-Br
N-N
Does either atom win in the following examples?
O-O
Se-S
Why? __________________________________________________________
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Bonding Type Practice
USING “TYPE OF ELEMENTS and END” to predict,
a) determine if the bond is IONIC (I), POLAR COVALENT (PC) or
NONPOLAR COVALENT (NPC)
b) Give a ranking of 1 to the bond with the largest |END|, 2 to next largest,
etc. There may be a tie for least END.
Bond
Element types
|END|
Bond Type
Ca-Cl
M, NM
3.2-1.0 - 2.2
I
Rank
Cl-Cl
K-F
C-S
P-Br
Mg-F
N-H
Ionic and Covalent Character:The most Ionic Character has the ________________
Electronegativity Difference. Least Ionic Character has the ___________________
Electronegativity Difference. #1 is most IONIC, ________________ is (are) least
IONIC.
III.
Shapes of Some Molecules & Special Molecules
a) What is a diatomic molecule? _______________________________________
Hint: look for 2 of the same nonmetal atoms.
Who is Dr. “Br I N Cl H O F” ? _______________________________________
How many bonds will form? Look at how far away you are from an octet (except for Hduet). That is how many bonds will form between the 2 atoms.
For example:
H has 1 valence electron, it needs 1 electron for a duet. H forms ___ bond.
O has 6 valence electron, it needs ___ electrons for a octet. O forms ___ bonds.
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Element # of valence electrons
# of electrons needed to get 8
# bonds formed
C
N
Cl
F
Based on F and Cl, how many bonds will Br and I form? ________________
b) Drawing Dr. “Br I N Cl H O F” :
Dot diagrams: show electrons & look like venn diagrams showing the shared electrons
between the nonmetal atoms
Structural diagrams: no dots but lines for bonds, each line represents one bond or 1
shared pair of electrons
Diatomic
Dot Diagram
Structural Formula
Number of
Molecule
Bonds
Br2
I2
N2
Cl2
H2
O2
F2
What is the shape of ALL 2 atom molecules: _______________________________
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c) Basic Shapes of Molecules: There are 4 basic shapes, which we are going to
learn for the molecules.
Helpful hint: Start by drawing the dot diagram of the atoms underneath molecular
formula to determine the # of bonds to make. Element that can form the most bonds
goes in the “center” called the central atom.
(Carbon shifts its electrons around to make 4 bonds.)
Shape
Molecular Formula Dot Diagram of
Structural Formula of
& Name of Ex.
Example
Example
Linear
HCl
Bent
H2O
Pyramid
NH 3
Tetrahedron
CH 4
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IV. Molecular Polarity and Attractive Forces
Electronegativity Difference (END) tells us if the BOND is polar or nonpolar.
Molecular Symmetry tells us if the MOLECULE is polar or nonpolar. Remember the
element’s symbol represents a sphere (ball). We are not talking about the symmetry of
the letter.
A. Nonpolar Molecules:
Number of lines of symmetry: _____________________
This gives a ____________________ distribution of the electron charge.
Examples: Group 18 & the “BrINClHOF”
He, Ne, Ar, Kr, Xe or Rn
Br2 , I2 , N2 , Cl2 , H2 , O2 or F2
Can a molecule have polar bonds but be a nonpolar molecule???? _________
Only if the the electrons are distributed __________________________
around the main or central atom (one with the most bonds).
Examples:
CO2
CH4
B. Polar molecules
Number of lines of symmetry: ____________________________
This gives an ________________________distribution of the electron charge
producing molecules with positive and negative ends or poles. A polar molecule is
called a DIPOLE...(2 poles).
Dipole Moment: direction the electrons are pulled along the only line of symmetry....
direction is toward the more electronegative element.
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Examples
H 2O
NH3
CH3Cl
Determine if the following molecules are
a) draw in the lines of symmetry
b) determine if molecules is Polar or Nonpolar
c) if Polar draw in the dipole moment
1)
O=O
2)
H-F
_______________
____________________
3) H-S
H
_______________
4)
H
5)
H-C-O-H
H
_________________
H
6)
Cl-C-Cl
Cl
____________________
7)
8)
N=N
O=C=O
____________________
_________________
O=S
(ignore = bonds)
O
____________________
9)
10)
H-O
H
_________________
I-I
____________________
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V. Attractive Forces between molecules (NM’s):
* Determined by what elements are bonded together and if the molecule
is polar or nonpolar.
* It is the force BETWEEN the individual molecules. It is what helps
form liquid phase or the solid phase.
* Strength of this force is what determines vapor pressure, melting and
boiling points of a substance
Type of Force
Type of Molecule
Strength
Examples
Regular Dipole
Force
Hydrogen Bonding
Look for H attached to one of
the
“NOF”
(Small but High
EN)
van der Waal
Forces
(London Dispersion
Forces)
increases with
increaed size,
What type of force holds H2O molecules together? ______________________
What type of force holds HCl________________________________
What type of force holds the noble gases (Group 18) the monatomic molecules together?
_______________________________________________________
What elements are present in an ionic solid? _______________________________
What force holds ions together in an ionic solid? _____________________________
Rank of forces:
___________> ____________>______________>_____________
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Attractive Forces Worksheet
Complete the chart below. For the rankings assign the lowest a value of 1, up to the
highest a value of 5.
Mind Jogger:
Type of compound.. use type of elements & lines of symmetry
Weak attractive force,,,, low melting & boiling point; high vapor pressure
Visa versa for strong attractive force
Formula
Polar, Non- Type of AtRank of Melt- Rank of Boil- Rank of Vapolar or
tractive Force ing Point
ing Point
por Pressure
Ionic
NaCl
H-O
H
Cl
Cl- P-Cl
H
H -C -H
H
H H
H -C -C -H
H H
VII. Molecular and Empirical Formulas
A. Empirical Formulas are formulas, which show the lowest possible ratio of elements
in a compound. Ionic compounds are always empirical formulas. In other words, ionic
formulas are always in lowest terms; NaCl, MgSO4, Al2O3, SnO2.
Covalent compounds (molecules formed by nonmetals) are not always in lowest terms.
Molecular formulas show the exact number of each nonmetal present.
For example, C2H6, is molecular formula of ethane. It contains 2 carbon and 6 hydrogen
atoms. To get the empirical formula, simplify the formula to lowest terms by dividing by
largest number possible. By dividing by 2, the empirical formula of C2H6 is CH3. Some
molecular formulas are already in lowest terms; H2O, CH4.
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Determine the empirical formulas of the molecular formulas given below:
Molecular Formula
Empirical Formula
Molecular Formula
C6H6
H2O 2
C6H12O 6
C4H6
N 2O 4
P4O 10
CH4
C2H2
C2H4
NH3
Empirical Formula
B. Calculating the Molecular Formula from the Empirical Formula
In analyzing compounds, chemists are able to determine the gram formula mass of the
molecular formula and the simplest ratio of the elements present (the empirical formula).
From this information, the molecular formula can be determined easily.
Molecular GFM of Mol.
Formula Formula (A)
Empirical
Formula
GFM of Emp
Formula (B)
Multiplier (C):
(Divide A/B)
C x Emp Formula
N 2O 4
C4H6
Steps to Calculating the Molecular formula:
Example: A hydrocarbon has a empirical formula of CH2 and a molecular mass (GFM) of
28g/mole. What is the molecular formula?
Step1: Determine the GFM of the empirical formula __________________________
Step 2: Divide the Molecular Mass (GFM) by the empirical formula to get the multiplier.
Step 3: Multiply the subscripts of the empirical formula by the multiplier from step 2 to
get the molecular formula: ______________________________________________
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Remember to show units & work! NO Work NO CREDIT!!!!
1. A hydrocarbon has a empirical formula of CH and a molecular mass (GFM) of
78 g/mole. What is the molecular formula?
GFM of Empirical Formula
Mulitplier
Molecular Formula
2. A compound has a empirical formula of HO and a molecular mass (GFM) of
34 g/mole. What is the molecular formula?
GFM of Empirical Formula
Mulitplier
Molecular Formula
3. A compound has a empirical formula of CH2O and a molecular mass (GFM) of 180g/mole.
What is the molecular formula?
GFM of Empirical Formula
Mulitplier
Molecular Formula
4. A compound has a empirical formula of NO2 and a molecular mass (GFM) of 92.0
g/mole. What is the molecular formula?
GFM of Empirical Formula
Mulitplier
Molecular Formula
5. Nicotine, the addictive drug in cigarettes, has the empirical formula of C5H7N.
If the molecular mass is 162.0 g/mole, what is the molecular formula?
GFM of Empirical Formula
Mulitplier
Molecular Formula
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VI. Naming using the Stock (Roman numeral) System: Molecules are named in a
similar fashion as ionic compounds containing transition elements with more than one
charge.
The last nonmetal in the covalent formula will have its first oxidation number listed on
the Periodic Table. Its like your best friend, you can always count on it. The first
nonmetal is a troublemaker. You need to figure out the first element’s oxidation number
by using the charge and how many of the second nonmetal. The oxidation number of the
first nonmetal is written as a roman numeral after the first element’s name and the
second nonmetal is just the name plus the ide ending. NO GREEK PREFIXES!!
Example: PCl3 Cl is -1, its first charge. Because there are 3 Cl’s, P has a +3 charge.
nonmetal (Roman numeral), nonmetal + IDE ending
phosphorus (III)
chlor + ide = phosphorus (III) chloride.
The roman numeral III tells you the oxidation number of the phosphorus.
Name the following binary covalent formulas using the stock (Roman numeral) system.
Formula
Name
Formula
CO
PCl 5
CO 2
CS2
CCl 4
N 2O
NO
NO 2
SO 2
SO 3
Name
C. Try Writing the formula from the name!!
Greek Prefixes are easy-just use the number equal to the prefix: phosphorous
pentafluoride: PF5 because penta means 5 (remember mono is not used with 1st NM)
Roman Numerals: for 1st NM, use the charge equal to the Roman numeral given in the
name; for the 2nd NM, look up its 1st charge ; write formula so charges add up to zeronitrogen (IV) oxide: N+4 and O-2 so formula is NO2
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Name
Formula
Name
chlorine dioxide
carbon (II) oxide
dichlorine heptaoxide
Nitrogen (II) oxide
carbon (IV) iodide
sulfur (VI) fluoride
dinitrogen pentoxide
phosphorus (V) bromide
sulfur tetrafluoride
dihydrogen monoxide
Formula
VII: Types of Solids formed by Nonmetals and Metalloids
A. Molecular Solids (Compounds): formed by covalent bonding, either polar or nonpolar.
1) These form individual particles called molecules, which can attract to each other to
form the solid or liquid phase.
2) Molecules can have oppositely charged ends (polar compounds) or temporary charged
ends (nonpolar compounds), which allow them to attract to one another.
3) Molecules held together intermolecular attractive forces, and are weaker than ionic
attractions.
4) Molecular compounds are more easily melted and boiled, so their melting and boiling
points are low compared to ionic compounds. They also tend to evaporate more quickly.
5) Their solids are soft (think wax or water ice, compared to something like steel!)
6) Dissolving in water and melting do not break the covalent bond. There are no ions to
carry electrical current, so molecules do not conduct electricity the covalent bond. .
Acids are the exception to this, but for now we will turn a blind eye to them…
Molecular Solid Examples:
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B. Network Solids: covalent bonding of nonmetals and/or metalloids
1) formed by covalent bonding (usually nonpolar), but it doesn’t form separate molecules.
2) forms one single crystal made of nonmetal atoms (sometimes metalloids) connected
with a continuous network of covalent bonds with no areas of weakness that can break
apart. Molecules can be separated from each other, but network solids have no such
weakness.
3) They are among the hardest substances known to science. They also occupy the top of
the Mohs hardness scale (talc at 1, diamond at 10). Quartz (SiO2) has a hardness of 7,
corundum (rubies and sapphires) have a hardness of 9, and diamond (pure crystalline
carbon) has a hardness of 10, the top of the scale.
4) Being made only of nonmetals, network solids are nonconductors of electricity and poor
conductors of heat. They are also quite brittle.
5) Network solids do not dissolve in water.
Network solid Examples:
Complete a Venn diagram comparing Molecular Solids and Network Solids:
Molecular Solids Only
Network Solids Only
BOTH