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Session 1:
The Chemical Formulaand Moles
Tom Hsu, PhD.
Manos Chaniotakis, PhD.
Marina Dang, PhD.
Copyright © 2012 Chaniotakas and Hsu
What do these symbols and diagrams mean?
Essential questions
• Identify the number of moles of each constituent element from a chemical formula, molecular model, or structural diagram.
• Interpret a chemical formula and build a 3D model from it.
• Write a chemical formula given a structural diagram.
• Draw a structural diagram from a 3D model.
• Create possible structures from a given chemical formula.
Objectives
8 (A) define and use the concept of a mole;
8 (B) use the mole concept to calculate the number of atoms, ions, or molecules in a sample of material;
8 (C) calculate percent composition and empirical and molecular formulas.
TEKS
• How many moles of chlorine are there in one mole of CCl4?
• If you have six moles of oxygen, how many moles of acetic acid (C2H4O2) could you produce assuming you had an unlimited supply of carbon and hydrogen?
• What is the chemical formula for a compound containing 1 mole of magnesium, 2 moles of oxygen, and 2 moles of hydrogen?
• Build and draw three possible ways in which 3 moles of carbon, 8 moles of hydrogen, and 2 moles of oxygen could be divided into one or more compounds.
Assessment
Molecular models
• Each ball represents both one atom and one mole of atoms
• Colors represent different kinds of atoms (elements)
• The grey “sticks” represent bonds between atoms
Molecules
The CPK color code
Use this code to assign the color of each element
The CPK color code
All molecular modeling programs use some variation of this color code.
Wikipedia
Complete the table
Use a periodic table to write in the element symbols for each “atom” in the kit.
Making a moleculeChoose 5 atoms and connect them with bonds.
At least two should be the same color – therefore the same element.
Writing a chemical formula
Use the boxes to describe the elements in your molecule.
Write 1 where there is a single atom.
Writing a chemical formula
Transfer the information to a chemical formula.
Use element symbols and subscripts to specify the number of atoms of each element in the molecule
Writing a chemical formula
Single atoms do not need a subscript.
The 1 is inferred to mean a single atom.
The structural diagram
The chemical formula does not specify the connections.
The structural diagram uses element symbols connected by lines.
The structural diagram
When possible, draw your structural diagrams with the lines at 90 degrees or 120 degrees.
Chemical formula rules
Is this written H4C or CH4?
Chemical formula rules
Is this written H4C or CH4?
Carbon is often written first in a carbon-containing compound (organic)
Chemical formula rules
Which is the preferred way to write the chemical formula for methanol?
Chemical formula rules
Which is the preferred way to write the chemical formula for methanol?
The second is better because the OH grouping makes this an alcohol and this spelling clearly identifies the OH.
What do the models mean?What does one of the colored balls represent?
What do the models mean?What does one of the colored balls represent?
Is it one atom?
Is it 1,000,000 atoms?
The mole
Each ball represents two things:
1. How atoms of oxygen are connected to other atoms in a specific compound.
2. One mole of oxygen atoms.
The size of atoms
Atoms are so small that they cannot be measured individually.
There are more than 1,000,000,000,000,000,000,000,000 atoms in a thimble of water.
A mole 1.01 grams of hydrogen contain 6 x 1023 atoms.
This number is called a mole.
Think of each plastic ball as representing one mole of that element.
Atomic masses
The periodic table lists the atomic mass, in grams, of one mole of each element.
Mass of one mole
How many moles of methane contain 1 mole of carbon?
A molecule of methane contains one carbon and four hydrogen atoms.
Write its chemical formula and draw its structural diagram.
1 mole of methane contains 1 mole of carbon.
How many moles of hydrogen are in one mole of methane?
How many moles of carbon?
What is the ratio of hydrogen atoms to carbon atoms?
How many moles of hydrogen are in one mole of methane? 4
How many moles of carbon? 1
What is the ratio of hydrogen atoms to carbon atoms? 4/1
Build this molecule with one carbon, one oxygen, and four hydrogen atoms.
Write its chemical formula and draw its structural diagram.
How many moles of oxygen are contained in 1 mole of methanol?
1 mole of oxygen is contained in 1 mole of methanol.
How many moles of hydrogen are in one mole of methanol?
How many moles of carbon?
What is the ratio of carbon atoms to oxygen atoms?
1 mole of oxygen is contained in 1 mole of methanol.
How many moles of hydrogen are in one mole of methanol? 4
How many moles of carbon? 1
What is the ratio of carbon atoms to oxygen atoms? 1/1
Build this molecule with two carbon, one oxygen, and six hydrogen atoms.
Write its chemical formula and draw its structural diagram.
How many moles of carbon are contained in 1 mole of ethanol?
2 moles of carbon are contained in 1 mole of ethanol.
How many moles of hydrogen are in one mole of ethanol?
How many moles of carbon?
What is the ratio of hydrogen atoms to oxygen atoms?
How many moles of hydrogen are in one mole of ethanol? 6
How many moles of carbon? 2
What is the ratio of hydrogen atoms to oxygen atoms? 6/1
How many moles of carbon are in 1 mole of Pentadecylcatechol
Main constituent of urushiol the irritant oil that is created by poison ivy.
How many moles of carbon are in 1 mole of Pentadecylcatechol
Main constituent of urushiol the irritant oil that is created by poison ivy.
The subscript tells you the number of moles of each element in 1 mole of the compound.
Build a compound containing 2 moles of carbon, 2 moles of oxygen, and 4 moles of hydrogen.
This is one possible solution – acetic acid.
Build a compound containing 2 moles of carbon, 2 moles of oxygen, and 4 moles of hydrogen.
Build TWO compounds that together contain 2 moles of carbon, 2 moles of oxygen, and 4 moles of hydrogen. The compounds may be identical or different from each other.
This new compound is the preservative formaldehyde. Very different from acetic acid!
Build TWO compounds that together contain 2 moles of carbon, 2 moles of oxygen, and 4 moles of hydrogen.
This new compound is the preservative formaldehyde. Very different from acetic acid!
Build TWO compounds that together contain 2 moles of carbon, 2 moles of oxygen, and 4 moles of hydrogen.
This coefficient tells us there are two moles of this compound.
Two moles of formaldehyde,a toxic preservative.
4 moles of hydrogen, 2 moles of oxygen, and 2 moles of carbon.
One mole of acetic acid,the sour flavor in lemons.
4 moles of hydrogen, 2 moles of oxygen, and 2 moles of carbon.
These are different substances even though they contain the same elements in the same proportions!
• How many moles of chlorine are there in one mole of CCl4?
Assessment
• How many moles of chlorine are there in one mole of CCl4?
4 moles since the subscript of chlorine is four.
Assessment
• If you have six moles of oxygen, how many moles of acetic acid (C2H4O2) could you produce assuming you had an unlimited supply of carbon and hydrogen?
Assessment
• If you have six moles of oxygen, how many moles of acetic acid (C2H4O2) could you produce assuming you had an unlimited supply of carbon and hydrogen?
One mole of acetic acid uses two moles of oxygen. That means six moles of oxygen could produce three moles of acetic acid.
Assessment
• What is the chemical formula for a compound containing 1 mole of magnesium, 2 moles of oxygen, and 2 moles of hydrogen?
MgO2H2
Assessment
• Draw three possible ways in which 3 moles of carbon, 8 moles of hydrogen, and 2 moles of oxygen could be divided into one or more compounds.
There are other possibilities.
Assessment
There are other possibilities.
Assessment
Carbon dioxide
Methane
Ethanol
Formaldehyde
Ethylene
Oxygen
Methane
51
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