Wednesday, September 30, 2020

Balancing Polyatomic Reactions with Color

General Chemistry Index

Balancing Polyatomic Reactions with Color

Once you have identified that the polyatomic chunks of an equation go through the reaction intact—that is they do not, in the products, appear differently than they did in the reactants—you can balance the equation by chunks and not actually keep up with the individual elements.

Color coding the chucks is one way to make this visually easier.

Fe(NO3)3 + (NH4)2CO3 → Fe2(CO3)3 + NH4NO3   <<<--- Unbalanced reaction
 
Fe(NO3)3 + (NH4)2CO3 → Fe2(CO3)3 + NH4NO3   <<<--- Unbalanced colorized reaction
 
            Reactant Side                    Product Side
Fe                 1                                           2
NO3              3                                            1
NH4              2                                            1
CO3              1                                            3


Color-coded, it becomes a matter of getting the same number of each color on each side. For instance, each side ends up with 6 "reds" and 6 "greens." This visual tool enhances awareness of the polyatomic ions moving across intactly.

2Fe(NO3)3 + 3(NH4)2CO3 → Fe2(CO3)3 + 6NH4NO3    <<<--- Balanced reaction

            Reactant Side                    Product Side
Fe                 2                                           2
NO3              6                                           6
NH4               6                                           6
CO3              3                                           3

Monday, September 21, 2020

Understanding Chemical Notation (Molecular Formulas)

General Chemistry Index

Where are we going with this? This page will give the ability to demonstrate an understanding of the law of conservation of mass through the use of particle diagrams and mathematical models.


Understanding Chemical Notation (Molecular Formulas)
This is where it all begins! 

The basis for understanding how to describe chemical reactions is a shorthand system we'll call chemical notation. It's very picky, but not hard.

The Atomic Symbol of each element is the first aspect of chemical notation. A few remarks…


1. The atomic symbol of an element MUST begin with a capital letter.

If it is a two (or more) letter symbol the following letter is lower case. This is absolutely required! Co is not the same as CO. Co is an element. CO is a compound made up of C and O.

The letters L and I present some issues, depending on the font used. It is possible that a lowercase l and an uppercase I look a lot alike. You should be careful with these! 



2. The next thing in chemical notation is the subscript attached to the atomic symbol. 
  • The subscript FOLLOWS the atomic symbol. 

  • The subscript tells how many of that atom are present. 

  • H2 means there are two atoms of hydrogen present.

  • If there is NO subscript, the number of that atom in the molecule is 1. For instance, in CO2, there is 1 carbon (C) because there is no subscript.

  • Sometimes, the "subscript" will not be depicted in a smaller font. (Because the person who wrote/typed it was lazy). But the number AFTER the atomic symbol should be considered the subscript.
3. For a compound the molecule is written by placing the atomic symbols and their subscripts in a string.  

So, H2O or (H2O if someone is lazy) means there are 2 H atoms and 1 O atom in the compound (water).

Generally, the element appearing on the left of the periodic table is listed first.


4. A number in front of the compound (or element) is called the coefficient, and it indicates how many molecules of that element are present.

2H2O means that there are 2 things—hold this thought—of water present.

The coefficient is a number, so 2 atoms. Or, you can apply any multiplier to the coefficient and the meaning carries through. It can be 2 atoms, 2 dozen atoms, 2 thousands of atoms… or moles… 

In chemistry, it is moles that are used. So, the coefficient establishes a ratio of moles of the molecules. This becomes the basis for the stoichometry process.

 
5. Sometimes it is convenient to keep groups of atoms together. Doing this brings in polyatomic notation, which brings in parenthesis and more subscripts!

Atoms inside parenthesis are considered to be polyatomic "chunks" (i.e. polyatomic ions).

The subscript FOLLOWING the parenthesis tells how many of the chunks are present.

The subscript multiplies all of the atoms inside the parenthesis, including those already having subscripts.

EXAMPLES:

Ca(OH)2
1 Ca and 2 (OH)
1 Ca, 2 O, and 2 H

2H2(SO4)
2 X 2 H and 2 (SO4)
4H and  2 S, and  2 X 4 O
4 H and 2 S and 8 O

4Ca(NO3)2 
4 Ca and 4 (NO3)2
4 Ca and 4 X 2 (NO3)
4 Ca and 8(NO3)
4 Ca and 8 N and 8 X 3 O
4 Ca and 8 N and 24O


That escalated quickly!



 





Law of Conservation of Matter

General Chemistry Index

Where are we going with this? This page will give the ability to demonstrate an understanding of the law of conservation of mass through the use of particle diagrams and mathematical models.


The Law of Conservation of Matter
This is far more important than it is difficult! 

This is pretty simple… No, really.

The Law of Conservation of Matter is one of the two Laws of Conservation. One has to do with energy. The other has to do with matter.  Ignoring the fact that matter can become energy and all that… relativity stuff and E=mC2


The Law of Conservation of Matter: matter can neither be created nor destroyed.


So what?

Chemistry… Conservation of Matter… moles… grams… There has to be a connection!

There are. A couple…



In any chemical reaction:
  1. The total mass of the reactants is equal to the total mass of the products.

  2. The total number of atoms among the reactants is equal to the total number of atoms in the products.

  3. The individual numbers of each type of atom in the reactants is equal to the individual numbers of each type of atom in the products. 

Let's make this page a little longer and discuss.

The total mass of the reactants is equal to the total mass of the products. This means that if you have some number of grams of one thing and some other number of something else, then when they react, the sum of the masses of whatever is produced will not change. If you start with 2 grams of hydrogen and 16 grams of oxygen, you'll end up with 18 grams of water.

The total number of atoms among the reactants is equal to the total number of atoms in the products. Same idea here… If you have 2 hydrogen atoms and 1 oxygen atom to begin with, you will end up with 3 atoms, total And since the individual numbers of each type of atom in the reactants is equal to the individual numbers of each type of atom in the products, then you will have exactly 2 hydrogen atoms and 1 oxygen atom. 

 

Let's add one more idea…

The number of moles does NOT add up. That water reaction we've been talking about…

You can start with 2 moles of hydrogen and 1 mole of oxygen…

2H2 + 1O2 --> 2H20

… and end up with 2 waters.

The number of moles did not "add up"!



Saturday, September 19, 2020

The Periodic Table

 General Chemistry Index

Where are we going with this? Getting to the current models of atomic theory didn't happen over night. This page will give the ability to explain how and why models of atomic structure have changed over time. 


The Periodic Table
That thing has a lot of information! 

Of all the tools in modern chemistry, the periodic table is the goto guy for information about the elements. It is a fantastic way to organize and manage many, many details related to elements.

Further… Well, it's the 21st Century. This is no ditto sheet with letters and numbers. Take a look at this!

I'm now wondering if anyone knows what a ditto sheet is, anyway. But that's not important. 


Organization

The periodic table was, once upon a time, arranged based on the masses of the samples, but in time, that was changed. The elements of the periodic table are arranged in ascending order based on the number of protons (i.e. the atomic number) in each element.

Further, it is arranged into 18 columns and 7 rows. How the columns and rows are organized is the basis for the "periodic" part of the name. 

Time for a not-chemistry break: Things that are periodic occur from time to time. Some things occur in regular periods. Full moons are periodic, occurring roughly every 28 days.

The periodic nature of the periodic table relates to the way electrons are located in the orbitals.

Orbitals? Yeah, the places in the atom where the electrons can be located.


Let's start with the rows

The rows on the periodic table represent the available sets of orbitals for the elements on that row. For example, the first row has only one available set of orbitals (an n1 orbital with only a s-type orbital). The second row has two sets of orbitals available: 1 n1 and 1 n2 set. The third row has three sets of orbitals. 

Rows are also called periods.

Okay, what about the columns?

So, the atomic number (number of protons) determines the sequence of the elements. However, the columns also partially indicate something very important.

The columns indicate how the available sets of orbitals are being filled. For instance, in column 1, all of the elements there have only one electron in the orbitals with the highest energy level. In column 17, all of the elements have every orbital full, except one which is missing 1 electron.

All of the elements in each column are similar with regard to where the electrons are and which ones are missing. Columns 1, 2, 13, 14, 15, 16, 17, and 18 are VERY similar in that their last n2 set of orbitals are uniformly filled.

The elements in columns 3 through 12 are less uniform, but the location of present and missing electrons in the orbitals is still influential in where they are located, coming in after atomic number to determine how the elements are arranged.

Columns are also called families or groups.

Looking Closer…

https://ptable.com/#Electrons

The Ptable.com site offers a great way to dig in and look at what's going on with the electrons. For instance, the image to the right shows where each of the electrons of scandium is located within the orbitals.

As you move from element to element, the configuration is shown.


Another thing…

Many periodic tables will include something called a valence number. This will be an integer with a + or - sign.

The valence number represents the tendency of the atom to either give up its electron in a reaction or take on the electrons from another atom. The plus valences tend to give up the electrons. The negative valences tend to take on electrons.


But That's Not All!

Another super important part of the periodic table is the atomic weight/mass. The atomic mass is a number usually presented at the bottom of the listing and it will not be a whole number. The atomic mass is the sum of the masses of the atom's sub-atomic particles. 

Now, for the magic. Okay, not really magic. But still awesome and important. 

The atomic mass is the weight in grams of one mole of the element. 

The importance of this fact is vast. When actually "doing chemistry" this relationship is massive!

This relationship will be used whenever "weighing out" reactants or mixing solutions. If you want to produce eighteen grams of water, you need to start with sixteen grams of oxygen and two grams of hydrogen. Okay, that's getting ahead. So, trust me. This is really, really important.







Wednesday, September 16, 2020

Electron Configuration

General Chemistry Index

Where are we going with this? Getting to the current models of atomic theory didn't happen over night. This page will give the ability to explain how and why models of atomic structure have changed over time. 


Composition of Atoms: Electron Configuration
How do those electrons arrange themselves? 

Understanding how the electrons are configured is sort of a big deal. Based on how the are arranged in an element's atoms determines how they will behave in the presence of other elements. That's to say that electron configuration plays a huge role in how different elements will react.

So… orbitals.

1. Electrons are located in orbitals outside the nucleus.

2. Each orbital can hold two electrons.

3. Orbitals occur in sets (which have fancy names).

4. Each set of orbitals represent higher and higher energy levels.


Orbitals and Electron Capacity

Energy Level (n)

Type of Orbital

Number of Orbitals Possible

Total Orbitals

Max Number of Electrons

n1

s

1

1

2

n2

s

1

4

8

p

3

n3

s

1

9

18

p

3

d

5

n4

s

1

16

32

p

3

d

5

f

7



5. Elements are arranged in rows on the periodic table depending on how many sets of orbitals they have.


Periodic Table Row and Energy Level Type

Orbital Configuration

Energy Levels

1 n1

1s

2

2 n1, n2

1s 2s 2p

2, 8

3 n1, 2n2

1s 2s 2p 3s 3p

2, 8, 8

4 n1, 2n2, n3

1s 2s 2p 3s 3p 4s 3d 4p

2, 8, 18, 8

5 n1, 2n2, 2n3

1s 2s 2p 3s 3p 4s 3d 4p 5s, 4d, 5p

2, 8, 18, 18, 8

6 n1, 2n2, 2n3, n4

1s 2s 2p 3s 3p 4s 3d 4p 5s, 4d, 5p, 6s, 4f, 5d, 6p

2, 8, 18, 32, 18, 8

7 n1, 2n2, 2n3, 2n4

1s 2s 2p 3s 3p 4s 3d 4p 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

2, 8, 18, 32, 32, 18, 8


6. Elements are arranged in columns on the periodic table depending on how the electrons are filling the available orbitals. For instance (and in simple terms), those in column 1 have only 1 electron in the highest energy level set of orbitals. Those in column 2 have only 2 electrons. Those in column 17 are missing only 1. Those in column 18 have no missing electrons. 



For more info:














Monday, September 14, 2020

Activity: Solubility and Conservation of Matter

 General Chemistry Index

Where are we going with this? The activity on this page provides a practical application that provides experience observing solubility and conservation of matter.

Activity: Solubility and Conservation of Matter

Overview: Mixing a solute into a solution conserves matter. Though the volume may change, the mass remains the same.

Link to activity worksheet:  CLICK HERE

The video below has two parts:
  • Setup
  • Collecting Results





Sunday, September 13, 2020

ACTIVITY: Using the Ideal Gas Law To Find Moles of Gas Collected

 General Chemistry Index

Where are we going with this? The activity on this page provides a practical application that allows the use the kinetic molecular theory with the combined and ideal gas laws to explain changes in volume, pressure, moles and temperature of a gas and to use lab data and a balanced chemical equation to calculate volume of a gas at STP and non STP conditions, assuming that the reaction goes to completion and the ideal gas law holds..

Activity: Using the Ideal Gas Law To Find Moles of Gas Collected

Overview: Using the ideal gas law, the number of moles of a gas can be calculated given the volume collected.

Link to activity worksheet:  CLICK HERE

The video below has four parts:
  • Setup
  • Result
  • Analysis  and Calculations
  • Further discussion of stoichometry








Tuesday, September 8, 2020

Universal Gas Law and Combined Gas Law

General Chemistry Index

Where are we going with this? Getting to the current models of atomic theory didn't happen over night. This page will support the ability to use the kinetic molecular theory with the combined and ideal gas laws to explain changes in volume, pressure, moles and temperature of a gas and apply the ideal gas equation (PV = nRT) to calculate the change in one variable when another variable is changed and the others are held constant.


The Math: Universal Gas Law and Combined Gas Law
I told you there'd be math! 


Universal Gas Law

When the number of molecules are included in calculations, the following formula can be used:

PV = nRT

where P is pressure, V is volume, n is number of moles, R is a number called the "gas constant", and T is temperature in Kelvin.

Just so you know… the gas constant changes depending on what units you are using. It can be Googled, such as: 82.05746  cm^3 atm / (K • mol)

Looking at the equation allows predicting how gases will behave in relationship to changing the number of molecules:

PV = nRT
(Remember, R cannot change because it is just a number like π (pi)
  • if n goes up, then P and/or V have to go up unless T goes down
  • if n goes down, the P and/or V have to go down unless T goes up.


The Combined Gas Law (revised)

Traditionally, the Combined Gas Law demonstrates a relationship between pressure, volume, and temperature and assumes that the number of molecules does not change.

Beginning with the Universal Gas Law, it is easy to derive the Combined Gas Law.

Start with the Universal Gas Law:


Divide both sides by nRT…

 


  

Using this, an equation can be set up for the "before / after" process used with Boyle's and Charles's Laws. Setting up an equation for a second state, should something from a first state change, would result in this:




Multiplying both sides by R would result in:




Now, using this equation to examine changes can result in deeper understanding. As n changes from state 1 to state 2, P, V and T must also respond in the second state as well. 

It is IMPORTANT to NOTE that there are only certain combinations of P, V, T, and n that are valid because they must work with R such that. 


 

or

  

If n is considered to be the same across both states, it can be omitted. Doing this will result in an equation that is identical to the commonly discussed Combined Gas Law, but including n.



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