Density and Moles

We told you how to convert from mass to moles and from moles to molecules, we event told you how to convert from mass to molecules. You thought you were finally finished, well you're not!
There's also Density.
Density or is measured in g/L or other variations such as kg/mL
well that's it for the non-gas density notes, how about a few example
How many moles are contained when the density of Li₂ O is 3.5 g/mL and the mass is 15 mL
15 mL  x           1 mol            = 29.9 mol
                 (2x6.94)+16.00

Thus you can now add this on to your growing number of possible conversions, exciting right?
Density of Gases
it's slightly different, you get a new formula (because we all love more new formulas)
molar mass over molar volume
  MMg/mol    = density g/L
22.4 L/mol

Oh boy, more examples!
Flourine gas at STP, find the density
2(19.00)g/mol  = 1.70 g/L
  22.4 L/mol

Now I want you to find the density of one Flourine at STP
1.70g/l  = 0.850 g/L (ridiculously simple)
    2

And so I leave you with a comic, so you can sit in your chair laughing while I go to sleep.
But remember conversions are important.

Moles to Volume

Finally, it's the long awaited post of MOLES TO VOLUME!!!!
Okay one quick thing you need to know
1 mole of any gas has the exact same volume at a specific temperature and pressure.
And what is this temperature and pressure you may ask?
At 0˚Celsius and 101.3 KPa 1 mole takes up 22.4 L
Very important stuff, however it's all very clear isn't it

Now on to the examples

What would you do if you had 3.2 L of some random unknowns substance we pulled out of a hat and you needed to figure out how many moles there are.

1.6 L x    1 mol      = 0.071 mol

              22.4 L

Now just to switch it up, let's say you had 7.2 mol of Ne, how many L of Ne are there at Standard Pressure and Temperature(STP)

7.2 mol  x    22.4    = 161.28 

                  1 mol

Making the answer (with significant digits) 1.6 x 10²

Mole to Atom/Molecule conversions

Today we learned how to convert, for example 2 moles of Iron into atoms.
To do this we cross multiply using avagadros number:

2 mol Fe x 6.02*1023    = 1.2*10 24 atoms of Iron
                      1 mol
This is just one of the many conversions we can do with avagadros number. Here are some more:


How many moles are present in 3.9*10 25 Nitrogen atoms?

3.9*10 25 Nitrogen atoms x 1 mol            = 64.8 moles
                                          6.02*10 23
or How many hydrogen atoms are there in 5.2 molecules of H2O?

5.2*10 13 molecules H2O x 2 Hydrogen atoms  = 2.6*10 13
                                          1 molecule H2O

These are just some of the different conversions we can do with moles!!!



Happy Calculating!!!!

Molar Mass

Molar Mass, as you've probably guessed, is the mass of 1 mole of a substance!
 It can be determined from the atomic mass on the periodic table

It's measured in grams per mole or g/mol.
I like the way that it is described in this phrase:
The atomic weight of an element expressed in grams contains 1 mole of that element.

To determine the molar mass of a compound, find the mass of each element individually and add them!
For example

NO2.  N= 14 amu, so 14 g
           O= 16 amu, so 16 g

           14+2(16)= 46 g/mol

What is the molar mass of Ammonium Phosphate?
Ammonium Phosphate is (NH4)3PO4
N= 14g x 3 = 42 g

H= 1g x 12 = 12 g

P= 31 g

O= 16 g x 4 = 64 g
42 + 12 + 31 + 64 = 149 g

Converting between Moles and Mass

To convert between moles and mass we use molar mass as the conversion factor. Make sure to cancel the appropriate units!

Examples:
How many grams are there in 1.5 mol of O2?

We are trying to cancel out mol, and convert it into grams, so when converting, we will put mol on the bottom, and grams on the top.

1.5 mol O2 x                   g   =               g

                           1 mol

We have to find the molar mass of O2, in grams. O= 16     16 x 2 = 32.0 g

1.5 mol O2 x 32.0 g    = 48 g

                      1 mol

How many moles are present in Fe2O3?

115 g Fe2O3 x 1 mol  =           mol
                               g

Fe= 55.8 x 2 = 111.6

O= 16 x 3 = 48 g                 111.6 g + 48 g = 159.6 g   * at this point, don't worry about sig fig's!

115 g Fe2O3 x 1 mol       =   0.721 mol Fe2O3

                         159.6 g

Here's another kind, that has more super cool detective problem solving:

A compound is made up of phosphorous and chlorine. It is found to contain 0.200 mol and has a mass of 27.5 g. Determine the molar mass, and a possible formula for this compound.

molar mass = g      = 27.5  g      =  137.5 g/mol          

                     mol      0.200 mol

To get the formula, you just have to try out different masses off the periodic table, and the one that works in this case is PCl3!

I wonder what the molar mass of this is?

Chemistry Pun of the day:

Q: What weapon can you make from the Chemicals Potassium, Nickel and Iron?
A: KNiFe.

The MOLE

you may think that a mole is a small furry blind creature who lives underground and looks something like this.....
cute right?
but we're talking chemistry so its not as simple as all that. For us the mole is a number that represents a huge number of particles. 6.02* 1023 particles, to be exact. But why do we even need a number to represent particles? Couldn't we just weigh and measure individual particles?

Here's the problem: atoms, molecules, and other particles are really small.

ex.  Helium has an atomic mass of 4.0 atomic mass units, but how much does one helium atom weigh in grams? The answer is an incredibly small amount, not very practical for day to day calculations.

So to fix that, a really smart, really old guy came up with an answer. This guy's name was Amadeo Avagadro and he came up with this number in 1811!  Here's his head shot.

Avagadro said, what if  4.0 grams of Helium contains a number of atoms? And what if this number of atoms is constant for all elements and compounds, depending on their atomic mass? According to Avagadro, 12 grams of Carbon, 4 grams of Helium, and 11 grams of Sodium would each have 6.02*1023 atoms.

There are 3 different conversions we usually do with Avagadro's number.

1. A sample of sodium has 5.6*1026 atoms. How many moles of sodium is this?

      5.6*1026 x 1 mol           = 9.3 mol
                       6.02*1023

2. 15 moles of chlorine equals how many atoms?
 
     15 x   6.02*1023 = 9* 1024
               1 mol
3. Or the opposite of number 1, which is how many molecules are in 3.09 moles of NaCl?

   3.09 mol x 6.02*1023 = 1.86*1024
               1 mol

These are the 3 different conversions you might need to do with the Mole.

oh and here's another mole:

Naming Compounds

Okay so the most common system for naming compounds is IUPAC (unfortunately I do not remember what this stands for though). The compounds which we learned about are:

Ions

Multivalent Ions
Binary Ions
Polyatomic Ions

Molecular Compounds

Hydrates
and
Acids/Bases
Of course some of these have already been explained in previous blogs so i won't go over all of them, just the ones we did in class.

Multivalent Ions -elements that can form more than one ion (ie. Tin has a +4 and +2 charge)

Thus I will teach you how to differentiate which charge it is without using the roman numeral way (Tin(II)).

It's quite simple actually if you are using the larger charge you add -ic on to the end the smaller charge is -ous, easy right? Oh and you take off any other suffix's. So for example Manganous Oxide. MO. However some of the ions don't sound very good when you just add the ending on so of course there are a few exceptions for the rule such as:

Fer-Iron

Cupp-Copper

Mercur-Mercury

Stann-Tin

Aunn-Gold

Plumb-Lead 

And I'm sure someone will realize that Fe 2+ is Ferrous easily making a....
How funny......



Next up...
Hydrates

These are basically water molecules, there's water inside of the molecule, and said water can be released with heat.

Now what to call these things, just follow these simple steps and you will be able to name hydrates (it's a very useful skill I'm sure, or at least I think)

1)write the chemical formula

2)add a prefix to show the number of water molecules (prefix's such as mono-, di-,tri-....deca- etc.)

3)write hydrate after the prefix

It's very complex isn't it.

An example of this would be LiF-3H₂O which becomes Lithium Flouride Trihydrate

On to the next topic which is.....
Acids and Bases
(don't worry this one is very brief)
Basically an acid has Hydrogen in it you add -ic onto the end and put in the word acid afterwards, for example SCNH is Thiocyanatic Acid.
Bases are a cation and hydroxide, the only thing you do for this is add Hydroxide on to the end of the name, it's pretty easy, as easy as KOH results in Potassium Hydroxide.
However I must leave now because I am about to eat dinner

Drawing Electron Dot Diagrams

Electron Dot Diagrams, or Lewis Diagrams are... cool. Lemme show you why:

 LEWIS DIAGRAMS FOR SINGLE ATOMS

When Drawing Electron dot diagrams, the nucleus is represented by the atomic symbol.

For example:   Cl            Na

Determine the number of valence electrons (meaning the electrons in the outermost shell). Represent these by drawing that amount of dots around the chemical symbol.

Keep in mind:

*There are four orbitals (one on each side of the nucleus) and each can hold a max of 2e
*Each orbital gets 1e before they pair up

For Example:
Chlorine atom has 17 electrons.
2 in the first shell

8 in the next.

And 7 in the outer shell.

LEWIS DIAGRAMS FOR COMPOUNDS AND IONS

In covalent compounds, electrons are shared

First, determine the # of valence electrons for each atom int he molecule

Then, place atoms so that valence electrons are shared to fill each orbital

Examples:

Here is a VERY common covalent compound, H20... water!
Oxygen originally has 6 electrons, while each Hydrogen has 1 electron.

This totals up to 8 electrons, which fills up oxygen entirely as well as hydrogen (which only requires 2 electrons each, since its the first shell!)
 

And children, that's an example of how we share!

DOUBLE AND TRIPLE BONDS
Sometimes the only way covalent compounds can fill all their valence levels is if they share more than one electron (hence the double and triple!).
Examples

Carbon has 4 electrons, while each Oxygen atom has 6 in their valence shell.
This means that there's a lonely electron in each of the oxygens, and 2 lonely electrons in the carbon atom... so why not pair up and form a double bond?

IONIC COMPOUNDS

In Ionic compounds. electrons transfer from one element to another.
First, determine the number of valence electrons on the cation (positive ion) and move these to the anion (negative ion)
Then, draw [ brackets ] around the metal and non metal
-Write the charges outside the brackets
Par example,

Aluminum is a charge of +3, and Chlorine has a charge of -1. Since the electrons are moving onto the chlorine (we know this, since chlorine's negative), we only draw the electrons around the chlorine.
Remember to write the charges on the outside of the brackets!

POLYATOMIC IONS
First ,determine the # of valence electrons for each atom int he molecule

Then, subtract one electron for each positive charge OR add one electron for each negative charge
Example

CO3 -2

Carbon- 4 electrons

Oxygen- 6 electrons x 3 = 18 e

+2 electrons (because the charge is -2)

Isotopes and Atoms

Okay, sorry for the late post but here it is, isotopes and atoms. Let's start with the basic definition of an atom.
Atom-- the smallest unit of an element, having all the characteristics of that element
Simple right?
Now i realize that the scientific atom might not seem as interesting as this guy right away but it can be quite amazing. (but maybe not quite so much right now)
 
and now a couple formulas you need to know
Atomic Number = Number of Protons
Atomic Mass- Atomic Number = Number of Neutrons
Where to find these numbers you're wondering? Well you can find them right here.

The 6 in the upper left corner represents the Atomic Number
The =/-4 represents the charge (it's not particularly important for this though)
The C is the symbol for Carbon
The 12amu represents the mass (in atomic measuring units)






However not all atoms of the same element are identical some have a different mass these are called isotopes
An Isotope has the same Atomic Number as the atom it represents but a different mass.
For example
 This is a Carbon isotope. When writing isotopes you see the two numbers in front of the C, the top number is the mass number, the bottom is the atomic number. Same atomic but different mass number.
Easy right.
Thus we shall finish off with a couple of comics. On chemistry related and the other not so much.
 
Because running is really going to save you.

Trends on the Periodic Table

Okay so this is a pretty cool lesson if you ask me. We learned that certain characteristics like melting point and reactivity follow patterns. There are 7 major trends :

1. Reactivity

• metals and non-metals show different trends
• reactivity increases as you move outwards from the middle of the table
• metals also increase in reactivity as you move down the table
• non-metals increase in reactivity as you move upwards on the table
• the exception to this is the noble gases which are the least reactive elements

2. Ion Charge

• elements ion charges depend on their group number

so all of the elements in group 2 for example, have a charge of +2 when they make ions

3. Melting point

• Moving from the outside towards the middle of the table, melting points of elements increase
• Elements in the middle of the table have the highest melting points
• Noble gases have the lowest melting points

* carbon is an exception to this rule
4. Atomic Radius

• The atomic radius of an element decreases as you move up and to the right on the periodic table

therefore, Helium has the smallest atomic radius while Francium has the largest

5. Ionization Energy

• this is the amount of energy required to remove and electron from an atom
• the amount of energy increases up and to the right

 Here, Helium has the highest energy requirement while Francium has the lowest. This is directly opposite from the trend in atomic radius. This is because the smaller the radius, the more attraction is exerted on the electrons from the nucleus. More energy is then needed to launch the electrons away from the atom because of this strong attraction.

6. Electronegativity

• This refers to the ability of an atom to attract electrons
• This trend increases up and to the right, like ionization

7. Density

• Density increases as you move towards the middle of the table and down

As you can see there are many patterns in the periodic table, all you have to do is look.
here is a really good interactive periodic table to help with all your chemistry needs.

http://www.ptable.com/

Quantum Mechanics!

We learned about an entirely new topic today, and we all left the classroom about 10 times more chemically advanced, if that makes sense! 

I guess it isn't ENTIRELY new, but it's just building on all of the stuff we learned x 100000! 

So here's the low-down:

The Bohr Theory states that: 

An electron is a negative particle that must in an orbital in an atom

The Quantum Theory states that:

An Electron is like a little cloud of negatives energy, or a wave. 

Orbitals are areas in 3D space where electrons are. The energy of the electron is in its vibrational modes- just like notes on a guitar string, or a bit like a slinky! Photons are produced when high energy modes shift down to lower energy modes.

These are what the orbitals look like:

First there are the S orbitals

-Each orbital holds 2 electrons

 

Then the P Orbitals which exist starting from the second S orbital:

-There are 3 sub-orbitals in the P orbitals

-Each contains 2 electrons, meaning there is a total of 6

 

Then the D orbitals that exist starting from 4s

-There are 5 suborbitals

-Each contains 2 electrons (as all orbitals do), meaning there is a total of 10

 

Then the F orbitals

-There are 7 suborbitals

-Each contains 2 electrons, totalling up to 14 electrons

Depending on the number of electrons in an atom, it takes up different amounts of different orbitals. This chart shows more precisely how these different electrons take up different orbitals

  

Here are some examples:

Oxygen has 8 electrons. It takes up the 1s (2 electrons) as well as 2s (2 electrons) and 2 2p orbitals (4 electrons), which totals up to 8!

Silver has 47 electrons. It takes up 1 s, 2 s, 2p, 3s, 3p, 4s, 3d, 4p and 5s (totalling up to 38 electrons) and then it takes up 4 4d orbitals.

New Examples:
Which element has the structure 1s, 2s, 2p, 3s, 3p, 4s, 4p, 3d, 5s^1
It's Rb, Rubidium! We know this because (if you look at the periodic table above) it is the first element on the 5th period, meaning it goes up to 5s, but only had one orbital in the 5s.

Which element has the structure 1s, 2s, 2p, 3s, 3p,4s, 3d^6 ?
It's iron! Because it's on the 4th period, we know it goes to at least 4s, and then it is 6 elements down!

Here's a video showing the shapes of s, p and d orbitals! It's really handy in terms of visualization!

Atomic Orbitals!

Bohr Diagrams!

It all begins with atoms. Atoms are electrically neutral because they have the same number of electrons(-) and protons(+). They also have neutrons which are not electically charged at all.One way we can show how many electrons and protons are in an atom is by making a Bohr Diagram or an energy level model.

A Bohr Diagram basically shows you how many electrons are in an atom and where they are placed. We use energy levels to show the placement of these electrons, with 2 electrons in the first level, 8 in the second, 8 in the third, and 18 in the fourth. To find out how many electrons are in an atom, we look at the atomic number

The atomic number tells us the number of protons in an atom, in this case 47. Since an atom is electronically neutral, there must also be 47 electrons.

This is a Bohr Diagram of an Aluminum atom. There are 13 protons in an aluminum atom and  therefore 13 electrons. We put 2 electrons in the first level, filling it up. Then we fill the second level with 8 electrons and then 3 in the next to make 13.

Some atoms have full outside levels, called valence shells. When an atom has a full valence shell it is very stable. Noble gases are the only atoms that naturally have full valence shells.


The other way of showing how many electrons are in an atom is by making an energy level model.
This looks sort of like a Bohr Diagram but instead of drawing the electrons, we simply write the number of electrons above the nucleus.

                                                2e-
                                                8e-
                                                8e-
                                                2e-
                                                20p
                                                20n

This is just a simpler way of communicating how many electrons there are and how many energy levels or shells are being used.

Bohr Model

Well, the Bohr model, let me tell a little bit about the theory first.
The theory behind Bohr's Model was
-electrons exist in orbitals
-when absorbing energy electrons move to a higher orbital

-as electrons fall from a high energy orbital (what comes up must come down) to a lower energy orbital they

  release energy

-this energy is released as a photon of light

And for all those visual learners here's a diagram

Okay so here's Bohr's model

Pretty simple right, 1 proton, 1 electron.
(oh yes, those arrows you see, that is the direction the electron is moving, yes it does move, however they are simply there to show that electrons move around on their orbital, i have no idea if that is actually the direction it goes in.)




But of course we couldn't just leave it like that, somebody out there just had to go and complicate things, while at the same time making them far more interesting.

Basically when photons of light fly past the atom without hitting the electron nothing happens, but as soon as a photon does hit an electron.

Bonk!                  





Then all of a sudden!                                   

Oh look!
It's transported, now the elecron
is on the second orbital!
Amazing!

And then if the electron gets hit by another electron

Bonk!

Ah, now we have a pretty blue photon flying away from where the electron and green photon collided. Coincidence, i think not (you may think so though). The blue photon was a result of a loss of energy.

See when the electron is on the first level and gets hit by a photon the electron takes the photon's energy and transports up a level or two. When the electron is on that higher level and is hit by another photon the electron will either go up another level or two or go back down. If the electron does go back down it will lose some energy, that energy being the photon.

Now for a site that was shown to us when we learned this, it may help you understand the concept a bit more easily, it also has some other interesting things you can do on it.

Here's the sight http://phet.colorado.edu/en/simulation/hydrogen-atom 

The Atomic Theory (and its looong history!)

When I left Chemistry today, I felt as though the last hour that I'd spent in the room at the corner of the science wing wasn't a Chemistry lesson, but a history lesson! We learned about the atomic theory and its looong history!





It all started out with Ancient Greece's (and other civilizations with similar theories) 4 element theory. This stated that 4 elements exist: Earth, Air, Fire and Water. This, of course, could not be tested, but with the technology then, it was the best guess they could give!




  
 

Next was the theory of Democritus in 300 BC, that stated that atoms are indivisble particles. There was no mention of the nucleus or constituents yet, and it couldn't explain atoms' roles in chemical reactions. This  theory was also not testable. 

Doesn't he look like such a nice fellow?

Next was Lavoisier's theory in the 1700's. He created:

-Law of Conservations of mass: There has to be the same number of atoms of each element in the reactants as there is in the product of the chemical reaction. 

-Law of definite proportions: Compounds have different proportions based on mass, for example water is always 11% hydrogen and 89% oxygen (even though there are 2 hydrogens for each oxygen atom, oxygen has a greater mass)

Now, is he working hard or hardly working? 

 

Next was Proust with his theory in 1799. He stated that if a compound is broken down into its constituents, the products have to exist in the same ratio as it did in the compound. I guess this would be like in decomposition, for example H20 -> H2 + O2  this would have to be balanced as 2H20 -> 2H2 + O2.

 

Next in line is Dalton in the 1800's who stated that atoms are solid, indestructable spheres, and that each atom provides for a different element (different spheres). This was based on the law of conservation of mass.

What a great person.

 

Next is JJ Thomson in the 1850's who created the Raisin Bun model. No, he was not a bakery chef, but he found that atoms are solid, positive spheres that have negative particles embedded in them. This was the first theory that stated atoms have positives and negatives (protons and electrons) in them. This WAS tested using a cathode ray tube! 

Well doesn't he just look like the friendliest person in town.

 

Rutherford was next (and last, on this list!) in 1905, and he showed that atoms have positive dense centres! Well where do the negatives go, he thought? This resulted in a planetary model (centre with 'orbit rings' around it) which explains why electrons spin around the nucleus, and this also explains that atoms are mostly empty space!

I think he's in the middle of a 'eureka' moment here!

Quite fascinating, I know. Shows the long history of chemistry, and how technology can help support our theories!

Here's a video that outlines the people that we learned about, and it's even thrown in a few extra names that aren't on this list! 

Atomic Theory History Lesson