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

Its a Lab!!!!

yay our first lab yesterday! it was terribly exciting, mixing salt into water. no i'm serious it was awesome!


The point of the lab was to find the saturation level of salt in 10ml, 20ml, 40ml, and 50ml of water. We started by donning our lab coats and goggles. so stylish!


next we got out everything we would need for the experiment:
salt
water
scale
wax measuring paper
a 50ml beaker
a scoopula
a glass stir rod
a graduated cylinder

to start off we measured a pile of salt(roughly) onto a piece of wax paper that was sitting on the scale. We then zeroed the scale by pressing zero. What this means is that now instead of the weight of the salt showing on the screen and subtracting everytime we took away salt, the number would start at zero instead and get higher, telling us exactly what we had taken away.
the next thing to do was to measure out 10ml of water in the graduated cylinder and transfer it to the beaker. we then started to add salt and mix it in until it looked like this:


Once we could see a deposit of salt on the bottom that was not being dissolved, we realised that we had reached the saturation level. The number on the scale showed how many grams to the hundredth of a gram were in the water.


then we wrote down the number, emptied and cleaned the beaker, zeroed the scale, and did it all over agian with 20ml, 40ml, and 50ml of water.
ta da!

Graphing and Density

On September 30 we learned about graphing and density.
The density formula being

                    or 

An example of how one might use this formula is say there was a person who wanted to find out their density (for whatever reason). The said person determined that they weighed 47 kg and took up 22L.
Thus to find the density you simple divide the mass by volume, which is 47kg/22L equaling 2.1 kg/L. (Remember your significant digits)


See with chemistry you can not only figure out what clouds are made of but also what the density of clouds compared to the air is.

We also went over graphing.
Graph can be used for 3 things
Examining the graph
Finding the slope
Finding the area

There are also five essential things needed in a graph
labeled axis
appropriate scale
title
data points
line of best fit (this can also become a curve of best fit)

For example

However in this graph due to the angles there is more than one line of best fit.

First off we will find out the slope, the formula for slope being
the slope for 0-2 s is 2/2 =1m/s
2-3 is 0/1=0m/s
3-4 is -2/1=-2m/s
With this information you could also figure out the average velocity but since we didn't go over that today I will simply give you the formula so that if you want you can figure it out yourself. The formula is

Now in order to find the area of the graph you need to take a few more steps, as shown in the graph below.

As you can see the graph is divided into 4 different sections A,B,C and D
note how the sections go right down to the x-axis. Once you have your sections separated you find the area of each using the appropriate formulas in this case you would use A=(l)(w) for A and C, you would use A= 1/2 (b)(h)
for B and D.

To show and example in order to find the area of a here's what you do

A=(l)(w)  B=1/2(b)(h)   C= (l)(w)
   =(4)(1)    = 1/2(2)(2)     =(1)(2)
   =4           = 4                  = 2
D=1/2(b)(h)
   =1/2(1)(2)
   =1
Thus the area would be11(m)(s)

Which is what we learned on Sept. 30 in a nutshell.