## Thursday, April 21, 2011

### Electronic Configuration of An Atom: Does This Mean Anything To You? 1s^2 2s^2 2p^6 3s^2 3p^6...(by Bev)

The above was definitely NOT proper English.
It's actually something called Electronic Configuration.
Today, you're going to learn how to write "chemists' gibberish".
Looking forward to it?

What is electronic configuration?
-description of an atom's orbitals & how many electrons occupy each orbital
-helps to group & learn about the elements of the periodic table

recall: Niels Bohr suggested that electrons occur only in particular energy states - when an electron emits/absorbs a particular amount of energy, it will instantly jump to a different orbital

important terms to know:

-energy level: amount of energy that an electron is able to have
'n' is the # of the energy level
-for a given value of  'n', different types of orbitals are possible
n=1     only s-type is possible
n=2     s- & p-types are possible
n=3     s-, p-, d-types are possible
n=4     s-, p-, d-, f-types are possible

-quantum: the difference of energy of 2 specific energy levels

-ground state: when all the atom's electrons are in the lowest possible state (ie. stable, like a noble gas)

-excited state:  when all the atom's electrons are temporarily occupying an energy state greater than its ground state
ex.  When an electron takes in extra energy, like a photon, or hits a neighbouring particle, it becomes excited.

-orbital: the actual area of space that an electron occupies in a specific energy level
-4 types: s, p, d, & f
-energy levels are not spaced apart evenly
-each orbital is symbolized by a circle

-shell: group of all orbitals with the same n-value
ex. 3rd shell: 3s, 3p, 3d orbitals

-sub-shell: group of orbitals with the same type
ex. group of 5 3d-orbitals of the 3d shell

 Type of subshell # of orbitals Max. # of electrons s-type 1 s-orbital 2 p-type 3 p-orbitals 6 d-type 5 d-orbitals 10 f-type 7 f-orbitals 14

order in which the orbitals are filled:

Writing Electronic Configurations for Atoms

Neutral atoms:
-always begin using the LOWEST energy
-determine the # of electrons (recall: in a neutral atom, the atomic # is the # of electrons), then start at 1s, continuing to add until there are no more electrons
-each electron has an opposite spin classified by up & down arrows

potassium: 19 electrons

***NOTE: FOR EACH ORBITAL, DRAW ALL THE UP ARROWS FIRST FROM LEFT TO RIGHT BEFORE PAIRING THEM WITH THE DOWN ARROWS!!!***

Ions:
-negative ions: add electrons (equal to the charge) to the final unfilled subshell, starting from where the neutral atom left off
-positive ions: start with the neutral configuration & take away electrons from the OUTERMOST shell first

Exceptions

Why are you so surprised?!  There are always exceptions!!

Cr (Chromium gains stability with a HALF-FULL d-subshell)
we would predict: 1s2 2s2 2p6 3s2 3p6 4s3d4
but it is actually -->1s2 2s2 2p6 3s2 3p6 4s13d5

Cu (Copper gains stability with a FULL d-subshell)
we would predict: 1s2 2s2 2p6 3s2 3p6 4s3d9
but it is actually -->1s2 2s2 2p6 3s2 3p6  4s3d10

Core Notation

-special type of electron configuration: core electrons are replaced by the nearest noble gas
-usually take part in chemical reactions
-outer electrons: outside of the core electrons (ie. the noble gas)

How to write core notation

1. locate the atom & the nearest noble gas at the end of the period ABOVE the element (it is crucial to use the noble gas in the PREVIOUS row!!!)

2. replace the first part of the electron configuration (core) with the matching noble gas with the noble gas' symbol in square brackets

Carbon (6 electrons):

electron configuration: 1s2 2s2 2p2   <-- replace 1s2 with [He]

core notation: [He]2s22p2

a joke to end it off, as usual:

## Tuesday, April 19, 2011

### A Little Review and Some New Calculations To Feed Your Inner Chemist.

Remember the parts of the atom facts you learned A LONG TIME AGO!?!?!
Well, dig it all back out from the back of your brain.
Just kidding, I'll just do a brief review with y'all.

There are THREE subatomic particles: Protons (p), Neutrons (n), and Electrons (e-).
p and n are located in the nucleus and have about the same mass (ie. relative mass of 1)
e- has a very small relative mass of around 0 and is located in a cloud around the nucleus.

**Remember in a neutral atoms: #p = #e-  AND that an element's atomic # is also the # of p.

Ions occur when atoms gain or lose electrons during chemical bonding.
**Remember in ions: #e- = #p - ionic charge.

Negatively charged anions gain electrons (non-metals)
Positively charged cations lose electrons (metals)

What is the difference between atomic mass and mass number?
Though they both are acquired by adding the # of protons and neutrons, atomic mass is the mass that has the trailing decimals, while the mass number is a rounded mass.

Now you try:
How many protons, neutrons and electrons are in:
1) Strontium +2
2) Sulphur
3) Neon

Then...what are isotopes?
These are just variations of an element, and usually, they are the more dangerous types.
Remember isotopes are written including their mass number! (This differentiates isotopes from isotopes)
Isotopes have the same # of protons and electrons or is normal atom, BUT DIFFERENT NEUTRONS!!
ie. heavier atomic mass

Now, the NEW stuff steps in.
We're going to learn how to calculate the NATURAL MIXTURE OF ISOTOPES.
How do we know there are a few isotopes that are present? A mystical being came riding down from the sky and told this withered old man, of course.
NO, that is definitely NOT what happened.

It's really simple, actually.
The decimals in the atomic mass signify an AVERAGE.
EUREKA, right?

Let's do a question together.
Given this information, calculate the average molar mass of Fluorine.

F-18: 36.89%
F-19: 14.73%
F-20: 9.06%
F-21: 39.32%

OK. First, we'll have to convert all of the percents into decimal numbers.
Then, multiply each isotope percentage to its respective atomic mass.

F-18: (0.3689)(18g/mol)= 6.6402g/mol
F-19: (0.1473)(19g/mol)= 2.7987g/mol
F-21: (0.0906)(20g/mol)= 1.812g/mol
F-21: (0.3932)(21g/mol)= 8.2572g/mol

Finally, the last step is to add all those masses together.
6.6402g/mol + 2.7987g/mol + 1.812g/mol + 8.2572g/mol= 19.50g/mol
**DONT FORGET SIG FIGS!

Written by Jialynn.

## Friday, April 15, 2011

### History of Chem (by:Mandy)

drop the math, and lets learn a bit about the history of chemistry.
here are some of the important historical chemists:

Aristotle believed matter was made of different combinations of earth, air, fire, and water Lavoisier, A.L. (1743-1794)Discovered nitrogen; studied acids and described composition of many organic compounds.

Dalton, John (1766-1844)He proposed atomic theory, stated law of partial pressure of gases. His ideas led to laws of multiple proportions, constant composition and conservation of mass.

Thomson, Sir J.J. (1856-1940)Research on cathode rays resulted in proof of existence of electrons. Won the Nobel Prize in 1906

Rutherford, Ernest (1871-1937): Discovered that the atoms of the heavier elements, which had been thought to be irreversible, actually decay into various forms of radiation. Rutherford was the first to establish the theory of the nuclear atom and discovered rays: alpha, beta, and gamma. He also revealed the half-life of radioactive elements and applied this to studies of age determination of rocks by measuring the decay period of radium to lead-206. Have fun!