## Monday, June 27, 2011

### Electron Config and Quantum Numbers: Exercises

We’ve already seen how to build electron configurations
Its time to talk about the Quantum numbers
Sulfur, has 16 electrons:
Now lets get the Quantum numbers of some of the electrons of Sulfur.
Quatum numbers of the LAST electron of Sulfur

First you will have to find out where is located the electron, the last electron is here
This is the n quantum number
This tells us the $\ell \$ quantum number, in this case p ---->$\ell \$ = 1
To get the last 2 numbers lets use this method:
Draw squares, one for each type of orbital, for p:
Now find the middle square and mark it as 0, squares in the right are positive, squares in the left are negative.
Start filling the squares with arrows representing the electrons, but careful, do it this way:
Now that you’ve filled all with one electron, start over and now the arrow will be downwards.
How many electrons where on this subshell (for Sulfur)? There were 4 so we only fill 4 electrons; the last one you marked is the last electron.
Its m quantum number is -1
Upward arrows have S = ½ and downward arrows have S = - ½
So the last electron of Sulfur has:
n = 3
$\ell \$ = 1
m = -1
s = -1/2

Now lets get the Quantum numbers for the Sulfur 9th electron

That electron is here, so:
Now the last 2 quantum numbers
Quantum numbers for the Sulfur 9th electron
n = 2
$\ell \$ = 1
m = 0
s = -1/2
Electron Configuration for Excited State

In ground state the number of electrons is equal to the number of protons giving the atom a neutral charge.
In excited charge status the atom has lost/gain electrons, this can be because of a chemical reaction or radiation.

Sodium (Na) has 11 electrons, but what happens with excited Sodium (Na+1)
As you can see the charge of Sodium is +1, that indicates that the atom has lost 1 negative charge being that an electron; so excited sodium has 10 electrons, 1 less than its ground state.

Oxygen (O) in ground state has 8 electrons, but excited Oxygen (O-2) has a negative charge of -2, meaning that it gained 2 electrons, getting 10 total electrons on excited state.

The process of building the electron configuration now is the same, just make sure you have the correct number of electrons for that atom.

Ground State
O = 1s2 2s2 2p4

Excited State
O-2 = 1s2 2s2 2p6

Some Periodic tables come with electron configurations included, but in that tiny square the whole configuration of lets say, Lead that has 82 electrons, wouldn’t fit in, that’s why we use one of our friends, the noble gases.

A peculiar characteristic of these elements is that the last shell of the atom is ALWAYS FULL.
So we use them to avoid writing a long electron configuration:

Pb = 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p2

Pretty long right? Now lets make the configuration of the Noble gas BEFORE Lead.
Xenon: with 54 electrons:

Xe =1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6

The short configuration for Lead would be:

Pb = [Xe] 6s2 4f14 5d10 6p2

This is what you will find in some Periodic Tables.

## Saturday, June 25, 2011

### Electron Configuration

Electron configuration is the arrangement of electrons of an atom or molecule. It concerns the way electrons can be distributed in the orbitals of the atom.

Orbitals

An atomic orbital is a mathematical function that describes the wave-like behavior of either one electron or a pair of electrons in an atom.
It’s a function that can be used to calculate the probability of finding any electron of an atom in any specific region around the atom's nucleus.

We will use this term to refer to the physical region defined by the function where the electron is likely to be.

There are 4 kinds of orbitals (recent studies may find new elements that will have 2 extra orbitals):

Orbital “s”
This can be explained with a sphere shape, electrons on this orbital spend their time in some point of this sphere, most likely near the center where the nucleus is, we can see that in this dot representation.
 There is only 1 orbital type s
Orbital “p”
This orbital can be represented by 2 spheres that are lightly shrinked into a connecting point (the nucleus).
 There are 3 orbitals type p

Orbital “d”
This orbital has diverse shapes, its like 4 lobes joined together in a center that is the nucleus.
 There are 5 orbitals type d

Orbital “f”
f orbitals have even more exotic shapes that wont be easy to explain but to show:
 There are 7 orbitals type f
The place of the atom in the periodic table will indicate which orbital is the last orbital of the last shell

Quantum numbers

Because of the quantum mechanical nature of the electrons around a nucleus, they cannot be described by a location and momentum. Instead, they are described by a set of quantum numbers that encompasses both the particle-like nature and the wave-like nature of the electrons.

Every atomic orbital is identified by the values of 3 quantum numbers, the forth number is for the electrons in those orbitals.

The principal quantum number, n, describes the energy of the electron, they are sometimes called electron shells.
Here your Periodic Table comes handy:
This numbers (Periods) tells the number of electron shells the atom has.
The azimuthal quantum number,$\ell \$, describes the orbital angular momentum of each electron. The set of orbitals associated with a particular value of “$\ell \$” are sometimes collectively called a subshell.
The max number of subshells for a shell is the quantum number minus 1, starting from 0.
n=2 would have 2 quantum numbers ---> 0 and 1
n=4 would have 4 quantum numbers ---> 0, 1, 2 and 3
Electrons on orbital s have $\ell \$=0
Electrons on orbital p have $\ell \$=1
Electrons on orbital d have $\ell \$=2
Electrons on orbital f have $\ell \$=4

The magnetic quantum number, m, describes the magnetic moment of an electron in an arbitrary direction.
This quantum number depends on the orbital and the different directions of it. e.g.
Orbital p has 3: px, py and pz, therefore the magnetic quantum number for each p orbital would be -1, 0, 1
This table explains it better:

 Orbital m s 0 p -1  0  1 d -2  -1  0  1  2 f -3  -2  -1  0  1  2  3

Each electron also has a spin quantum number, s, which describes the spin of each electron (spin up or spin down). The number s can be +1⁄2 or -1⁄2.

The Pauli Exclusion Principle states that no two electrons can occupy the same quantum state: every electron in an atom must have a unique combination of quantum numbers. So there can be only 2 electrons on each type of orbital.

Number of Electrons

Here your Periodic Table comes into play again, your table gives the information about all the elements in its Ground State, in this state they have neutral charge: Protons (+) are equal to Electrons (-).

The number of protons is given by the Atomic Number: so this is the number of electrons of the element, but in its ground state, not in its ionic (excited) state.

So Oxygen would have 8 electrons
Hydrogen has 1

Let’s build electron configurations

First we have to use this chart:
Just follow the line until you run out of electrons, and remember each orbital type can hold up to 2 electrons, so s orbital holds 2 electrons max, p orbital holds 6, d orbital holds 10 and f orbital 14.
Why we do it this way? Because some orbitals must be filled before others, this is because some have more energy than others.

Lets try with some examples:

Carbon, it has 6 for atomic number, so it has 6 electrons aswell.
Using the chart carbon’s electron configuration would be:

C = 1s2 2s2 2p2

Sulfur, has 16 electrons:

## Friday, June 24, 2011

### How to use your Periodic Table (Basic)

The periodic table of elements classifies, organizes and distributes the chemical elements, according to their properties and characteristics.

The creation of the periodic table can be attributed to Dmitri Mendeleyev, although wasn’t the only one, there were more scientists researching and trying to organize all the chemical elements discovered at their time.
 Source: Wikipedia.org
We have discovered 118 elements so far. At first elements are arranged by atomic number, Atomic number (Z) represents the number of PROTONS in the nucleus, not to be confused with Mass Number.
This can be found (In most tables) here:
As you can see element’s atomic number increases as you go RIGHT and DOWN.

 Source: Modified table from http://www.periodni.com by Aditya Vardhan
Horizontal Rows are called PERIODS and Vertical Columns are called GROUPS; elements on the same group have similar configurations of the outermost electron shells of their atoms (on how many electrons are on that last shell), and elements on the same Period have the same number of electron shells.
There are 18 groups and 7 periods.

Basic periodic tables give at least the abbreviation, the atomic number and mass weight.
More advanced tables give more information, like the oxidation state, electronegativity, the boiling and melting point, electronic configuration, density and more.
Mass number (A) is the sum of the number of protons (atomic number Z) and neutrons (N), and the number of electrons is the same as protons giving a neutral charge (on a primary state).

So basically:
Mass # = Atomic # + # Neutrons
A = Z + N

ISOTOPES

In the nature there is more than 1 kind of atom of the same element, they are called ISOTOPES. The only difference between isotopes is the number of NEUTRONS, therefore different Atomic Number; they have the same number of protons and electrons though.

To give an example lets see the isotopes of Carbon (C),

• Carbon-12, the most common accounting for 98.89% of total carbon in the nature.
Mass Number (A) = 12
Atomic Number (Z) = 6 --> every element including isotopes have the
same atomic number.
Number of Neutrons (N) = A – Z = 12 – 6 = 6

• Carbon-13, that makes up about 1.1% of all natural carbon on Earth.
Mass Number (A) = 13
Atomic Number (Z) = 6
Number of Neutrons (N) = A – Z = 13 – 6 = 7

• Carbon-14, this one only occurs in trace amounts, something like 0.000001%
Mass Number (A) = 14
Atomic Number (Z) = 6
Number of Neutrons (N) = A – Z = 14 – 6 = 8

Don’t confuse mass number (A) with ATOMIC WEIGHT; mass number of an atom as we saw is the sum of neutrons and protons; in the other hand Atomic Weight is the average atomic mass of the different isotopes of that element (weighted by abundance)

To avoid trying to understand a difficult equation lets see examples:

Carbon, 3 isotopes C-12 C-13 C-14

Note: Whenever you may need the atomic weight, use ONLY the rounded number in the periodic table, e.g. Carbon = 12.0112 but we use 12, Oxygen weights 15.9994 but we use 16.

Coming up Next! Getting the most of your Periodic Table: Electronic Configurations
For those in need: Ger your own Printable Periodic Table

## Thursday, June 23, 2011

### Inorganic Chemistry: Introduction

Inorganic Chemistry studies the formation, composition, structure and chemical reactions of inorganic elements and compounds (except C-H bond compounds, these are Organic Chemistry's work).

But what are ELEMENTS and COMPOUNDS?

By now you've probably already seen or asked for a PERIODIC TABLE in school, these are called Elements. See how are they arranged?, each element has its specific place on the table thanks to its characteristics, both physical and chemical; like MASS for example, Hydrogen comes to be the lightest Element in the nature, the following elements increase their mass as you go Right or Down.
In the other hand Compounds consists of 2 or more atoms, like Water (H2O).
I will explain more about the periodic table later but for now you should start learning each element’s abbreviation.
Oxygen = O
Hydrogen = H
Helium = He
Calcium = Ca
Easy right?, you will have some problems with elements where the name has nothing to do with the abbreviation but one afternoon repeating them and you will be good to go.
Iron = Fe
Mercury = Hg
Just remember, DON’T SKIP THIS STEP, its important for you to recognize each element by its abbreviation or else you will have problems. Don’t go hard on yourself if you can’t memorize them all, I will tell you which are more important (For now) for you to memorize.
Concentrate your attention on those elements crossed with the red line, you may leave the rest when your teachers take a test about it.

Each element consists of a single ATOM, in ancient times people believed that the single smallest indivisible particle of the matter was the Atom, now we now it’s not true; atoms consist of 3 particles: Neutrons, Protons and Electrons. There are smaller particles in the atom but this doesn’t concern us…yet.
Many scientists have argued and researched a lot trying to figure out the true structure of the atom, the arrangement of the particles inside of it. Many theories have came out, some pretty crazy, some that made sense.

Atomic Theory

In 1808, John Dalton tried to explain what was matter made of, stating that all matter consist of little indivisible particles called atoms, and these particles interact with each other forming molecules.

In 1897, Joseph Thomson took Dalton’s work beyond stating that inside atoms were little particles with Negative charge calling them Electrons, with the nucleus of the atom with a Positive charge.

In 1911, Ernest Rutherford developed a theory closer to the one we use today, he said that atoms have a positive and a negative side, just like Thomson said, but he said that the positive charge was concentrated in the nucleus and electrons orbit around it in circular trajectories. He also predicted the existence of the Neutrons.

In 1913, Niels Bohr proposed an improvement to Rutherford’s theory, saying that electrons didn’t move in 1 single orbit, but in different levels or “distances” of the nucleus, just like the planets around the Sun.

In 1926, Erwin Schrodinger continuing the work of Louis-Victor de Broglie, proposed a new theory, he said that electrons doesn’t behave like particles but like waves, he proposed a mathematical structure leaving behind the “planetary orbits” theory, and introducing a new theory, he said that electrons move around the nucleus but we could only “predict” with mathematical equations where will be more likely to find an electron, giving birth to atomic orbitals, electrons would be in different orbitals depending its energy.
 These are the orbitals where electrons are moving around, following not a single trajectory but a chaotic movement, in the center of these orbitals would be the nucleus
Of course these 4 people weren’t the only ones developing and helping with atomic theory, but to be brief I believe they are the most important.

So basically atoms consist of a NUCLEUS, where NEUTRONS and PROTONS "live", ELECTRONS move around the nucleus in orbitals. Neutrons (with neutral charge) and protons (with positive charge) give the mass to the atom and electrons have negative charge; in Chemical Reactions the elements gain and lose electrons, giving them positive and negative overall charges, these are called IONS.

## Monday, June 20, 2011

### So another one about energy: Batteries

We can find batteries all over our home, on cellphones, remotes, laptops and more; essentially batteries have chemicals that produce electrons through electrochemical reactions.

Every battery has 2 terminals, one marked with (+) being the positive terminal and one with (-) being the negative terminal.

Unless electrons are flowing from the negative to the positive terminal, the chemical reaction does not take place. That is why a battery can sit on a shelf for a year and still have plenty of power.

How a chemical reaction makes electricity?

It’s very simple, you’ve probably heard about metal rusts if you leave it outdoors, that’s an oxidation chemical reaction, where the oxygen (O2) “steals” electrons from metals forming oxides.
That reaction involves a movement of electrons and that’s the principle of batteries.
A common battery will have 3 main parts for it to work.
2 Different Metals (Copper and Zinc that are more common)
1 Electrolite (this is a solution saturated with ions)
On the electrochemical reaction the Zinc Terminal (Zn) loses electrons and flow through the wire to the Copper (Cu) terminal, the copper accepts the electrons.
While the reactions goes on the Zinc terminal will “dissolve” as it becomes oxidized to Zn2+ and the Copper terminal will get thicken from the Cu+2 ions on the solution reduce to Cu0 metallic state.

Want to try yourself? Will give you 2 ways to make electricity

Materials

For the first one: Pennies, Nickels, Dimes, Salt, Wires and Paper Towels
And a Voltmeter or a LED

Mix salt with water (as much salt as the water will hold) and soak the paper towel in this brine. Then create a pile by alternating pennies and nickels. See what kind of voltage and current the pile produces. Try a different number of layers and see what effect it has on voltage. Then try alternating pennies and dimes and see what happens. Also try dimes and nickels.
Be careful when you try the led on this battery because it may burn the LED depending on how many coins you stacked.

Now the second

You will need potatoes or lemons, wire, a Copper and a Zinc foil or you can use pennies and nickels.
Get the potatoe and stab the copper and zinc bars, you just made a battery :), you can try the lemon and see which gives you more voltage.

There are 2 ways to connect batteries: Serial or Parallel
You can try to stack potatoes in Serial to get more voltage and make your cellphone work, but will you really go to the street and walk around with a sack of potates on your back?