Predicting the Number of Valence Electrons

Valence Electrons are the electrons in the outermost (energy level) open electron shell of an atom.
They are the electrons that can take part in chemical reactions, also called the "reactable electrons".
Some things you may need to know:
Open Shell: A shell that contains less than its maximum number of electrons
Closed Shell: A shell that contains exactly its maximum number of electrons.

All Noble Gases have 0 valence electrons, because they all have something called a stable octet.
A stable octet is when the shell has exactly 8 electrons on it.

example: Neon.
Atomic number: 10.
We all think back to grade 10, and remember the order of the number of electrons each shell can hold.
First shell holds 2 electrons.
Second shell holds 8.
Third shell holds 8.
Fourth (and final) shell holds 16.

As you can see, there is a perfect shell - or a stable octet. There is no room for any more electrons.

Valence electrons are all the electrons in an atom except those in the core, or in the filled d- or f- subshells.
A quick way to determine the number of valence electrons for a representative element is to look at which group is it in. 

As you can see in this periodic table, I have drawn on (messily) the group numbers. 

In group 1, there is 1 valence electron for each element. For group 2, there are 2 valence electrons for each element. And so on, until group 8, where there are no valence electrons, because Noble Gases ALWAYS have a stable octet.

The number of valence electrons stays the same as you go up or down a group, but they increase as you go from left to right across the periodic table. 

I'm tired now.

Core Notation

So by this point, we all know how to do electron configuration.

Core Notation is basically just simplifying core notation!

The set of electrons for an atom can be divided into two subsets: core and outer.

The CORE of an atom is the set of electrons with the configuration of the nearest noble gas (He, Ne, Ar, Kr, etc.) that comes before it.

The OUTER electrons consist of all electrons outside the core. These normally take part in chemical reactions.

So, how do you do this "core notation"? 

At first, it made absolutely no sense to me at all.

But as I continued practicing, I found out it's actually pretty simple.

Step 1: Locate the atom and note the noble gas at the end of the row ABOVE the element.

As you can (hopefully) see in this picture of the periodic table, I've highlighted the noble gases that can be used in Core Notation.

For example - Chlorine.

The Electron configuration for Chlorine is 1s² 2s² 2p⁶ 3s² 3p⁵

Okay, so what is the noble gas at the end of the row above the element? Locate Chlorine. You will see that at the end, and up one, is Neon. 

The Electron Configuration for Neon is 1s² 2s² 2p⁶

STEP 2: Replace the part of the configuration corresponding to the configuration of the noble gas, with the SYMBOL for the NOBLE GAS in SQUARE BRACKETS. 

So in this case, the CORE NOTATION of Chlorine would be: 

It's simple! This way, you don't have to keep writing out 1s² 2s² 2p⁶ etc.

More of the Periodic Table!

The 1800s was huge for discoveries regarding the periodic table. Here's what you need to know:

Law of Octaves - John Newland
He proposed that elements are arranged according to their atomic weight

Mendeleev:
Discovered that certain features of elements recurred when elements were arranged in order according to mass. Therefore, he decided to organize the elements in periods and families or groups, also known in the general English language as a row or a column. He even left gaps in the table, leaving room for other elements with similar characteristics to be discovered. (Smart cookie!) He is known as the 'father' of the periodic table.

                                                      The smart cookie! (Mendeleev)
Modern Times:
Periodic Law : Elements recur periodically when arranged from lowest to highest atomic number.
-Elements are arranged according to their atomic number. (Got that wrong on the test, damn! But at least you'll know now!)

Here are some fun videos for you!

The Mendeleev Song!
History on Mendeleev
Newland documentary

Now your daily chemistry related lolcat!

Enjoy and I hope everyone did great on the test!

Electron Configuration

For me, electron configurations started out very confusing, but now that I understand, I'll try and show you what works best for me.

First thing to do is to memorize this chart. We aren't given it during quizzes/tests so it is important to know the order.

You also need to know this:
S-types have one orbital (2 electrons or spaces)
P-types have 3 orbitals (6 electrons or spaces)

D-types have 5 orbitals (10 electrons or spaces)

F-types have 7 orbitals (14 electrons or spaces)

Now if I were you, I would be saying spaces? I'm confused!

But here is how it helps!

_    _      _ _ _    _      _ _ _
 
1s  2s    2p         3s    3p

Now, let's start with something easy like a Helium atom. If it is an atom, it has the same number of protons and electrons. Helium's atomic number is 2 therefore it has two protons/electrons. Because it has 2 electrons, fill in one upwards arrow and one downwards arrow. That shell is now full.

Not only is that shell full, we have used up all the electrons!
Therefore the electronic configuration for Helium is 1s2.

Lets use a more complicated one now and test that knowledge!
Lets try a sodium atom. This atom has 11 protons/electrons. Keep going until all those electrons are full.

I would draw it but since its on the computer I can't. So we'll use an astrix to show it.
 
**   **     ** ** **     *    
_     _       _ _ _            _     _ _ _

1s   2s     2p               3s    3p

As you can see we have used all 11 electrons. So let's write it!

In written form it would be 1s2 2s2 2p6 3s1
As you can see the exponents add up to the number of electrons.

If you are still completely confused what I mean when I say arrows, here is a visual example of what I am talking about.

                                                     Orbital diagram for Sodium


Now lets try one with ions!

Electron configuration for N3-

Because it has a charge of -3, there are three extra electrons to deal with. Normally, nitrogen has 7 electrons. But because of its charge, we have to add 3 more.
If it has 10 electrons, write it out until you run out of electrons.

1s2 2s2 2p6
As you can see the exponents add up to 10, the number of electrons for the N3- ion!

The nitride ion, N3­­­ˉ, has an electron arrangement of 1s2, 2s2, 2p6

Without the 3- charge, N would look like this: 1s2 2s2 2p3. The extra 3 electrons fill the 2p orbital and stabilizes the ion, making it similar to a noble gas, which all elements want to be like. (But you will learn more about that later)

What else you need to know:

Ground State: electrons are in their lowest possible level
Excited State: Electrons are in energy levels other than the one that is lowest available.

If the electrons in the excited state, you should try for extra practice to put them in their ground state.


Thanks for reading, of course I will include a lolcat to thank you for following along!

Periodic Table Trends

This class we did an activity to discover the trends in the periodic table.

We found out the trends by graphing and finding out what we noticed was a trend.
Here is what we found:

Density: the degree of compactness of a substance. As the atomic number increases, so does the density.

Melting Point: The temperature at which a given solid will melt.
Boiling Point: The temperature at which a liquid boils and turns to vapor

Melting points decrease as you move down a group, and increase as you move across a period.

Ionization Energy: The energy required to remove the outermost electron in the atom. It increases as you move across a period, and decreases as you move down a group.

Electronegativity: The tendency of an atom to attract electrons in the formation of anionic bonds. Elements become less electronegative as you move down a group, and more electronegative when you move across a period.

Atomic Radius: Measure of the size of its atoms, usually the mean or typical distance from the nucleus to the boundary of the surrounding electrons. This decreases as you move across a period, and increases as you move down a group.
Next class we focused on elaborating on these trends so stay tuned!

Also, Ms. Chen showed us this great website http://www.ptable.com/ where you can play around with the trends and find out some new trends! I know I will be using it to study!

Atoms

Today you are going to learn how to determine things like isotopes, number of protons, number of neutrons, etc. So lets get started!


REVIEW: Atoms consist of electrons, protons and neutrons.




Proton: Mass = 1, charge = +1, located in the nucleus

Neutron: Mass >1, charge = 0, located in the nucleus

Electron: Charge = -1, located around the nucleus




Atomic Number: Number of protons found in a nucleus


The atomic number = the number of protons which also equals the number of electrons. It's that easy!


Got all that? Time to move on to ions.

Ions are atoms able to gain or lose electrons
The number of protons subtracted by the number of electrons equal the charge of the ion.

Moving on to the mass number. This is the total number of protons and neutrons!
Knowing this, here are some equations to remember:

number of neutrons = mass number - atomic number

mass number = number of protons + number of neutrons

Moving on to atomic mass!

Atomic Mass: the average mass of an isotope

Wondering what an isotope is?

Isotopes: when there is the same number of protons and electrons but a different number of neutrons

Here is a problem that deals with isotopes:

There is an element with 4 naturally occuring isotopes. Their atomic mass and percent is as follows: a = 46 (25%), b = 47 (50%), c = 48 (15%), and d = 49 (10%)

Find the atomic mass for the element.
First, multiply the atomic mass by the percent abundance.

A = 36 x 25 = 11.5
B = 47 x 50% = 23.5

C = 48 x 15% = 7.2

D = 49 x 10% = 4.9

Now add them together to get your answer.

11.5 + 23.5 + 7.2 + 4.9 = 47.1

I just high-fived my cat who is sitting beside me so I felt this picture was necessary.

Thanks for reading!