Octet+Rule+and+Using+the+Periodic+Table+to+Assign+Ionic+Charges

=Using the Periodic Tale to Predict an Ionic Charge= One can use the periodic chart to predict the Ionic charge of an element simply by looking at what Group it's in. The Main Group A's tells how many valence electrons there are.

http://www.chemprofessor.com/ptable4.gif = =

From left to right, the Main Groups of the periodic table, which are the ones with the A in their names, are designated with an ionic charge that counts from 1 to 4 then back down to 1. Starting with the left IA group, the Alkali metals, they all contain an ionic charge of +1. The Main Group IIA, the Alkaline Earth metals, they all contain a +2 ionic charge. From there, the charge counting skips the transition metals and goes all the way to Group IIIA which has a +3 ionic charge. Starting with Group IVA, the charges start to become negative charges, and the counting goes down. Group IVA itself has can have a positive or negative ionic charge.

The transition metals have uncertain charges associated with them, thus when having to identify their ionic charge, one has to use the roman numeral that goes along with its name to know.

For example Mercury is a transition metal that has an uncertain charge. When scientists write out the name for a compound containing Mercury, like (HgO) they write it out as Mercury (II) oxide.

The noble gases, which contain all 8 valence electrons don't need to get or remove electrons because they are stable as it is, so their ionic charge is 0.

The Island of Certainty:
A few elements not within the Main Group rows, always have a certain ionic charge to theProxy-Connection: keep-alive Cache-Control: max-age=0 3A Silver (+1) Zinc(+2) Aluminum(+3) Cadmium(+2)

What is an Ionic Charge?
All atoms want to become a noble gas which have its valence shell filled. The ionic charge comes when an atom does not have it's valence shell at 8. The Alkali metals all have 1 valence electron, which if they got rid of it would give them a filled valence electron shell just like its closest noble gas (which is one element back). By getting rid of this electron, they now have a charge of +1 due to the absence of the electron. Another example would be the halogen gases, which have -1 charge on them. They have 7 valence electrons and the fastest way to get become a noble gas is to gain one electron, which when they do they receive a negative charge of -1 from the additional electron.

http://www.gcsescience.com/Sodium-Atom-Sodium-Ion.gif = = = =

=**Octet Rule**= = =

Octet Rule-
Atoms tend to gain, lose, or share electrons until they are surrounded by eight valence electrons.

The atoms like to become noble gases, which are nonreactive to most things.

Hydrogen, which only needs 2 electrons for it's valence shell is the exception.

The most common occurrence is that when compounds are formed they do so in combining with other elements that will give it eight electrons in its outermost valence shell.

For example:

Carbon has 4 valence electrons because its in Group IVA. This means that it can gain or lose 4 electrons to get 8 valence electrons. If it combines with one oxygen, which has 6 valence electrons (in Group VIA) in a double bond, which means oxygen is sharing two of its electrons with carbon is that carbon feels like it has 6 valence electrons, and carbon shares two of its electrons to oxygen making it feel like it has 8 valence electrons. Oxygen is satisfied but carbon is not, so it combines with another oxygen in a double bond, meaning oxygen shares two of its electrons with carbon, making carbon now have a total of 8 valence electrons, so it's satisfied. Carbon shared two of its electrons with oxygen so that makes it feel like it has 8 valence electrons as well. All the elements are happy.

=Ionic Compounds:= Atoms take and lose electrons until it gets 8 valence electrons. They do not share the electrons, which makes them take on an ionic charge. This makes them stick together. For example: In ionic compounds, an ion of Sodium would give away one of its electron to get 8 valence electrons. This electron goes to an element such as chloride which needs an electron to get 8 valence electrons. This follow the octet rule, and so the sodium becomes a positive charge and the chloride becomes a negative charge. This causes them to stick together making an ionic compound.

Using the Octet to Make Compounds in the Lewis Structure:


Step 1: Make a skeletal structure of the molecule, which is just hooking up all the atoms together with single bonds following the bonding tendencies.

Step 2: Add up the total number of valence electrons that are available.

Step 3: Add electrons around the elements in pairs of two around the elements until there are 8 total electrons around the element. Note: Every bond is equal to two electrons.

Step 4: If you are short any electrons in completing the octet rule for any of the atoms, add a double bond or triple bond between elements until all elements are satisfied with the octet rule and all electrons have been used.

=Exceptions to the Octet Rule:= Other than hydrogen, there are some elements that do not follow the octet rules such as beryllium (which is stable with 4), and boron (which is stable with 6). Some elements can even contain more than 8 valence electrons.

Work Cited: http://en.wikipedia.org/wiki/Lewis_structure http://www.saskschools.ca/curr_content/chem20/covmolec/e