How many valence electrons?

Valence electrons:
1) Exist on the outermost shell of an atom
2) Take part in chemical reactions
3) Are all electrons except those IN THE CORE, THOSE IN FILLED D- or F- SUBSHELLS

Here is some important terminology:
An open shell is a shell that has fewer than the maximum amount of electrons occupying it. In this picture, the 2nd or outermost shell of the oxygen atom is the open shell. While it can hold 8 electrons, only 6 occupy the shell.

A closed shell is a shell that contains the maximum number of electrons that it can hold. In this example, the closed shell is the first one. It contains two electrons - the most that it can hold.


Let's look at the core notation for SULPHUR
S = 1s^22s^22p^63s^23p^4 CORE: [Ne]3s^23p^4

From the core notation, we look at the portion that is not within brackets. We then add up the superscripts of the s and p orbitals and get 6. Thus, we can conclude that there are six valence electrons in sulphur. We don't add up the superscripts of the d- or f- orbitals unless they aren't full.

Some unrelated terminology on the periodic table.

Periodic Law - the properties of certain chemical elements that occur every so often when the elements are placed in their order.
Ianthanides - the first row under the table that starts with lanthanum.
Actinides - the row under Ianthanides.

Electronic Structure of the Atom!

What is the electronic structure of an atom? It's a notation that describes the orbitals in which electrons occupy and the total number of electrons in each orbit. 

Remember back to when we learned about Neils Bohr? The guy in that picture? He proposed that electrons exist in specific energy states and when electrons absorb/emit specific amount of energy, it instantaneously moves from one orbital to the next.


Now for some vocab:
Energy level- amount of energy which electrons in atoms can possess ( "n"= number of energy levels) 
Quantum of energy- energy difference between 2 particular energy levels
Ground state- when electrons of atoms are in their lowest possible energy level
Excited state- when 1 or more of an atom's electrons are in energy levels other than the lowest available level
Orbital- region of space occupied by an electron in particular energy level
Shell- set of all orbitals having the same "n" value
Subshell- set of orbitals of the same type

Orbitals are split into 4 different types: s, p, d, f
Each subshell consists of:
1: s-orbital
3: p-orbital
5: d-orbital
7: f-orbital


Pauli Exclusion Principle: maximum of 2 electrons can be placed in each orbit
This principle means that the maximum number of electrons in each subshell is:
2: s-subshell
6: p-subshell
10- d-subshell
14- f-subshell

This picture will help with writing the electronic configuration of atoms. For neutral atoms:
1) Always start with lowest energy level (Aufbau principle)
2) Figure out how many electron you have (neutral atom=atomic number)
3) Start at lowest energy level (1s) and keep adding on until none is left.

Each electron has an apposite spin designated by upward and downward arrows. An example is silicon. The last line of the picture shows the electronic configuration. Silicon has an atomic number of 14 thus it has 14 electrons at its neutral state. Notice that 2 electrons in 3p occupy separate orbitals and aren't paired? This is due to...
Hund's rule- when electrons occupy orbitals of equal energy, they don't pair up until they have to. 
So in written form: 1s^22s^22p^63s^23p^2
The exponents represent the number of electrons.




Now for writing electronic configurations for ions. 
For negative ions: 
Add electrons (equal to charge) to last unfilled subshell starting where neutral atom left off. An example is N -3
Nitrogen in its neutral state has 7 electrons but with the charge of -3 it is actually 10


For positive ions:
1) Start with neutral atom and remove electrons from outermost shell depending on the charge.
2) If there are electrons in both s and p orbital of the outermost shell, elextrons in the p-orbital are removed first.


Core Notation- way of showing electron configuration in terms of core and outer electrons
A set of electrons belonging to a given atom can be divided into 2 subsets: 
1) Core- set of electrons with configuration of the nearest noble gas (He, Ne, Ar, Kr, etc.) having an atomic number less than that of the atom being considered
2) Outer- consists of all electrons outside the core. Since core electrons, normally don't take part in chemical reactions.


So to find the core notation:
1) Locate the atom and note the noble gas at the end of the row and above the element
2) Write the electron configuration normally. BUT replace the part of the electron configuration corresponding to the configuration of the noble gas.
3) Write the noble gas in square brackets. Ex. [Ne]...
4) Follow the core symbol with the electron configuration of the remaining outer electrons.
Ex. Al: 1s^22s^22p^6 3s^23p^1      
      Ne: 1s^22s^22p^6 Bolded is the core. The rest is the outer. Therefore the core notation is: [Ne] 3s^23p^1


Exceptions!
Instead of: Cr --> [Ar] 4s^23d^4 (One electron short of half-filled subshell)
Cu--> [Ar] 4s^23d^9 (One electron short of a filled subshell)
In actuality:
Cr--> [Ar] 4s^13d^5 (Now both subshells are exactly half-filled)
Cu--> [Ar] 4s^13d^10 (4s^1 is exactly half-filled and 3d^10 is filled)
These 2 atoms indicate: A filled or exactly half-filled d-subshell is especially stable.


Link to awesome quiz to test your genius knowledge. :D

HAHAHA. SO FUNNY.

Modern Atoms

Modern atoms consist os electrons, protons and neutrons.

Remember the characteristics of each atom?
Proton ,  , mass = 1, charge = +1, located in the nucleus
Neutron,  ,mass is >1, charge = 0, located in the nucleus
Electron,  , does no = to 0, charge = -1, located around the nucleus

The # of protons = # of electrons

Atomic number (Z): number of protons found in a nucleus
  - the atomic number  = the number of protons = the number of electrons

Ions: atoms able to gain or lose electrons
  - # of protons - # of electrons = the charge

Electrically charged atoms:
 - negative charged ion are electrons added to a neutral atom
  - positive charged ion are electrons removed from a neutral atom

Mass number: the total number of protons and neutrons
  - atomic mass = # of protons + # of neutrons
  - number of neutrons = mass # - atomic #
  - mass # = # of protons + # of neutrons

Atomic mass: the average of an isotope

Isotopes: same number of protons and electrons but different number of neutrons

Natural Mixtures of Isotopes:
We have an element with 4 naturally occuring isotopes. Here are their atomic masses and percent abundance: a = 46 (25%), b = 47 (50%), c = 48 (15%), and d = 49 (10%). Find the atomic mass!

46 x 25% = 11.5

47 x 50% = 23.5

48 x 15% = 7.2

49 x 10% = 4.9

11.5 + 23.5 + 7.2 + 4.9 = 47.1 atomic mass units

You try some with the link below!
http://www.chem4kids.com/activities.html

Atomic Theory.

Aristotle: -believed that atoms were made from the 4 elements; earth, air, fire, and water Democritus: -in 300B.C, he believed that atoms were indivisible particles
Lavoisier (late 1700's) -stated earliest version of both the Law of Conservation and the Law of definite proportions
Proust (1799) - Proust believed that if a compound were to be broken down, it would still contain the same ratios as in the compound
Dalton (early 1800's) - believed that atoms are solid
-all atoms of given element are identical
-atoms of one element can combine with another to form chemical compounds
J.J. Thompson (1850) - proved existance of electrons
Rutherford (1905) - showed atoms had dense centres and electrons outside of them
-suggested atoms are mostly empty space
Niels Bohr (1885-1962) - studied gaseous samples of atoms
-proposed that electrons surrounds the nucleus in shells
The modern atom - an atom is the smallest particle of an element
-all atoms are made of three kinds of subatomic particles
         -electrons
         -protons
         -neutrons

Percent Yield and Percent Purity!

Percent Yield=   actual mass produced (grams)    x 100

           theoretical mass produced (grams)

The percent yield is found by dividing the actual mass of product formed by the mass of the product expected (this is found with stoichiometry).

Because not all the products will be used, the actual mass of product formed is always less than what was first expected.

E.g. If 12.5g of copper are reacted with an excess of chlorine, then 25.4g of copper(II)chloride are obtained. Calculate the percent yield. 

First, balance the equation:

1Cu + 1Cl2 > 1CuCl2

We can use the 12.5g of copper to calculate the theoretical mass produced. 

12.5g Cu x 1 mol Cu/63.5g x 1mol CuCl2/1 mol Cu x 134.5g/1 mol CuCl2 = 26.48g

So we know that IN REALITY, 25.4g of CuCl2 were produced, this is our actual mass produced.

Percent Yield=   25.4    x 100

                 26.5

So our percent yield is 95.9%. 

 

Percent Purity=   Mass of pure substance    x 100

                     Mass of impure sample

Only the pure part of the sample will react. So, before we can calculate how much product will form, we first need to know how much of the reactant is pure and available to react.

If a 5.67g sample of metal ore contains 4.65g of Nickel, what is the percent purity?

Percent Purity=   4.65    x 100

                     5.67

So our percent yield is 82.0%. 

GOOD DAY!