The Periodic Table

This chart is known as the Periodic Table because elements had similar properties at regular intervals

In the Periodic Table, each element is identified by a symbol which relates to its name in a particular language 

Above the symbol is the atomic number of the element and below is the mass number of the element

When protons, neutrons and electrons were discovered, the elements were arranged in order of atomic number instead of relative atomic mass as Newlands and Mendeleev both decided to do. 
This principle was proposed by Henry Moseley, a British scientist, in 1913. 
This eliminated Mendeleev's problem of elements not being placed in the correct row (according to their properties) 
For example, Tellurium should have been placed after Iodine, as Tellurium has a higher relative atomic mass than Iodine. However, in order for Iodine to be placed in the same group as elements with similar properties (such as bromine, chlorine and fluorine), it had to be placed after Tellurium. 
By organising the elements in order of their atomic number, Iodine could be placed in the correct group without breaking the rules (as Iodine has a higher atomic number than Tellurium) 

In the Periodic Table, the rows are referred to as periods
                                    the columns are referred to as groups

All of the elements in a particular period have the same number of energy shells (atomic orbitals)
For example, all of the elements in Period 2 have 2 energy shells

All of the elements in a particular group have the same number of electrons in the outermost energy shell
For example, all of the elements in Group 6 have 6 electrons in their outermost shell
These outer electrons are known as valence electrons because these are the ones that are used to form chemical bonds

In the Periodic Table, there are three types of elements - Metals, Non-Metals and Metalloids
However, Metalloids are commonly classed as Non-Metals

PICTURE

The Periodic Table shows the reactivity trend of the elements:
Metals
Period
Reactivity decreases from left to right (there are less electrons that need to be lost to obtain a full outer shell)
Group
Reactivity increases from the top to the bottom (there are more energy shells so the electrons are further away from the nucleus which results in weaker bonds which causes the atom to be more reactive)
Non-Metals
Period 
Reactivity increases from left to right (there are more electrons that need to be lost to obtain a full outer shell)
Group
Reactivity decreases from the top to the bottom (there are more energy shells so the shielding effect [decrease in attraction between an electron and a nucleus which prevents the atom from gaining an electron] is greater which causes the atom to be less reactive)

Elements in Group 1 are known as Alkali Metals
Elements in Group 2 are known as Alkali Earth Metals
Elements in the block between Group 2 and Group 3 are Transition Metals
Elements in Group 7 are known as Halogens
Elements in Group 8 are known as Noble Gases

N.B - 1/08/2012
I am currently editing a copy of the Periodic Table to show the different sections (metals & non-metals and groups). This should be completed later today

The History of the Periodic Table - Mendeleev's Periodic Table

In 1869, Dmitri Mendeleev improved on Newlands' idea. Like Newlands, he too organised the elements known at the time in order of relative atomic mass. He also realised that the physical and chemical properties of every eighth element were similar, so he arranged them so that elements with similar properties were placed in the same column. This method is the same as Newlands.


However, Mendeleev noticed that by organising the elements this way, there would be gaps in the rows (now known as periods) as there wasn't an element that hadn't been discovered that had the required atomic mass. To overcome this problem, he left gaps in the table where he believed that a particular undiscovered element should be placed. From this, he could predict the mass of the missing elements and he could also predict their properties.


One problem with Mendeleev's periodic table was that he arranged the elements in order of atomic mass. This meant that some of the elements weren't in placed in the same group as other elements with the same properties. However, he overcame this problem by placing them in the correct rows, even though this meant that the pattern of ascending atomic mass was broken. 


Due to the fact that Mendeleev correctly predicted the properties of undiscovered elements, other chemists were convinced by his ideas and therefore decided to use his table. This is why Mendeleev is was credited for the invention of the Periodic Table. 

The History of the Periodic Table - Law of Octaves

In 1864, a British scientist called John Newlands came up with the idea of arranging elements in order of their atomic mass. This was known as the Law of Octaves. He did this by arranging them into columns in order of relative atomic mass (this is the mass of the protons + the mass of the neutrons).





Newlands placed the elements into eight columns, as he discovered that every eighth element had similar properties, so in theory, the elements in a particular row should all have the same properties. 


However, due to the fact that not all of the elements are in the table, this wasn't entirely accurate as gaps weren't left for the missing elements, so some elements were placed with others that had completely different properties. For example, Iron (Fe) has been placed in the same row as two non-metals, Oxygen (O) and Sulphur (S) which have completely different properties to metals. For this reason, other chemists didn't use it.


Also, another way in which this was incorrect is that some elements are shown to have the same atomic number. This is incorrect due to the fact that no two elements have the same relative atomic mass, as this is a unique number that determines what element an atom is and it is impossible for one atom to be two different elements.

Chemical Symbols

Each element has a unique chemical symbol

The chemical symbol relates to its name in a particular language (not necessarily English)

The symbol usually consists of one or two letters, apart from newly discovered elements (which have 3 letters)

The first letter of a chemical symbol is always a capital - any letters that follow are lower case

First 20 elements (needed at GCSE level):

Hydrogen - H

Helium - He

Lithium - Li

Beryllium - Be

Boron - B

Carbon - C

Nitrogen - N

Oxygen - O

Fluorine - F

Neon - Ne

Sodium - Na

Magnesium - Mg

Aluminium - Al

Silicon - Si

Phosphorus - P

Sulphur/Sulfur - S

Chlorine - Cl

Argon - Ar

Potassium - K

Calcium - Ca

On the Periodic Table, each element is identified by its chemical symbol

Chemical symbols are used in symbol equations to show which elements and compounds are reacting

Before the Periodic Table was created, certain elements already had symbols that were devised as part of alchemy:

Aluminium       

Antimony        

Arsenic           

Bismuth           

Boron             

Cobalt            

Copper           

Gold                  

Iron                

Lead                     

Magnesium    

Mercury              

Nickel             

Phosphorus       

Platinum        

Potassium      

Sulphur/Sulfur   

Silver                    

Tin                      

Zinc                

N.B - 20/07/2012
There is currently a problem with the photo links - this will be resolved a.s.a.p
Sorry about this!

Electron Configuration

Electrons are found in shells orbiting the nucleus


The number of electrons found in the atom of an element is shown by its atomic number


Electron Configuration shows us how electrons are arranged in an atom


At GCSE level:
The first shell can contain 2 electrons
The second shell can contain 8 electrons
The third shell can contain 8 electrons
The fourth shell can contain 2 electrons


Here is the electron configuration of the first 20 elements:

Atoms with a full outer shell are stable and unreactive


When an atom reacts, it gains/loses (ionic bonding) or shares (covalent bonding) electrons to achieve a full outer shell


During a chemical reaction, even though the number of electrons changes, the elements remain the same, as it isn't the number of electrons that determines the element - it's the number of protons that does this

Atoms

An atom contains a nucleus in the centre


This nucleus consists of protons and neutrons


Electrons surround the nucleus in specific shells (aka. energy levels)


Protons, neutrons and electrons are all known as sub-atomic particles


Each subatomic particle has a different charge and mass


Particle      Charge       Mass     
Proton           +1              1
Neutron          0               1
Electron         -1       Negligible


To remember that the proton is positive - Positive Proton
To remember that the neutron is neutral - Neutral Neutron


A way to remember the two sub-atomic particles that have a mass is by remembering that the mass of an atom is contained within the nucleus, so this must be the proton and the neutron


The atomic number of an element shows the number of protons in the nucleus
In an element, this is equal to the number of electrons surrounding the nucleus of the atom
Because the two particles with a charge are equal, the atom is neutral as the positive protons and the negative electrons cancel out each others charge


The mass number of an element shows the number of protons and neutrons in the nucleus


To calculate the number of neutrons in an atom, subtract the mass number from the atomic number

Substances

An atom is neutral particle which is the smallest unit of an element that has all the characteristics of that element


An element is a substance that consists of only one type of atom, so all elements in the Periodic Table are made up of atoms which are unique to that element


A compound is a mixture of elements that have chemically reacted with each other to become bonded to each other


A mixture contains two or more substances which have not reacted with each other