Relative formula mass
Finding the relative formula mass is simple. All you have to do is add up the masses of each atom in the compound or molecule.
E.g. Carbon dioxide.
CO2
Carbon has a molecular mass of 12 and Oxygen has a molecular mass of 16.
There are 2 oxygens so we do (16*2)+12=44
Another example is water.
H2O The sum for this would be (1*2)+16=18
Empirical Formula
Empirical formula tells us the ratio of each element within a compound. To work it out we must first find the number of moles, we do this by dividing the mass (or percentage) of each element and dividing but it molecular mass.
E.g. Carbon Dioxide.
In a compound there contains 12g of carbon and 32g of oxygen, work out the formula.
First of all we divide the mass by the molecular mass:
12g/12=1mol 32g/16=2mol we divide both the numbers by the smallest, which is 1, to find the ratio. In this case the ratio is 1:2 so the compound is CO2
Percentage yield
Percentage yield tells us what percentage of product was formed compared to what we should have received from the reaction. We don't always get 100% due to impure compounds and human errors.
%yield=(Actual yield/ theoretical yield)*100
E.g. Johnny thermally decomposes 60g of CaCO3 which give s him 15g of CaO, find the percentage yield.
To do this we first need to work out how many grams of CaO should have been produced.
Write down the equation to help:
CaCO3->CaO+CO2
We need to find out the number of moles in CaCO3 60/100=0.6moles
Because it's a 1:1 ratio CaO will also contain 0.6moles. We then find the mass by multiplying moles by molecular mass. 0.6* 56=33.6g (our theoretical amount)
We then do (15/33.6)*100=44.6%
That's the final answer.
Tuesday, 5 November 2013
The Structure of The Atom
Never trust an atom, they make up everything! The structure of an atom is very easy to understand once it has been explained.
Atoms are made of 3 sub-atomic particles which are; protons and neutrons (in the nucleus) and electrons in shells orbiting it.
Protons and neutrons give an atom its mass. Electrons have a minute mass (1/2000th) so we say it has no mass.
Protons carry a +1 charge and electrons carry a -1 charge so overall an atom has no charge. It can gain a charge from losing or gaining an electron, this creates an ion.
'A neutron walks into a bar; he asks the bartender, "How much for a beer?" The bartender looks at him, and says "For you, no charge."'
At GCSE we learn that in the 1st shell there can be up to 2 electrons, it then fills the 2nd shell and then the 3rd which can contain up to 8 each.
This is a Lithium atom. As you can see there are 3 protons and neutrons in the nucleus and 3 electrons orbiting it. Lithium on the periodic table looks like this:
The top number is called the atomic number, it tells us how many protons and electrons are in the atom. The bottom number is known as the mass number, it tells us the mass, this is the number of protons and neutrons.
Orbitals
At alevel we learn a more detailed explanation about the atom and its shells, these shells are now called energy levels.
On each energy level there are subshells. Within these subshells there are orbitals. Each orbital can contain 2 electrons.
S subshell; 1 orbital
P subshell: 3 orbitals
D subshell: 5 orbitals
The 1st energy level contains one subshell, this is an s-subshell. Within this subshell there is only one orbital, this one orbital can contain up to 2 electrons, thus the first energy level contains up to 2 electrons.
The 2nd energy level contains an s and a p subshell. The p subshell has 3 orbitals which can contain 2 electrons each. This 6 plus the 2 in the s subshell equals 8.
The 3rd energy level contains an s, p and d subshell. Within the d subshell there are 5 orbitals. The total number of electrons is 18.
S subshells are spherical and P subshells are like dumbbells:
Never trust an atom, they make up everything! The structure of an atom is very easy to understand once it has been explained.
Atoms are made of 3 sub-atomic particles which are; protons and neutrons (in the nucleus) and electrons in shells orbiting it.
Protons and neutrons give an atom its mass. Electrons have a minute mass (1/2000th) so we say it has no mass.
Protons carry a +1 charge and electrons carry a -1 charge so overall an atom has no charge. It can gain a charge from losing or gaining an electron, this creates an ion.
'A neutron walks into a bar; he asks the bartender, "How much for a beer?" The bartender looks at him, and says "For you, no charge."'
At GCSE we learn that in the 1st shell there can be up to 2 electrons, it then fills the 2nd shell and then the 3rd which can contain up to 8 each.
The top number is called the atomic number, it tells us how many protons and electrons are in the atom. The bottom number is known as the mass number, it tells us the mass, this is the number of protons and neutrons.
Orbitals
At alevel we learn a more detailed explanation about the atom and its shells, these shells are now called energy levels.
On each energy level there are subshells. Within these subshells there are orbitals. Each orbital can contain 2 electrons.
S subshell; 1 orbital
P subshell: 3 orbitals
D subshell: 5 orbitals
The 1st energy level contains one subshell, this is an s-subshell. Within this subshell there is only one orbital, this one orbital can contain up to 2 electrons, thus the first energy level contains up to 2 electrons.
The 2nd energy level contains an s and a p subshell. The p subshell has 3 orbitals which can contain 2 electrons each. This 6 plus the 2 in the s subshell equals 8.
The 3rd energy level contains an s, p and d subshell. Within the d subshell there are 5 orbitals. The total number of electrons is 18.
S subshells are spherical and P subshells are like dumbbells:
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