relative atomic mass mass of atoms is incredibly small! so we have to use relative atomic mass. the...
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Relative Atomic MassMass of atoms is incredibly small! So we have
to use relative atomic mass.The symbol for relative atomic mass is ArCarbon- 12 atom contains 6 protons, 6
neutrons and 6 elections. Its relative atomic mass is defined as exactly 12.
Every other atom is compared to this. E.g Helium is one 3rd of a carbon atom. So its
relative atomic mass is 4.
Calculate the relative atomic masses of an element using masses and abundance (A/A*)
The relative atomic mass of bromine is 80
This is because in any sample of bromine, there are just about
equal numbers of its two isotopes 79Br and 81Br.
So the ‘average’ bromine atom has a relative mass of 80.
What about Chlorine and Copper?
Chlorine has two isotopes
Copper has two main isotopes
Chlorine35 75%37 25%
Copper63 69%65 31%
Finding the RAM of Chlorine
If you assume you have 100 atoms then the average is easier to find.
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Finding the RAM of ChlorineYou have
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Finding the RAM of ChlorineThat’s a mass
of 75 x 35
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25 x 37 To give the mass of the 100 atoms
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Using Weighted AveragesSo the
average mass of a chlorine atom isn’t (35+37)/2
Its (35 x 75) + (37 x
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From Weighted Averages to RAMWeighted = (mass x number) + (mass x
number) ave total number
So RAM = (35 x 75) + (37 x 25) 100
RAM = (2625 + 925)/100
RAM = 35.5 amu
Weighted AveragesUse RAM = (mass no x %) + (mass no x %) 100
To work out the RAM of Copper
RAM of copper RAM = (mass no x %) + (mass no x %) 100
So RAM = (63 x 69) + (65 x 31) 100
RAM = (4347 + 2015)/100
RAM = 63.6 amu
Here are various Isotopes- Attempt to calculate the number of electrons neutrons and protons for each.
C – 12C- 14
He – 4He- 5
Li – 7Li- 6
IsotopesIsotopes are atoms of the same element
with different numbers of neutrons.
That is;Same Atomic NumberSame no. of protons
Different Mass NumberDifferent no. of neutrons
Define an isotope in your own words before your
see my definition
http://www.youtube.com/watch?v=EboWeWmh5Pg
Watch the clip and answer the questions!
Isotopes of hydrogenIsotope Symbol P N E
Protium 1 0 1Used as fuel, for
hardening margarine.
Deuterium 1 1 1
Used in heavy or deuterated
water, solvent
Tritium 1 2 1Radioactive, Used in H-
bombs, glow in the dark paints
Isotopes of hydrogenProtium Deuterium Tritium
1 proton, 0 neutron, 1 electron
1 proton, 1 neutron, 1 electron
1 proton, 2 neutron, 1 electron
IsotopesElement Symb
olMass No
Atomic No Protons Neutron
sElectron
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Chlorine-35 Cl 35 17
Chlorine-37 Cl 37 17
Copper-63 Cu 63 29
Copper-65 Cu 65 29
Bromine-79 Br 79 35
Bromine-81 Br 81 35
Objective check -