2.1.1 (b) Sub-atomic particles & Mass/Atomic Numbers
Syllabus
Learners should be able to demonstrate and apply their knowledge and understanding of:
(b) atomic structure in terms of the numbers of protons, neutrons and electrons for atoms and ions, given the atomic number, mass number and any ionic charge
What does this mean?
There is little to learn here that would not have been covered in any GCSE course.
You should recall the properties of the 3 basic subatomic particles.
There are many other sub-atomic particles but those are in the realm of Physics - and therefore of no interest to anyone.
For the purposes of Chemistry, the relative mass of an electron is generally treated as zero.
With any luck you'll recall the location of the Atomic and Mass numbers.
If not there is a key on the Periodic Table in the exam but if you need to refer to it perhaps you should consider swapping to Media Studies while there's still time.
Physicists refer to the Atomic number as the Proton number to remind them that this is what it counts.
But since atoms are neutral - any atom with 9 protons in its nucleus would also have to have 9 electrons in its shells.
Though this isn't true for ions - which have charges.
Physicists refer to the Mass number as the Nucleon number because it makes them feel clever.
This is because the Mass number counts the particles which have significant masses (protons and neutrons) and these are found in the nucleus (hence nucleon).
So, the first isotope of Hydrogen, Protium, has 1 proton because its Atomic Number is 1.
It has 1 electron because it is neutral and the negative charge of 1 electron cancels the positive charge of the proton.
It has 1 neutron because the Mass Number says there are 2 nucleons - and one of them is a proton so 2-1 = 1 neutron.
Deuterium and Tritium also have 1 electron and 1 proton each because they still have the Atomic Number 1
It's just that, unlike Protium, they have neutrons ( 1 and 2 of them respectively)
This isotope of Colbalt must have 27 protons (because that is its Atomic Number)
It must also have 27 electrons (because it is a neutral atom)
It must have 59 - 27 = 32 neutrons (because that's how the system works!)
On Earth, Chlorine is made up almost entirely of two isotopes.
Both must have the same numbers of protons (& hence electrons) or they'd be different elements.
But clearly, 37Cl must have 2 more neutrons (20) than 35Cl (18)
What about ions?
This is an ion - it has a charge.
It's Atomic Number still tells you that it has 11 protons.
The difference in Atomic & Mass Nos still tells you it has 12 neutrons.
But if it also had 11 electrons it would be a neutral atom.
It must have more protons (+) than electrons (-) because it's positive.
It must have only one fewer electrons because it is only 1+
So it must have 10 electrons
Chlorine has Atomic Number 17
So, Chloride (Cl-) has 17 protons (+) and 18 electrons (-)
Oxygen has Atomic Number 8
So, Oxide (O2-) has 8 protons (+) and 10 electrons (-)
Nitrogen has Atomic Number 7
So, Nitride (N3-) has 7 protons (+) and 10 electrons (-)
Sodium's Atomic No. = 11
Sodium ions (Na+) have:
11 protons & 10 electrons
Beryllium's Atomic No. = 4
Beryllyium ions (Be2+) have:
4 protons & 2 electrons
Aluminium's Atomic No. = 13
Aluminium ions (Al3+) have:
13 protons & 10 electrons
Videos
PowerPoint
Back to 2.1.1?
Click here