Atomic Number & Mass Number | Properties of Matter | Chemistry | FuseSchool

Atomic Number & Mass Number | Properties of Matter | Chemistry | FuseSchool

How do we tell elements apart from each other? Find out in this video from the Properties of Matter chapter of FuseSchool GCSE Chemistry.

When you look at the periodic table you will see that each element has its own box, and within that box, you will find two numbers. The atomic number, or proton number, and the mass number, but what do these numbers mean?

The atomic number has the symbol 'z', this number tells you how many protons are in one atom of an element. The number is always the same for all atoms of a particular element.

Atoms of different elements have different atomic numbers, meaning they have different numbers of protons. For example, an atom of Hydrogen has an atomic number of 1 because it has 1 proton, but an atom of Oxygen has and atomic number of 8 because it has 8 protons.

The next number we look at is the mass number. The mass number has the symbol A.

The mass number tells you how many protons and neutrons are in one atom of an element. We need to remember that Protons and Neutrons each have a relative mass of 1 and that Electrons are so small, that their mass does not need to be considered in the mass number of an atom.

So if we know the mass number of an element, and we know the atomic number, we can calculate the number of Neutrons in an atom of a particular element. So the Mass Number = The Atomic Number + the Number of Neutrons. The Atomic Number is just the number of Protons and Atoms, therefore, the Mass Number = protons + neutrons.

So if we take oxygen: oxygen has a mass number of 16 and 8 Protons, how many neutrons does it have?

Remember, Mass Number = protons + neutrons We can rearrange this to show that Neutrons = Mass Number - Atomic Number. Neutrons = 16 - 8 = 8 Oxygen therefore has 8 neutrons.

Let take another example. Lithium has a mass number of 7 and an atomic mass of 3, how many neutrons does it have?

Mass Number = protons + neutrons; we can rearrange this to show that Neutrons = Mass Number - Atomic Number. Neutrons = 7 - 3, = 4 Lithium therefore has 4 neutrons.

So the atomic number is the number of protons in an atom and the mass number is the number of protons and neutrons in an atom.

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[emranger]

this was probably the most helpful video I have watched, thanks a lot. Keep up the good work!!

[pepperskulll]

Why cant my chemistry teacher explain it like this?? geesh.... Thnk you!

[ChampionBlk]

omg i love the voice, so angelic <3

[coras_love]

I love how the elements have little faces to show if their positive or negative or no charge lols

[fuseschool]

Thank you for your message on the atomic number placement.
Position varies on all periodic tables. The point is that we need to remember is that Z is the number of protons and the A number is the mass number. Usually there a key or a legend to point it out on any periodic table given in an exam. There are so many periodic tables, but when you write down an element outside of the periodic table you would write it with the mass at the top the protons at the bottom so
4
He
2

[hadiabashir]

For all those being confused over mass number being on top and atomic number being on bottom in this video, you can always remember that the larger number of the atom is always the mass number.

[pankajkishore]

Thank you so much... Through this video now I am able to understand the concept

[PedroBastozz]

2012?! that's nice quality for 2012.

[hanquiyi]

wait, I don't want to sound rude, but shouldn't the atomic number be on top?
Thanks from Korea

[sanikajagtap]

Thanks a It really helped me in understanding the concept!!!

[nicolavincent]

We found the recording distracting which makes it difficult to concentrate on the information being delivered.

[jangirrahul]

Wow... its really helpful... Thnx mam.. I m from india..

[cuz_amj]

thx for the help u help me so much <3

[daisyh]

Very helpful! But why is her voice so echoey? It gives me the creeps...

[sirmeh]

Thanks for explaining i heard of atomic number but didnt know but thanks you now i do

[missannie]

I literally cannot figure any of this out I am so confused how are y'all understanding this I'm on the verge of tears I am this close to dropping out

[reema]

thank you so so much this is so so helpful.

[careeraimers]

I think atomic number should be on top

[giladhazi]

Thank you so much, this helped a lot.😃

[rameenjamshed]

thanku for such an easy video... really helpfull