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Working out Specific Charge!

How do I calculate the specific charge of say oxygen 16 nucleons 8 protons
when I'm not sure whether I have the masses and charges or Do I just multiply the charge of one proton by the charge ona singular one ? Thanks !

Reply 1

Jooeee

2

You've got 8 protons, so multiply the charge on a proton by 8 and divide by the mass of the oxygen.

Reply 2

Hamrg

OP

1

divide by 12? thank you

Reply 3

MichaelRM1991

don't you need to know how many electrons? or am i thinking of something different?

Reply 4

Hamrg

OP

1

yeah it's the charge over mass thing, except I don't know either... :s-smilie:

Reply 5

Freshtah

Im also quite stuck

Im not sure whether to multiply the charge by 8 or...whether you are meant to work out how many electrons it should gain for example oxygen is meant to gain 2 electrons so you times 2 by the charge.

arghh its confusing

Reply 6

spread_logic_not_hate

8

Freshtah

Im also quite stuck

Im not sure whether to multiply the charge by 8 or...whether you are meant to work out how many electrons it should gain for example oxygen is meant to gain 2 electrons so you times 2 by the charge.

arghh its confusing

That depends what you're asked to find the specific charge of. Presumably it is the oxygen nucleus, so the electrons gained or lost (via bonding, ionisation etc) are irrelevant as they are not part of the nucleus... In this case Unbounded has posted all the info you'll need!

If you need to find the specific charge of the overall oxygen ion, you need to use:

specific charge

= \dfrac{e(n_p - n_e)}{n_pm_p+n_em_e+n_nm_n}

where n= number of, m = mass of and the subscripts refer to electron, proton and neutron

To save time, remember that an atom is always overall electrically neutral and as such always has a specific charge of zero. (i.e.

n_p = n_e

)

Reply 7

Freshtah

spread_logic_not_hate

That depends what you're asked to find the specific charge of. Presumably it is the oxygen nucleus, so the electrons gained or lost (via bonding, ionisation etc) are irrelevant as they are not part of the nucleus... In this case Unbounded has posted all the info you'll need!

If you need to find the specific charge of the overall oxygen ion, you need to use:

specific charge

= \dfrac{e(n_p - n_e)}{n_pm_p+n_em_e+n_nm_n}

where n= number of, m = mass of and the subscripts refer to electron, proton and neutron

To save time, remember that an atom is always overall electrically neutral and as such always has a specific charge of zero. (i.e.

n_p = n_e

)

Thank you i get it now!

Reply 8

humma.andleeb

When you're working out the specific charge of a particle, is the mass/charge of an electron ignored? i keep doing it with the electon and getting it wrong and doing it without and getting it right? but i'm not sure why the mass or charge of an electron is ignored?

Reply 9

username785532

Specific Charge is just as simple as the charge on whatever it is you have divided by the total mass:

Specific Charge = Charge/Mass

it is usually used on measuring the specific charge of a nucleus of an atom:

What is the specific charge of a nucleus consisting of 10 protons and 11 neutrons?

In this it would simply be (10 x e)+(10 x 0) divided by (20 x Mp)

where e is the charge of an electron (1.60x10-19) as the charge on a proton and electron are the same just an electron is negative

and Mp is the mass of a proton, since the mass of a proton and neutron are the same (at least for AS level, there is only a difference after the 3rd significant figure) - you are given the mass of a proton in the data sheet (1.67x10-27)

In your case, you would do:

Specific Charge = (8 x e) / (16 x Mp)
= (8 x 1.60x10-19) / (16 x 1.67x10-27)
= 47904191.62
= 47.9 x10_6 (3SF)

where 10_6 is 10 to the power of 6 - if your not familiar with standard form it is worth learning it as everything in physics is given like this!

Hope this helps everyone who is unsure about this :smile:

Reply 10

rumtumtugger

Hi - haven't used a scientific calculator for years - how would I plug in the above calculation? Thanks!

Reply 11

IRIUIDIY

It's charge over mass.
So the charge of 8 protons (8x 1.60x10^-19)
Divided by the mass of the atom. So 8 protons and 8 neutrons. Means 16x 11.67x10^-27

Reply 12

HikariUchiha

Could anyone help me? What if it's an isotope of oxygen with (15 mass,) 8 protons 7 neutrons and 6 electrons ? Then how do I do it?
Thanks

Reply 13

HikariUchiha

Yh but what if its not the nucleus and the specific charge of the whole ion? Then u hv to include the electrons - especially if the whole thing has a ie -2 charge

Reply 14

Stonebridge

13

Original post by HikariUchiha

Yh but what if its not the nucleus and the specific charge of the whole ion? Then u hv to include the electrons - especially if the whole thing has a ie -2 charge

Then divide the net (total) charge on the ion by the mass of the ion.

The definition of specific charge tells you what to do in every case.
Definition: Total charge divided by total mass.
What is the problem you have with this definition?

(edited 10 years ago)

Reply 15

Protoxylic

14

Original post by AlphaNick

DONT NEED TO CONSOLIDATE ELECTRONS SINCE ITS JUST THE NUCLEUS.

The answer will be (proton number x 1.6x10^-19) / (nucleon number x 1.67x10^-27)

OP said "oxygen", not an oxygen nucleus, I think this is where the confusion is. Either way, Q of e-s cancel Q of Ps.

(edited 10 years ago)

Reply 16

Oblogog

4

Specific Charge = Charge / Mass
So to find the specific charge you need to know the overall charge and overall mass something has.
You have a nucleus with X nucleons and Y protons.
For charge: Y * charge of a proton (on a data sheet)
For mass: X * mass of a nucleon (on a data sheet)

Because the proton is the only particle giving the nucleus a charge and the nucleons (protons and neutrons) are the only particles giving the nucleus mass. Do the calculation and you'll know the charge per unit mass (specific charge) for your nucleus

Be careful not to say you are finding the specific charge of the atom because if you think about it that would give 0.