# The Naked Scientists Forum

#### harryneild

• Full Member
• Posts: 88
##### Quick question about the atom
« on: 06/01/2006 16:37:11 »
In my class today my teacher told me that the electrons orbiting the nucleus of an atom were held in orbit by two forces. Magnetic and mainly gravitational. I thought that this was questionable because ive heard of the analogy that the nucleus of an atom is relatively the size of a fly if the electrons orbits were the size of st. pauls cathedral. That is relatively large distance and the masses involved, especially the electron's tiny mass, are small. Because the force of gravity depends on the mass the distance between both of the particle i thought that this force would be negligible. Would appreciate any help.
Thankyou :)

#### rosy

• Neilep Level Member
• Posts: 1018
• Chemistry
##### Re: Quick question about the atom
« Reply #1 on: 06/01/2006 17:13:46 »
Interesting... are you sure you heard your teacher right? What level is this class at? Is he/she supposed to be a physics teacher?

The main force holding electrons in their atomic orbits is the attraction of opposite charges, which doesn't seem to be mentioned at all.

For a hydrogen atom:
Gravitational force
G=6.6742 x 10^-11 M^3 kg^-1 s^-2
m(proton)=1.67 x 10^-27 C
m(electron)=9.11 x 10^-31 C
F(gravitational)=G*m(proton)*m(electron)/r^2
Coulomb's law
epsilon0=8.85 x 10^-12 C^2 N-1 m-2
e=1.60 x 10^-19 C
F(coulomb's)=1/(4*pi*epsilon0)*e^2/r^2

So, for a hydrogen atom (one electron, one proton)
F(coulomb)/F(gravitational)= 2.27 x 10^39

The effect of the gravitational force here is as near zero as makes no difference.

#### harryneild

• Full Member
• Posts: 88
##### Re: Quick question about the atom
« Reply #2 on: 06/01/2006 17:18:28 »
Lol thanks. Im at GSCE and my chemistry teacher's knowlegde is not so good i think. Thanks aloot for clearing that up for me and for quick reply.

#### simeonie

• Sr. Member
• Posts: 351
##### Re: Quick question about the atom
« Reply #3 on: 09/01/2006 21:01:29 »
A lot of complicated equasiony thingys there! Yeah I am at GCSE and I learnt about that. I did learn though that the opposite charges are what holds the electrons in there shells. Coz electrons hav -ve charge right? and Protons have +ve so I presume that why they stay in.
« Last Edit: 27/06/2009 15:12:54 by BenV »

#### rosy

• Neilep Level Member
• Posts: 1018
• Chemistry
##### Re: Quick question about the atom
« Reply #4 on: 10/01/2006 12:15:42 »
Yes... the positive charge of the nucleus holds the negatively charged electrons in their orbits (um, it's all a bit more complicated than that in that the electrons are wave- as well as particle- like, and don't really have orbits in the sense in which planets do, just regions where they're likely to be found, but that's probably not something you want to worry about at the moment).
What holds the protons (all of them positively charged) together is another question entirely. I'm told it's called "the strong force" (yes, there is a weak force, but I've *no* idea what that does, ask a physicist).
If you really want to wind your teachers up, try asking them about that. Tho' if your teacher thinks electrons stay put due to gravity you might not want to trust their answer.

#### Soul Surfer

• Neilep Level Member
• Posts: 3345
• keep banging the rocks together
##### Re: Quick question about the atom
« Reply #5 on: 10/01/2006 14:03:45 »
Please check carefully and politely with your teacher if you heard right when you thought that you had been told that the main force holding an atom together was gravitiational.  If he or she thinks that it IS gravity holding atoms together please refer them to this web page and we will sort them out.  This is a very bad error in the understanding of basic physics and it must not be allowed to continue.

The strong force is a bit like having the particles connected by elastic bands they are quite floppy when the particles are close together and get stiff when they get far apart and when they break the ping back and there are new particles at the broken ends of the elastic bands.  That's why you never find quarks on their own.

The weak force is more like induced electromagnetism except that it also works for neutral particles.  It involves very heavy "photons" and only has a very short range.

Learn, create, test and tell
evolution rules in all things
God says so!

#### harryneild

• Full Member
• Posts: 88
##### Re: Quick question about the atom
« Reply #6 on: 10/01/2006 16:01:05 »
yes i have sorted it out and the teacher did actually believe that it was gravity. I think that she may have gotten mixed up with the analogy of the planets that is often used. But i suppose everyone makes mistakes :)

About the strong force, is that the force that holds quarks together to make the particles such as proton neutron etc.

If weak force is for neutral particles what stops the protons escaping and being pulled towards the elctron shells
« Last Edit: 10/01/2006 16:05:14 by harryneild »

#### wim

• Full Member
• Posts: 66
##### Re: Quick question about the atom
« Reply #7 on: 10/01/2006 21:58:53 »
finally a question i like
atoms are kept together by four forces
gravitation, electromagnetism, strong and weak force
electromagnetism : the elektrons are kept in orbit bij the positive charge of the nucleus
gravitation : most weak force of the four , gravitation occurs everywhere butt it isn't really important for keeping the atom together, kick that teachers ass
strong force: keeps the protons(positively charged) together and forms the nucleus
weak force: Important because they are responsible for stabilizing particles through the process of radioactive decay, in which a neutron(no charge) in the nucleus changes into a proton and an electron.

#### The Naked Scientists Forum

##### Re: Quick question about the atom
« Reply #7 on: 10/01/2006 21:58:53 »