# Homework Help: Neutral atoms

1. Jun 29, 2006

### boris16

hiya

1)

2)

3)
thank you

Last edited: Jun 29, 2006
2. Jun 29, 2006

### DaveC426913

1) and 2) : Neutral doesn't mean "without charge", it means "without net charge".

3) : "Since hydrogen also contains one neutron..." This is not true; you're describing http://en.wikipedia.org/wiki/Deuterium" [Broken], a less common isotope of hydrogen. 99.985% of hydrogen atoms have no neutron in their nucleus.

Last edited by a moderator: May 2, 2017
3. Jun 29, 2006

### boris16

I only vaguely understand what you are saying. I know about terms such as "net force" or "net electric force", but am not quite sure how to interpret "net charge"

Is that also true for atoms of other elements?

4. Jun 29, 2006

### Kurdt

Staff Emeritus
If you have something with a charge of +1 being orbited by a charge of -1 then the net charge in the system is +1 + (-1) = 0

All other elements' atomic nucleus contain neutrons.

5. Jun 29, 2006

### boris16

But how does that affect atom's surroundings (in terms of electric field this atom creates etc )? Net force can be explained using vectors...is that also true for net charge?

So an atom containing 6 protons has mass 12 u?

6. Jun 29, 2006

### 3trQN

The reason Hydrogen has a amu or u of 1 is that its the definition of u, all other elements are compared to the mass of H.

7. Jun 29, 2006

### 3trQN

No, that is ony true if it also has 6 neutrons, which is not allways the case.

Last edited: Jun 29, 2006
8. Jun 29, 2006

### Kurdt

Staff Emeritus
Atomic mass unit if I remember correctly is based on the mass of carbon twelve not hydrogen. The mass of 1u is an approximation. You are correct in saying that the atoms affect their surroundings but only very slightly. The elctron 'orbits' the atom and time averaged effect of the electric fields is zero.

9. Jun 29, 2006

### boris16

For the following to be true atom must have same amount of protons and electrons?

You mean because electron orbits the protons it changes its position with great speed in such a way, that while it does create EF1 in time T1 ( at time T1 electron is at position P1 ), it then changes position and in time T2 is at position P2 and creates another electric field EF2.
Forces created by EF2 and EF1 sum to zero ( almost ) and thus there is almost no EF present nearby this atom?

It would make sense, but since effect of gravity force is instant and way faster than speed of any electron, by the time electron is at position P2, electric field EF1 does no longer exist!

Last edited: Jun 29, 2006
10. Jun 29, 2006

### Kurdt

Staff Emeritus
I'm not sure what you're getting at with the gravity? Also gravity does not act instantaneously.

11. Jun 29, 2006

### boris16

uh, I meant the effect of electric force is instant. So by the time electron is at position P2, EF1 is long gone and thus EF2 and EF1 can't cancel eachother out. This is why I think the following can't be true:

12. Jun 29, 2006

### Kurdt

Staff Emeritus
I said time averaged which means over a period of time the average electric field is zero. Think about this.

13. Jun 30, 2006

### boris16

I only vaguely know what you mean by this. I'm guessing this isn't the same as calculating average speed or something similar?

Anyways, my reasoning is :

electron orbits nucleus extremely fast and such even though test charge near this atom might feel EF field when electron is at position P1, electron moves from position P1 to new position so fast that before electric forces ( created by electric field when electron is at position P1 ) manage to move this test charge, electron is already at such position that now new electric forces have opposite direction than they had when electron was at position P1, and since this is all happening so fast, the end result is that test charge doesn't get moved at all ... and thus it is as if there were no forces affecting this test charge? Right?!

14. Jun 30, 2006

### Kurdt

Staff Emeritus
Kind of right, its not true that a test charge would not feel any minute electric fields its that over a period of time the force from the field cancels. This field cancels due to the movement of electrons as you say.

15. Jun 30, 2006

### boris16

When electron is at position P!, it creates electric field EF1
When electron is at position P2 it creates EF2

But no matter how fast electron is when it is at position P2 there is only one electric field existing, which is EF2. EF1 and electric forces created by EF1 stoped existing the very moment electron moved away from P1. So I don't see how EF1 and EF2 could cancel eachother out, since the two electric fields don't exist simultaneously.

16. Jun 30, 2006

### Kurdt

Staff Emeritus
If you graph the field strength as a function of time and then integrate over a certain interval it will be zero much like a sine wave.

17. Jun 30, 2006

### boris16

That is too advance for my little brain. I prefer if things are explained in simpler terms. In short, answers need to be dumbed down

18. Jun 30, 2006

### Kurdt

Staff Emeritus
Sorry but I've run out of ideas for explaining it any other way :|

19. Jun 30, 2006

### DaveC426913

OK, for one thing, electrons do not orbit the nucleus. Throw away everything about orbits and T and V.

Let's go back to your basic atomic chemistry questions.

Hydrogen has several isotopes. By far the most common is 1H, which means one proton, no neutron. N?ext most common (15/1000ths of 1% of H atoms) is an isotopew commonly called deuterium, 2H (one proton, one neutron). There are traces of the isotope tritium 3H (one proton, two neutrons).

A neutral H atom will have one electron. An ionized H atom will be stipped of its electron and have a net negative charge -1.

Helium is a noble gas, meaning it very much likes to be electrically neutral (this gets into electron orbitals). It has 2 protons and almost always 2 neutrons and almost always 2 electrons.

Lithium's most common isotope is 6: 3P+3N, though there are other isotopes. It, like H, can be stripped of one of its e, leaving it -ive.

Some atoms, rather than losing electrons, like to gain extra electrons (again, orbitals). These atoms become +ively charged.