Electron energy?

[Gareth56]

If it's not too technical could someone explain why the closer an electron is to the nucleus of an atom, the less energy it has and the farther away from the nucleus, the more energy it has.

 

I've always understood that the closer an electron is to the nucleus the more energy is required to remove it.

[hermanntrude]

Your understanding is correct. The closer an electron is to the nucleus, the more energy it takes to remove it.

 

The fact that you have to ADD energy to the electron to get it into a higher energy orbital means that those at the lowest energy (closest to the nucleus) require MORE energy to be added.

[Gareth56]

I'm obliged for the confirmation. The website I read this on was clearly wrong then! I've also just checked the website also states that the mass of an Oxygen atom equates 16.0044 amu and 1amu ~ 1.6753 × 10^−24g (which I somewhat agree with) and this means that the mass of one oxygen atom measured in grams is 5.36 × 10^−23g!!

 

I get 2.6561 X 10^-23g so conclude the website means Oxygen molecule and not atom!

[Klaynos]

Their value for an oxygen atom looks about right.

 

16 neucleons, about 16 AMU....

[Gareth56]

Doesn't 16 amu equate to 16 x (1.6753 × 10^−27kg) = 2.68 x 10^-26kg?

[insane_alien]

yes, you used a false value for 1amu the first time round. you were out by a factor of a thousand

[Gareth56]

Sorry slightly confused now; is the website therefore correct when it says that the mass of one oxygen atom measured in grams is 5.36 × 10^−23g ?

[insane_alien]

no, that would be the wrong value for 1 amu. 1 oxygen atom is a thousandth of that value.

[Gareth56]

Ok still confused as to what the mass of an oxygen atom is.

 

I note from the literature that 1 atomic mass unit (amu) = 1.66053886 × 10^-27 kilograms and from the literature and above that the atomic mass of oxygen is 16amu. So am I correct in saying that, expressed in kilograms, the mass of an oxygen atom is 16 x 1.66053886 × 10^-27kg = 2.6569 x 10^-26kg? (to 5 s.f.)

 

If it isn't 2.6569 x 10^-26kg? (to 5 s.f.) would someone please indicate what the mass, expressed in kilograms, of an oxygen atom is.

 

Thanks.

[insane_alien]

yep. that is a single oxygen atom.

[Gareth56]

So when the website concerned said that mass of one oxygen atom measured in grams is 5.36 × 10^−23g, they are incorrect?

 

Also insane_alien I'm not too sure what you mean by "no, that would be the wrong value for 1 amu. 1 oxygen atom is a thousandth of that value."

 

Had I incorrectly quoted the value for the amu somewhere?

[insane_alien]

1amu ~ 1.6753 × 10^−24g (which I somewhat agree with)

 

post 3

[Gareth56]

A typo on my part.

 

So we can [now hopefully ] agree that the mass of one oxygen atom measured in grams is NOT 5.36 × 10^−23g.

[insane_alien]

i always agreed it wasn't that.

[CaptainPanic]

Perhaps unnecessary, but I'll just dump some explanation here for other people. Too often people seem to miss the whole point because they don't know what a "mole" is. It's simple:

 

Calculating the mass of any atom or molecule is as simple as calculating the mass of 1 egg when you know a dozen eggs are 720 grams. One egg is then 1/12th of 720 g = 60 g (because 12 = a dozen). But we should add a disclaimer here that we're assuming that all eggs are of exactly the same weight (it could also be 1 big one, and 11 small ones, in which case we could be quite wrong!).

 

In the same way, a mole = 6.02214*10^23. "Mole" is just a number... nothing more, nothing less. Just a really big number. It's written in your textbooks as: N = 6.02214*10^23 /mol. But that's just saying there are 12 eggs per dozen (or 12 /dozen).

 

To the calculation then:

 

We know that 1 oxygen atom (the O-16 isotope) is 15.99492 g/mol. So, 1 atom is 15.99492 / (6.022*10^23) = 2.65602*10^-23 g / atom.

 

I specified that we're only looking at the O-16 isotope because that's the analogue of saying that all eggs are equally big.

 

If you took the default (average) weight of oxygen (15.9994 g/mol) then we'll arrive at an average weight of 1 atom of 2.65676*10^-23 g/atom, but then we still have to admit that we know for a fact that there exist some O-17 and O-18 atoms, which are heavier than that, and some O-16 that are lighter.

 

The analogy of an electron around a nucleus for me is the same as potential energy. It takes more energy to bring a satellite to a high orbit around earth than to a low one.