# Number of atoms in helium liquid

Joined May 11, 2018
158
Hello I have a question in my exercise that I need to ask about .

the number of atoms in a helium liquid particle whose size is 0.708nm (I did not want to say lattice constant because I imagine helium liquid does not have a lattice structure because it is not crystalline.)

Another thing,I think we need to use the avogadro's constant but I dont know how to do it .

Thanks very much

#### jpanhalt

Joined Jan 18, 2008
11,088
Do you know what Avogadro's constant is used to convert, i.e., from what value/unit to what value/unit?

#### Papabravo

Joined Feb 24, 2006
16,773
Hello I have a question in my exercise that I need to ask about .

the number of atoms in a helium liquid particle whose size is 0.708nm (I did not want to say lattice constant because I imagine helium liquid does not have a lattice structure because it is not crystalline.)

Another thing,I think we need to use the avogadro's constant but I dont know how to do it .

Thanks very much
On a periodic table of the elements you will find two numbers. The atomic number, equal to the number of protons in the nucleus, locates an element's position in the table. It should have elements with atomic numbers from 1 (Hydrogen) to the vicinity of 118 (Oganesson). The other number is the atomic weight. The units of the atomic weight are grams/mole. One mole of any atom or molecule is equal to Avogadro's Number. This number is approximately 6.02E23 and the weight, in grams, of one mole is just the grams/mole of the atomic weight times 1. I don't think it will help you with this problem.

If a figure of 140 pm is assumed for a helium atom, how many of those spheres can you fit in your droplet?
Hint: this problem is called "sphere packing". Look it up.

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#### jpanhalt

Joined Jan 18, 2008
11,088
Is it valid to assume that "size" is a sphere? What temperature?

Joined May 11, 2018
158
Is it valid to assume that "size" is a sphere? What temperature?
Actually its liquid helium at temp of 4.2k

Joined May 11, 2018
158
Do you know what Avogadro's constant is used to convert, i.e., from what value/unit to what value/unit?
YeH but I do not have the number of moles so its complicated

#### jpanhalt

Joined Jan 18, 2008
11,088
You need to know the shape of the particle. Can you calculate the volume and mass of a sphere given the density? Assuming the helium is the natural mixture of isotopes. Also, Avogadro's number has changed since I was born. Which value are you supposed to use? (https://en.wikipedia.org/wiki/Avogadro_constant )

#### WBahn

Joined Mar 31, 2012
26,398
Hello I have a question in my exercise that I need to ask about .

the number of atoms in a helium liquid particle whose size is 0.708nm (I did not want to say lattice constant because I imagine helium liquid does not have a lattice structure because it is not crystalline.)

Another thing,I think we need to use the avogadro's constant but I dont know how to do it .

Thanks very much
What information do you have? Do you have, or are you allowed to look up, the density of liquid helium, for instance?

Going the other way, what information do you need that you don't have and how might you go about getting it?

Joined Nov 7, 2020
8
Helium consists of two electrons in the atomic orbitals surrounding the nucleus of two protons and (usually) two neutrons.

#### WBahn

Joined Mar 31, 2012
26,398
Helium consists of two electrons in the atomic orbitals surrounding the nucleus of two protons and (usually) two neutrons.
And this relates to the TS's query... how?

#### RBR1317

Joined Nov 13, 2010
662
...look up, the density of liquid helium, for instance?
The density may not be certain unless the temperature is also known. See attached extract from a report on the properties of helium downloaded from the Brookhaven National Laboratory.

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#### jpanhalt

Joined Jan 18, 2008
11,088
The density may not be certain unless the temperature is also known. See attached extract from a report on the properties of helium downloaded from the Brookhaven National Laboratory.
Does 4.2°K ring a bell?

#### RBR1317

Joined Nov 13, 2010
662
Does 4.2°K ring a bell?
Don't piss off old people. The older we get the less "LIFE IN PRISON" is a deterrent.