# The concept of mole

1. May 23, 2012

### cooper607

i need to get the hang of the mole concept that , 1.008 g of hydrogen constitutes 1 mole atom, whereas 12g of carbon constitute that 1 mole atom! does it mean that these amounts for H & C contains the Avogadro number of atoms??
does it imply the hydrogen is more denser (or heavier or something crucial) than the carbon as it needs to be only 1 gm of it to be 1 mole?? why does this difference in mole amount (of grams ) happen??

2. May 23, 2012

### phyzguy

A mole is just a number of things, like a dozen. A mole of carbon atoms weighs more than a mole of hydrogen atoms because each carbon atom weighs more than each hydrogen atom. Just like a dozen bowling balls weighs more than a dozen ping-pong balls.

3. May 23, 2012

### tiny-tim

welcome to pf!

hi cooper607! welcome to pf!
… to be precise (almost), 6.022142 1023 things

(see http://en.wikipedia.org/wiki/Mole_(unit [Broken]))

if you go into the garden and find 602,214,200,000,000,000,000,000 moles, that's a mole of moles!

Last edited by a moderator: May 6, 2017
4. May 23, 2012

### Philip Wood

Why is NA, the Avogadro number, chosen to be $6.02\times10^{23}$ (to 3 sf)?

Because this number is the number of atomic mass units (u) in 1 gram.

That is $1 \text{g} = 6.02\times10^{23} \text{u} = N_A \text{u}$

So, because the mass of a C12 atom is 12 u, the mass of a mole of them (Avogadro's number of them) will be $N_A \times 12 \text{u} = 12 \times N_A \text{u} = 12 \text{g}.$

[Note:in the SI, the Avogadro constant is defined to be a quantity with units, namely
Avogadro constant = $6.02\times10^{23} \text{mol}^{-1}.$]

5. May 23, 2012

### Staff: Mentor

No, the only thing it is related to is the mass of a single atom (molecule). Light atom (molecule) - low molar mass, heavy atom (molecule) - large molar mass.