'A single molecule of H2O' vs 'a single atom of H2O'

[DrClaude]

This is not my question. My question is simple. What should I say from the equations below?
1. H2 + O = H2O
My first question is
What should I say from this equation? I think we say one H2 molecule(two H atoms) and one O atom combines to form one molecule H2O. Here one H2 molecule means what? two H atoms which weigh 2.014g/mole ( molar mass of two H atoms) and one O atom means what? molar mass of one O atom is 16g/mole. So my question is one H atom means 1.007g H atom and one O atom means 16g O atom which represents the molar mass of one H atom and one O atom.
And
My second question is If we look at the periodic table and find the mass of H. We find the mass of H is 1.007. Here my question what does 1.007 mean? it means 1.007 g/mole, the molar mass of one H atom?

There are a few things I would like to comment on here.

When you look at the periodic table, what is given is the molar mass of the atoms, which includes relative isotopic abundance. Take hydrogen, for instance. You will find that the number is 1.007 97 g/mol. That means that if you collect 1/2 mole of hydrogen gas (H₂), which is the natural form for that element, such that you have a total of 1 mole of H atoms, that sample is going to have a mass of 1.007 97 g.

But if you divide that mass by Avogadro's number, you get 1.67377×10^-24 g, which is not the mass of one hydrogen atom. The mass of the most common isotope of hydrogen, ¹H, is actually 1.007 825 032 23 g/mol, or 1.67353×10^-24 g for one atom. This is because 0.0115% of hydrogen atoms are the deuterium isotope, ²H.

While the difference is small for hydrogen, it is not far all elements. A good example is chlorine. The periodic table will give a molar mass of 35.453 g/mol, but an actual sodium atom will either have a mass of 34.969 g/mol (³⁵Cl) or 36.966 g/mol (³⁷Cl). A sample of naturally occurring chlorine will be 75.8% ³⁵Cl and 24.2% ³⁷Cl.

 

[Indranil]

There are a few things I would like to comment on here.

When you look at the periodic table, what is given is the molar mass of the atoms, which includes relative isotopic abundance. Take hydrogen, for instance. You will find that the number is 1.007 97 g/mol. That means that if you collect 1/2 mole of hydrogen gas (H₂), which is the natural form for that element, such that you have a total of 1 mole of H atoms, that sample is going to have a mass of 1.007 97 g.

But if you divide that mass by Avogadro's number, you get 1.67377×10^-24 g, which is not the mass of one hydrogen atom. The mass of the most common isotope of hydrogen, ¹H, is actually 1.007 825 032 23 g/mol, or 1.67353×10^-24 g for one atom. This is because 0.0115% of hydrogen atoms are the deuterium isotope, ²H.

While the difference is small for hydrogen, it is not far all elements. A good example is chlorine. The periodic table will give a molar mass of 35.453 g/mol, but an actual sodium atom will either have a mass of 34.969 g/mol (³⁵Cl) or 36.966 g/mol (³⁷Cl). A sample of naturally occurring chlorine will be 75.8% ³⁵Cl and 24.2% ³⁷Cl.

'1.67353×10-24 g for one H atom or one H proton'?

 

[DrClaude]

'1.67353×10-24 g for one H atom or one H proton'?

Atom. The mass of the proton is 1.6726219 × 10^-24 g. The atom is heavier because of the presence of the electron.

 

[Indranil]

Atom. The mass of the proton is 1.6726219 × 10^-24 g. The atom is heavier because of the presence of the electron.

I knew that mass of an atom means the mass of protons and neutrons. So the H atom has one proton and one electron. So one proton weighs 1.6726219 × 10-24 g But you mentioned the difference value for mass for one H atom. Then the mass of one H atom does not mean mass of one proton of H atom?

 

[DrClaude]

Then the mass of one H atom does not mean mass of one proton of H atom?

What is "one proton of H atom"?

The mass of the hydrogen atom is the mass of the entire atom, namely the proton, the electron, and the mass equivalent to the binding energy (a hydrogen atom weighs less than the sum of the mass of a lone proton and a lone electron).

 

[Indranil]

What is "one proton of H atom"?

The mass of the hydrogen atom is the mass of the entire atom, namely the proton, the electron, and the mass equivalent to the binding energy (a hydrogen atom weighs less than the sum of the mass of a lone proton and a lone electron).

Then which one I use for the mass of one H atom 1.1.67353×10-24 g or 2 1.6726219 × 10-24 g. Could you suggest me?

 

[DrClaude]

Then which one I use for the mass of one H atom 1.1.67353×10-24 g or 2 1.6726219 × 10-24 g. Could you suggest me?

I said it already. The mass of one hydrogen atom, made up of 1 proton and 1 electron, is 1.1.67353×10^-24 g.

The mass of the most common isotope of hydrogen, 1H, is actually 1.007 825 032 23 g/mol, or 1.67353×10-24 g for one atom.

 

[Indranil]

I said it already. The mass of one hydrogen atom, made up of 1 proton and 1 electron, is 1.1.67353×10^-24 g.

Thank you all

 

[berkeman]

Thank you all

This sounds like a good place to close out the thread. Thank you to all who have tried to help @Indranil