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Atomic Mass, Relative Atomic Mass, Mass Number & The Mole.

What are the definitions of these words? Why is everything compared to Carbon-12? What is Avogadros Number & What is an atom & molecule, is their only one atom in every element? Thanks :smile:

Reply 1

thefatone

Original post by Paranoid_Glitch

What are the definitions of these words? Why is everything compared to Carbon-12? What is Avogadros Number & What is an atom & molecule, is their only one atom in every element? Thanks :smile:

dunno just feels right i guess, like your habits which are specific to you?
number of particles in 1 mole of any given substance
this one's a bit more difficult but the smallest thing which constitutes a chemical element?
molecule is 2 or more atoms chemically combined
if you're asking if every element exists as 1 atom of itself then no, Oxygen exists as O2 for example and Bromine exists as Br2 not Br

Reply 2

derpz

Original post by Paranoid_Glitch

What are the definitions of these words? Why is everything compared to Carbon-12? What is Avogadros Number & What is an atom & molecule, is their only one atom in every element? Thanks :smile:

Relative Atomic Mass:

" average mass of one atom of an element (x12) "
mass of one atom of Carbon-12

This might look like a formula, but you do not need ot use it, all the Relative Atomic Masses are given on the periodic table.

As for why you multiply by 12, its because the RAM of Carbon is 12 and every other element's RAM is measured relative to Carbon.

The Mole:

"Avogadro's number of particles"

The value for Avogadro's constant is 6.022×10²³.

Atomic Mass:

" Sum of (mass of isotope x relative abundance) "
Sum of (all abundances)

You will be required to use this with Mass Spectometry data which you're given, but its pretty straight forward, just use that formula.

Mass Number:

"The total number of protons + electrons in an atom."

This is the number over elements on the periodic table.

Atom:

"Consists of a nucleus (protons + neutrons) and electrons."

Molecule:

"Consists of atoms."

In other words, atoms make up molecules and they are the standalone things where as molecules are made up of different atoms. For example you can have an atom of Oxygen or a molecule of H2O which contains Oxugen atoms.

Some elements such as Chlorine (which is diatomic) consist of two atoms but typically, any element which is not diatomic will have 1 atom.

Hope that helps :smile:

(edited 8 years ago)

Reply 3

username1560589

Hydrogen and helium are gaseous in standard conditions, lithium and beryllium are reactive. Boron is fairly suitable as far as I know but wasn't discovered until later and has multiple common isotopes, which would need to be separated. Others are rare or gaseous or reactive or were undiscovered or too heavy to use easily as a standard.
Carbon literally grows on trees and is mostly made up of one isotope. It's relatively unreactive and solid in standard conditions.