Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    9
    ReputationRep:
    My textbook says don't confuse relative atomic mass Ar, with mass number so whats the difference? I know relative atomic mass is calculated using isotopes and carbon-12. But then whats the mass number?????
    Offline

    10
    ReputationRep:
    Sum of number of protons and neutrons.
    • Thread Starter
    Offline

    9
    ReputationRep:
    (Original post by haarithiop)
    Sum of number of protons and neutrons.
    Yes i know thats the mass number but whats relative atomic mass?
    Offline

    10
    ReputationRep:
    (Original post by HN786)
    Yes i know thats the mass number but whats relative atomic mass?
    Why ask what's the mass number when you don't want to know what it is?
    Offline

    9
    ReputationRep:
    RAM: weighted average of atomic mass numbers between *isotopes*
    Atomic mass number: sum of protons and neutrons
    Offline

    18
    ReputationRep:
    (Original post by HN786)
    My textbook says don't confuse relative atomic mass Ar, with mass number so whats the difference? I know relative atomic mass is calculated using isotopes and carbon-12. But then whats the mass number?????
    Isn’t that Mr? I’m confused
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    18
    ReputationRep:
    (Original post by HN786)
    My textbook says don't confuse relative atomic mass Ar, with mass number so whats the difference? I know relative atomic mass is calculated using isotopes and carbon-12. But then whats the mass number?????
    It’s 1/12 carbon-12
    Posted on the TSR App. Download from Apple or Google Play
    Offline

    13
    ReputationRep:
    (Original post by HN786)
    My textbook says don't confuse relative atomic mass Ar, with mass number so whats the difference? I know relative atomic mass is calculated using isotopes and carbon-12. But then whats the mass number?????
    The relative atomic mass is the weighted mean mass of all the isotopes of an element relative to one twelfth the mass of the carbon-12 isotope.

    The mass number is the number of nucleons (protons and neutrons added together).

    There are two common isotopes of chlorine: 35Cl and 37Cl.

    Both have the same number of protons (since they are the same element) but different numbers of neutrons, so different mass numbers (35 and 37 respectively).

    But they exist in an approximately 3:1 ratio, or 75% of the first and 25% of the second.

    So the weighted mean mass, called the relative atomic mass or Ar is calculated as:

    A_r = \dfrac{(35 \times 75) + (37 \times 25)}{100} = 35.5 g/mol.
    • Thread Starter
    Offline

    9
    ReputationRep:
    (Original post by K-Man_PhysCheM)
    The relative atomic mass is the weighted mean mass of all the isotopes of an element relative to one twelfth the mass of the carbon-12 isotope.

    The mass number is the number of nucleons (protons and neutrons added together).

    There are two common isotopes of chlorine: 35Cl and 37Cl.

    Both have the same number of protons (since they are the same element) but different numbers of neutrons, so different mass numbers (35 and 37 respectively).

    But they exist in an approximately 3:1 ratio, or 75% of the first and 25% of the second.

    So the weighted mean mass, called the relative atomic mass or Ar is calculated as:

    A_r = \dfrac{(35 \times 75) + (37 \times 25)}{100} = 35.5 g/mol.
    Thanks
    Offline

    9
    ReputationRep:
    i dont wanna confuse u (i could be wrong) but from what i understand mass number changes whereas RAM doesn't--

    r.a.m is the AVERAGE mass of all the versions of the atom whereas mass number is just the mass of any one of the versions of the atom.
 
 
 
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • Poll
    Did TEF Bronze Award affect your UCAS choices?
  • See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  • The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

    Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

    Quick reply
    Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.