How do we determine the number of protons in a atom?

How do we determine the number of protons in a atom?

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  1. The answer is B

    Explanation:

    The atomic mass ([tex]m_{a}[/tex]) is the average mass of all the isotopes an element has, therefore it is unique, an in this case the element will be Halfnium, as the number is 178.

    The atomic mass however, does not relate to the number of protons and neutrons directly, given that the atomic mass takes all the isotopes into account.

    The mass number (A) on the other hand, does consider the number of protons and neutrons. The definition of mass number is A=N° neutrons+N° protons.

    Let us consider the Hydrogen as an example. Hydrogen has three isotopes:

    [tex]1_{H}[/tex] which abundance is 99.98%

    [tex]2_{H}[/tex] which abundance is 0.02%

    [tex]3_{H}[/tex] (traces)

    In this case, the mass number for each one of the isotopes, will be 1, 2 and 3 respectively. However, the atomic mass will be the average mass of the three isotopes, therefore:

    [tex]m_{a}=Abundance*mass number=(99.98 * 1)+(0.02*2)=1.0078[/tex]

  2. The atomic number of an element is equal to the number of protons. It the element has a neutral charge then the number of protons equals the number of electrons. The number of neutrons equals the atomic mass minus the atomic number.

    ex:
    Sodium
    Atomic number:  11 
    Atomic mass: 23 

    Protons: 11
    Electrons: 11
    Neutrons: 23 - 11 = 12

  3. it can be determined for a set of simple rule.

    the number of proton in the nucleus of the atom is equal to the atomic number

  4. Yes you can. The atomic mass measured from the proteins and neutrons in an atom, since you know he number of protons, you can subtract and be left with the number of neutrons.

  5. You can find the number of neutrons in an element by subtracting the number of protons (or the atomic number) from the atomic weight. This is because the protons plus the neutrons are what make up the atomic weight. So, the number of neutrons is equal to the atomic weight minus the number of protons.

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