how so you work out a mass number???

Question

i have science homework but i don't know how you work out the mass number or the number of neutronz an element has...

Answer 1

the atomic mass of an element is on the periodic table underneath the element. you don't need to work it out.
for the number of neutrons, subtract the atomic number from the the atomic mass..

Answer 2

The mass number (A), also called atomic mass number or nucleon number, is the number of nucleons (protons and neutrons) in an atomic nucleus. The mass number is unique for each isotope of an element and is written either after the element name or as a superscript to the left of an element's symbol. For example, carbon-12 (12C) has 6 protons and 6 neutrons. The full isotope symbol would also have the atomic number (Z) as a subscript to the left of the element symbol directly below the mass number: . Note that this is redundant, as there is a one-to-one mapping between atomic number and element symbol, so it is rarely used, except when we want to clarify the number of protons in a nucleus, such as in atomic reactions

Answer 3

Use the Periodic Table.

Mass Number is the sum of all the protons and neutrons in an atom.
The atomic Number is the total of all the protons in an element.
By subtracting the Mass Number from the Atomic Number you will find the number of Neutrons.

e.g. Carbon - 12
Carbon from the periodic table :-

Atomic No. = 6
Mass No. = 12
Therefore Number of neutrons is 12 -6 = 6
If the isotope Carbon -13 is used then;-

Atomic No = 6
Mass No. = 13
Therefore Number of neutrons is 13 - 6 = 7

Answer 4

The mass number (A), also called atomic mass number or nucleon number, is the number of nucleons (protons and neutrons) in an atomic nucleus. The mass number is unique for each isotope of an element and is written either after the element name or as a superscript to the left of an element's symbol. For example, carbon-12 (12C) has 6 protons and 6 neutrons. The full isotope symbol would also have the atomic number (Z) as a subscript to the left of the element symbol directly below the mass number: . Note that this is redundant, as there is a one-to-one mapping between atomic number and element symbol, so it is rarely used, except when we want to clarify the number of protons in a nucleus, such as in atomic reactions.

The difference between the mass number and the atomic number gives the number of neutrons (n) in a given nucleus: n=A−Z.

For example: Carbon-14 is created from Nitrogen-14 with seven protons (p) and seven neutrons via a cosmic ray interaction which transmutes 1 proton into 1 neutron. Thus the atomic number decreases by 1 (Z: 7→6) and the mass number remains the same (A = 14), however the number of neutrons increases by 1 (n: 7→8).

Before: Nitrogen-14 (7p, 7n)
After: Carbon-14 (6p, 8n).
This should not be confused with the relative atomic mass which is the average abundance atomic mass number of the differing isotopes found. For instance, there are two isotopes of chlorine: Chlorine-35 and Chlorine-37. In any given sample of chlorine that has not had any mass separation there will be roughly 75% of chlorine atoms which are chlorine-35 and only 25% of chlorine atoms which are Chlorine-37. This gives chlorine a relative atomic mass of 35.5 (actually 35.4527 g/mol).

Answer 5

In the periodic table, there are two numbers next to each element. The bigger one is the relative atomic mass or mass number. It represents the number of protons and neutrons present in the nucleus (and this results in its mass). Sometimes, this number is not a whole number as there exists more than one type of the same element (isotopes), so the average based on its existing proportion is given instead.

The smaller of the two numbers is the atomic number or the number of protons present.

In some periodic tables, the mass number is on top and the atomic number below, but others display it with the atomic number on top. So be careful!

The number of neutrons present = mass number - atomic number

Answer 6

Atomic number = the number of protons
Atomic number = the number of electrons

Mass number = protons + neutrons

Wikipedia.com to find out where these numbers are on the Periodic table. I don't think they include mass numbers on the PT.

Answer 7

I think this is a good site