Rounding Mass Numbers of Elements?

Question

Do you round the mass number of elements when trying to determine the number of protons and neutrons it has?

For example, Oxygen has a mass number of 15.994 ...Is it's total number of protons and neutrons 15 or 16? Thanks :D

Answer 1

Indeed, it looks as if everyone is correct. You do round to the nearest whole number.

This gives you the most commonly occurring isotope for that element. In this case O-16, which gives you the total number of neutrons + protons. To get Neutrons subtract the Atomic No. from the AMU.

Oxygen has other isotopes (same element with different numbers of neutrons), thus different weights. Ex: O-15, O-14, O-17, etc.

Get an "A".

Answer 2

For some of the lighter elements, the atomic mass is slightly less than logic would dictate (if something has 1 proton and 1 neutron, it should weigh 2). For that reason, the atomic mass of O-16 is 15.994914635.
When the atomic mass is very close to an interger (say, within 0.05) use that interger. The atomic mass listed on the periodic table is actually the average of the stable (non-radioactive) isotopes of each particular element. For example, oxygen is found as O-16 99.76% of the time, O-17 0.038% and O-18 0.205%. That is why the mass listed in the periodic table is listed as 15.999.

Not every nuclear isotope is stable, and not every radioactive isotope is unstable (C-14 is an example of that). If you don't know what isotope to use, do a google search for 'nuclear isotope' and whatever element you want to know about.

Answer 3

Generally you would round the mass number to the nearest whole number. The most abundant isotope of oxygen has 8 protons and 8 neutrons and a mass of 16.

Answer 4

Each atom of an element contains a whole number of protons and neutrons. Most elements, in the bulk state, are made up of atoms, all of which don't contain identical numbers of neutrons. The atomic weights given on the Periodic Table are averages. For instance, if half the atoms of a particular element have atomic weights of 35, and half are 36, the at. wt. will be listed as 35.5. Usually, if you round off to the nearest whole number, you'll have the at. wt. of the most prevalent isotope of that element.

Answer 5

When the mass number is close to a whole number, round up or down as apprpriate. The number of protons is always the atomic number. When the mass number is halfway between two numbers, such as chlorine , at 35.453, that means it has two main stable isotopes and you can say the number of neutrons is 18 or 19..

The other option is just do what your teacher tells you.

Answer 6

Unless you are getting picky about isotopes and some type of statistical "average" mass, the "standard" periodic table lists the atomic mass of the elements. The element number (atomic number) is the number of protons, 1 of H, 92 for U, etc. A good periodic table also provides information about the most common isotopes (where the nucleus has a extra nuetron or two or is missing a nuetron or two compared to the most common isotope). If you want to see some good periodic tables, google "periodic table". hope this helps.

Answer 7

I do, and O I round to 16

Answer 8

yes we round the number to 16 because the next number to 5 is 9 which is greater than 5 so we round it up
hope i helped