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May 25, 2015

Homework Help: Final Exam- Honors Physical Science

Posted by Kate on Monday, June 4, 2007 at 6:10pm.

how can you determine the number of protons, electrons,neutrons, atomic number, and the atomic mass of an element using the periodic table?

Atomic mass is given in the table, as well as the atomic number and atomic mass number.

Atomic number is the number of protons, which is equal to the number of electrons.

Atomic mass number is the number of protons plus neutrons.

so for H meaning Hydrogen it would be 1 for all of them, except nuetrons being 0 because 1 atomic mass- 1 proton= 1 neutron.

That's correct, but note that for the mass (expressed in atomic mass units) it is just an approximation. The atomic mass is slightly different from the atomic mass number.

The atomic mass unit is defined such that the carbon-12 isotope has a mass of exactly 12 atomic mass units. So, for carbon-12 (this isotope has 6 neutrons and 6 protons) the atomic mass expressd in atomic mass units is exactly the same (by definition) as the atomic mass number.

For other elements this is not the case. The atomic mass number will, of course, always be an integer number, being equal to the sum of the number of protons and neutrons. But the value of the mass expressed in atomic mass units won't be an exact integer (except for the carbon-12 isotope).

what is on the final exam

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