Atoms - fast replys needed please

[elerrina]

how do you work out the number of protons neutrons and electrons in an atom as we have a hwk tht requires us to do this and it doesnt explain it very clearly in the text book please could some one explain to me thanks

[mibn2cweus]

The number of protons determine what element the atom is; this is the atomic number; (hydrogen 1, carbon 12, etc.).

The electrons are typically of the same quantity as protons unless the atom is charged; (charge +1 short one electron), (charge -1 one extra electron). Protons have a positive charge; electrons have a negative charge.

The average number of neutrons can be found by subtracting the number of protons from the mass number. To find the mass number round the atomic weight to the nearest whole number; (19.49 = 19) and (19.5 = 20). This is because protons and neutrons have the same mass, (weigh the same), and together determine the atomic weight; (electrons have comparatively little mass and are not considered in the atomic weight).

The atomic weight of an element depends on the number of neutrons in an element. The number of neutrons vary according to which isotope of the element we are looking at. The atomic weight given in the periodic table is the average weight of the element.

[mibn2cweus]

http://education.jlab.org/qa/pen_number.html

[mibn2cweus]

Whoops! Carbon�s atomic number is 6.
[This is what happens when I rush.] (Carbon 12 is the most common isotope of the carbon atom having 6 protons, 6 neutrons and 6 electrons.

Magnesium has the atomic number 12. And its atomic weight is 24.305. Rounding the atomic weight gives us the mass number 24. Since the atomic number is 12, magnesium has 12 protons.
Subtracting the number of protons (12) from the mass number (24) leaves 12 which is the number of neutrons.

Unless the atom is specified as having a charge, it is considered neutral (having no charge), then the number of electrons is the same as the number of protons.