Question

Explain how you can use the periodic table to identify the number of protons, electrons and neutrons in an element. Provide an example of this process, using an element of your choice.

Answer 1

Each element has two numbers beside it, a whole number (atomic number) and a rational number (mass number). The atomic number is the number of protons. The mass number is the (average) mass of an atom of the element (in atomic mass units), and is the sum of protons and neutrons (electrons are not considered since its mass is so small). Subtract the number of protons from the mass number to get the number of neutrons.

In the neutral state, the number of electrons equals the number of protons. In a charged state, the number of electrons is either greater than (if negatively charged) or less than (if positively charged) the atomic number by the magnitude of the charge.

For example, lithium (Li) has an atomic number of 3 (meaning it contains three protons). It has a mass number of about 7, meaning it has 7-3=4 neutrons. In its neutral state, it must have 3 electrons (to balance its 2 protons). However, lithium often exists as an ion, Li+. It still has 3 protons and 4 neutrons, but has one less electron than proton since it has one positive charge.

Answer 2

eg we have Al which has the number 27 on top and the number 13 below. Well the number of protons is the number below, 13. And the number of protons = the number of electrons in an atom which is neutral. To obtain the number of neutrons, we take the top number, 27- the bottom number, 13 which gives 14, the number of protons. the top number equals to the number of protons and neutrons. That's it! hope it helps! =)