How are the elements differentiated? And how many protons occur in hydrogen, helium, and lithium?
Not hard ... we'll take it step by step.
The number of protons is the same as the atomic number (hydrogen is one, helium two, lithium three etc.) and the number of electrons is the same as the number of protons (assuming the atom is neutral.)
The more tricky bit is figuring out the number of neutrons. You do this by finding the mass number from the periodic table and subtracting the atomic number (the number of protons you found earlier.) Thus hydrogen has zero neutrons, helium has 2 (the mass 4, minus the no. of protons, 2), lithium has 4 (7 - 3) etc.
A quick check is to find the number of protons uranium-238 has. If you get the number 146, you've sussed it.
The atomic number is the number of protons in an atom of the element.
The atomic weight equals (very nearly) the number of protons plus the number of neutrons. Subtract the atomic number from the atomic weight and you'll be very close to the number of neutrons.
(but see the exception noted below)
The number of electrons will usually equal the number of protons. This is in a "normal", electrically neutral charged atom. Atoms often give up one or more electrons (or accept an additional one or more electrons), in which case they are "ions".
Atoms may also have more (or fewer) neutrons, in which case they are called "isotopes" of the element. "Deuterium", for example, is an isotope if hydrogen with an extra neutron. Chemically, these atoms behave the same as for the normal version of the element. Atomic number is the same, but atomic weight will be greater (or less) than the atomic weight given on the periodic table.
Whew. Haven't read up on this stuff for years. You now know everything I know on this subject.
An element on the Periodic Table is characterized by its chemical symbol, which is specific to its
And have you got a Table handy? Of course you have because you are doing your chemistry homework.
The nucleus also contains massive, neutrally charged particles, i.e.
The nucleus of given element can contain various number of neutrons, and this gives rise to the phenomenon of isotopes. These are nuclei of the same element (because
I will give you one example of common isotopes. Hydrogen comprises (as far as we know) maybe 70% of the matter in the universe. Most hydrogen atoms contain only the one proton, i.e. we gots
Confused yet? Remember chemists and physicists are simple folk, and I don't think these concepts are entirely off the wall and inaccessible.
And see this old answer.