can somebody tell me the atomic structure?

Question

like eg... helium symbol =He
atomic number = 2
Mass number = 4
Number of protons ?
Number of neutrons ?
Number of electrons ?

there mus be a table with that information no?

Answer 1

You need to wake up in class.
Look up the Periodic Table and all your answers are there.

Answer 2

The short answer:

# of protons = atomic number

# of neutrons = mass - atomic number

for a neutral molecule:
# of electrons = # of protons for a neutral molecule

for an ion:
# of electrons = # of protons - charge (so that positive ions have less electrons than protons and negative ions have more electrons than protons.)

All of this comes from the following facts:

1.)Elements are defined by the number of protons they have. So, for example, all Carbon atoms have 6 protons, and every atom with exactly 6 protons is a Carbon atom.

2.)Neutrons and protons contribute mass to an atom, but electrons don't. (Actually electrons do have mass but its really tiny and atoms don't really notice it. Kind of like how you don't feel any lighter if one of your hairs falls off.) They weigh about the same so the mass in atomic units is just the total number of protons and neutrons.

3.)Charge is carried by protons and electrons. They have roughly equal charge, but protons are positively charged and electrons are negatively charged. So a neutral atom must have an equal number of protons and electrons, while an ion has extra of one or the other.