atomic+number+and+mass

__Atomic Number__
The chemical elements can be distinguished by the number of protrons in thier nucleus. Different sorts of atoms cannot share the same number of protons. For example)
 * 1) Be has 4 protons in its nucleus, which also means an atom containing 4 protons must be Be.
 * 2) C has 6 protons in its nucleus, so an atom having 6 protons must be C.

In addition,
**atomic number = the # of protons = the + charges in nucleus = the # of electrons = the - charges surrounding the necleus.** ( This is only for neutral atoms.) For example) The picture below shows that Ca has 20 protons and 20 electrons, then check with the periodic table its atomic number is also 20.  picture#1   picture#2 If electrons are added in or taken away from a netral atom, a new partical with charges is produced called ion.  For an ion, the atomic number, the # of protons and the + charges in its nucleus do not change, but the # of electrons and the - charges do change depending on how many electrons are added in or taken away. **Such as：** charges ||
 * 1) The atomic number of F is 9.
 * 2) There are 9 protons in one atom.
 * 3) An F atom has 9 positive charges in its necleus.
 * 4) There are 9 electrons in an F atom.
 * 5) There are 9 negative charges surrounding its nucleus.
 * Adding an electron ( negative charge ) produces a negative ion.
 * Taking an electron away (negative charge) produces a positive ion
 * Atomic symbol || Atomic number || the number of protons || + charges || the number of electrons || - charges || overall
 * F- || 9 || 9 || +9 || 10 || -10 || -1 ||
 * Cl- || 17 || 17 || +17 || 18 || -18 || -1 ||
 * Mg2+ || 12 || 12 || +12 || 10 || -10 || +2 ||

__**Atomic Mass**__ The mass of an atom is calculated by adding the number of protons and the number of neutrons together. The electrons are too tiny and light to be considered as part of the mass of an atom. **// Definition: //** The Atomic Mass of an atom is the sum of the # of protons and neutrons.

**atomic number = # of protons atomic mass = # of protons + # of neutrons So: number of neutrons = atomic mass - atomic number**

Look at the picture below, it shows both atomic mass and atomic number with the atomic symbol,

picture#3

Accrounding to the picture, though the same kind of atoms may have different atomic mass atomic mass = 12 The picture below also shows the same thing: picture#4
 * 1) of protons = 6
 * 1) of neutrons = 12 - 6 = 6

** Review: **
 * 1) An element's or isotope's **atomic number** tells how many protons are in its atoms.
 * 2) An element's or isotope's **mass number** tells how many protons and neutrons in its atoms.

__**Links:**__ picture#1 [] picture#2 [] picture#3 [] picture#5 []