Tuesday, April 26, 2011

Atomic Structure

Subatomic Particles of an Atom:   Neutron, Proton, and Electron.

A neutral atom doesn't have any charges and the number of protons will equal the number the of electrons in the atom.

# of protons = # of electrons

The Atomic Number ( Z )

Also the same number of protons in an atom. Atoms do not have an overall charge. The atomic number is the same as the number of protons which are the same as the number of electrons.

Atomic number = # of protons = # of electrons

If a proton ( ¦ p ) is added to an element's nucleus,  a new element will be created.

For ex:   19 F + ¦ p ---> 20 Ne
               9                     10


Atoms have the ability to gain or lose electrons. Not many can do both, one such as hydrogen can though. They are able to do this by accepting electrons or giving them away to other atoms. Atoms that have done so are then called ions.

# of electons = protons - charge

Ions are electrically charged atoms.

  • Negatively charged ion (anion) : when an electron is added to a neutral atom. non- metals tend to gain a positive charge and become neutral.
  • Positively charged ion (cation) : when an electron is taken away from a neutral atom.
Mass Number, the total number of protons and neutrons

Because, atomic number = the number of protons, then :

  • the atomic mass = the number of protons + the number of electrons
  • the number of neutrons = the mass number - the atomic number
Atomic Mass

  • the average mass of an element's isotope
  • since most of the mass of an atom is concentrated in the protons and neutrons, the atomic is very close
  • the mass number plus the atomic mass (weight) are not the same thing. atomic mass is the average of the naturally occurring isotopes, while the mass number is calculated by rounding the atomic mass to the nearest whole number instead of keeping decimal points
  • if a neutron is added to an element's  nucleus, a heavier version of the same element (isotope) will be produced
For ex:   19 F + 1 n ---> 20 F
                9       0             9

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