1. Anatomy of the Atom

2. Subatomic Particles In each atom there are three subatomic particles: ParticleLocationChargeSize/MassSymbol Proton Inside the nucleus +1 1 a.m.u (atomic mass unit) “p + “ Electron Outside the nucleus 1/2000 a.m.u“e - “ Neutron Inside the nucleus 01 a.m.u“n 0 “

3. Anatomy of an Atom p+nop+no Shells Nucleus (proton and neutron) Electron

4. Important Notes about Subatomic Particles Every element is identified on the periodic table by its atomic number. The atomic number tells us the amount of protons an atom of that element has. No two elements have the same atomic number. Protons cannot move! The atomic number also tells us the number of electrons present. In all neutral atoms, the # of protons = the # of electrons.

5. The atomic mass of an atom represents the total sum of the protons and neutrons inside the nucleus. We can use Standard Atomic Notation to note these important features: He 4 2 Atomic mass Atomic number

6. Electrons can move from one atom to another. This is how an ion is formed. Positive Ion (Cation): # of protons > # of electrons Negative Ion (Anion): # of electrons > # of protons Neutral Ion: # of electrons = # of protons An element can have atoms with different numbers of neutrons. These are called an element’s isotopes. Most elements have several isotopes.

7. Bohr-Rutherford Diagrams 1. Draw the nucleus as a solid circle. 2. Put the number of protons (atomic number) in the nucleus with the number of neutrons (atomic mass – atomic number) under it. 3. Place the number of electrons (same as protons) in orbits around the nucleus by drawing circles around the nucleus. Remember, 1 st shell – 2 electrons, 2 nd shell – 8 electrons, 3 rd shell – 8 electrons, 4 th shell – 18 electrons.