1. Electron Cloud Model As a result of continuing research throughout the 20th century, scientists today realize that energy levels are not neat, planet-like orbits around the nucleus of an atom. Instead, they are spherical regions of space around the nucleus in which electrons are most likely to be found. (like lanes of a track) Electrons travel in lanes like a runner on a track. Electrons can be anywhere in their lane. The lanes are called electron clouds.

2. Electron Cloud Model Electrons themselves take up little space but travel rapidly through the space surrounding the nucleus. These spherical regions where electrons travel may be depicted as clouds around the nucleus. So....The space around the nucleus of an atom where the atom’s electrons are found is called the electron cloud.

3. Electron Cloud Model Nucleus Electron clouds No electrons here. Electrons will be found here 90% of the time. Each cloud is determined by the probability of an electron’s location. An electron will be found in it’s cloud about 90% of the time.

4. Properties of Subatomic Particles ParticleSymbolRelative Charge Relative Mass (amu*) Actual Mass (g) Electrone-1/18409.11 x 10 -28 Proton p+p+ +111.66 x 10 - 24 Neutron nono 011.66 x 10 - 24 1 amu = 1.66 x 10 -24 grams amu = atomic mass unit

5. The NUCLEUS The Nucleus contains protons and neutrons Atomic Number — the number of protons in an element. Hydrogen’s is 1, Neon’s is 10, Gold’s is 79 ** As the atomic number changes, so does the identity of the element. Mass Number — the total number of particles in the nucleus (protons + neutrons). # of Neutrons = Mass # - Atomic #

6. Using Atomic Number and Mass Numbers to determine the number of protons, neutrons and electrons  19 K 39 Mass # Atomic # Element Symbol Number of Protons = Atomic number = 19 protons Number of Neutrons = Mass # - Atomic # = 39 – 19 = 20 neutrons Number of electrons = # protons = 19 electrons (In a neutral atom!)

7. How Can Atoms of the Same Element be Different? Isotopes — Atoms of the same element that have different number of neutrons  Since neutrons do not have a charge, adding more does not affect the atom.  This only adds to the mass of the atom (increases mass number).  Each particle in the nucleus has a mass of one. That means... The number of particles in the nucleus = Mass Number  The number of electrons will still be the same as the protons.

8. Ions — Atoms of the same element that have a different number of electrons than protons. Having more or less electrons creates an imbalance in the charge of the atom. The number in the charge is how many more or less electrons there are. If there are more protons than electrons, then the charge is positive. (Loss of electrons) If there are more electrons than protons, the charge is negative. (Gain of electrons)

9. Ions 8 O8 O 16 -2 Charge Protons Neutrons Electrons 8 8 10 (-2 )charge means that there was a gain of 2 electrons, so you add 2 to the number of protons.

10. Practice – Finding the number of p +, n o and e - 1.) 56 Ba 142 2.) 13 Al 27 +3 3.) 17 Cl 38 4.) 27 Co 60 p+ ___ n o ___ e-___ p+ ___ n o _____ e-___ p+ ___ n o ___ e-___ 568656172118 131410 2733 27 * (-) charge means add to p+ * (+) charge means subtract from p+