A New Approach to the Atom:

Objectives:

1.    Describe the atomic orbitals in terms of their shape, size, and energy.

Key Terms:

quantum-mechanical model    electron density    orbital    principle energy level    sublevel

Web Resources:

Notes: (4-4)

Probability & Orbitals:

Electron orbitals can more correctly referred to as electron clouds.  An orbital is simply the region around the nucleus where an electron is likely to be found.  Since we learned from Heisenberg's uncertainty principle that we can never be sure of where an electron is, we can say that wherever the electron cloud is dense electrons are more likely to be found.  There are s,p,d,& f orbitals.  Here are examples of the s & p orbitals:

s orbital

(www.imsa.edu/~ishmael/bonding/ ao/images/t1index.gif)
 The s orbital is spherical in shape the probability of finding the electron diminishes as you reach the outer limit of the orbital and is greater at the center

p orbital

(www.imsa.edu/~ishmael/bonding/ ao/images/t1index.gif)

 The p orbital is dumbell shaped the probability of finding the electron diminishes as you reach the outer limit of the orbital and is greater at the center The orbitals can extend out on the x, y, & z axis

d orbital

(www.chem.columbia.edu/~yuling/ SHP/week2/econfig.gif)

Principle Energy Levels;

The principle energy levels relate to Bohr's model of n=1, n=2, & n=3.  As you will see, as the energy levels of the atom increase, so do the sublevels within that energy level.

 The number of the energy level is equal to the number of sublevels n=1        1 sublevel      1s                    (2 electrons) n=2        2 sublevels     2s, 2p             (8 electrons) n=3        3 sublevels     3s, 3p, 3d      (18 electrons) n=4        4 sublevels     4s, 4p, 4d, 4f (32 electrons)

Number of electrons possible for each sublevel:

 s = 1        (2 electrons) p = 3        (6 electrons) d = 5        (10 electrons) f  = 7        (14 electrons)

Spin and anti-spin:

(www.uwinnipeg.ca/.../images/atoms/ electron-spin-smartdr.gif)

Electrons come in pairs.  As the electron spins on its axis it creates a small magnetic force (like a magnet).  In order to be neutral, the atom must also posses an electron with an opposite spin (anti-spin).

 The spins of the electrons are The net force = 0 The experimental measurement of this phenomena helped explain why each orbital can only hold 2 electrons