ATOMIC STRUCTURE & PROPERTIES
A1: History of the Atom
Ernest Rutherford
Niels Bohr
-Discovered the proton with his gold foil
experiment by testing Thomson's model
-Created his own model of the atom called
the Bohr model using what we knew
-Launched alpha particles at a gold foil
and thought they would pass straight
through
-Electrons orbit the nucleus in the atom at
discrete distances / orbits.
-Some of the
particles bounced
back, meaning
there's a positively
charged core
within the atom
-Each orbit has a distinct energy
level that increases as the orbital
increases in size
-If an electron absorbs energy, it
jumps to a higher energy level. As
it falls to a lower level, it releases
energy in the form of a photon
A2: Electron Configurations and
Orbital Diagrams
-We can describe where electrons are
generally located in an atom using
quantum numbers, n, l, ml and ms
2p^4
(See table for their meaning)
-Orbital diagrams are also another way to
describe where e-s are generally located
Pauli exclusion principle: No two electrons can
have the same quantum number.
-There are rules for both these types of
diagrams.
Aufbau principle: Orbitals must be filled from
lowest energy to highest energy (See diagonal
rule for order)
Hund's rule: When subshells are being filled with
electrons, they are added as unpaired electrons
before they are paired up. (See diagram on left)
A3-A4: VSEPR Theory & Intra/intermolecular Forces
-VSEPR theory is used to predict the shape and polarity of
a molecule.
A: Central atom
X: Bonding Sets
E: Lone pair
Subscript is added to the X & E if there are multiple sets/pairs
AX2E2
=
-Match the VSEPR notation
to the correct model on the
table to determine its shape
-If a molecule's shape is
symmetrical in all directions,
its intermolecular force is
nonpolar, otherwise it's polar
H2O
-Intramolecular forces can be determined by calculating
the EN difference between bonds.
0-0.4 = Nonpolar 0.4-1.7 = Polar
1.7-3.3 = Ionic
-The more EN atom is
labeled with sigma-, the
other is labeled with sigma+
-Nonpolar molecules have dispersion forces (LDF) as their main
intermolecular force
-Polar ones can have LDF or dipole-dipole (D-D) depending on
their molecular shape. (symm. = LDF, nonsymm. = D-D)
-If there are H atoms bonded to N, O or F there's H-bonding
-The intermolecular force determines the molecule's state
at room temp. Stronger forces = solid/liquid. Weak = gas
Force Strength: LDF < D-ind. D < ion-dipole < D-D < H-bonding