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NOTES: 5.1 – Revising the Atomic Model
Atomic Models ~ REVIEW!
● ATOM: the smallest particle that
● From the early Greek concept of the atom to the modern atomic theory, scientists have built on and modified
existing models of the atom.
● Atoms are composed of a
surrounded by an
-NUCLEUS: (99% of atom’s mass) uncharged
.
and positively charged
.
-ELECTRON CLOUD: negatively charged electrons in constant motion creating a “cloud” like a fan.
Electron arrangements…
● the chemical properties of atoms, ions, and molecules are related to the
within them
● models of the atom will be reviewed with an emphasis on the electrons
JOHN DALTON:
Dalton’s Atomic Theory:
-All elements are made of tiny atoms.
-Atoms
.
-Atoms of the same element are exactly alike.
-Atoms of different elements can
.
● As it turns out, the atom can be divided into
.
● Thomson and Millikan are given credit for the first discoveries relating to electrons.
● Rutherford discovered the
3 types of particles that make up atoms:
Particles:
Mass (amu):
Charge:
PROTON
NEUTRON
ELECTRON
J.J. Thomson (1856-1940)
● proposed the “plum-pudding” model: neg. charged electrons are dispersed throughout a lump of pos. charged
material (like raisins stuck in dough)
How is the atom structured?
● each atom has a tiny, positively charged, massive (very dense) center called an
● The area around the nucleus is
.
.
● How do we know?
Rutherford’s “Scattering” Experiment:
-positively charged alpha particles (helium nuclei) were shot through a thin gold foil.
-most alpha particles passed through the foil, or were deflected through moderate angles.
-a few were reflected at extreme angles, or even came shooting right back to the source!
NIELS BOHR
● In 1913, this Danish scientist suggested that
.
● In Bohr’s model, electrons are placed in different energy levels based on their distance from the nucleus. (
)
Bohr’s Atomic Model
● What prevents an electron from falling into the nucleus?
● The electrons in a particular path have a
● The energy levels are like rungs of a ladder:
-lowest rung of ladder =
-one can climb up or down a ladder by going from rung to rung = an electron can “jump” from one energy level to
another (
)
● The Bohr Atom was a “
“
or “
“
.
● In the process of changing energy levels the electron gains or loses energy by
● the higher an electron is on the energy “ladder”, the
● in the atom, the steps become closer together as an electron climbs higher
● similarly, the higher energy level occupied by an electron,
from the atom…WHY?
Erwin Schrodinger (1887-1961)
In 1926 Schrodinger proposed an equation describing the location and energy of an electron in a hydrogen atom.
Quantum Mechanical Model:
Solving the Schrodinger Equation gives the
at a given place around the nucleus.
The solution also gives rise to energy level
.
● The quantum mechanical model of the atom predicts energy levels for electrons; it is concerned with the
probability, or likelihood of finding an electron in a certain location.
● In quantum theory, each electron is assigned a set of
**analogy: like the
!
● The first number is called the
(n). It describes the main energy level the electron is on.
● The second quantum number (l) describes the sub level, or orbital type, the electron is in. (s, p, d, f)
Electron Configurations
● Regions where electrons are likely to be found are called orbitals.
!
Energy level
Sublevel
Orbitals
# Orbitals
Max # elec.
n=1
n=2
n=3
Sublevel
s
p
d
f