CHEMISTRY
Unit 03 Lesson 01
Models of the Atom
• Atom A submicroscopic particle that
constitutes the fundamental building block of
ordinary matter; the smallest identifiable unit of
an element
• Subatomic particles Any of various particles
that are smaller than an atom (Ex. Protons,
electrons, neutrons)
• Nucleus The very small, dense core of the atom that
contains most of the atom’s mass and all of its
positive charge; composed of neutrons and protons
• Proton(p+) An electrically positive subatomic particle
found in the nucleus of an atom
• Neutron(n0) An electrically neutral subatomic particle
found in the nucleus of an atom, with a mass almost
equal to that of a proton
• Electrons(e-) Negatively charged subatomic particles
with negligible mass that are found in orbitals
surrounding the nucleus of an atom, making up
nearly all of the atom’s volume
• Electromagnetic spectrum The range of
wavelengths of all possible
electromagnetic radiation
• Wavelength (λ)  The distance between
adjacent crests of a wave
• Frequency (ν) The number of cycles (or
complete wavelengths) that pass through a
stationary point in one second
• Photon The smallest possible packet of
electromagnetic radiation with an energy equal
to hν
• Planck’s constant A value of h= 6.626x10-34 J·s
which is used in the equation E=hν to calculate the
energy in a photon
• Speed of light A value of 3.00x108 m/s
• Isotope Atoms with the same number of protons but
a different number of neutrons and subsequently a
different mass
• Spectroscope A piece of equipment used to
observe a spectrum of light or radiation from a particular
substance
• Mass number The sum of the number of
protons and neutrons
• Atomic number The number of protons in an
atom; defines the element
• Average atomic mass The average mass of
the atoms of a particular element based on the
relative abundance of the various isotopes
• Nuclear symbol Consists of the atomic
number, atomic mass, and the mass of the
particular isotope of that element
• Hyphen notation Element- Atomic mass
(Ex. Carbon- 12)
• Write hyphen notation for the following
elements:
• Lithium(6.9amu), Nitrogen(14amu),
Argon(39.9amu)
The Atom and the
Solar System
Analogies:
nucleus: Sun
electrons: planets
ATOM
SOLAR SYSTEM
> 99.9% of total mass is in nucleus
~ 99% of total mass is in Sun
Mostly empty space
Mostly empty space
Electrons held by mutual attraction
with nucleus
Planets held by mutual attraction with
the Sun
Electrons behave as spinning bodies.
Planets rotate on their axes.
The Atom and the
Solar System
Analogies:
nucleus: Sun
electrons: planets
ATOM
SOLAR SYSTEM
Paths of electrons are unpredictable;
can only determine probability that an
electron can be found within a given
space
Planets move in relatively fixed,
predicable paths.
Electrons moving around the nucleus
in three dimensions
Orbits of planets lie in nearly the same
plane.
Electrons held by electrical attraction
with nucleus
Planets held by gravitational attraction
with the Sun
Electrons repel each other.
Planets attract each other.
Electrons sometimes “fall” into the
nucleus, and sometimes they pass
through the nucleus.
Motion of the planets prevents them
from being pulled into the Sun
All electrons are alike.
Planets differ greatly from one
another.
History of the Atom
• Leucippus and Democritus proposed the first
theory of matter being composed of atomos,
small indivisible particles (460-370 B.C.)
• In the sixteenth century, the scientific revolution
began with works of scientists such as, Francis
Bacon, Johannes Kepler, Galileo Galilei, Robert
Boyle and Issac Newton
Discovery of the Electron
• J.J. Thompson, an English physicist, used
cathode rays to discover electrons in the
late 19th century
• In 1909 Robert Millikan, an American
physicist, discovered the charge of an
electron and confirmed Thompsons theory
that an electron is 2000 times lighter than
hydrogen
Early Models of the Atom
• Thompson proposed the plum pudding
model
Ernest Rutherford
• In an attempt to confirm the plum-pudding
model, he proved it wrong
• Performed a gold foil experiment and
discovered that atoms are mostly empty
space with a central nucleus
Comparing Models
• Make a T-chart for the similarities and
differences of these models
A.
B.
Model Limitations
What are the limitations of the following models?
A
B
Model Limitations
• What are the limitations of the following
models?
C
D