CHAPTER 3
Atoms: The Building Blocks of Matter
CHEMISTRY
Foundations of Atomic Theory

History
– Greek


Democritus – “atom” – could not be divided anymore
Aristotle and Plato - argued
– 1600-1700s

Natural Philosophers
– Experimentation – balances – quantitative measurements

Atom
– Comes from Greek



“a” – not
“tomos” – cutting
indivisible
Foundations of Atomic Theory

Chemical Reaction
– Transformation of substances into one or more
new substances
– Chemical change

Law of Conservation of Mass
– Mass is neither created nor destroyed in
ordinary chemical reactions
– http://www.youtube.com/watch?v=dExpJAECS
L8

Law of Definite Proportions
– A chemical compound contains the same
elements in exactly the same proportions by
mass regardless of size of sample
– Ex – H2O, CO2
Foundations of Atomic Theory
 Law
of Multiple Proportions
– If two or more compounds are
composed of the same 2 elements, the
masses can be expressed as ratios of
small whole numbers
Dalton’s Atomic Theory
John Dalton
 English School Teacher
 1803

Dalton’s Atomic Theory

5 Points in his theory
– All matter is composed of extremely small
particles called atoms
– Atoms of a given element are identical in size,
mass, and other properties
– Atoms cannot be subdivided, created, or
destroyed
– Atoms of different elements combine in simple
whole number ratios to form compounds
– In chemical reactions, atoms are combined,
separated, or rearranged
Dalton’s Atomic Theory
Modern Atomic Theory
 There
have been some changes since
Dalton’s Theory
 Important concepts of modern
theory
– Atoms of one element can differ from
each other - ISOTOPES
– An atom is made of smaller parts
Structure of the Atom

Atom – smallest particle of an element
that can exist alone
– Two regions of an atom
 Nucleus
– Center of atom
– Protons and neutrons
 Electron
“cloud”
– Area surrounding nucleus
containing electrons
Discovery of the electron
Symbol  e Cathode ray tubes (CRT)

– Vacuum tube containing an electron gun (a source of
electrons) and a fluorescent screen, with internal or external
means to accelerate and deflect the electron beam, used to
form images in the form of light emitted from the fluorescent
screen.
– Used in TV, computer monitors
Discovery of the electron

Charge and mass of the electron
– JJ Thomson – 1897
 Discovered
the electron
 1907 Nobel Prize in Physics
 http://videos.howstuffworks.com/hsw/6298-atomicstructure-electrons-video.htm
 Did experiments with CRT –
– Found that the charge to mass
ration was always the same
Discovery of the atomic nucleus
Ernest Rutherford – 1908
 Gold Foil Experiment

Composition of the nucleus
 Protons
– Positive charge
http://videos.howstuffworks.com/hsw/5
806-atomic-structure-the-nucleusvideo.htm
 Neutrons
– Neutral charge
http://videos.howstuffworks.com/hsw/58
07-atomic-structure-neutrons-video.htm
Forces in Nucleus
 Nuclear
forces
– Forces that hold nuclear particles
together
– Binds protons and neutrons into the
atomic nucleus
Sizes of Atoms
Based on distance electrons travel away
from the nucleus
 http://videos.howstuffworks.com/hsw/578
8-size-of-atoms-matter-video.htm

Summary
Counting Atoms

Atomic Number
– Symbol  Z
– Number of protons in nucleus
– The number of protons determines
identity of the element!!
Counting Atoms
 Isotopes
– Atoms of the same element with varying
number of neutrons
– Nuclide – general term for any isotope
of any element
– Mass Number – total number of protons
+ neutrons
Counting Atoms
 The
isotope of hydrogen
– Protium – one proton only; 1e– Deuterium – one proton, one neutron,
one electron
– Tritium – one proton, two neutrons, one
electron; radioactive
– http://www.citycollegiate.com/isotopeso
fhydrogen.htm
Counting Atoms
 Designating
Isotopes
– Hyphen notation
 Name-mass
#
 Uranium-235 – How many p, n, e-?
 Ex – Neon with 12 neutrons?
– Nuclear Symbol Notation



MN
AN Element
3 H
1
235 U
92
symbol
How many p,n,e- in chlorine-37?
Relative Atomic Mass
 Relative
scale
– Standard needed to be set
– Carbon-12
 All
others compared to Carbon-12
 Atomic
mass unit
– amu
– The mass of an individual atom
– Honors: Approximate mass of a proton
or a neutron
Average Atomic Mass
 Weighted
average of the atomic
masses for all known isotopes
– Calculating average atomic mass:
Relating mass to the number of
atoms
 “Particle”
– a generic term
 Mole – SI unit for amount of
substance, counting unit
– Symbol – mol
– Avogadro’s number
 6.02
x 1023 – number of particles
in 1mol of substance
– Molar mass
 Mass
of 1mol of substance – on P.T.
Conversions
 Gram
 Mole
 Mole  Particle
 Gram  Particle
Mole  Gram
Particle  Mole
Particle  Gram
Facts (Conversion Factors):
#g PT = 1 mol
6.02 x 1023 particles = 1 mol
Conversions
 Gram
 Mole; Mole  Gram
Conversions
 Mole
 Particle; Particle  Mole
Conversions
 Gram
 Particle; Particle  Gram