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STRUCTURE
The Atom
broken down
chemical
atoms
protons nucleus
Atomic Number
protons
nucleus
neutral protons
electrons
electrons
abbreviatedsymbol
two
capitalized
lower case
Fe iron
old
languages
Chlorine
yellowish green
elements
approved
protons neutrons
mass one
NOT
mass tiny
decimal
isotopes
Subatomic ParticlesParticle Symbol Charge Mass Location
proton p+ positive 1 nucleus
electron e- negative 0 electron
cloud
neutron n0 neutral 1 nucleus
Element-ology
6
12.01
Carbon
C
Atomic Number
Atomic Mass
Elemental Symbol
Element Name
The number of
protons in the
nucleus. Also the
number of electrons.
The mass of an
atom of that
element.
One or two letter
symbol that
represents the
element.
The element’s
common name.
Atomic CalculationsThe number of protons in
the nucleus of the atom is
equal to the atomic
number.
# Protons = Atomic #
The number of electrons
in a neutral atom is equal
to the number of protons.
#Electrons = # Protons
The mass number of the atom is equal to the sum of the number
of protons and neutrons in the
nucleus.
Mass # = # Neutron + # Protons
The number of neutrons is equal
to the difference between the
mass number of the atom (M)
and the atomic number (Z).
# Neutrons = Mass # – Atomic #
Check for Understanding
Element
Name
Element
SymbolProton #
Neutron
#
Electron
#
Relative
Mass
Number
32 32
20 20
Si 28.00
P 30.00
Bismuth 83
SCIENTIFIC THEORY
A hypothesis or group of
hypotheses that have been
supported with repeated testing.
If enough evidence exists, it
becomes accepted as a valid
explanation of a phenomenon.
A statement based on repeated
experimental observations that
describes some aspects of the universe.
Always applies under the same
conditions.
!
The Atom
Democritus and Leucippus
442 BCE
This Is what they thought atoms looked like.
Aristotle 384 BCE
Studied a very wide variety of sciences.
These sciences include logic,
philosophy, ethics, physics, biology,
psychology, politics, and rhetoric.
Aristotle did not believe in the atomic
theory.
He thought that all materials on Earth
were not made of atoms, but of the four
elements, Earth, Fire, Water, and Air.
Aristotle’s idea, caused Democritus’
idea to be over-looked for about 2,000
years!
John Dalton ~1808
Developed a theory
that matter is simply
composed of atoms
of different weights.
Also proposed that
these atoms are
spherical, and are in
motion.
Daltons Theory1. Everything is composed of atoms, which are
the indivisible building blocks of matter and
cannot be destroyed.
2. All atoms of an element are identical.
3. The atoms of different elements vary in size
and mass.
4. Compounds are produced through different
whole-number combinations of atoms.
5. A chemical reaction results in the
rearrangement of atoms in the reactant and
product compounds.
Law of Definite ProportionsThe Law of Definite Composition, a chemical compound always
contains the same elements in the same proportions by mass
regardless of the size of the sample.
Examples: Table Salt (NaCl)
60.66% Chlorine
39.34% Sodium
?
How much of this is Sodium?
How much of this is Chlorine?
J.J. Thompson 1898Developed the cathode ray experiment
Discovers the electron
Create the plum pudding model.
Thompson’sCATHODE RAY EXPERIMENT
Over the course of three experiments J. J. Thomson discovered the existence of electrons.
A Cathode Ray tube is a vacuum-sealed tube with a cathode (+) and anode (-) on one end that creates a beam of electrons travelling towards the other end of the tube.
ANODE
CATHODE
e- e- e- e- e- e- e- e- e- e-
Flo
ure
sce
nt
scre
en
A Fluorescent spot
appears
!
Thompson’sPlum Pudding Model
The plum pudding model is an
obsolete scientific model of the
atom proposed by J. J.
Thomson in 1904.
It was devised shortly after the
discovery of the electron.
The atom is composed of
electrons surrounded by a
“soup” of positive charge to
balance the electrons' negative
charges
Ernest Rutherford 1909He used a GOLD FOIL EXPERIMENT, observing the
scattering of alpha particles, and demonstrated
for the first time the existence of the ATOMIC
NUCLEUS.
Gold Foil Experiment
1. Shot alpha rays (from a radioactive source) through gold foil.
2. Although most of the alpha rays passed through, some of the particles were deflected.
3. The atom is made up of mainly empty space except for the nucleus in the middle which has the most mass in the atom.
Alpha Particles
Atoms
(• = nucleus)
CFU!
1. What did Dalton theorize the atom looked like?
2. Who discovered the electron?
3. Who discovered the nucleus? What was his
evidence?
Bohr’s Model
Introduced by Niels Bohr in 1913
The atom as a small, positively
charged nucleus surrounded by
electrons that travel in circular
orbits around the nucleus
Similar in structure to the solar
system, but with attraction
provided by electrostatic
forces rather than gravity.
ERWIN SCHRODINGER
◦Used math to guess where the
electrons COULD be in any
given moment
◦Electron clouds
Current atomic theoryAtoms are made of smaller particles called protons,
neutrons and electrons (and these are made of even
smaller particles – quarks!)
Electrons do not travel in definite paths
The exact path of electron cannot be predicted.
Orbitals are regions where electrons are likely to be found.
They are also known as electron clouds.
IONS/ISOTOPESREVIEW
The Atom
?
Charged atoms the result from either too many or two few electrons.
CFU
Ion
SymbolProton # Neutron # Electron #
Relative
Mass
Number
B+3
F-1
Li-2
Isotopes• The atoms of a
chemical element
can exist in
different types.
These are called
isotopes.
• Different isotopes
of the same
element have
different masses.
Atoms want stability!
Why do isotopes occur
◦ Isotopes exist because the atomic
nuclei of many elements are stable
with different numbers of neutrons in
them.
◦ Different numbers of neutrons change
neither the element nor its chemical
properties.
STABILITY IN THE NUCLEUS
Unstable nuclei will break down (decay over time) …more about that later….
Check for Understanding
Isotope
Name
Isotope
SymbolProton # Neutron #
Electron
#
Relative
Mass
Number
Oxygen – 18
Arsenic - 75
Phosphorus -
31
