THE PERIODIC TABLE TRENDS
 Matter is composed of extremely
EARLY IDEAS ABOUT
small particles called atoms
MATTER
 Atoms are indivisible and
indestructible
JOHN DALTON
 Atoms of a given element are
identical in size, mass, and
chemical properties
 Atoms of a specific element are
different from those of another
element
 Different atoms combine in simple
whole-number ratios to form
compounds
 In a chemical reaction, atoms are
separated, combined, or
rearranged.
1. All elements are composed of tiny
indivisible particles called atoms. (this was later
shown to be false)
2. Atoms of the same element are identical.
The atoms of any one element are different
form those of any other element.
3. Atoms of different elements can physically
combine with one another in simple
whole-number ratios to form
compounds.
4. Chemical reactions occur when atoms are
separated, joined, or rearranged. Atoms
of one element, however, are never
changed into atoms of another element as
a result of a chemical reaction.
Atom – the smallest particle of an element that retains
the properties of that element .
Example: How many atoms are in each compound?
CO2
H2O
3
3
H2SO4
7
THE ELECTRON
 Cathode ray tube is a vacuum
THE
pump,
they
passed
electricity
CATHODERAY
through the glass tubes from
TUBE
which most of the air had
been removed.
The ELECTRON
SIR WIILLIAM  Cathode ray- a ray originating
from the cathode and
CROOKESEnglish physicist
Noticed a green
flash was
produced in
cathode ray tube
traveling to the anode.
 Led to the invention of the
television
 Cathode rays were a stream of
charged particles
 The particles carried a
negative charge
 The negatively charged
particles were called electrons
THE ELECTRON
Mass and Charge of an
electron
 English physicist JJ Thompson
(1856-1940) began a series of
cathode ray experiments to
determine the mass and charge
of an electron.
 Discovered mass to be less than
that of a hydrogen atom.
 Shock to science community
because it meant Dalton was
wrong-atoms were divisible
 Determined mass to be 1/2000
the mass of a hydrogen atom
and did not depend on the gas
in the cathode ray tube.
THOMPSON’S
MODEL
PLUM PUDDING
THE ELECTRON
MILLIKAN OIL DROP
EXPERIMENT
CHARGE OF AN
ELECTRON
 American physicist Robert Millikan
determined the charge of an
electron using the oil –drop
apparatus
 Determined charge of electron to
be 1.602 x 10-19 Coulombs. Later
changed to -1
THE ELECTRON
 Millikan was able to calculate
the mass of an electron using
the mass to charge ratio. The
mass of an electron is 1/1840
of the mass of a hydrogen
atom.
PROTONS AND
NEUTRONS
 Atoms have no net electric
charge
 Electric charges are carried by
particles of matter
We have an electron
which is negative so  Electric charges always exist in
what is happening
whole-number multiples of a
inside the atom?
single basic unit
 When a given number of
FOUR IDEAS ABOUT MATTER
What are scientists
missing?
negatively charged particles ,
an electrically neutral particle
is formed
PROTON
E. Goldstein
 Observed the cathode ray
tube and found rays traveling
in the opposite direction of
that of the cathode rays. He
called these rays canal rays
and concluded that they were
composed of positive particles
called protons.
 Each has a mass about 1840
times that of an electron.
NEUTRON
English Physicist
James Chadwick
(1891-1974)
Showed the nucleus also has a neutral
particle that had a mass nearly equal to
that of a proton, but it carries no
electrical charge. He called it a Neutron
THE NUCLEUS
Ernest
Rutherford (18711937)
 Gold Foil Experiment- studied
how positively charged alpha
particles interacted with solid
mater. A narrow beam of
alpha particles was aimed at a
thin sheet of gold foil. The
atoms in the gold foil
deflected the alpha particles.
Rutherford’s Model of the Atom
Concluded Plum pudding model was
incorrect.
Concluded that almost all of the
atom’s positive charge and all of its
mass were contained in a tiny dense
region in the center of an atom,
which he called the nucleus.
The negatively charged electrons are
held within the atom by their
attraction to the positively charged
nucleus.
HOW DO ATOMS DIFFER?
HOW IS THE ATOMIC NUMBER USED TO
DETERMINE THE IDENTITY OF AN ATOM?
WHY ARE ATOMIC MASSES NOT WHOLE
NUMBERS?
GIVEN THE MASS NUMBER, HOW ARE THE
NUMBER OF ELECTRONS, PROTONS, AND
NEUTRONS IN AN ATOM CALCULATED?
ATOMIC NUMBER
HENRY MOSELEY
English Scientist (18871915)
 Discovered that atoms of each
element contain a unique
positive charge in their nuclei
through his experiments with xrays.
 The number of protons
identifies it as an atom of a
particular element.
 He rearranged the periodic
table by atomic number and
issues because of mass
arrangement disappeared.
Reading the
periodic table
Atomic
number =
number of
protons =
number of
electrons (in
a stable
atom)
Think challenge
How many protons
and electrons do the
following elements
have in a stable
atom?
 H _______ p, _________e
 Si _______p, _________e
 Br _______ p, _________e
 Mg ______p, _________e
 Li _______p, _________e
 Fe _______p, _________e
 W _______p, ________e
 F ________p, _________e
 Xe _______p, _________e
Think Challenge
Element
Fill in the chart
A
Atomic
number
Protons
electrons
Kr
B
30
C
17
D
20
E
66
F
K
G
14
H Be
I
12
Isotopes
All atoms of an
element that have
the same number of
protons and
electrons, but the
number of neutrons
may differ
(DALTON was
WRONG)
 Atoms with the same number
of protons but different of
neutrons are called isotopes!
 Ex. Potassium occurs
naturally in three types. All
types contain 19 protons and
19 electrons but contain 20,21,
or 22 neutrons.

In spite of these differences,
isotopes have the same
chemical behavior.
Isotope notation
Isotopes continued
In nature, most elements are found
as mixtures of isotopes. The
relative abundance of each isotope
is constant.
Two isotopes of carbon are carbon -12
and carbon-13. Write the symbol for
each isotope using superscripts and
subscripts to represent the mass
number and the atomic number.
Three isotopes of oxygen are
oxygen-16, oxygen-17, and oxygen18. Write the complete symbol for
each, including the atomic number
and mass number.
The three isotopes of chromium are chromium-50,
chromium-52, chromium-53. How many neutrons,
are in each isotope, given that chromium always has
an atomic number of 24?
Atomic Mass
Why is the mass not a whole
number?
 Atomic mass of an element is
the weighted average mass of the
isotopes of that element.
Because isotopes have different
masses, the weighted average is
not a whole number.


Masses are so small that we work
with relative masses. The isotope
of C-12 was assigned a mass of
exactly 12 amu (atomic mass
units).
Mass = protons + neutrons
Isotope abundance
Example: In a banana, 93.26% is
potassium-39, 6.73% is
potassium-41 and 0.01% is
potassium-40. In another banana
or in a different source of
potassium, the percentage
composition of the potassium
isotopes will still be the same
Atomic mass is a weighted
average, the atom which
occurs in greater abundance
have a greater effect in
determining the atomic mass.
Calculated by multiplying each
isotopes percent abundance
by its atomic mass and then
adding the products.
Teacher Example
 Boron has two naturally occurring
isotopes: boron-10 (abundance
19.8% mass 10.013 amu) and
boron-11 (abundance 80.2%, mass
11.009 amu). Calculate the atomic
mass of boron.
Teacher Example
 Copper has 2 isotopes Cu-63
(abundance 69.2%, mass
62.930 amu) and Cu-65
(abundance 30.8%, mass
64.928). Calculate the atomic
mass of copper.
YOUR TURN
THINK CHALLENGE
t
 Three Magnesium isotopes
have atomic masses and
relative abundances of 23.985
amu (78.99%), 24.986 amu
(10.00%), and 25.982 amu
(11.01%). Calculate the atomic
mass of magnesium.
THINK CHALLENGE
Calculate the atomic
mass of unknown
element X. Then
identify the
unknown element,
which is used to
medically to treat
some mental
disorders.
Isotope
Mass (amu)
Percent
abundance
6X
6.015
7.59%
7X
7.016
92.41%
__________________3. silver tarnishing
THINK CHALLENGE
 There are three isotopes of
silicon; they have mass
numbers of 28, 29, and 30.
The atomic mass of silicon is
28.086 amu. Comment on the
relative abundance of the
three isotopes.
THINK CHALLENGE
 How can atomic number and
mass number be used to find
the numbers of protons,
electrons and neutrons?
THINK CHALLENGE
 How are isotopes of the same
element alike?
 How are isotopes of the same
element different?
THINK CHALLENGE
 Explain why the atomic
masses of elements are
generally not whole numbers?
What is the relationship between
unstable nuclei and radioactive decay?
How are alpha, beta, and gamma
radiation characterized in terms of
mass and charge?
Radioactivity
NUCLEAR REACTION
 A nuclear reaction can
change an element into a new
element due to a change in an
atom’s nucleus.
 In the late 1890’s scientists
noticed that some substances,
spontaneously emitted
radiation in a process called
radioactivity.
 Radiation is the rays and
particles emitted by
radioactive material.
Radioactivity
Why is this break through
important?
 Radioactive atoms emit
radiation because their nuclei
are unstable. The neutron to
proton ratio determines
stability.
 Unstable nuclei lose energy
by emitting radiation in a
spontaneous process called
radioactive decay.

Undergo this process until the
nucleus becomes stable,
forming a different element.
Types of Radiation
 Alpha radiation- radiation
that was deflected toward a
negatively charged plate.
 Alpha particle contains two
protons and two neutrons,
and thus have a +2 charge,
which is why they are
attracted to negatively
charged plates
Equivalent to a helium-4
nucleus
Represented by
Types of Radiation
Alpha Radiation
What do you notice
about these
equations?
Is there a rule you
could write?
 Nuclear Equation (shows the atomic
numbers and mass numbers of the particles
involved. The mass number is conserved.)
Alpha Radiation
Formula for writing an alpha radiation equation and
determining new element created.
THINK CHALLENGE
What change in mass number occurs when a
radioactive atom emits an alpha particle?
What is the primary factor that determines whether a
nucleus is stable or unstable?
Boron-10 emits alpha particles. Write a balanced nuclear reaction for the
radioactive decay.
TYPES OF
RADIATON
BETA Radiation
 Radiation that is deflected
toward the positively charged
plate was named beta
radiation.
 The radiation consists of fast
moving beta particles


Each beta particle is an
electron with a 1- charge
Represented by the symbol
Types of Radiation
Beta Radiation
What do you notice
about these
equations?
Is there a rule you
could write?
 Nuclear Equation (shows the atomic
numbers and mass numbers of the particles
involved. The mass number is conserved.)
Beta Radiation
Formula for writing an alpha radiation equation and
determining new element created.
Types of Radiation
Gamma Radiation
 Gamma ray is a high-energy
radiation that possesses no mass
and is denoted by the symbol



Because they are neutral, gamma
rays are not deflected by electric
or magnetic fields.
Often accompany alpha and beta
radioactive decays.
Because they are massless, the
emission of gamma rays cannot
result in the formation of a new
element
Illustration of types
of radiation