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Atomic Structure & the Periodic
Table
Democritus (460-370 BC)

The first to propose that matter was not
infinitely indivisible
 Believed that matter was made up of atomos
(or atoms)
 He also said that atoms could not be created
or destroyed
Democritus’ Theory
1.
2.
3.
4.
5.
Matter is composed of empty space through
which atoms move
Atoms are solid, homogeneous, indestructible,
and indivisible
Different atoms have different sizes and shapes
The differing properties of matter are due to the
size, shape, and movement of atoms
Changes in matter result from changes in the
groupings of atoms and not the atoms
themselves
John Dalton

John Dalton was the next scientist to
propose a theory about the atom in the
19th century
Dalton’s Atomic Theory
1.
2.
3.
4.
5.
All matter is composed of extremely small particles
called atoms
All atoms of a given element are identical, having
the same size, mass, and chemical properties.
Atoms of a specific element are different from other
elements
Atoms cannot be created, destroyed, or broken into
smaller particles
Different atoms combine in simple whole number
ratios to form compounds
In a chemical reaction, atoms are separated,
combined, or rearranged
History of Atomic Structure
Scientist
Experiment
Knowledge Obtained
Crookes
Cathode Ray
Tube
Neg. particles of
some kind exist
J.J. Thomson
Cathode Ray
Deflection
Oil Drop
Experiment
Mass/Charge ratio
of electron
Charge of electron
Gold Foil
Experiment
Nucleus present
Millikan
Rutherford
Basic Definitions

Atom – smallest unit of an element that
retains the properties of that element

Atoms - made up of several subatomic
particles: protons, neutrons, and
electrons
Protons, Neutrons, & Electrons

Protons



Neutrons



no charge
found in the nucleus of an atom
Electrons



+1 charge
found in the nucleus of the atom
-1 charge
found on the outside of the nucleus
Nucleus


made up of protons and neutrons
overall + charge
Atomic Structure
Atomic Numbers

Atomic number (Z) - number of protons in the
nucleus of an atom of that element.

The number of protons determines the identity
of an element

The number of protons for an element
CANNOT be changed.
Atomic Numbers

Atoms have no overall electrical charge so the
number of protons must equal the number of
electrons.
 So, the atomic number of an element also tells
the number of electrons in a neutral atom of
that element.

The number of electrons can be changed
when determining the charge of an ion.
Masses

The mass of a neutron is almost the same as
the mass of a proton.
 The sum of the protons and neutrons in the
nucleus is the mass number (A) of that
particular atom.
 Isotopes of an element have different mass
numbers because they have different numbers
of neutrons, but they all have the same atomic
number (number of protons & electrons)
Isotopes




When writing isotopes, the atomic number (or number
of protons) will appear at the bottom left of the formula
The mass number (number of protons plus neutrons
will appear at the top left of the formula.
The element symbol will appear to the right of the
numbers
The different number of neutrons has NO bearing on
chemical reactivity
12
12
6 C
6
Writing the Names of Isotopes
When writing the name of an isotope,
you will write the name of the element
– the mass number
 For example 126 C would be named:
 Carbon - 12

Try the following
Name
Symbol
# Protons
# Neutrons
1
2
# Electrons
Mass #
25
55
Carbon – 11
197
Au
79
Oxygen - 15
Try the following
Name
Symbol
# Protons
# Neutrons
# Electrons
Mass #
Carbon – 11
11
6
5
6
11
79
118
79
197
1
2
1
3
C
6
Gold - 197
Hydrogen –
3
197
Au
79
3
H
1
Manganese 55
55
Mn
25
25
30
25
55
Oxygen - 15
15
8
7
8
15
O
8
Try this one
Name
Iodine -1 - 130
Symbol
# Protons
# Neutrons
# Electrons
Mass #
Try this one
Name
Symbol
# Protons
# Neutrons
# Electrons
Mass #
Iodine -1 - 130
130
53
77
54
130
I -1
53
Atomic Mass
Atomic mass –the
weighted average mass
of all the naturally
occurring isotopes of
that element.
 The number is usually
located at the bottom of
the periodic table and
has decimal places

Calculating Atomic Mass
Calculating Atomic Mass
Copper exists as a mixture of two
isotopes.
 The lighter isotope (Cu-63), with 29
protons and 34 neutrons, makes up
69.17% of copper atoms.
 The heavier isotope (Cu-65), with 29
protons and 36 neutrons, constitutes the
remaining 30.83% of copper atoms.

Calculating Atomic Mass

First, calculate the contribution of each
isotope to the average atomic mass,
being sure to convert each percent to a
fractional abundance.
Calculating Atomic Mass

The average atomic mass of the element
is the sum of the mass contributions of
each isotope.
Try this one…
Calculate the atomic mass of germanium.
72.59 amu
You can tell many things from an
isotope formula

Hydrogen has three naturally occurring
isotopes in nature: Hydrogen – 1,
Hydrogen – 2, and Hydrogen – 3.

Which is the most abundant in nature?


Hydrogen – 1
Which is the heaviest?

Hydrogen - 3
Periodic Table

Periodic Table – arrangement of
elements in order of increasing atomic
number with elements having similar
properties in vertical columns
Groups – vertical columns
 Periods – horizontal rows

Group Names
Group
1A
2A
6A
7A
8A
Name
Alkali Metals
Alkaline Earth Metals
Chalcogens
Halogens
Noble Gases
Groups
The group tells you the number of
valence electrons that the element has
 Valence electrons - electrons in the
outermost shell of the atom
 All group 1A elements have 1 valence
electron. Likewise, all group 8A elements
have 8 valence electrons.

Characteristics
Elements in the same group exhibit
similar chemical characteristics due to
the fact that they all have the same
number of valence electrons.
 The most stable number of valence
electrons is 8
 This is called an octet

Charges



Every element wants 8 valence electrons to become
stable. They will gain or lose valence electrons to form
an octet
For example…Group 1A elements have 1 valence
electron. They can either gain 7 electrons to have an
octet or lose 1.
What is easier?
Lose 1

If an element loses 1 electron (1 negative charge)
what charge will the resulting ion have?
+1
Charges
Let’s go to group 7A. This group has 7 valence
electrons
 It can either loose 7 or gain 1
 What is the easiest?

Gain 1

What will be the resulting charge if the element
gain 1 electron (1 negative charge)?
-1
Physical States and Classes of
the Elements
The majority of the elements are metals.
They occupy the entire left side and
center of the periodic table.
 Nonmetals occupy the upper-right-hand
corner.


Metalloids are located along the
boundary between metals and
nonmetals.
Metals

Metals are elements that have luster, conduct
heat and electricity, and usually bend without
breaking.

All metals except mercury are solids at room
temperature; in fact, most have extremely high
melting points.

The periodic table shows that most of the metals are
not main group elements.
Transition Metals

The elements in Groups 3 through 12 of the
periodic table are called the transition
elements.

All transition elements are metals.

Many transition metals can have more than
one charge
Inner Transition Metals

In the periodic table, two series of elements,
atomic numbers 58-71 and 90-103, are placed
below the main body of the table.

These elements are separated from the main
table because putting them in their proper
position would make the table very wide.

The elements in these two series are known
as the inner transition elements.
Inner Transition Metals

The first series of inner transition
elements is called the lanthanides
because they follow element number 57,
lanthanum.

The second series of inner transition
elements, the actinides, have atomic
numbers ranging from 90 (thorium, Th)
to 103 (lawrencium, Lr).
Non Metals

Most nonmetals don’t conduct electricity,
are much poorer conductors of heat than
metals, and are brittle when solid.

Many are gases at room temperature;
those that are solids lack the luster of
metals.

Their melting points tend to be lower than
those of metals.
Properties of Metals and
Nonmetals
Metalloids
Metalloids have some chemical and
physical properties of metals and other
properties of nonmetals.
 In the periodic table, the metalloids lie
along the border between metals and
nonmetals.
