Download The Periodic Law

The Periodic Law
Chapter 5
Essential Question
What were the roles of Mendeleev
and Moseley in the development of
the periodic table?
Periodic Table groups
Write the names of the
groups of elements.
1.Yellow
2.Blue
3.Pink
4.Red
5.Green
Before 1860
• More than 60 elements had been discovered.
• There was no method to accurately determine an elements atomic mass
or number of atoms of an element in a compound.
• 1860, Germany, first international congress of chemists
• Stanislao Cannizzaro presented a method for accurately measuring
relative atomic masses of atoms, it was accepted.
• Chemists began to look for relationships between the atomic mass and
other properties of an element.
Mendeleev and Chemical Periodicity
• Mendeleev hoped to organize the elements by their properties
while looking for other trends or patterns.
• Mendeleev noticed that certain patterns and similarities appeared
at regular intervals when the elements were arranged in order of
increasing atomic mass.
• Such a repeating pattern is referred to as periodic.
The First Published Periodic Table
• Similar properties were grouped together
• Elements listed in order of increasing atomic mass
• Several empty spaces were left in the periodic table
• With great accuracy, Mendeleev predicted the properties
of the elements that would fit these spaces.
• Periodic table was accepted and Mendeleev was given
credit for discovering the periodic law.
The First Published Periodic Table
Stop and Think
What do you notice
different about the first
published periodic table
and the now universally
accepted periodic table?
Find and write down the
three main differences.
Moseley and The Periodic Law
• Mendeleev’s periodic table left some unanswered questions.
• Why could most of the elements be arranged by increasing atomic
mass and others couldn’t?
• What was the reason for chemical periodicity?
• Moseley, while working with Ernest Rutherford found other
patterns that Mendeleev didn’t find.
• Moseley found that the elements fit into the periodic table better
when they were arranged by the atomic number or number of
protons in the nucleus.
• This led to the definition of atomic number, and the recognition
that atomic number not atomic mass as the basis for the
organization of the periodic table.
Stop and Think
Why didn’t Mendeleev
think of arranging the
periodic table by the
atomic number instead of
the atomic mass?
The Periodic Law
The physical and chemical
properties of the elements
are periodic functions of
their atomic numbers.
(When elements are
arranged in order of
increasing atomic number,
elements with similar
properties appear at
regular intervals on the
periodic table.)
Stop and Think
1.What patterns do
you notice in the
groups of elements?
2.What do you think
that this pattern
relates to?
The Modern Periodic Table
The periodic table is an arrangement of the elements in order of
their atomic numbers so that elements with similar properties fall
in the same column or group.
Groups added to Mendeleev’s modern periodic table by other
scientist are:• The Noble gases (group 8A/18)
• The Lanthanides (elements 58-71 –period 6)
• The Actinides (elements 90 -103 –period 7)
The Noble Gases
• 1868- He was discovered as a component of the sun.(Strut and Ramsay)
• 1894- Ar was discovered (but was not considered important)
• Both elements had a total lack of reactivity, so a new group was
proposed by Ramsay.
• 1898- Kr and Xe were discovered and added to the group.
• 1900- Rn, the final noble gas was discovered and added to the group
Stop and Think
Why were He and Ar
considered not
important at the time of
their discovery?
The Actinides and Lanthanide Series
• The lanthanides are 14
elements with atomic
numbers from 58 to 71.
• Elements are very similar in
chemical and physical
properties.
• The Actinides are 14 elements
with atomic numbers from 90
to 103.
Lanthanides and Actinides
The actinides and lanthanides are placed below the main periodic table only
to save space and to give the table a more uniformed appearance.
Periods and Blocks
• The length of each period
is determined by the
number of electrons that
can occupy the sublevels
in that period.
• The period of an element
can be determined by the
elements electron
configuration by looking at
the highest occupied
energy level.
The s- Block Elements: Groups 1 and 2
Group 1- Alkali Metals
• 1 electron in their outermost shell
• Silvery appearance
• Soft enough to cut with a knife
• Very reactive because of the one outer electron
• Combine vigorously with nonmetals
• React strongly with water to produce hydrogen gas and alkali solutions
• Stored in kerosene because they also react with the air and any type of
moisture.
• Moving down the group they melt at successfully lower temperatures.
Hydrogen
Hydrogen is the first element in the
periodic table
Over ninety percent of all the atoms in the
universe are hydrogen atoms
Reacts easily with most Halogens(group 7)
Found in the sun, plants and sugars, and
used in cryogenics
Lithium
The first metal encountered in the
periodic table
Silvery colored solid when purified
Never found alone in nature
Found in batteries, medicine, rocks and
soils, nuclear reactors, air conditions
Potassium
Never found by itself in nature
Softer metals with a silver color
Found in bananas, crust of the
earth, fireworks, fertilizer,
oceans, and nuclear reactors.
Group 2- Alkaline Earth Metals
• A pair of electrons in their outer shell
• Ns2 electron configuration
• Harder, denser, and stronger than group 1 (alkali metals)
• Higher melting points
• Less reactive than group 1
• Too reactive to be found in nature as free elements
Berylium
Purified beryllium is a grey, hard, steellike metal that is very poisonous
Non-magnetic metals are very useful in
electronics
Never found alone in nature
Found in emeralds and gems, machine parts,
space crafts, and satellites.
Magnesium
Very light and silvery metal.
Used in many other metal alloys to
increase strength without increasing the
weight
Both humans and plants need magnesium
to live and be healthy.
Found in medicine, chlorophyll, and
camera flash bulbs.
Calcium
Calcium (Ca) is an important element
that helps your bones stay strong
Your nervous system also uses calcium
to help transmit impulses through your
body
Hard silver-colored metal.
Hydrogen and Helium
• Hydrogen’s properties are not similar to any of the other groups.
• Can be placed in group one because it has one valance electron
• Helium has a ns2 configuration, but is in group 18 because its highest
shell/orbital is full
• Stable because it cannot accept any electrons
The d-Block groups 3-12
•
•
•
•
•
•
•
•
Transitional metals
Typical metallic properties
Consists of 5 orbitals (holds 10 electrons)
Good conductors of electricity
High luster
Less reactive than groups 1 and 2
Some exist as free elements in nature
Palladium, platinum and gold are the least reactive and are found free
in nature
The p- Block groups 13-18
• All elements except He
• Called main group elements
• The right side of the block contains all nonmetals
• Six metalloids are also in the p-Block
•
•
•
•
Brittle solids
Intermediate conductivity
Harder and denser than s block elements
Softer and less dense than d block metals
Group 17 Halogens
• Most reactive nonmetals
• React vigorously with most
metals to form salts
• Seven electrons in the outer shell
makes it very close to being
stable.
Noble Gases
• Six noble gases (He, Ne, Ar, Kr, Xe, and Rn)
• Oxidation n umber is 0
• Maximum level of electron makes them very stable
• Odorless and colorless
• Monatomic gases
• Largest ionization energy
• Size increase down the periodic table
Electron Configuration
The electron configuration of an element tells you a number of things
about that element.
• Group
• Period
[Xe] 6s
• Block
For example:
2
Tells you that the element is in the:
6th period
S block
Group 2 (2nd element in the block)
Does it have a high or low reactivity