The Periodic Table
Chapter 17.3
Why is the Periodic Table important
to me?
• The periodic table is the most
useful tool to a chemist.
• You get to use it on every test.
• It organizes lots of information
about all the known elements.
• It enable scientists to study
their physical and chemical
properties easily
Pre-Periodic Table Chemistry …
• …was a mess!!!
• No organization of
elements.
• Imagine going to a grocery
store with no organization!!
• Difficult to find information.
• Chemistry didn’t make
sense.
Dmitri Mendeleev: Father of the
Table
HOW He WORKED…
• Put elements in rows by
increasing atomic mass
(check pattern)
• Put elements in columns
by the way they reacted.
Periodic table of elements
SOME PROBLEMS…
•He left blank spaces for what he said were
undiscovered elements. (Turned out he was right!)
•He broke the pattern of increasing atomic weight to
keep similar reacting elements together.
The Current Periodic Table
• Mendeleev wasn’t too far off.
• Henry Mosely later put the elements in rows by
ATOMIC NUMBER!!
increasing
• The horizontal rows are called periods and are
labeled from 1 to 7.
• The vertical columns are called groups are
labeled from 1 to 18.
Parts of a periodic table
• Visist www.ptable.com
and check the parts of
the periodic table:
• We have three main
parts of the periodic
table:
- metals, non metals and
metalloids.
Metals
•
•
•
•
•
•
Are good conductor of heat and
electricity
Are shiny and sonorous
Are ductile and malleable
Are solid at room temperature
except: mercury which is liquid
Have high melting and boiling
points
Are on the left side of the periodic
table
Non- metals
•
•
•
•
•
Are bad conductor of electricity (
with the exception of carbon
graphite) and heat.
Are brittle and dull in appearance
Are generally gases with the
exception of bromine (liquid) and
some solids ( carbon, silicon,
sulfur…)
Have low melting and boiling points
Are on the right side of the periodic
table
Metalloids
• Possess some properties of
metals and non metals
• They are sometimes called
semi metals and are used in
semi conductors ( Si and Ge
are used in transistors)
• They conduct electric current
under very low temperatures.
• Located on the stair line in
the periodic table
( check figure at the right)
Periods in a periodic table
• Remember that electrons
surround the nucleus, it is
very difficult to locate an
electron but electrons are
mainly found in orbit (also
called energy levels shells
). In the nucleus, we have 7
energy levels. Electrons
occupy the energy levels
close to the nucleus
because they have lower
energy.
• These energy levels
show in the peiodic table
as the horizontal rows.
• We have 7 periods in
the periodic table.( 7
energy levels)
• The period of an element
is the number of shells
occupied by electrons in
an atom.
Periods in periodic table
• Energy level are usually
represented by the letter “n”
• Each energy level ( if n≤4)
contains : 2n² electrons.
• For n≥5, check explanation.
• Now, calculate the number of
electrons in each shell.
Periodic table of elements:
According to this rule:
- First shell: 2 electrons
- Second shell: 8 electrons
- Third shell: 18 electrons
- Fourth shell: 32 electrons.
However, this is not the case in
the periodic table Why? You
will be able to understand this
in grade 10 when you learn
the concept of suborbits and
sublevels.
Groups in the periodic table
• Groups in the periodic table
represent the vertical
columns. We have 18
groups in the periodic table.
• To understand the concept
group, we should know the
concept of valence
electrons.
• Valence electrons are the
electrons present in the
outer shell of an atom
Groups…Here’s Where the
Periodic Table Gets Useful!!
• Elements in the
same group
have similar
chemical and
physical
properties!!
•
(Mendeleev did that on purpose.)
Why??
• They have the same
number of valence
electrons.
Families on the Periodic Table
• Columns are also grouped
into families.
• Families may be one column,
or several columns put
together.
• Families have names rather
than numbers. (Just like your
family has a common last
name.)
Hydrogen
• Hydrogen belongs to a family
of its own.
• Hydrogen is a diatomic,
reactive gas.
• Hydrogen was involved in the
explosion of the Hindenberg.
• Hydrogen is promising as an
alternative fuel source for
automobiles
Periods in a periodic table
Alkali Metals
• 1st column on the
periodic table (Group 1)
not including hydrogen.
• Very reactive metals,
always combined with
something else in nature
(like in salt).
• Soft enough to cut with a
butter knife
Alkaline Earth Metals
• Second column on the
periodic table. (Group 2)
• Reactive metals that are
always combined with
nonmetals in nature.
• Several of these
elements are important
mineral nutrients (such
as Mg and Ca
Transition Metals
• Elements in groups 3-12
• Less reactive harder
metals
• Includes metals used in
jewelry and construction.
• Metals used “as metal.”
Boron Family
• Elements in group 13
• Aluminum metal was
once rare and expensive,
not a “disposable
metal.”
Carbon Family
• Elements in group 14
• Contains elements
important to life and
computers.
• Carbon is the basis for
an entire branch of
chemistry.
• Silicon and Germanium
are important
semiconductors.
Nitrogen Family
• Elements in group 15
• Nitrogen makes up over
¾ of the atmosphere.
• Nitrogen and phosphorus
are both important in
living things.
• Most of the world’s
nitrogen is not available
to living things.
• The red stuff on the tip of
matches is phosphorus.
Oxygen Family or Chalcogens
• Elements in group 16
• Oxygen is necessary for
respiration.
• Many things that stink,
contain sulfur (rotten
eggs, garlic, skunks,etc.)
Halogens
• Elements in group 17
• Very reactive, volatile,
diatomic, nonmetals
• Always found combined
with other element in
nature .
• Used as disinfectants
and to strengthen teeth.
The Noble Gases
The Noble Gases
• Elements in group 18
• VERY unreactive,
monatomic gases
• Used in lighted “neon”
signs
• Used in blimps to fix the
Hindenberg problem.
• Have a full valence shell.
Periodic table of elements
• Use the periodic table : find the group and the
period of the 20 first elements. Identify the
number of valence electrons for each element.
Periodic Law
• PERIODIC LAW, in chemistry, law stating that many of the
physical and chemical properties of the elements tend to recur in
a systematic manner with increasing atomic number. Progressing
from the lightest to the heaviest atoms, certain properties of the
elements approximate those of precursors at regular intervals of
2, 8, 18, and 32. For example, the 2d element (helium) is similar
in its chemical behavior to the 10th (neon), as well as to the 18th
(argon), the 36th (krypton), the 54th (xenon), and the 86th
(radon). The chemical family called the halogens, composed of
elements 9 (fluorine), 17 (chlorine), 35 (bromine), 53 (iodine),
and 85 (astatine), is an extremely reactive family.
• Watch carefully the video and visit www.ptable.com to compare
properties of same group elements.
Electron dot diagram
• Electronic configuration:
Representation of electrons in
shells around nucleus
1. The first shell can fit up to 2
electrons
2. The second shell can fit up to 8
electrons
3. The third shell can fit up to 8
electrons ( remember not 18 )
4. Use the periodic table to draw the
electronic configuration of the 20
first elements.
Electron dot diagram
Electron dot diagram
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•
•
Electron dot structure is a dot
representation of the valence
electrons ( remember valence
electrons are electrons on the outer
shell).
Electron dot diagrams are used to
represent compounds such as
H2O( Ch 20)
Use the blank periodic and your
results in slide 33 table to write the
electron dot structure of the 20 first
elements
Electron dot structure