Transcript The Periodic Table

The Periodic Table
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.
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
SOME PROBLEMS…
HOW HIS WORKED…
• Put elements in rows by • He left blank spaces for
what he said were
increasing atomic weight.
undiscovered elements.
• Put elements in columns
(Turned out he was
by the way they reacted.
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.
• 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.
• Now the elements are put in rows by increasing
ATOMIC NUMBER!!
• There is a periodic repetition of their physical &
chemical properties when elements are arranged by
their atomic number……this is called The Modern
Periodic Law.
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.
• They will form the same
kinds of ions.
METALS
More that ¾ of the known elements are metals.
Metals share similar properties:
•
•
•
•
•
•
•
Good conductors of heat & electricity
Luster
Malleable & ductile
High densities
High boiling points & melting points
Resists stretching & twisting
Solids at room temperature
NONMETALS
•
•
•
•
•
No luster
Poor conductors
May be solid, liquid or gas
Low densities
Low melting & boiling points
METALLOIDS
• Also called semimetals
• Have properties of both metals and
nonmetals
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
• German airship (called a zeppelin)
• 804 feet long
• In 1937 it caught fire killing 35 of the 97 people on
board.
• Travelling from Germany to US; caught fire as it was
landing in NJ
• LZ 129 Hindenburg was a German zeppelin.
Together with its sister-ship LZ 130 Graf Zeppelin II
it was the largest aircraft ever built.
• LZ 129 Hindenburg was a German zeppelin.
Together with its sister-ship LZ 130 Graf
Zeppelin II it was the largest aircraft ever built.
• A Zeppelin is a type of dirigible, more
specifically a type of rigid airship
• An airship is a buoyant aircraft that can be
steered and propelled through the air.
Unlike aerodynamic craft (e.g. airplanes
and helicopters) which stay aloft by moving
an airfoil through the air in order to produce
lift, aerostatic craft such as airships (and
balloons) stay aloft primarily by means of a
cavity (usually quite large) filled with a gas
of lesser density than the surrounding
atmosphere.
• In the early days of airships, the
primary lifting gas was hydrogen.
Until the 1950s, all airships, except
for those in the United States,
continued to use hydrogen because
it offered greater lift and was
cheaper than helium.
Alkali Metals
• 1st column on the periodic table (Group
1) not including hydrogen.
• Low densities & melting points
• React with oxygen & moisture in air
• Most reactive metals, always
combined with something else in
nature, they are not found uncombined
(like salt)
• Soft enough to cut with a butter knife
• Will react violently with water & are
stored under oil or kerosene
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
• Harder than alkali metals
• Less reactive than alkali
metals, not stored under oil
or kerosene
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
• 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 .
• Form salts when
combined with Groups 1
or 2 metals
• Used as disinfectants
and to strengthen teeth.
The Noble Gases
The Noble Gases
• Elements in group 18
• VERY unreactive, monatomic
gases
• Occur in atmosphere in very
small amounts
• Used in lighted “neon” signs
• Used in blimps to fix the
Hindenberg problem.
• Have a full valence shell.
TRENDS IN THE
PERIODIC
TABLE
#1 ATOMIC SIZE
The size of an atom is generally given in
terms of
the atomic radius.
GROUP TRENDS:
Atomic size generally increases as
we move down a group.
As we descend, electrons are
added to successively higher
energy levels.
PERIOD TRENDS:
Atomic size generally decreases
as we move from left to right
across a period.
As we move across a period, electrons
are added to the same energy level.
Protons are also added to the
nucleus. The effect of the
increasing nuclear charge on
the outermost electrons is to pull
than closer to the nucleus.
Atomic size, therefore
decreases.
#2 IONIZATION ENERGY
The amount of energy required to
remove an electron from an atom.
• When the outermost electron is
located close to the nucleus, there is
a greater attraction between the
positive protons (in the nucleus) and
the negative electrons.
• Because of this, more energy is
required to remove an electron.
When the outermost electrons are
further from the nucleus, the
attractive force is less, and it is
easier to remove an electron.
Therefore, the smaller the atom,
the higher the ionization energy.
• GROUP TRENDS:
Ionization energy decreases as we
go down a group
PERIOD TRENDS:
Ionization energy increases as we
go across a period
#3 ELECTRON
AFFINITY
The amount of energy
released when an
electron is added to an
atom.
• When electrons are added close to
the nucleus, there is a greater
attraction between the negative
electron and the positive nucleus
and electron affinity is higher.
• Therefore, the smaller the atom,
the higher the electron affinity.
GROUP TRENDS:
• Electron affinity generally
decreases as we go down
a group
PERIOD TRENDS:
Electron affinity generally
increases as we go
across a period.
#4 IONIC
SIZE
The size of an ion.
• Metals…… low ionization energy
form positive ions easily
• Nonmetals…. high ionization
energy form negative ions easily
• CATIONS: are always smaller than the
neutral atom
• Atom loses outer shell electron
• Increased attraction of nucleus on
remaining electrons
• ANIONS: are always larger than the
neutral atom
• Nuclear attraction is less for the
increased number of electrons
• Additional electrons also increases the
repulsive forces between electrons
GROUP TRENDS:
• Ionic size generally increases as we go
down a group
PERIOD TRENDS:
Ionic size generally increases for anions
And decreases for cations
as we go across a period left to right.
#5 ELECTRONEGATIVITY
Describes an atoms ability to
attract electrons. This trend is
similar to electron affinity.
GROUP TRENDS:
• Electronegativity generally decreases
as we go down a group
PERIOD TRENDS:
Electronegativity generally increases
as we go across a period.
EXCEPTIONS……….
• Nobel gases are not
included in this general
trend.
CHEMISTRY NEGATIVITY
The feeling you
have the day
after a
Chemistry
term Test!