The Periodic Table
With due credit to the extraordinary PeriodicTable.com
History of the Periodic Table
• Dmitri Mendeleev developed first periodic table where elements
were arranged according to increasing atomic mass. Spaces in
table due to unknown elements predicted by Mendeleev...
• Henry Moseley rearranged the Periodic Table so elements are
arranged according to increasing atomic number (the number of
protons)
• Arrangement by atomic number is better than arrangement by
atomic mass because no element will ever have the same
number of protons but elements may have similar atomic mass
may vary due to varying numbers of neutrons in isotopes
Conventions of the Periodic Table
•
Elements are arranged by groups and periods...
• Groups are vertical and elements have the same number of
valence electrons in the outer orbital
• Periods are horizontal and elements are arranged by
increasing atomic number (the number of protons)
• Element keys may be colored based on metal, metalloid,
and nonmetal classification of elements
• Element keys may also denote if element is a solid, liquid,
or gas at room temperature
Example of Element Key
Two major groups of elements…
Representative elements and transition elements
Group 1: Alkali Metals
•
One valence electron in outer orbital,
therefore very reactive!
•
Silvery solids with low densities and low
melting points
•
Increase in reactivity as you move down the
group, therefore Francium will be the most
reactive
•
Although hydrogen is in Group 1, it is not an
alkali metal! It is just a gas with one valence
electron in its outer shell...
Group 1: Alkali Metals
•
Lithium is using lithium
batteries
• Sodium complexes with chlorine
to form table salt
• Potassium is found in potatoes
and bananas
Group 2: Alkaline Earth Metals
•
Two valence electrons in outer orbital,
therefore less reactive than group 1
elements
•
Denser, harder, with a higher melting
point than alkali metals in the same
period
Group 2: Alkaline Earth Metals
•
Beryllium is found in gems like
emeralds and aquamarines
• Magnesium is an important
element in chlorophyll, the
light-capturing pigments in
green plants
• Calcium is important in bones
and teeth
Groups 3-12: Transition Elements
• Number of valence electrons in outer orbital varies
• All are metals, therefore they are solids that are malleable, ductile, and
conduct electricity and heat
• Most have higher melting points than representative elements
Groups 3-12: Transition Elements
•
The Iron Triad (iron, cobalt, and nickel)
are magnetic metals
•
Iron is necessary to carry oxygen in
hemoglobin and is used with other
elements to make steel
• Mercury has the lowest melting point of
any metal and is liquid at room
temperature
•
The Platinum Group, including
platinum and iridium, maybe used as
catalysts (substances that decrease the
activation energy needed to start a
chemical reaction)
Groups 3-12: Inner
Transition Elements
Lanthanide Series - Very soft... May be cut with a
knife and difficult to separate from other elements
(complexes like Play-doh)
Actinide Series - All are radioactive
Lanthanide Series
Actinide Series
Lanthanide Series
•
Originally named the rare earth
metals, but then geologists
realized the Lanthanides are not
so rare...
• Cerium is more prevalent in the
Earth's crust then lead, and is
used to make flint for lighters
Actinide Series
•
Thorium, protactinium, and
uranium are naturally found on
Earth
• Half-life of uranium is 4.5 billion
years
• All other actinides are synthetic
elements made by colliding nuclei of
atoms using a particle accelerator...
Synthetic products may be very
unstable and break down into other
elements within seconds!
Group 13: Boron Group
• Three valence electrons in outer orbital, therefore
even less reactive than groups 1 & 2
• Group 13 contains one metalloid and four metals...
• Boron is a brittle black metalloid often used in making
pots and pans that may tolerate large temperature
changes over a short time (refrigerator to oven)
• Aluminum is used to make soda cans,
cookware,
baseball bats, housing siding, and of course,
aluminum foil
Group 14: Carbon Family
•
Four valence electrons in outer orbital, therefore not very reactive
due to energy necessary to gain or lose four electrons...
•
•
Group 14 consists of one nonmetal, two metalloids, and two metals
•
Silicon & Germanium are both metalloids used in industry as
semiconductors because they can conduct electricity in small
amounts and not generate a lot of heat. Silicon found in sand is
used to make glass...
Carbon is the element necessary for all organic molecules. It's small
atomic mass and the ability to form four covalent bonds enables it to
form a wide variety of complex molecules...
Group 15: Nitrogen Group
• Five valence electrons in outer orbital, therefore more reactive
than group 14
• Group 15 contains two nonmetals, two metalloids, and one
metal
• Nitrogen is a nonmetal gas that comprises about 80% of air, is
converted by bacteria from nitrogen gas to organic nitrogen
compounds, and is necessary for making proteins in the body
• Phosphorus is flammable when it combines with oxygen and is
used for making matches... Phosphorus is also necessary for
mineralization in teeth & bones, production of ATP, and
building DNA
Group 16: Oxygen Group
•
Six valence electrons in outer orbital, therefore more reactive than
group 15, but less reactive than group 17
•
•
Group 16 contains three nonmetals and two metalloids
Oxygen is a nonmetal gas that comprises about 20% of the air.
Oxygen is necessary for combustion to occur, for the formation of
ozone in the upper atmosphere of the planet (which protects living
organisms from harmful radiation from the Sun), and for all
organisms who perform aerobic respiration (like us...)!
• Sulfur is a yellow nonmetal usually produced in areas of volcanism,
and used to make a variety of chemicals in industry
•
Selenium conducts electricity in the presence of light and is used
to make solar cells
Group 17: Halogen Group
•
Seven valence electrons in outer orbital, therefore very reactive!
Reactivity increases towards the top of the group...
•
Group 17 elements are all non-metals that form salts with alkali
metals. Halogen means "salt former"
•
At room temperature, Fluorine & Chlorine are gases, Bromine is a
liquid, Iodine & Astatine are solids
•
•
Chlorine is added to water to kill bacteria
Iodine is used by the thyroid to make hormones needed by the body
Group 18: Nobel Gases
•
Eight valence electrons in outer orbital, therefore not very reactive
(inert)...
•
Glass tubes filled with gas glow when electricity passes through the
gas
•
Noble gases (Neon, Argon, and Krypton) are used in neon lights,
strobe lights, and in lights on airport runways
•
•
Helium does not burn and is used to fill balloons and blimps
Radon is a radioactive gas produced from the decay of uranium and
can cause lung cancer if inhaled over time