C7 The Periodic Table
G8 Science
The Periodic Table
 Of the 118 elements we
know about, only 88 occur
naturally. The rest are
make in laboratories.
 The periodic table is a
display of the known
elements and shows how
they relate to each other.
What is the periodic table?
 The periodic table is
arranged by increasing
atomic number from
hydrogen to element 118.
 What is the atomic
number?
Who designed the periodic table?
 Scientists spent a long
time trying to find a logical
way to organize the
elements. The
breakthrough came with
Dmitir Mendelev in 1869.
What are the parts?
 The horizontal rows are
called periods. The
properties of elements
change gradually across
the period.
 The vertical columns are
called groups. Elements in
the same group have
similar properties.
What are the main categories?
 Metals are typically shiny,
opaque, ductile, and good
conductors of heat and
electricity.
 Nonmetals are poor
conductors, brittle and dull
(or gasses)
 Metalloids have properties
between the two.
What is usually on a table entry?
 Entries on the periodic
table will contain:
 Element name (maybe)
 Element symbol – Capital
letter with maybe a
lowercase letter after it
 Atomic number
 Atomic mass (in amu)
 What is an amu?
What else can be on it?
 You may also find:
•
Stable mass numbers
 Count of electrons in each shell
 Picture of the element
 Link to element information
Groups on the periodic table
 Alkali metals: group 1, soft, silvery, highly reactive. Combines
2:1 with oxygen Li2O
 Alkaline Earth metals: group 2, combine 1:1 with oxygen
CaO. Reactive, but less so that alkali metals.
 Halogens: group 17, toxic, very reactive, seldom found in
pure form, when combined with alkali metals form salts.
 Noble Gases: group 18, unreactive, inert, almost always
found in pure form.
 Transition metals: center of table, good conductors
Energy levels and the periodic table
 Period 1: only one shell (k), up to 2 electrons
 Period 2: two shells (k, l), 2 in first, up to 8 in second
 Period 3: three shells (k, l, m), 2 in first, 8 in second, up to 8 in third
 Period 4: four shells (k, l, m, n) 2 in first, 8 in second, 8 – 18 in third,
up to 8 in fourth.
 Period 5: five shells (k, l, m, n, o)
 Valence electrons are those in the outermost shell. For period 3 we
only care about the m-shell.
Warning Warning Warning
 The periodic table that we
talk about is not the only
periodic table of elements.
Physical and Chemical Properties
 Physical properties are things you can see through direct
observation, like density, boiling point, and melting point.
 The chair seat is a dull red, flexible, low-odor flexible solid at
room temperature.
 Water is a colorless, odorless substance that is liquid at room
temperature.
 Physical properties are sometimes reversible and do not
create new substances.
 If you cool water it becomes ice. I can heat it to make a liquid
again. If you heat water it becomes steam. Both are still H2O
 If you heat plastic it gets softer. If you cool plastic it gets brittle.
If I break it I have more than one piece of plastic, but, it is still
plastic.
 Chemical properties can be observed when an object is
changed from one substance to another – when it undergoes
a chemical reaction.
 If you send an electric current through water, you get hydrogen
gas and oxygen gas.
 If you burn plastic, you get a dark solid substance and some
gases.
 Chemical changes take for effort to reverse – another
chemical reaction.
 Changing H2 and O2 back into water is expensive and delicate.
Room Temperature
 Most pure elements are solid a room temperature
 11 of the 92 naturally occurring elements are gas: H, He, N, O, F, Ne,
Cl, Ar, Kr, Xe, Rn
 2 of the 92 are liquids: Br, and Hg
 Elements are solid when intermolecular forces are stronger than
thermal motion.
 Noble gases (group 18) are gases because their valence shell is full,
with 8 electrons, and so they have a weak intermolecular force
Periodic Properties
 First elements have a low
melting and boiling point.
They increase until you reach
the middle of the table, then
decrease again.
 Melting and boiling points
reflect strong intermolecular
forces.
 Intermolecular
forces are
strongest when the
valence shell is half
full – because a half
full valence shell
has the most
electrons to
participate in
bonding.
Thermal and Electrical Conductivity
 Good electrical conductors allow electrons to flow easily through
them. This is a property of metals.
 Most metals are good thermal conductors
 Elements to the right of the table are good insulators, i.e. poor
conductors.
Metals and Metal Alloys
 An alloy is a solid mixture of one or more elements, of which one is
a metal.
 Steel – iron and carbon (rusts but stronger than iron)
 Stainless steel – iron, carbon, chromium, vanadium, manganese
(does not rust)
 Bronze – copper, tin
 Brass – copper, zinc
 Aluminum alloys
 Titanium alloys
Carbon and Carbon-like Elements
 < .01% of Earth’s crust
 Most molecules that make up plants and animals are build
around carbon (Organic Chemistry)
 Pure carbon
 Diamond
 Tetrahedral crystal,
 Hardest natural substance (diamond tip drill bits)
 Highest thermal conductivity
 Graphite
 Sheet like
 Lubricant for locks and keys
 Silicon
 Second most abundant
element in Earth’s crust (after
Oxygen)
 Sand, rocks, minerals
 Glass (SiO2)
 Semiconductors (also make
with Germanium)
Nitrogen, Oxygen, Phosphorus
 Nitrogen
 Colorless, tasteless, odorless
 78% of Earth’s atmosphere
 N2
 Boils at -196°C
 Crucial to to life
 Oxygen
 21% of Earth’s atmosphere
 46% of Earth’s crust
 Crucial to life
 Phosphorus
 Key ingredient in DNA
 Glow in the dark