The Periodic
Table
Organization, Names, Trends, and Properties
• What is an isotope?
• What value determines the number of protons?
Electrons?
• What is the mass number and how can we use this to
determine the number of neutrons?
Review
• The three isotopes of chromium are chromium-50,
chromium-52, and chromium-53. How many neutrons
are in each isotope, given that chromium always has an
atomic number of 24?
Isotopes
The Periodic Table!!
• Elements vary widely in their patterns, but in a very
orderly way.
• Elements in a similar row have similar chemical and
physical properties.
• Dmitri Mendeleev organized the elements based on their
sets of properties.
Periodic Pattern
• The Periodic Law states that when the elements are
arranged according to their atomic numbers, elements
with similar properties appear at regular intervals
The Periodic Law
• Elements in each column have the same number of
electrons in their outer most level.
• These outer most electrons are known as the valence
shell electrons
• These valence electrons are the ones that do all the
reacting and interacting.
Valence Electrons
Valence Electrons
• A vertical column on the periodic table is known as a
group
• A horizontal row on the periodic table is known as a
period
• Elements in the same period have the same number of
occupied energy levels.
• Elements in the same group tend to react the same (same
number of valence electrons)
Arrangement
• Elements in groups 1, 2 and 13-18 are known as the
main-group elements
• The electron configurations of the elements in each main
group are regular and consistent.
• The elements in each group have the same number of
valence electrons
• Ex: elements in group 2 all have two valence e-’s
• ns2, where n is the period number
• The main-group elements are sometime referred to as
representative elements
Main Group Elements
• Group 18 elements are known as the noble gases
• Octet Rule = 8 outermost electrons (STABLE)
• They HAVE their octet achieved already (8 valence
electrons)
• Soooooo, are they reactive????
• It is the full outer shell than lead scientists to believe 8
was nonreactive, not the other way around
Noble Gases
• Elements in Group 17 are known as the halogens
• The halogens are the MOST reactive group of nonmetal
elements because they are soooo close to achieving their
octet (they have to STEAL one electron)
• React with most metals to form salts
• In fact, the name halogen is Greek for “salt maker.”
Halogens
• Group 2 elements are called the alkaline-earth metals
• Also, HIGHLY reactive
• Because they are highly reactive they are usually found as
compounds rather than as pure elements.
• Slightly less reactive than the alkali metals because they
have two electrons to get rid of instead of just one to
achieve the octet rule
Alkaline-Earth Metals
• Elements in Group 1 are called alkali metals
• Name this because they all react with water to make
alkaline (basic) solutions
• Ex: K reacts vigorously with H2O to yield KOH
• Because alkali metals have ________ valence electron(s)
they are __________ reactive.
• They need to ________________ to obtain their octet.
Alkali Metals
• Hydrogen is in a class all by itself
• It is the MOST COMMON element in the universe
• Roughly 3 out of every 4 atoms in the universe is H
• Hydrogen has _________ electron(s) but wants _______.
• Does not follow the ______________ rule
Hydrogen is Special
• Most elements are metals
• All metals are excellent conductors of electricity
• Great conductors of heat
• Ductile (can be squeezed into a wire) and malleable (can be
pounded into shape)
• Alloys are mixtures of elements, giving them a mixture of
properties  eliminate bad properties and give the good ones.
Metals
• Transition Metals are groups 3–12 (we know them as??)
• Sometimes called the d-block b/c of their position
• DO NOT have the same number of valence electrons
• This causes the varying charges
• May lose or gain DIFFERENT numbers of electrons
depending on who its bonding with (again, explaining the
varying charges)
• Also good conductors or heat / electricity
Transition Metals
• Lanthanides and Actinides
• Lanthanides - Shiny metals similar in reactivity to the
alkaline-earth metals
• Actinides – Nuclei are unstable, making all of them
radioactive. The best known actinide is U, or
_______________.
f - Block
• Electron Shielding blocks the outer electrons from the
inner nucleus attraction, making them less tightly held.
• Electronegativity decreases from right to left and top to
bottom.
• Atomic radius increase from right to left and top to
bottom. (The “F” rule)
• Ionization Energy decreases right to left and top to
bottom.
Periodic Trends
• Electronegativity – a measure of the ability of an atom in a
chemical compound to attract electrons
• Decreases as you move down a group
Decreases
Decreases
Electronegativity
• Atomic Radius – the overall size of the energy levels
surrounding the atom
• “F-rule” = Francium is HUGE and Fluorine is TINY
Increases
Increases
Atomic Radii
• Ionization Energy – the energy required to remove an
electron from an atom or ion. (Decreases down and to the
left)
Decreases
Decreases
Periodic Trends
• Why are the atomic masses of most elements on the periodic
table not exact whole numbers?
• These are relative atomic masses
• Most have isotopes and are a mixture of these
differently massed species.
Average Atomic Mass
• The periodic table reports Average Atomic Mass, a
weighted average of the atomic mass of an element’s
isotopes.
• Example: If I said there was a larger abundance of C-12
than C-13, which value would the average atomic mass
be closer to?
Most Elements are
Mixtures of Isotopes
• If you know the abundance of each isotope, you can
calculate the average atomic mass of an element.
• The mass of a Cu-63 atom is 62.94 amu, and that of a Cu65 atom is 64.93 amu. Abundance of Cu-63 is 69.17%
and Cu-65 is 30.83%. Find the average atomic mass of
Cu.
Calculating Average
Atomic Mass
• Calculate the average atomic mass for gallium if 60.00%
of its atoms have a mass of 68.926 amu and 40.00% have
a mass of 70.925 amu.
• Calculate the average atomic mass of oxygen. Its
composition is 99.76% of atoms with a mass of 15.99
amu, 0.038% with a mass of 17.00 amu, and 0.20% with
a mass of 18.00 amu.
More Practice
• Calculate the molar mass for each of the following
compounds:
CsI
C12H22O11
HC2H3O2
CaHPO4
I2
Molar Masses
Mg3(PO4)2