Lecture Notes:
The Periodic Table
Families, Groups, & Trends
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Reading the Periodic Table
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Atomic Symbol: A unique symbol
used to represent the element in formulas
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Atomic Number: Tells you both the number of protons
(p+) and electrons (e-)
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Mass Number: Tells you the average atomic mass of an
element. To find this average scientists had to find
the mass of each isotope and their natural abundances
- Elements come in different types called isotopes that differ based
on the number of neutrons they contain.
Each isotope has its own
precise, whole number mass number:
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The mass number of an isotope minus the atomic number
tells you the number of neutrons (no) in
that isotope
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Isotopes of an element have slightly different
properties: Carbon-14 is radioactive while the more
common Carbon-12 is not
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Groups and Properties
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The properties of elements follow the periodic law:
physical and chemical properties are functions of
their atomic numbers.
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This follows from similarities between electron
configuration within groups
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Hydrogen doesn’t fit into any group because its
simple structure gives it unique properties
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Group 1, the Alkali Metals, all have 1 electron in
their outermost s orbital. They ionize to have a +1
charge by losing the s e-
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The alkali metals violently replace hydrogen in
water to make a basic (alkaline) solution and are
generally very reactive
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Soft and can be cut with a knife
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Good conductors of electricity
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Group 2, the Alkaline Earth Metals, all have 2
e- in their outermost s orbital. They
ionize to have a +2 charge by losing both their s
e-
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Harder, denser and have higher melting points
than the alkali metals
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Less reactive than the alkali metals because it
takes more energy to remove 2 e- than
to remove 1
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Group 3 through Group 12, the Transition Metals, fill
up the d orbitals and their properties change
very gradually from reactive metals at the left to
less reactive metals at the right side of the family
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Except for mercury (Hg), which is a liquid, the
transition metals are harder and denser than the
first two groups
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They are all conductors of electricity, though
slightly less conductive as you move toward the
right
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The ions that metals form are very variable
although all of them tend to form positively
charged ions by losing 1 or more e-
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The lanthanides and actinides are separated from
the main body of the periodic table because they
fill the f orbitals and because they do
not follow the same patterns of periodicity as
the other transition metals
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The Main Block elements show the greatest variation
of any of the groups in the periodic table
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There are four types of elements in these groups:
metalloids, non-metals, halogens, and the noble
gases
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Metalloids represent a 'border' between metals
and non-metals since they have properties of both
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The solid non-metals are characterized by their
brittle properties and their lack of conductivity
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The halogens are particularly reactive and have a
strong tendency to gain an electron to obtain the
electron configuration of the neighboring noble
gas
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The halogens are very often found in combination
with the alkali metals as salts
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The noble gases are the elements that have the
most stable electron configurations, having
completely filled out shells
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Periodic Trends
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Atomic radius: For groups 1
and 2 and groups 13 through 18 atomic radius
increases toward the bottom of the table and
decreases toward the right
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Atomic size: this follows the same trend as atomic
radius and can be explained by noting that
e- are drawn closer to the nucleus as
protons are added
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Ionization energy: the energy required to remove one
electron increases from left to right and decreases
from top to bottom
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Electron affinity: the energy released when an
electron is added to an atom, making it a negative
ion, increases from left to right and decreases from
top to bottom
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Electronegativity: this tendency to attract electrons
from another atom in a chemical bond increases as you
move to the right and decreases from top to bottom;
cesium (Cs) is the least electronegative element and
flourine (F) is the most electronegative element