Transcript Periodic Trends - Naperville Community Unit School

Ch. 6 The Periodic Table
Mendeleev’s Periodic Table
• Elements in the
periodic table are arranged
by repeating properties
• Arranged in order by
increasing atomic mass
• Left spaces where he
predicted future elements
would fit
Mendeleev’s Periodic Table
However…..
• Mendeleev ordered his elements in order of
their relative atomic mass, and this gave him
some problems. For example, iodine (126.90)
has a lower relative atomic mass than tellurium
(127.60), so it should come before tellurium in
Mendeleev's table - but in order to get iodine in
the same group as other elements with similar
properties such as fluorine, chlorine and
bromine, he had to put it after tellurium, thereby
breaking his own rules
Moseley
• Soon after Rutherford's landmark experiment of
discovering the proton in 1911, Henry Moseley
(1887-1915) subjected known elements to xrays. He was able to derive the relationship
between x-ray frequency and number of protons.
When Moseley arranged the elements according
to increasing atomic numbers and not atomic
masses, some of the inconsistencies associated
with Mendeleev's table were eliminated. The
modern periodic table is based on Moseley's
Periodic Law (atomic numbers).
At age 28,
Moseley was
killed in action
during World War
I and as a direct
result Britain
adopted the policy
of exempting
scientists from
fighting in wars.
Periodic Law
• In the modern periodic table, elements are
arranged in order by increasing Atomic
Number
• 7 horizontal rows called periods
• Each period corresponds to a principle
energy level
• Elements within a group (column) have
similar properties
Periodic Law
• States: When elements are arranged by
increasing atomic number, there is a
periodic repetition of their physical and
chemical properties
Metals, Nonmetals, Metalloids
Metals
• 80% of the periodic table
is metals
• Good conductors of heat
and electricity
• Malleable- can be shaped
• Ductile- can be drawn
into wires
• Lustrous
• Solids at room
temperature (except Hg)
• Many react with HCl and
CuCl2
MAGNESIUM
ZINC
Nonmetals
•
•
•
•
Poor conductors of heat and electricity
Not malleable
Not ductile
Dull
Metalloids
• Generally has some properties of a metal,
some of a nonmetal
Alkali Metals
Lithium (Li)
1s22s1
Sodium (Na)
1s22s22p63s1
Potassium (K)
1s22s22p63s23p64s1
Alkaline Earth Metals
Beryllium (Be)
Magnesium (Mg)
Calcium (Ca)
1s22s2
1s22s22p63s2
1s22s22p63s23p64s2
Halogens
Fluorine
(F)
1s22s22p5
Chlorine
(Cl)
1s22s22p63s23p5
Bromine
(Br)
1s22s22p63s23p64s23d104p5
Noble Gasses
Neon
(N)
1s22s22p6
Argon
(Ar)
1s22s22p63s23p6
Krypton 1s22s22p63s23p64s23d104p6
(Kr)
Trends in Atomic Size
• Atomic radius is ½ the
distance between the
nuclei of 2 like atoms
• As you move DOWN
a group, atomic size
increases
• As you move LEFT to
RIGHT across a
period size decreases
Why?
As you move across the period
you gain electrons but you also
gain protons. More + protons
hold their electrons tighter
As you move down the group you
gain more electrons which are in
electron orbitals further away from
the nucleus. The nucleus has less
influence the further out you move.
Trends in Ionization Energy
• Ionization Energy is
the energy required to
remove 1 electron
from a gaseous atom
• As you move DOWN
a group ionization
energy DECREASES
• As you move LEFT to
RIGHT across a
period ionization
energy INCREASES
Why?
• As you move down a
• As you move across a
group you add more
period, you add more
energy levels. The
protons in the
valence electrons are
nucleus, but not more
now further from the
energy levels. There
positive nucleus and it
is less “electron
is easier to “lose”
shielding” between
them.
the positive nucleus
and electrons…the
positive nucleus pulls
the electrons closer
into it.
Why?
Trends in Electronegativity
• Electronegativity is the
tendency of an atom to
attract electrons in a
compound
• As you move DOWN a
group Electronegativity
DECREASES
• As you move LEFT TO
RIGHT across a period
Electronegativity
INCREASES
Why?
• Do any of the atoms
in group 1A want to
gain electrons????
• NO!...They are
looking to give them
away…please take
them..I won’t fight you
for them!
• Just ask yourself….
who really, really wants
to gain electrons?
Fluorine….it is the
T.Rex of the periodic
table.---Small radius
and just needs one
more electron!
Fluorine
Fluorine
Atomic Radius
The atomic radius is a term used to describe the size of the atom, but
there is no standard definition for this value.
atomic radius is the
average distance from the center of the nucleus
to the outer orbital.
We will use the following definition:
Trends in Atomic Ion Radius
For METALS: as you lose electrons there is
less electron-electron repulsion (remember
like charges repel) and the radius gets
smaller. You “lose” all the electrons in the
outer energy level the resulting ion is MUCH
smaller.
For NONMETALS: as you add electrons, you
increase the electron-electron repulsion (they
want to get far away from one another) and
the radius “fills out” thus getting larger.
Summary of Periodic Trends