Transcript Periodic Table

The Periodic Table of
Elements
Organization of the Periodic Table
• Arranged to make predicting the properties
of the elements easier.
• The order is based on the # of protons an
atom of that element has in its nucleus.
– This order is known as the periodic law
(arranged this way, similarities in their
properties will occur in a regular pattern).
Arrangement of the P.T.o.E
•
The periodic table is arranged in:
– Horizontal rows (period)
•
# of protons/electrons increase as you move
from left to right. Because of this… you can
determine the electronic configuration of the
atom. Look at the location on the periodic table.
What period is the element in? Where in the row
is the element located?
Arrangement of the P.T.o.E
Aufbau’s electronic shell filling by period & energy.
•
•
•
•
•
•
•
Period 1= 1s
Period 2 = 2s, 2p
Period 3 = 3s, 3p
Period 4 = 4s, 3d, 4p
Period 5 = 5s, 4d, 5p
Period 6 = 6s, 4f, 5d, 6p
Period 7 = 7s, 5f, 6d, 7p
– The 1st 2 columns- electrons always occupy the s-orbital.
The last 6 columns- electrons always occupy the p-orbital.
Arrangement of the P.T.o.E
• Vertical columns (family or group)
– all have the same #of valence electrons. These elements
have similar properties.
• The elements in the 1st column are called the alkali metals and
each have 1 valence electron.
• The elements in the 2nd column are called the alkaline earth
metals and each has 2 valence electrons.
• The elements in the 7th column are called the halogens and each
has 7 valence electrons.
• Finally, the elements in the 8th column are known as the inert or
noble gases. They have a full octet or 8 valence electrons and
are not likely to react.
http://www.dayah.com/periodic/
Atoms, Ions and Isotopes
• Some Atoms form Ions:
– When atoms have partially full outermost
energy levels, they may undergo ionization
(the gaining or losing of valence electrons).
– As atoms gain or lose electrons they no
longer have the same # of electrons as
protons. The charges no longer cancel out
and you are left with a charged atom or ion.
Ex: Li loses an electron to form Li+
Mg loses 2 electrons to form Mg2+
F gains an electron to form F-
Ion Classification
• Atoms who lose electrons, become positively
charged (like Li and Mg), and are called
cations.
• Atoms who gain electrons, become negatively
charged (like F), and are called anions.
• ** HINT** Cations: Alkali metals +
Alkaline-earth metals
Anions: Group VI (O to Po) 2Halogens (F to At) -
2+
• The Noble/ Inert gases do not make ions.
Atomic Number
• Atomic # (Z) - how many protons are in a
atom.
– Remember: atoms are electronically neutral
so they have an equal # of protons as
electrons. Thus, the atomic # also tells us
how many electrons the atom has.
Ex: Pu Z=94
Rf Z=104
Atomic Mass
• Atomic mass # (A) = the # of protons +
neutrons in an atom.
– Because the bulk of the atoms mass is provided by
the protons and neutrons, we only consider their
masses when calculating the atomic mass #.
• Ex: F has 9 protons and 10 neutrons, so A= 19.
ISOTOPES
• Atoms of the same element
will ALWAYS have the same #
of protons, however, they may
differ in the # of neutrons.
– This means that different atoms
of the same element may/will
have different masses. These
are isotopes (atoms having the
same # of protons but different
# of neutrons).
Isotopes cont.
• Some isotopes are more common than
others.
– H is present on the earth and the sun. The most
common isotope is protium, then deuterium and finally,
tritium.
Ex: 3 isotopes of H (why A isn’t just 1 but 1.00794).
Protium (only has one proton in the nucleus) A=1
Deuterium (1 proton + 1 neutron) A=2
Tritium (1 proton + 2 neutrons) A=3
Calculating # of neutrons: A – Z= # of neutrons
Atomic Mass Units
• The mass of a single element is extremely
small (in the one trillionth of a billionth range) and is
very difficult to work with. So instead we
express the mass of atoms in atomic mass
units (amu).
• One amu is equal to 1/12th of the mass of
a carbon-12 atom.
– This isotope has exactly 6 protons and 6
neutrons so the mass of each has to be about
1.0 amu.
Atomic Mass Unit cont.
• The atomic mass of an element is often
listed as the average atomic mass as
found in nature.
• This is a weighted average of the
isotopes for that particular element. The
more commonly found isotopes have a
greater effect on the averages mass
than the more rare isotopes.
Ex: Cl 24% Cl-37 and 76% Cl-35, thus the
average atomic mass (35.45 amu) is much
closer to 35 than 37.