Transcript Unit #4 Periodic Table Families Notes

Periodic Table Families
Kelley Kuhn
Center for Creative Arts
Welcome to the Periodic Table!!!
– The periodic table is made up of both rows and
columns of elements.
– Each element is identified by its chemical
symbol.
– The number above the symbol is the atomic
number
– The number below the symbol is the average
atomic weight of the element.
– A row is more formally called a period
– A column is more formally called a group
• (A) Groups of the periodic table, and (B) periods of
the periodic table.
Periodic Table and Electron Configurations
• Note the patterns of the electron configurations in
both the periods and columns.
• Elements in same column will have the same outer shell
electron configuration.
– Each period ends with a completely filled outer
shell that has the maximum number of electrons
for that shell (the noble gases).
– The number identifying the A families identifies
the number of electrons in the outer shell,
except helium.
– The outer shell electrons (aka valence shell
electrons) are responsible for chemical reactions
of elements and the ions they form.
– Group A elements are called representative
elements
– Group B elements are called transition elements.
Elements on the periodic table can be
grouped in different ways.
Metal: Elements that are conductors, shiny, hard,
malleable, ductile, and are found to the left of the
stair step line on the table. Most elements are
metals.
Non-Metal: Elements in the upper right corner of
the periodic table that are insulators, brittle, and
dull. Their chemical and physical properties vary
greatly from metals.
Metalloid: Elements that lie on a stair step line
between the metals and non-metals. They are semiconductors with chemical and physical properties
that are intermediate between the others.
So, how did the elements get organized this way?
• Dmitri Medeleev gave us a functional method by which
to classify and organize the elements.
– Mendeleev’s scheme was based on chemical
properties of the elements.
– He noticed that the chemical properties of elements
reoccurred in a periodic manner which led to the idea
of the Periodic Law which states that similar
physical and chemical properties recur periodically
when the elements are listed in order of increasing
atomic number.
– The “periodicity” of the elements was demonstrated
by Medeleev when he used the table to predict the
occurrence and chemical properties of elements
which had not yet been discovered.
• Mendeleev left open
spaces in his table when
the properties of the
elements above and below
did not seem to match. He
predicted the existence
of unknown elements on
the basis of these blank
spaces. When the
unknown elements were
discovered, it was found
that Mendeleev had
closely predicted the
properties of these
elements as well as where
they would be discovered.
Periodic Properties
• Periodic law = when elements are
arranged by atomic number, their
physical and chemical properties
vary periodically.
• We will study the following
periodic trends:
– Atomic radii
– Ionization energy
– Electron affinity
Atomic Radius/Atomic Size
• Sizes of the atoms decrease as we move from
left to right across a period
• This is due to the increasing number of
protons in the nucleus, so the electrical
attraction between the nucleus and the
orbiting electrons gets stronger and pulls the
electrons closer to the nucleus.
• As you move down a group, the sizes of the
atoms increase due to the addition of
additional electron orbitals.
Atomic Size based on radius
Predict:
• Predict the order of the following
elements, from smallest atomic radius
to greatest, based on their position on
the periodic table.
• Ba, Ca, Na, K
• B, Li, F, Cd, Fe
ELECTRON AFFINITY
• Electron Affinity, E, is a
reflection of how easily
an atom in the gaseous
state will gain an
electron. It is a measure
of how much energy is
released when this
occurs. More energy =
higher electron affinity
As you can see, the halogens (group VIIA) clearly have a
strong tendency to gain an electron/become negatively
charged based on their large E values.
The alkali metals (group IA) elements have a very small E
ea so they do not easily gain electrons.
Electron Affinity
• So, to sum up:
• Electron affinity _____________
across a period.
• Electron affinity _____________
down a group/family.
Predict:
• Predict the order of the following
elements, from smallest electron
affinity to greatest, based on their
position on the periodic table.
• Si, Mo, Ti, Na
• B, P, Cl, Ga
Ionization Energy: Periodic table
Ionization energy reflects how easily an atom
will lose an electron. Lower energy = more likely
to lose electron.
Ionization Energy vs
atomic #
Ionization energy….
• So, to sum up:
• Ionization energy _____________
across a period.
• Ionization energy _____________
down a group/family.
Predict
• Predict the order of the following
elements, from smallest ionization
energy to greatest, based on their
position on the periodic table.
• Si, Mo, Ti, Na
• B, P, Cl, Ga
How do atoms achieve stability?
– Most atoms are NOT stable in their atomic form.
– In order to achieve stability, they gain or lose
electrons to reach noble gas electron
configuration (EC).
– When an atom or molecule gain or loses an
electron it becomes an ion.
• A cation has lost an electron and therefore
has a positive charge
• An anion has gained an electron and therefore
has a negative charge.
FYI: How can I predict the ions that form
from various elements?
– Elements with 1, 2, or 3 electrons in their outer
shell tend to lose electrons to fill their outer
shell and become cations.
• These are the metals which always tend to lose
electrons. This helps them attain noble gas EC.
– Elements with 5 to 7 electrons in their outer
shell tend to gain electrons to fill their outer
shell and become anions.
• These are the nonmetals which always tend to gain
electrons. Once again, this gives them noble gas EC.
– Semiconductors (metalloids) occur at the
dividing line between metals and nonmetals and
can either gain or lose electrons.
Predict:
•
•
•
•
•
•
•
What ions will form from:
Ca?
K?
Cl?
B?
O?
S?