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Transcript
Intro To The Periodic Table
How Was The Periodic Table Created?
• Throughout history elements were discovered at
different times but they were not put in any order
to classify them.
• By 1828, 53 elements were discovered.
• To bring ORDER out of CHAOS, to classify is a
basic need of man. Therefore, scientists began
looking for similarities among the elements as
more were continuing to be discovered.
Who Is Dmitri Mendeleev?
• In 1871, Russian scientist Dmitri Mendeleev organized the
known elements of the time according to increasing atomic
mass.
• He left spaces on the periodic table where elements were yet
to be discovered.
• Mendeleev also recognized that certain similarities in the
chemical properties of elements occurred at regular
intervals. He implemented John Newland’s law of octaves.
• Law of Octaves – every 8 elements tend to have the same
chemical properties (groups 1-2 and 13-18 on your periodic
table)
26
Fe
55.845
28
Ni
58.6934
27
Co
58.9932
Mendeleev
51
Sb
121.760
53
I
126.9045
52
Te
127.60
Who Is Henry Moseley?
• In 1911 English scientist Henry Moseley discovered that the
elements on the periodic table fit into patterns better when
they are arranged in order of increasing atomic number, or
the number of protons in the nucleus.
• Moseley’s periodic table represents the periodic law which
is what we follow when we study chemistry today.
• Periodic Law - the physical and chemical properties of the
elements are periodic functions of their atomic numbers
• *When elements are arranged in order of increasing atomic
number, elements with similar properties occur at regular
intervals.
26
Fe
55.845
27
Co
58.9332
28
Ni
58.6934
Moseley
51
Sb
121.760
52
Te
127.60
53
I
126.9045
Organization Of The Periodic Table
How are the Elements Classified?
• Elements can be classified as metals,
nonmetals, or metalloids (semimetals).
Metals
Nonmetals
Metalloids
(Semimetals)
Located to the left of the
staircase on the periodic
table
Tend to lose electrons
and form positive (+) ions
to look like a noble gas
Have a shiny appearance
(luster)
Good conductors of
electricity
Located to the right of
the staircase on the
periodic table
Tend to gain electrons
and form negative (-) ions
to look like a noble gas
Dull in appearance
Poor conductors of
electricity
Located along the
staircase on the periodic
table
May form + or – ions gas
OR share electrons to look
like a noble gas
Appearance varies
Intermediate conductor
of electricity
Alkali Metals
Located in group 1 on the periodic table
Highly reactive metallic elements that rapidly
react with water to form hydrogen and an
alkaline solution
Must be stored in mineral oil to prevent it
from reacting with water vapor in the air and
EXPLODING!
Tend to lose the 1 electron on its valance
(outermost) shell to look like a noble gas
Alkaline Earth Metals
Located in group 2 on the periodic table
Reactive metallic elements but not as reactive
as the alkali metals
Tend to lose the 2 electrons on its valance
(outermost) shell to look like a noble gas
Alkali & Alkaline Earth Metal
Videos
• http://www.youtube.com/watch?v=sNdijknRx
fU
• http://www.youtube.com/watch?v=DFQPnHk
QlZM
Transition Metals
Located in the center section of the periodic
table
This group contains precious metals (Cu, Au,
Ag, Pt)
This group contains magnetic elements (Fe, Ni,
Co)
Tends to lose electrons (amount varies) on its
valance (outermost) shell to look like a noble
gas
Electrons usually fill the d subshells
Halogens
 Located in group 17 on the periodic table
Nonmetallic group of elements that has the
nickname “Salt Formers”
 Tend to gain 1 electron on its valance
(outermost) shell to look like a noble gas
 Most reactive nonmetals on the periodic table
Noble Gases
Located in group 18 on the periodic table
 Nonmetallic group of elements that are
characterized by low reactivity because of
their full valance shell (all noble gases have 8
valance electrons with the exception of He)
Every element on the periodic table wants to
look like a noble gas because of its stability
achieved by having a full valence shell
Halogen & Noble Gases Videos
• http://www.youtube.com/watch?v=u2ogMUD
Baf4
• http://www.youtube.com/watch?v=QLrofyj6a
2s
• http://www.youtube.com/watch?v=3TYuym2j
qjM
Lanthanides
Elements with the atomic numbers 58-71
Rare earth elements that occur in minerals
Electrons fill the 4f subshell
Actinides
Elements with atomic numbers 90-103
Rare earth elements that are radioactive
(because they are very heavy)
Electrons fill the 5f subshell
Lanthanides & Actinides Videos
• http://www.youtube.com/watch?v=IFmAhhia
m9g
Periodic Table Trends
• Group # tells how many valence electrons are
in the outer shell of an atom
• This only applies to groups 1-2 and groups 1318. Remember for groups 13-18, subtract 10
from the group # to tell how many valence
electrons are present
• Period # tells how many energy levels an atom
has and where the valence shell is located
Visuals to Group & Period # Trends
*Group # indicates the # of
valence electrons in outer
shell of the atom
The carbon atom
has 2 energy levels
because it Is located
on period 2
The cesium atom
has 6 energy
levels because it
is located on
period 6
What does Atomic Radius
Measure?
• Atomic radius is calculated by measuring the
distance between the nuclei of 2 identical
bonded atoms and then cutting this distance
in half
3.72 angstrums/2 = 1.86 angstrums
3.72 angstrums
Atomic Radii Group Trend
• Atoms become larger as one moves down a
group (column)
• As you move down a group, more e-’s lie
between the nucleus and the highest energy
level/outermost valence shell.
• These inner shell e-’s SHIELD the outermost
valence e-’s from the positively charged
nucleus
Atomic Radii Group Trend
Versus
Cesium
Cesium has a larger atomic radius because there is more energy levels which
SHIELD the effect of the positive nucleus from attracting to the negatively charged
outermost electrons
Lithium has a smaller atomic radius because there are less energy levels, resulting in
less SHIELDING between the positively charged nucleus and the outermost valence
electrons. The nucleus attracts and pulls the valence electrons closer to it, resulting
in a smaller atom
Atomic Radii Period Trend
• Atoms become smaller as one moves across a
period from left to right.
• As you move across a period, the inner shells
of the atom do not get any “thicker.”
• More e-’s are added to the outer shell of the
atom and more protons are added to the.
nucleus
• As a result, the nuclear charge is greatly
increased and the greater attraction between
the protons and electrons shrinks the atom.
Atomic Radii Period Trend
Lithium Z=3 has a larger atomic radius than fluorine Z=9 because of the
increased nuclear charge as we move across period 2. A greater attraction of
electrons and protons causes the atoms to shrink in size when moving across
a period.
Summary of Atomic Radii Trend
Cation & Anion Trend
• Negative ions (anions) are larger than their
parent atoms.
• A larger radius will result from greater
repulsion on the valence shell due to the
addition of e-’s.
• Positive ions (cations) are smaller than their
parent atoms.
• A smaller radius will result from less repulsion
on the valence shell due to the removal of e-’s.
What does Ionization Energy
Measure?
• Ionization energy measures the quantity of
energy needed to remove an electron from an
atom or ion
Ionization Energy Group Trend
• As we go down a group, IE decreases due to
the SHIELDING effect.
• It is easier and doesn’t take as much energy to
remove an electron from larger elements
because of the minimal pull from the nucleus
and larger distance to the outermost
electrons.
• The inner electrons shield or protect the
valence electrons from the attraction from the
nucleus.
Ionization Energy Period Trend
• As we go across a period, IE increases due to
an increase in nuclear charge.
• It is harder to remove or pull away an electron
from a smaller atom because of the close
proximity of the valence electrons to the
nucleus and the strong attraction that results.
What does Electron Affinity
Measure?
• Electron affinity measures the amount of
energy that is released when electrons are
added to the outer shell of an atom or ion.
• The greater the negative EA, the easier it is for
that atom or ion to accept an atom
Electron Affinity Group Trend
• As we go down a group, EA decreases due to
electron SHIELDING.
• There is less attraction between the nucleus
and the valence electrons due to the distance
between them.
• It is harder to add and hold another electron to
the outermost shell because of the weak pull
from the nucleus.
• Only a small amount of energy (if any) would be
released because most of it would be used to
hold on to the added electrons
Electron Affinity Period Trend
• As we go across a period, EA increases
because of greater nuclear charge.
• The addition of protons to the nucleus and
electrons to the valence shell causes great
attraction to one another.
• It becomes easier to add an electron and a
larger amount of energy will be released in
the process
What does Electronegativity
Measure?
• Electronegativity is the ability of an atom to
attract an electron from another element
during bonding.
• It is closely related to electron affinity.
Electronegativity Group Trend
• As we go down a group, the ability of atoms or
ions to attract another electron and form a
bond will decrease.
• There is less attraction between the nucleus
and the valence electrons due to the distance
between them.
• It is harder to add and hold another electron
to the outermost shell because of the weak
pull from the nucleus.
Electronegativity Period Trend
• As we go across a period, the ability of atoms
or ions to attract another electron and form a
bond will increase.
• The addition of protons to the nucleus and
electrons to the valence shell causes great
attraction to one another.
• It becomes easier to add an electron and form
a bond due to the increase in nuclear charge.