Transcript The Periodic Table

The Periodic Table
Organization
• Group/family = vertical column
• Period = row
Grouping of elements
• Metals – most elements on the table, left side
• Nonmetals – far right and hydrogen
• Metalloids – along zig-zag line; divides metals
and non-metals
Metals
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•
•
•
•
•
•
•
•
Good conductors of heat/electricity
Malleable (can be formed)
Ductile (made into wires)
Reflects light
High densities
High melting points
Most are solids at room temperature
Easily lose electrons
corrode
Nonmetals
•
•
•
•
•
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Not good conductors of heat/electricity
Dull
Brittle
Low melting points
Low densities
Are solids, liquids and gasses at room
temperature
• Tend to gain electrons
Metalloids
•
•
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•
•
•
Cross between metals and nonmetals
Solids at room temperature
Can be shiny or dull
Malleable
Ductile
So-so conductors (better than nonmetals,
but not as good as metals)
– Form semiconductors when bonded
Groups/families
• Group 1 – alkali
metals
– React with water to
form alkalines (bases)
– Very reactive; not
found alone in nature,
found as compounds
– Very soft metals
– Have one valence
(outermost) electron
Groups/families
• Group 2 – alkaline
earth metals
– Also form alkalines
with water
– Also very reactive, so
not found as pure
elements in nature
– Not as reactive as
group 1
– Have 2 valence
electrons
Groups/families
• Group 17 – halogens
– Means “salt former”
– Tend to form salts with
group 1 elements
– Most reactive of the
nonmetals
– Have 7 valence
electrons
Groups/families
• Group 18 – noble
gases
– Very unreactive
– All are gases at room
temperature
– Have a full set of
valence electrons
• Full set = 8, except for
helium which has 2
Groups
• Groups 3 – 12:
Transition metals
– Can put more than 8
electrons in their
outermost orbital
– Can use the 2 most
outer orbitals to bond
(the others use only
the outermost)
– Can form ions with
different charges
Development of the
periodic table
• In 1865, John Newlands, an English
Chemist, arranged the elements according
to their properties and in order of
increasing atomic mass.
• He noticed a pattern that repeated every 8
elements, so he called it the law of
octaves
Development of the
periodic table (cont)
• Dimitri Mendeleev, in 1869, used this
information and produced the first orderly
arrangement of all 63 known elements.
• He arranged them in a similar way to Newlands
and created the first periodic table.
• Mendeleev started a new row each time he
noticed that the chemical properties of the
elements repeated.
• He left gaps where he thought newly discovered
elements should go and made predictions about
these elements
Mendeleev’s table
Mendeleev’s predicted elements
Modern Periodic Table
• Elements did not always fit neatly on the table in
order of atomic mass
• Henry Moseley studied the x-ray spectra of 38
different elements
• He noticed a pattern as the atomic mass
increased
• However, after further study, he realized that the
correlation was to atomic number and not atomic
mass.
• The table was arranged in increasing atomic
number and any discrepancies from
Mendeelev’s table disappeared
Modern Periodic Table (cont)
• Periodic Law: the principle of chemical
periodicity.
– When elements are arranged according to
their atomic numbers, elements with similar
properties appear at regular intervals.
• This law works because of the pattern in
the electron configuration of the elements.
– Elements in each column of the periodic table
have the same number of valence electrons
(electrons in their outer energy level)
Valence electrons
• Electron located in the outermost energy
levels
• Valence electrons are the ones that
participate in chemical reactions.
• Elements with the same number of
valence electrons tend to react in similar
ways.
• This allows scientists to predict the
properties and behavior of unknown
elements.
Periodic trends
• Tells you how certain characteristics
change as you move across and down the
periodic table
• 3 trends that we will look at:
– Atomic radius
– Ionization energy
– electronegativity
Atomic radius
• The “size” of the atom
• Decreases as you move from left to right across
a row
– Reason: as you move across a period, you add
electrons to the atom in the same energy level. You
also add protons to the nucleus, thus increasing the
pull of the nucleus on the electrons, drawing them
closer to the nucleus (effective nuclear charge)
• Increases as you move down a column
– Reason being is that when adding electrons, you add
them in increasing energy levels, making the atom
larger
Ionization energy
• The energy needed to remove an electron from an atom
• Increases as you move across
– Reason: effective nuclear charge increases requiring more
energy to take them away (the outermost electrons are the first
ones to be removed)
• Decreases as you move down
– Reason: the electrons that are added to increasing energy levels
are further away from the nucleus, thus the attraction is
decreased making it easier to take them away
– Also, you have “electron shielding” which is when the inner
electrons “shield” the outer ones from the pull of the nucleus
Electronegativity
• An atom’s desire to attract electrons
• The more electronegative atom will take
electrons away from a less electronegative atom
(like a big brother takes toys from the little
brother)
• Increases as you move across
– Reason: effective nuclear charge increases so
electrons are attracted more strongly
• Decreases as you move down
– Reason: electron shielding decreases effective
nuclear charge, decreasing the attraction
Natural Elements
• Only 93 of the elements on the periodic
table occur in nature
– Technetium (Tc) and Promethium (Pm) were
detected in the stars, but not found on earth
• Some elements can form through nuclear
reactions (fusing of nuclei)
– Center of stars
– transmutations
Transmutations
• One element changes into another
through a nuclear reaction
– Radioactive elements do this naturally
– We have “created” synthetic elements using
particle accelerators
• cyclotron
Cyclotrons
• Speeds particles up to very high energies
and then collides them
– Nuclei of the particles fuse, creating “new”
elements
– Some of these are “superheavy” elements
• Atomic number greater than 106
• Usually only a few nuclei are created, making it
hard for scientists to study
• They usually decay within a fraction of a second
Cyclotron at Berne, Switzerland
Cyclotron