Download representative elements

CHAPTER 6
CHEMICAL PERIODICITY
DEVELOPMENT OF THE PERIODIC
TABLE
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Scientists needed a way to organize and refer to
the growing number of known elements
Categorized the elements according to
similarities in their physical and chemical
properties (Dobereiner’s Triads, Mendeleev’s and
Newland’s Periodic Tables)
•
Relationship between atomic structure and
properties of elements (Moseley’s Periodic Table)
MENDELEEV’S PERIODIC TABLE
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Mendeleev listed the elements in horizontal rows in order of
increasing atomic mass
Regular patterns of physical and chemical properties occurred
in vertical columns
Blank spaces left where unknown elements belonged, but able to
predict their properties
MOSELEY’S PERIODIC TABLE
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Moseley determined atomic number
of the atoms of the elements
Arranged the elements by order of
atomic number, not by atomic mass
MODERN PERIODIC TABLE
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The horizontal rows of the periodic table are
called periods (organized by increasing atomic
number)
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The vertical columns are called groups or families
(organized by chemical properties)
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Periodic Law: when the elements are arranged in
order of increasing atomic number, there is a
periodic pattern in their physical and chemical
properties
ORGANIZATION OF THE PERIODIC
TABLE
Group
Period
METALS, METALLOIDS, AND
NONMETALS
Metalloids
MAIN GROUP OR
REPRESENTATIVE ELEMENTS
IA
IIA
VIII
A
IIIA IVA VA VIA VIIA
p-block
s-block
TRANSITION ELEMENTS
IIIB IVB VB VIB VIIB
VIIIB
d-block
f-block
(inner transition elements)
IB IIB
SPECIAL GROUPS WITHIN THE
PERIODIC TABLE
ELECTRON CONFIGURATIONS AND
PERIODICITY
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Electron plays the greatest part in determining the
physical and chemical properties of an element
Elements can be classified into four different
categories based on their electron configurations
ELECTRON CONFIGURATIONS AND
PERIODICITY
1.
The noble gases are elements in which the outermost
s and p sublevels are filled Called inert gases because
they do not partake in chemical reactions
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Valence: outermost s and p orbitals
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Octet: 8 electrons in valence shell
2.
The representative elements are elements whose
outermost s or p sublevels are only partially filled
(group A)
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Alkali metals: group 1A elements
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Alkaline earth metals: groups 2A elements
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Halogens: nonmetallic elements of group 7A
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Group number = number of valence electrons
ELECTRON CONFIGURATIONS AND
PERIODICITY
2. The representative elements are elements
whose outermost s or p sublevels are only
partially filled (group A)
• Alkali metals: group 1A elements
• Alkaline earth metals: groups 2A
elements
• Halogens: nonmetallic elements of group
7A
• Group number = number of valence
electrons
ELECTRON CONFIGURATIONS AND
PERIODICITY
3.
The transition metals are elements whose
outermost s sublevel and the nearby d sublevel
contain electrons (group B)
3.
The inner transition metals are elements whose
outermost s sublevel and the nearby f sublevel
contain electrons
ELECTRON CONFIGURATIONS AND
PERIODICITY
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S block: groups 1A and 2A and He
P block: groups 3A, 4A, 5A, 6A, 7A, and 8A except
He
D block: transition metals
F block: inner transition metals
Period number corresponds to the principal energy
level for the S and P blocks only
PERIODIC TRENDS IN ATOMIC SIZE
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The radius of atoms: atomic radii
• From one group to the next, atomic radius decreases because the
electrostatic attraction between increasingly larger nuclei increases,
pulling the electrons closer to the nucleus
• From one row to the next, atomic radius increases because increasing
numbers of neutrons shield the electrostatic force and valence
electrons are located further and further away from the nucleus
PERIODIC TRENDS IN IONIC SIZE
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Ionic radii is the size of an ion compared to same neutral atom
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Cations (positive ions) are smaller because of the reduced energy
level with the same number of protons
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Anions (negative ions) are larger because of a reduced effective
nuclear charge on outer electrons
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From one row to the next, atomic radius increases because
increasing numbers of neutrons shield the electrostatic force and
valence electrons are located further and further away from the
nucleus
PERIODIC TRENDS IN IONIZATION
ENERGY
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The energy that is required to overcome the attraction of the nuclear
charge and remove an electron to create a positive atom is the
ionization energy
Increased nuclear charge that occurs from one group to the next
accounts for electrons being held more tightly within the atom. The
more tightly they are held, the greater the amount of energy that is
required to remove and electron from an atom
From one row to the next, ionization energy increases because
increasing numbers of neutrons shield the electrostatic force and
valence electrons are located further and further away from the
nucleus
PERIODIC TRENDS IN
ELECTRONEGATIVITY
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The electronegativity of an element is the ability of
an atom to attract electrons within a bond
Electronegativity increases as you go across a period
form left to right and decreases as you move down a
group