Download Chapter 7 Periodic Properties of Elements - GCG-42

Periodic Properties of Elements
SANTOSH
CHEMISTRY DEPT
The Periodic Table of Elements
•Elements are organized according to their
physical and chemical properties in the Periodic
Table of the Elements. Historically, several
people contributed to this effort in the late 19th
century:
–Dobereiner- “triads”: Ca, Sr, Ba; Li, Na, K
–Newlands- similarity between every eighth element
–Mendeleev (1870) - Arranged elements according
to atomic mass. Similar elements were arranged
together in a “group”.
Triads of Elements
Mendeleev
• Father of the Periodic Table
• Periodic Law- Both physical and chemical
properties of the elements vary periodically
with increasing atomic mass.
• Exception placed Te (M = 127.6) a head of I
(M=126.9) because Te was similar to Se and S,
and I was similar to Cl and Br.
• Left gaps in periodic table and predicted new
elements would be found. Predicted the new
elements’ properties.
Example for “Eka-Silicon”
Property
Mendeleev’s predictions
for “eka-silicon”
(made in 1871)
Observed properties
of germanium
(discovered in 1886)
Atomic mass
72
72.5
Density (g/mL)
5.5
5.35
Specific Heat
0.305 J/g-K
0.300 J/g-K
Melting point (oC)
High
947
Color
Dark gray
Grayish white
Oxide formula
XO2
GeO2
Density of oxide
4.7 g/mL
4.70 g/mL
Formula of chloride XCl4
GeCl4
Periodicity (continued)
– Meyer (1870)-Arranged elements according to
their physical properties.
– Elements changed properties gradually in a row
or period.
– Moseley (1930)- Arrange atoms according to
atomic number (nuclear charge). He found a
direct correlation between the square root of Xray energy and nuclear charge (atomic number).
Nuclear charge increases by one unit for each
element.
Periods of Elements
•Periods of elements are the horizontal rows
of the Periodic Table.
•The properties of the elements vary as you
move from left to right across the periods.
•On the left, the periodic table starts with
shiny reactive metals, followed by dull
solids and reactive non-metals. Each period
ends with a non-reactive noble gas
Valence Electrons
•Starting with one valence electron for the first
element in a period, the number of electrons
increases as you move from left to right across a
period.
•The periodic changes in properties of elements
coincide with their placement in the periodic
table.
Groups and Families
•Vertical columns of elements in the periodic
table are called groups or families.
•Elements in the same group or family have
similar chemical properties.
•Representative Elements are those in the first
two groups and the last six groups (s-block and
p-block) in the periodic table. These groups are
designated 1,2,13-18 or the A group elements
Electron Configurations can be
Determined From the Position
in the Periodic Table:
•Elements in group 1(1A) end in ns1.
•Elements in group 2 (2A): end in ns2
•Elements in group 13 (3A) end in ns2np1
•Elements in group 14 (4A): end in ns2np2
•Elements in group 15 (5A) end in ns2np3
•Elements in group 16 (6A) end in ns2np4
•Elements in group 17 (7A) end in ns2np5
•Elements in group 18 (8A) end in ns2np6
Periodic Trends in Properties
of Elements
•Various Elemental Properties change fairly
smoothly going across a period or down a
group.
•Properties include:
–Atomic and Ionic Radius
–Ionization Energy
–Melting Points and Boiling Points
–Density and Conductivity
Atomic Size of Elements
–Atomic size (radius) is based on the average
distance between the outer electrons and the
nucleus.
–A measure of atomic size is the Atomic Radius
(AR).
–AR decreases as you move from left to right
across a period.
–AR increases as you move down a group
Trends in Atomic Radius
Relative Radii of Atoms
Periodic Trends in Atomic Radius
Ionic Radius
•When anions are formed, electron(s) are
added, the radius increases.
•When cations are formed, electron(s) are lost,
the radius decreases.
•Ionic radius decreases going down a group.
•Going from left to right across a period ionic
radius decreases for cations, then increases for
anions, then decreases.
Ionic Radius of Isoelectronic
Atoms and Ions
•When chlorine forms an anion by adding an electron,
it has the same electron configuration as argon the
noble gas, [Ar]. The radius of a chloride ion is larger
than the chlorine atom. It is also larger than the argon
atom.
•When potassium forms a cation by losing an electron,
it also has the same electron configuration as argon,
yet the radius of the potassium cation is smaller than
the potassium atom. It is also smaller than the argon
atom.
•For isoelectronic ions, the radius decreases as the
nuclear charge increases.
Comparing the Size of Atoms and Ions
An Isoelectronic Series
C4- N3- O2- F- Ne Na+ Mg2+ Al3+
Increasing radius
Ionization Energy
•Ionization Energy (or Ionization Potential)
–Ionization Energy (IE) is the energy required
to remove one mole of electrons from one
mole of gaseous atoms or ions.
Na + IE
Na+ + e•IE increases (irregularly) as you move from left
to right across a period.
•IE decreases (irregularly) as you move down a
group.
Trend in Ionization Energy