Transcript Periodic Trends

History of the Periodic
Table
 Dimitri Mendeleev published
a
periodic table that arranged
elements by increasing atomic
mass
 This did not accurately group
elements by similar properties
 The modern table is arranged by
increasing atomic number
 Periodic Law – there is a periodic
repetition of physical and chemical
properties when elements are
arranged by increasing atomic
Some of Medeleev’s work (1869)
number
Periodic Table (a review)
 Groups go down the table
 Elements in the same
group have similar
properties
 Periods go across the table
 Chemical properties of the
elements change in a
predictable manner going
across a period
Periodic Table review
(cont)
 Group 1A – alkali metals
 Group 2A – alkaline earth metals
 Group 6A - chalcogens
 Group 7A – halogens
 Group 8A – noble gases
 Metals are to the left of the staircase
 Non-metals are to the right of the staircase
 Metalloids are along the staircase (B, Si, Ge, As, Sb, Te, Po)
Periodic Trends
 Atomic radius
 Ionization energy
 Electronegativity
Atomic Radius
 The size (radius) of an
atom of that element
 Increases moving down
a group
 Decreases moving from
left to right across a
period
Ionization Energy
 Amount of energy
needed to remove an efrom an atom to form
an ion
 Decreases moving
down a group
 Increases moving from
left to right across a
period
IONS --> Atoms with a
Lithium
Ion
Lithium
Atom
charge
3+
320+1charge
charge
3+
The ionization
energy
is the amount
of energy
needed to
remove this e-
Octet rule and ions
 Atoms with a filled outer
energy level (stable octet)
are more stable
Group
Charge of most
common ion
1A
+1
 Atoms lose/gain electrons
in an effort to obtain a
filled outer energy level.
2A
+2
3A
+3
4A
+4, -4
 Anions (- ions) form by an
atom gaining e-
5A
-3
6A
-2
7A
-1
 Cations (+ ions) form by
an atom losing e-
8A
Usually do not
form ions
Electronegativity
 The ability of an atom
to attract electrons in a
chemical bond
 Increases moving from
left to right across a
period
 Decreases going down a
group