Transcript Atomic Radius - Atomic radius is simply the radius of

TRENDS IN THE
PERIODIC TABLE
Dmitri Mendeleev
In 1869 Mendeleev and Lothar Meyer (Germany)
published nearly identical classification schemes for
elements known to date. The periodic table is base on
the similarity of properties and reactivities exhibited by
certain elements. Later, Henri Moseley (
England,1887-1915) established that each elements has
a unique atomic number, which is how the current
periodic table is organized.
http://www.chem.msu.su/eng/misc/mendeleev/welcome.html
The Periodic Law
• When elements are arranged in order of increasing atomic
number, there is a periodic repetition of their physical and
chemical properties.
• Horizontal rows = periods
– There are 7 periods
• Vertical column = group (or family)
– Similar physical & chemical prop.
– Identified by number & letter (IA, IIA)
Across the Periodic Table
•
Periods: Are arranged horizontally across the
periodic table (rows 1-7)
•
These elements have the same number of valence shells.
1
IA
1
18
VIIIA
2
IIA
13
IIIA
2nd Period
2
3
3
IIIB
4
IVB
5
VB
6
VIB
4
5
6
7
6th Period
7
VIIB
8
9
VIIIB
10
11
IB
12
IIB
14
IVA
15
VA
16
VIA
17
VIIA
Down the Periodic Table
•Family: Are arranged vertically down the periodic table
(columns or group, 1- 18 or 1-8 A,B)
•These elements have the same number electrons in the outer most shells,
the valence shell.
1
IA
1
18
VIIIA
Alkali Family:
1 e- in the valence shell
2
IIA
13
IIIA
14
IVA
15
VA
16
VIA
2
3
3
IIIB
4
IVB
5
VB
6
VIB
7
VIIB
8
9
VIIIB
10
11
IB
12
IIB
4
5
6
7
Halogen Family:
7 e- in the valence shell
17
VIIA
All Periodic Trends
• Influenced by three factors:
1. Energy Level
– Higher energy levels are further away from the
nucleus.
2. Charge on nucleus (# protons)
– More charge pulls electrons in closer. (+ and –
attract each other)
• 3. Shielding effect
Shielding
• The electron on the outermost
energy level has to look through
all the other energy levels to see
the nucleus.
• The inner electrons shield the
outer electrons from the pull of
the nucleus. This effect is known
as electron shielding
• Second electron has same
shielding, if it is in the same
period
What do they influence?
Energy levels and Shielding have an effect on
the GROUP (  )
Nuclear charge has an effect on a PERIOD (
)
Atomic Radius
• Average distance from
the nucleus to the
electron cloud.
• The electron cloud
doesn’t have a definite
edge.
• They get around this
by measuring more
than 1 atom at a time.
© 1995-2002. Prentice-Hall, Inc.
#1. Atomic Size - Group trends
• As we increase the
atomic number (or
go down a group). .
.
• each atom has
another energy
level,
• so the atoms get
bigger.
H
Li
Na
K
Rb
#1. Atomic Size - Period Trends
• Going from left to right across a period, the size
gets smaller.
• Electrons are in the same energy level.
• But, there is more nuclear charge.
• Outermost electrons are pulled closer.
Na
Mg
Al
Si
P
S Cl Ar
Atomic Radius
Trends in Ionic Size: Cations
• Cations form by losing
electrons.
• Cations are smaller
than the atom they
came from – not only
do they lose electrons,
they lose an entire
energy level.
• The ionic radius
decreases as the
nuclear charge on the
ion increases
Cation Group trends
• Each step down a group
is adding an energy
level
• Ions therefore get
bigger as you go down,
because of the
additional energy level.
Li1+
Na1+
K1+
Rb1+
Cs1+
Ionic size: Anions
• Anions form by
gaining electrons.
• Anions are bigger than
the atom they came
from – have the same
energy level, but a
greater area the
nuclear charge needs
to cover
Ion Period Trends
• Across the period from left to right, the nuclear
charge increases - so they get smaller.
• Notice the energy level changes between anions
and cations.
Li1+
B3+
Be2+
C4+
N3-
O2-
F1-
Ionization Energy
• Energy needed to remove an electron from a
neutral atom
• Period - First ionization energy increases as you
go from left to right across a period.
• Why?
• Group - ionization energy decreases as you go
down a group.
• Why?
ELECTRON AFFINITY
• Energy change that occurs when an electron is added to an
atoms outer level to form a negative ion
• Period - electron affinity (EA) increases from left to right
across the periodic table
• Why?
• Group - electron affinity decreases down a group
• Why?
ELECTRONEGATIVITY
• a quantitative measure of the electron-attracting
ability of an atom in a molecule
• Period - electronegativity
across a period
• Group - electronegativity
down a group
• The most electronegative element is fluorine. What
is the least electronegative element?
Trends in the Periodic Table
© 1995-2002. Prentice-Hall, Inc.