Transcript Atoms

-1 0
10
Atoms
m
Nu cleus (protons an d neu trons)
Space occupied by electrons
Proton
Neu tron
10-1 5 m
Periodic Table and Electron Configurations
• Build-up order given by position on periodic table; row
by row.
• Elements in same column will have the same outer
shell electron configuration.
The relation between orbital filling and the periodic table
Electron Configuration
• Orbitals have definite shapes and
orientations in space
(insert Fig 2.11 of text)
(if it will not all fit on one screen, put part
(a) on one screen and part (b) on the
next )
Orbital occupancy for the first 10 elements, H through Ne.
Trends in the
Periodic Table
Atomic radii of the maingroup and transition
elements.
Trend for atomic radii
• Left to right atoms get smaller
• Why?
– Increase in nuclear charge
– More protons and more electrons means greater
electrostatic attractions (stronger magnet)
• Top to bottom atoms get larger
• Why?
– Increase in energy levels (You are adding floors to
your hotel). Electrons are further from the nucleus
Atomic Radius
• Atomic radii actually
decrease across a
row in the periodic
table. Due to an
increase in the
effective nuclear
charge.
• Within each group
(vertical column),
the atomic radius
tends to increase
with the period
number.
Atomic Radii for Main Group
Elements
The Size of Atoms and Ions
Radii of neutral atoms
The atomic radius of an atom is defined as half the distance between the
nuclei in a homonuclear bond.
r decreases
In general:
r increases
- radii decrease across a period
because of increasing Z*.
-radii increase down a group
because of the increasing
distance of the electrons from
the nucleus.
- increasing distance from the
nucleus outweighs effective
nuclear charge for atomic radii
down a group.
Remember that the maximum probability for an orbital moves
further away from the nucleus with increasing n.
0.1 nm = 1 Å = 100 pm
Bohr model for H; radius(n) = n2a0
The “d-block contraction” causes
Ga to be about the same size as Al.
This is caused by the introduction of
the 3d elements which cause a
vastly larger Z* for Ga.
Trend for Ion Size
• Ion is a charged atom.
• Metals lose electrons and nonmetals gain electrons to
create ions.
• Cations are pawsitive (positive) and Anions are
negative.
• Cations are smaller than their corresponding atom.
Why?
• Loss of electrons means the positive nucleus has a
greater attraction on the remaining electrons
• Anions are larger than their corresponding atom.
Why?
• Gain of electrons means the nucleus has less
attraction for the electrons as well as the electrons are
repulsing each other causing an increase in the size
of the electron clouds
Radii of ions
This is a “self-consistent” scale based
on O-2 = 1.40 (or 1.38) Å.
Ionic radii depend on the magnitude
of the charge of the ion and its
environment. (more later)
Positively charged ions are smaller
than their neutral analogues because
of increased Z*.
Negatively charged ions are larger
than their neutral analogues because
of decreased Z*.
Same periodic trends as atomic
radii for a given charge
Trend for ion size
• Decrease across a period then jumps in
size at nonmetals and continues to
decrease
• Increases on the way down a group as
you are adding energy levels (electrons
are farther from the nucleus)
Ionization energy
• The energy required to remove an
electron
First ionization
energies of the
main-group
elements
Trends in the
Periodic Table
Ionization Energy
• Ionization energy is a periodic property
Ionization energy
• In general, it increases across a row. Why?
• increasing attraction as the number of protons
in the nucleus increases (stronger magnet)
• it decreases going down a group. Why?
• Outer shell electrons are further from the
nucleus so less electrostatic attraction.
Nucleus has less pull on them
6) The trend across from left to right is
accounted for by a) the increasing nuclear
charge.
Electronegativity (electron
affinity - This is the most important trend to
understand for this class.
• The tendency for an atom to attract electrons
when chemically bonded.
• Same trend as ionization energy.
– In general, it increases across a row. Why?
– increasing attraction as the number of protons in
the nucleus increases (stronger magnet)
– it decreases going down a group. Why?
– Outer shell electrons are further from the nucleus
so less electrostatic attraction. Nucleus has less
pull on them
Trends in three atomic properties
See chart in book for
summary
Check for understanding
• Which of the following atoms has the
largest atomic radii, ion size,
electronegativity, and ionization energy
• Na, Mg, K, Ca, S, Cl, Se, Br
van der Waals radii
van der Waals radii are established from contact distances between nonbonding atoms in “touching” molecules or atoms
VDW radii allow us to
determine whether there
can be a bonding
interaction between two
atoms:
If the distance between
the nuclei is larger than
the sum of the VDW radii,
then the atoms are
probability not bonded.
rVDW increases
rVDW decreases