Download The Periodic Table

The Periodic Table
Jedediah Mephistophles Soltmann
Dmitri Mendeleev
Studied the properties of
elements and organized
the elements by similar
properties (families) and
by increasing atomic
mass.
He left blanks for
elements he knew had to
exist, such as:
Ekaaluminum (gallium)
Property
In 1871 Mendeleev predicted
the existence of yet
undiscovered element he
named eka-aluminum (because
of its proximity to aluminum in
the periodic table). The table
below compares the qualities of
the element predicted by
Mendeleev with actual
characteristics of Gallium
(discovered in 1875).
Ekaaluminum
Gallium
atomic mass
68
69.3
density (g/cm³)
5.9
5.93
melting point (°C)
Low
30.15
oxide's formula
Ea2O3
Ga2O3
chloride's formula
Ea2Cl6
Ga2Cl6
Ekasilicon (Germanium)
Property
Germanium was
isolated in 1882, and
provided the best
confirmation of the
theory up to that time,
due to its contrasting
more clearly with its
neighboring elements
than the two previously
confirmed predictions of
Mendeleev do with
theirs.
Ekasilicon
Germanium
atomic mass
72
72.59
density (g/cm³)
5.5
5.35
melting point (°C)
high
947
color
gray
gray
oxide type
refractory dioxide
refractory dioxide
oxide density (g/cm³)
4.7
4.7
oxide activity
feebly basic
feebly basic
chloride boiling point
under 100°C
86°C (GeCl4)
chloride density (g/cm³)
1.9
1.9
Effective Nuclear Charge
Protons in the nucleus attract the electrons
Electrons repel each other.
So inner electrons push the outer electrons
(shielding), negating much of the pull of the
nucleus. Thus higher energy levels means
less lower effective nuclear charge.
Zeff = Z - S
Calculating Zeff
Na11: 1s2 2s2 2p6 3s1
Zeff = 11 – 10 = 1
Mg12: 1s2 2s2 2p6 3s2
Zeff = 12 – 10 = 2
Cl17: 1s2 2s2 2p6 3s2 3p5
Zeff = 17 – 10 = 7
As you can see, the outer electrons of chlorine are pulled more
by the nucleus than those of the sodium or magnesium.
Isoelectronic Atoms/Ions
Iso = same
electronic = from electrons
Isoelectronic particles are those with the
same # of electrons in the same
configuration.
Size of Atoms
Atomic Size on the Periodic
Table
As we compare elements in a period, the Zeff
increases which means that the valence electrons
are being pulled harder by the nucleus. So, from
left to right, the atomic size decreases.
Atomic Size on the Periodic
Table
As we compare
elements in a
family, the main
difference is the
number of
shells. From top
to bottom, the
number of shells
increases, so
the atomic size
increases.
Do
Now
What is the effective nuclear charge of:
An electron in the 3rd energy level of
Mo?
An electron in the 2nd energy level of
S?
An electron in the 4th energy level of
Br?
List these elements in size order: P, S, As,
Se
List these particles in size order: S, S2-, O
Do Now Answers
What is the effective nuclear charge of:
An electron in the 3rd energy level of
Mo?
Zeff=42-10=32
An electron in the 2nd energy level of S?
Zeff = 16 - 2 = 14
Do Now Answers
An electron in the 4th energy level of Br?
Zeff=35-28=7
List these elements in size order: P, S, As,
Se
S, P, Se, As
List these particles in size order: S, S2-, O
O, S, S2-
Bond Length
When a bond forms, two atoms are held next
to each other by electrical attractions. So the
distance from nucleus to nucleus is called the
bond length.
Bond length is thus the sum of atomic radii.
For example a C-H bond has a length of
1.14A, because C has a radius of .77A and H
has a radius of .37A. .37A + .77A = 1.14A.
Chart of Atomic Radii
What is the bond length of:
C-S?
S-H?
N-Cl?
Na-Cl?
What is the bond length of:
C-S = 1.79A
S-H = 1.39A
N-Cl = 1.74A
Na-Cl = 2.79A
Why is the bond length of NaCl
2.79A?
NaCl is an ionic compound and thus
depends on the radii of the ions, not the
atoms!
Na+ has a radius of .98A and Cl- has a
radius of 1.81A. Thus the sum is 2.79A!
Ionic Radii
Ionization Energy
Ionization energy is the minimum energy
required to remove an electron from the
ground state of an isolated gaseous atom,
or ion.
Na(g) --> Na+ (g) + e-
IE = 496 kJ/mol
Na+ (g) --> Na2+ (g) + e- IE = 4560 kJ/mol
Why does the first electron come from sodium
so much easier than the 2nd?
Because...
Na11: 1s2 2s2 2p6 3s1
The first electron comes from the 3rd energy
level, but the next electron must come from a
lower energy level, closer to the nucleus, with a
higher Zeff. Thus it takes a lot more energy to
get 2 electrons than 1 from a sodium atom.
So think about this...
An element in the 3rd period requires 787
kJ/mol to remove its first electron.
It requires 1575 kJ/mol to remove the 2nd
electron.
It requires 3220 kJ/mol to remove the 3rd
electron.
It requires 4350 kJ/mol to remove the 4th
electron.
It requires 16,100kJ/mol to remove the 5th
electron.
What element is this?
Chart of Successive Ionizations
The Answer is Silicon
Ionization and the Periodic
Table
It is easier to remove a valence electron from
a bigger element than a smaller one. Why?
A valence electron in a smaller atom is closer
to the nucleus, and thus held more tightly by
electrical attraction.
Ionization across a Period
We now know that the size of the atoms
decreases as we compare the elements
going from left to right across a period. This
means that more energy is required to
remove electrons from elements on the right
(nonmetals) and less for elements on the left
(metals).
Ionization energy increases from left to right.
Could this be why metals give off electrons
easily?
Ionization within a Family
We also know that each successive member
of a family is larger because of additional
energy levels. This means that elements
near the top of the periodic table require
more energy to remove an electron than
elements near the top.
Ionization energy decreases from top to
bottom.
Ionization as a Periodic
Function
Electron Affinity
Instead of taking electrons, we could also
add electrons. One such property of atoms is
called Electron Affinity.
Electron affinity is electron affinity is the
energy released when 1 mole of gaseous
atoms each acquire an electron to form 1
mole of gaseous 1- ions.
Like Ionization energy, there are successive
electron affinities.
However...
Electron affinity is not a clear periodic
property like ionization energy. The reason is
that energy shifts based on whether
subshells or orbitals are partially filled or
completely filled. This makes it hard to come
up with a good rule.
Still, it makes sense that a smaller atom can
attract electrons better than a larger atom.
So more energy is released when a smaller
atom captures an electron than a larger
atom.
Electron Affinity and the Periodic
Table
If smaller atoms release more energy, than
electron affinity should increase from left to
right across a period.
Likewise, electron affinity should decrease
from top to bottom.
Electron Affinity and the Periodic
Table
Metals
What defines a metal?
We’ve used words like:
luster, ductility,
malleability, &
conductivity. Why do
metals behave this
way?
Metallic Behavior
Metals tend to be larger atoms. Since it is easier to
remove an electron from a larger atom, it should
make sense then that metals tend to form cations.
Conversely we can say that the larger an atom is
(or the lower its first ionization is) the more metallic
the atom is.
So if we compared O, S, and Se (all nonmetals) we
could say that selenium, being the largest atom, is
the most metallic - even though it is a nonmetal.
Nonmetallic Behavior
Nonmetals tend to be smaller atoms. Since it is
easier to add an electron to a smaller atom, it
should make sense then that nonmetals tend to
form anions.
Conversely we can say that the smaller an atom is
(or the higher its first ionization is) the more
nonmetallic the atom is.
So if we compared Li, Na, and K (all metals) we
could say that lithium, being the smallest atom, is
the most nonmetallic - even though it is a metal.