Download Chapter 7

Chemistry 101 : Chap. 7
Periodic Properties of the Elements
(1) Development of the Periodic Table
(2) Effective Nuclear Charge
(3) Sizes of Atoms and Ions
(4) Ionization Energy
(5) Electron Affinity
Reading Assignment : 7.6-7.8
Periodic Table
 Mendeleev ordered known elements according to their weight
D. Mendelejeff, Zeitscrift für Chemie 12, 405-406 (1869)
 In the modern
version, elements
are ordered
according to
atomic number
Dimitri Mendeleev
(1834-1907)
 Elements within a same vertical group have similar properties
Periodic Table
Halogen
Alkaline earth
metal
Alkali
metal
Transition metals
rare
gas
Periodic Properties
 Properties (e.g. reactivity) of atoms depends on…
 Number of electrons
 Electron configuration
 How tightly electrons are bound to nucleus
Periodic Table and
Electron Configurations
Effective Nuclear Charge
 Effective nuclear charge (Zeff) is used to measure how tightly
(outer-shell) electrons are bound to nucleus
Zeff = # of proton - # of core electrons
-
-
-
++
++
+ ++
-
core
valence electrons
-
 Valence electrons see nucleus and
core electrons as a single unit
 Valence electrons experience
approximately the total charge of
protons and core electrons
Effective Nuclear Charge
 Example : What is the effective charge of 2p electron of N ?
 Example : What is the effective charge of 4s electron of Ca?
Effective Nuclear Charge
Effective charge, Zeff,, increases with the atomic numbers
within a period.
….
11Na
12Mg
13Al
14Si
+11-10= +1
+12-10= +2
+13-10= +3
+14-10= +4
Zeff increases along a period
 # of protons increases, but the # of core electrons stay
the same along period.
 Valence electrons are more strongly bound as
atomic number increases within a period
Effective Nuclear Charge
 Example : Which electron is more tightly bound: 2p electron of Ne
or 3s electron of Na? Which electron would be easier
to remove?
Atomic Radius
Atomic radii decrease with the atomic numbers within a period.
Increasing Zeff along a period attract valence electrons more
strongly, making the atom more compact
Lithium
Fluorine
Atomic Radius
Atomic radii increase with the atomic numbers within a group.
11Na
+11 – 10 = +1
19K
+19 – 18 = +1
37Rb
+37 – 36 = +1
 Zeff essentially remains constant
However, more main shells are added and principal quantum
number of valence electrons increase
atomic radius increases
Atomic Radius
atomic radius increases
Ion Radius
cations are always smaller than their parent atoms
anions are always larger than their parent atoms
Ion Radius
 Example : Which of the following ions has the largest radius?
(1) S, S2-, O2(2) O2-, Na+, Al3+
Ionization Energy
 Ionization Energies (IE) : Energy required to remove electrons
from an atom in the gas phase
 First Ionization Energy : Energy required to remove one electron from
a neutral atom in the gas phase
Na (g)
Na+ (g) +
e-
IE1 = 495 kJ/mol
 Second Ionization Energy : Energy required to remove second electron
from an atom in the gas phase
Na+ (g)
Na2+ (g) +
e-
IE2 = 4562 kJ/mol
Ionization Energy
First IE increases in general with atomic numbers within a period
Increasing IE
First IE decreases with atomic numbers within a group
Ionization Energy
 First IE increases with atomic numbers in a period because ..
 Effective nuclear charge increases
 decreasing the distance from the nucleus
 stronger interaction between valence electron and nucleus
 First IE decrease with atomic numbers in a group because ..
 Atomic radius increases with little change in effective
nuclear charge
 weaker interaction between valence electron and nucleus
Ionization Energy
 Example : Why there is a huge gap between the 5th and 6th
Ionization E (kJ/mol)
ionization energy of nitrogen?
Ionization number
Ionization Energy
 Example : Why there are irregularities in the first IE within a period?
2p4
2s2
2p1
Electron Affinity
 Electron Affinity (Ea) : Energy change that occurs when an
electron is added to a neutral atom in the gas phase
Cl (g) +
100 pm
[Ne]3s23p5
e-
Cl- (g)
167 pm
[Ne]3s23p6
Ea = - 349 kJ/mol
Energy is released !
More negative Ea means greater attraction between a given
atom and an added electron
Electron Affinity
Added electron
goes to new shell
Added electron
goes to new subshell
Added electron leads to
noble gas configuration
Supplementary Material
 Metals : Tend to loose electrons
Small ionization energy (IE)
Reactivity of metal is related to the IE
 smaller IE = more reactive
Which one is the most reactive: Na, Mg or K?
Reactions (not covered in the class):
(a) Metal Oxide with water
Na2O (s) + H2O(l)  2NaOH (aq)
(b) Metal Oxide with acid
NiO(s) + 2HCl(aq)  NiCl2(aq) + H2O(l)
Supplementary Material
 Non-Metals : Tend to gain electrons
Usually have negative electron affinity (EA)
Seven nonmetals that exist as diatomic molecules
H2, N2, O2, F2, Cl2, Br2, I2
Reactions (not covered in the class):
(a) Non-Metal Oxide with water
P4O10 (s) + 6H2O(l)  4H3PO4 (aq)
(b) Non-Metal Oxide with base
CO2(g) + 2NaOH(aq)  Na2CO3 (aq) + H2O(l)