Chapter 7
7.2 Effective Nuclear Charge
7.3 Size of Atoms & Ions
7.4 Ionization
7.5 Electron Affinity
7.1 PERIODIC TRENDS
• Arises from the Periodic patterns in
ELECTRON CONFIGURATIONS.
• Elements in the same GROUP have the
same number of VALENCE electrons
• VALENCE electrons = electrons in the
outermost orbital
7.2 EFFECTIVE NUCLEAR CHARGE
The NET positive charge experienced by an electron.
Core electrons pulled in tightly
Valence electrons held less tightly
Shielding effect reduces the full nuclear charge of outer electrons
BASED On The PERIODIC
RECURRENCE Of PROPERTIES
Periodic Trends In
7.3 Sizes of atoms and ions.
7.4 Ionization energy.
7.5 Electron affinity.
7.3 SIZES OF ATOMS
BUT !!
As we move ACROSS ACROSS ACROSS ACROSS a period, {left to right}
atoms become SMALLERSMALLERSMALLERSMALLER
WHY ?
As we move ACROSS the periodic table, the number of core electrons remains constant, but the nuclear charge increases
Which of the following ATOMSATOMSATOMSATOMS is largest
N , O , F
S or O
Na , Mg , Al
Na or Cl
Na or K
?
?
?
?
?
• CATIONSCATIONSCATIONSCATIONS lose electrons and are
SMALLER THAN THE PARENT IONSMALLER THAN THE PARENT IONSMALLER THAN THE PARENT IONSMALLER THAN THE PARENT ION.
• ANIONSANIONSANIONSANIONS add electrons and are
LARGER THAN THE PARENT IONLARGER THAN THE PARENT IONLARGER THAN THE PARENT IONLARGER THAN THE PARENT ION.
ISOelectronic series
A group of ions all containing the same number of electrons
How many electrons do
O2- ; F- ; Na+ ; Mg2+ and Al3+ have ?
10
-- Increasing nuclear charge �
O2- > F- > Na+ > Mg2+ > Al3+
--- Decreasing ionic radius �
In an isoelectronic series
Ionic size decreases with
an increasing nuclear charge
{See Text page 269}
Which of the following is largest ?
• Na or K ?
• Na or Mg ?
• S2– or O2– ?
• S2–, S, or O2– ?
• K+, Cl–, Ca2+, or S2– ?
• O 2- , F - , Na + , Mg 2+ , or Al 3+
Arrange the ions K+, Cl–, Ca2+, and S2– in order of DECREASING size.
These form an isoelectronic series of ions
Size decreases as the nuclear charge of the ion increases.
The atomic numbers of the ions are S (16), Cl (17), K (19), and Ca (20)
Arrange O 2- , F - , Na + , Mg 2+ , Al 3+
according to size
As nuclear charge increases in an
isoelectronic series the ions become
smaller
IONIZATION ENERGY
How Much ENERGY is Required To
REMOVE An ELECTRON From
An ATOM In Its GROUND STATE
for example
H ���� H + + e-
Periodic Trends in Ionization Energies
Ionization energy decreases going
down a group
Ionization energy generally increases
across a period.
Ionization energy decreases down a group
• The outermost electron is more readily
removed as we go down a group.
Why ?
The further the electron is from the nucleus
the less tightly it is held
Ionization energy generally increases across a
period.
As we move across a period, Zeff increases.
Therefore, it becomes more difficult to
remove an electron.
Electron Configuration of Ions
Cations: electrons removed from orbital with
highest principle quantum number, n, first:
Li (1s2 2s1) ⇒ Li+ (1s2)
Fe ([Ar]3d6 4s2) ⇒ Fe3+ ([Ar]3d5)
Anions: electrons added to the orbital with
highest n:
F (1s2 2s2 2p5) ⇒ F- (1s2 2s2 2p6)
Ionization Energy & Electron Affinity
Ionization Energy change accompanying
loss of electron Na → Na+ + e−
Electron Affinity Energy change accompanying addition of electron
Cl + e− → Cl−
7.5 Electron Affinities7.5 Electron Affinities
• Electron affinity is the opposite of ionization energy
• Electron affinity is the energy change when an atom gains an electron
Cl(g) + e- →→→→ Cl-(g)
ELECTRON AFFINITY
THE ENERGY CHANGE
THAT OCCUR WHEN
AN ELECTRON IS ACCEPTED
BY AN ATOM
Cl + e- ���� Cl -
CLASSIFICATION
BASED ON SUBSHELL BEING FILLED
Representative Elements (s & p electrons)
a) ALKALI Metals
b) ALKALINE EARTH Metals
Transition Elements (d electrons)
Lanthanides & Actinides (f electrons)
PERIODIC TABLE
Divided Into PERIODS (ROWS) And
GROUPS (COLUMNS)
I. METALS
1. REPRESENTATIVE
a) ALKALI ………GROUP IA
b) ALKALINE EARTH……IIA
2. TRANSITION……(B GROUPS)
II. METALLOIDS
III. NONMETALS
WHICH INCLUDE THE HALOGENS AND THE NOBLE GASES.
The Alkali Metals
Alkali metals react with water to form
the BASE MOH and hydrogen
gas:
2M(s) + 2H2O(l) → 2MOH(aq) + H2(g)
Alkali metal oxides
4Li(s) + O2(g) → 2Li2O(s) (oxide)
2Na(s) + O2(g) → Na2O2(s) (peroxide)
K(s) + O2(g) → KO2(s) (superoxide)
The Alkaline Earth Metals
• The chemistry is dominated by the loss of
two s electrons: M →→→→ M2+ + 2e-.
• Be does not react with water.
• Mg will only react with steam.
• Ca onwards:
Ca(s) + 2H2O(l) →→→→ Ca(OH)2(aq) + H2(g)
Oxygen• Two allotropes:
– O2
– O3, ozone
• Three anions:
– O2−, oxide
– O22−, peroxide
– O21−, superoxide
The Oxygen Group
• As we move down the group the metallic
character increases
• O2 a nonmetal, Te a metalloid, Po a
metal
halogens
All halogens consists of diatomic molecules
Fluorine is one of the most reactive substances known:
2F2(g) + 2H2O(l) → 4HF(aq) + O2(g) ∆H = -758.7 kJ
The Noble Gases
• They are all nonmetals and monatomic.
• They are notoriously unreactive because they have
completely filled s and p sub-shells.
• In 1962 the first compound of the noble gases was
prepared: XeF2, XeF4, and XeF6.
• To date the only other noble gas compounds
known are KrF2 and HArF.
Metals
Metallic character increases down a group.
Metallic character decreases across a period.
Metals have low ionization energies
All group 1A metals form M+ ions.
All group 2A metals form M2+ ions.
Most metal oxides are basic:
Metal oxide + water → metal hydroxide
Na2O(s) + H2O(l) → 2NaOH(aq)
Nonmetals
Most nonmetal oxides are acidic:
nonmetal oxide + water → acid
P4O10(s) + H2O(l) → 4H3PO4(aq)
CO2(g) + H2O(l) → H2CO3(aq)
MetalloidsMetalloids
• Metalloids have properties that are intermediate
between metals and nonmetals.
• Metalloids have found fame in the semiconductor
industry.
P7.8 Arrange the following atoms in order of
increasing effective nuclear charge
experienced by the electrons in the n = 3
electron shellK Mg P Rh Ti
What information do I need to answer this question ?
P7.18 Using only the periodic table, arrange the following atoms in increasing radius
(a) Cs K Rb
(b) In Te Sn
(c) P Cl Sr
? < ? < ?
? < ? < ?
? < ? < ?