Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
Dimitri Mendeleev (1834-1907)
• ordered known elements according to atomic weight
• elements with similar propertiesfell into vertical groups
=> in the modern version, elementsare ordered according to atomic number
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
Properties (e.g. reactivity) of atoms depends on…
… electron configuration
… number of electrons
… how tightly electrons are bound to nucleus
(and many more properties)
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
How tightly electrons are bound to nucleus…
… is measured by effective nuclear charge, Zeff
Core electrons shield (mask) nuclear charge
++++
+ ++
-
-
-
-
-
-
-
core
7N: 1s22s22p3
core electron configuration:[He] = 1s2
Zeff = +7 – 2 = 5 +
Effective Nuclear Charge:
valence electrons
#protons # core electrons
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
What happens to Zeff along a period in the periodic table?
11Na 12Mg 13Al 14Si ….
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
What happens to the atomic radius along a period ?
The effective nuclear charge increases along a period and draws in thesurrounding electrons, making the atom more compact
Lithium Fluorine
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
What happens to the atomic radius as we go down a group ?
=> but - more main shells are added
=> Zeff essentially remains constant
11Na
19K
37Rb
atomic radius increases as we go down a group
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
atom
ic ra
dius i
ncre
ases
atom
ic r
adiu
s in
crea
ses
atomic radius increases
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
which radius is largest?
which radius is smallest?
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
How about the radii of ions?
cations are always smaller than their parent ions
anions are always larger than their parent ions
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
Which of the following has the largest radius?
S2-, S, O2-
Why does the ionic radius decrease along the following series?
O2- F- Na+ Mg2+ Al3+
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
Ionization Energies measure the energy required to remove electrons from an atom in the gas phase
1st ionization energy: energy required to remove 1st electron
K (g) K+ (g) + e- I1 = 419 kJ/mol
Mg (g) Mg+ (g) + e- I1 = 738 kJ/mol
2nd ionization energy: energy required to remove 2nd electron
3rd ionization energy: energy required to remove 3rd electron …
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
Trends in 1st Ionization Energies
1st ionization energy
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
Why does the ionization energy increase sharply after removalof the 5th electron for Nitrogen?
What would a similar graph look like for beryllium (Be)?
Nitrogen
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
Some Group trends:
• Reactivity of alkali metals increases with increasing atomic number
• Melting point of alkali metals decreases with increasing atomic number:
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
General Properties of Metals:
• compounds made of metals and non-metals tend to be …
…ionic substances
2 Ni (s) + O2 (g) → 2 NiO (s)
• Metal oxides dissolve in water to make metal hydroxides:
Na2O (s) + H2O (l) → 2 NaOH (aq)
strong base!
Chapter 7: Periodic Properties of the ElementsChapter 7: Periodic Properties of the Elements
• Metal oxides tend to make basic solutions in water
Na2O (s) + H2O (l) → 2 NaOH (aq)
• Non-metal oxides tend to make acidic solutions in water
CO2 (g) + H2O (l) → H2CO3 (aq)
SO3 (g) + H2O (l) → H2SO4 (aq)
SO2 (g) + H2O (l) → H2SO3 (aq)
natural wateris always slightly
acidic !
contribute toacid rain!