Chapter 7: Periodic Properties of the Elements. Dimitri Mendeleev (1834-1907) ordered known 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


Properties (e.g. reactivity) of atoms depends on…

… electron configuration

… number of electrons

… how tightly electrons are bound to nucleus

(and many more properties)


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


What happens to Zeff along a period in the periodic table?

11Na 12Mg 13Al 14Si ….


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


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


atom

ic ra

dius i

ncre

ases

atom

ic r

adiu

s in

crea

ses

atomic radius increases


which radius is largest?

which radius is smallest?


How about the radii of ions?

cations are always smaller than their parent ions

anions are always larger than their parent ions


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+


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 …


Trends in 1st Ionization Energies

1st ionization energy


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


Some Group trends:

• Reactivity of alkali metals increases with increasing atomic number

• Melting point of alkali metals decreases with increasing atomic number:


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!


• 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!

Chapter 7: Periodic Properties of the Elements. Dimitri Mendeleev (1834-1907) ordered known elements...

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Transcript of Chapter 7: Periodic Properties of the Elements. Dimitri Mendeleev (1834-1907) ordered known elements...