Chapter 8 Periodic Properties - Manu's...

Chapter 8Periodic Properties

Dr. Sapna Gupta

Periodicity

• Initially the periodic table had been arranged by atomic weight but was later changed by Mendeleev to atomic numbers.

• When organizing these elements Mendeleev found that elements in each group had the same chemical properties.

• There was also a trend in the rows and within the groups of the periodic table. This is periodicity.

• There are three main trends to study:

• Atomic radii

• Ionization energy and

• Electron affinity

• Effective Nuclear Charge – all the above three trends are based on the fundamental understanding of effective nuclear charge.

Dr. Sapna Gupta/Periodic Properties 2 2

Effective Nuclear Charge (Zeff)

• This is the attraction of negative electrons to the positive nucleus.

• All periodic trends are based on Zeff

• As electrons are added to the same shell the Zeff increases

• As electrons are added to a shell farther away from the nucleus the Zeff decreases.


Atomic Radii; Ionization Energy; Electron Affinity; Metallic Character

• Atomic radius is half the distance between two nuclei.

• Ionization Energy is the amount of energy required to remove one electron from an atom in a gas phase.

• Electron Affinity is the measure of energy change when an electron is added to a valence shell. A negative energy measurement means an anion is formed and positive energy measurement means cation is formed.

• Metallic Character is how much a metal behaves like a metal e.g. conducts electricity and heat, malleability, reactivity with acids etc.


Atomic Radii


Atomic radius is half the distance between two nuclei.

Atomic Radii


Ionization Energy


Ionization Energy is the amount of energy required to remove one electron from an atom in a gas phase.

Ionization Energy


Ionization Energy

• Left of the line, valence shell electrons are being removed. Right of the line, noble-gas core electrons are being removed.


Electron Affinity


Electron Affinity is the measure of energy released when an electron is added to a valence shell. A higher energy measurement means more energy is released and lower energy measurement means less energy is released.

Metallic Character


Metallic Character Nonmetals Metalloids

•Shiny, lustrous, malleable•Good conductors•Low IE (form cations) •Form ionic compounds with chlorine•Form basic, ionic compounds with oxygen•Metallic character increases top to bottom in group and decreases left to right across a period

•Vary in color, not shiny•Brittle •Poor conductors•Form acidic, molecular compounds with oxygen•High EA (form anions) •Group VII and VIII are all non metals

•Properties both of metals and nonmetals

TrendsTrend Definition Across a Group Down a Group

Effective nuclear charge

This is the attraction of negative electrons to the positive nucleus

IncreasesBecause electrons are added to the same shell

DecreasesBecause electrons are added to a new shell

Atomic radii Atomic radius is half the distance between two nuclei

DecreasesBecause electrons are added to the same shell

IncreasesElectrons are added to a new shell

Ionization energy

IE is the amount of energy required to eject one electron from an atom in a gas phase

IncreasesZ increases, so harder to remove an electron

DecreasesZ decreases so easy to remove an electron

Electron affinity

Electron Affinity: the measure of energy released when an electron is added to a valence shell

Increaseseasier to gain electrons

Decreasesharder to add electrons

Metallic Character

how much a metal behaves like a metal e.g. conducts electricity and heat, malleability etc.

DecreasesZ increases so harder to lose electrons

IncreasesZ decreases so easier to lose electrons


Ionic Radii

• Cations give electrons: so protons > electrons radii gets smaller

• Anions accept electrons: so protons < electrons radii gets larger



Solved Problem:

Refer to a periodic table and arrange the following elements in a) order of increasing atomic radius: Br, Se, Te.

35Br

34Se

52Te

Te is larger than Se.Se is larger than Br.

Br < Se < Te

b) order of increasing ionization energy: As, Br, Sb.

Sb is larger than As.As is larger than Br.

Ionization energies:Sb < As < Br

35Br

33As

51Sb

Isoelectric Elements/Ions

• Two or more species having the same electron configuration but different nuclear charges

• Atomic/ionic size varies significantly


Properties of the Groups

• Groups I and II – all metals

• Groups VII and VIII – all non metals

• Transition metals – all metals

• Groups III, IV, V and VI – has non metals, metalloids and metals.

• Oxides: dissolving oxides in water give bases and acids. • Metal oxides give bases

• Non metal oxides give acids

• Amphoteric oxides can give both acids and bases


Reactions of Oxides

• Metal oxides are usually basic

• Nonmetal oxides are usually acidic

• Amphoteric oxides are located at intermediate positions on the periodic table


Group I – Alkali Metals (ns1)

• All metals

• Reactivity increases down the group

• Never found in nature in elemental state

• Oxides are M2O

• All metals very reactive – have to be stored in special containers.

• All metals are very soft (unlike typical metals)

Na

Li


Group II – Alkaline Earth Metals (ns2)

• These elements are metals

• Reactivity increases down the group.

• Less reactive than group I

• The oxides have the formula MO

• Some react with acids to form hydrogen gas

Sr

Ca


Group III (ns2 np1)

• Metalloid (B) and metals (all others)

• Al forms Al2O3 with oxygen and is an amphoteric oxide

• Al reacts with acid

• Other metals form +1 and +3

GaB


Group III

Group IV (ns2 np2)

• Nonmetal (C) metalloids (Si, Ge) and other metals

• Form +2 and +4 oxidation states

• Sn, Pb react with acid to produce H2

• CO2, SiO2, and GeO2 are acidic (decreasingly so).

• SnO2 and PbO2 are amphoteric.

CGe


Group IV

Group V (ns2 np3)

• Nonmetal (N2, P) metalloid (As,Sb) and metal (Bi)

• Nitrogen, N2 forms variety of oxides

• Phosphorus, P4

• As, Sb, Bi (crystalline)

• HNO3 and H3PO4 important industrially

• Nitrogen, phosphorus, and arsenic oxides are acidic.

• Antimony oxides are amphoteric.

• Bismuth oxide is basic.

N2

Sb


Group V

Group VI (ns2 np4)

• Nonmetals (O, S, Se)

• Metalloids (Te, Po)

• Oxygen, O2

• Sulfur,S8

• Selenium, Se8

• Te, Po (crystalline)

• Oxides form acids in water; SO2, SO3, H2S, H2SO4

Se

S


Group VI

Group VII – Halogens (ns2 np5)

• All non metals

• All elements are diatomic molecules

• Gain one electron during reactions

• Physical property trend is gas (F2 and Cl2), liquid (Br2), solid (I2).

• Halogens form acids (HX, where X is a halogen)

I2

Br2


Group VIII – Noble Gases (ns2 np6)

• All monatomic

• Filled valence shells

• All are gases

• Considered “inert” until 1963 when Xe and Kr were used to form compounds

• No major commercial use

He Ne


Noble Gases

Key Words

• Effective nuclear charge

• Atomic radii

• Ionization energy

• Electron affinity

• Metallic character

• Ionic radii

• Isoelectric elements/ions

• Basic oxide

• Acidic oxide


Chapter 8 Periodic Properties - Manu's...

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