Periodicity

  •  The periodic table
  •  Physical properties
  •  Chemical properties
HideShow resource information
  • Created by: Priscilla
  • Created on: 23-04-11 12:15

The Periodic Table

A list of the chemical elements arranged into Groups (the columns going down) and Periods (the rows going across).

The group number gives the number of valence (outer shell) electrons around the atom.

The period number is the same as that of the outer energy shell. Elements increase in atomic number across each period by one.

1 of 11

Physical Properties

Ionization Energy:

The first ionisation energy is the energy required to remove the most loosely held electron from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of 1+.

This is more easily seen in symbol terms.

(http://www.chemguide.co.uk/atoms/properties/padding.GIF)(http://www.chemguide.co.uk/atoms/properties/1stieeq.GIF)

It is the energy needed to carry out this change per mole of X.

Factors affecting the size of ionisation energy

Ionisation energy is a measure of the energy needed to pull a particular electron away from the attraction of the nucleus. A high value of ionisation energy shows a high attraction between the electron and the nucleus.

The size of that attraction will be governed by:

  • The charge on the nucleus.
  • The distance of the electron from the nucleus..
  • The number of electrons between the outer electrons and the nucleus.
2 of 11

Physical Properties II

Electronegativity:

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.

The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to caesium and francium which are the least electronegative at 0.7.

Factors affecting electronegativity

  • the number of protons in the nucleus;

  • the distance from the nucleus;

  • the amount of screening by inner electrons.

3 of 11

Physical Properties III

Period 3:

CharacteristicTrend (left to right)Reason Atomic radius decreases in size from left to right increased attractive force (acting on the same energy shell) of the nucleus increases as the number of protons increases Ionic radius decreases across the period until formation of the negative ions then there is a sudden increase followed by a steady decrease to the end In general as above. The sudden increase on formation of negative ions is due to the new (larger) outer shell Electronegativity Increases More electron attracting power of the larger nuclear charge as we move to the right Metallic character Decreases - Na, Mg, Al metals; Si metalloid; P, S, Cl, Ar non-metals Metallic character is a measure of the ease of loss of electrons from the outer shell. This decreases with increasing nuclear charge. Melting point Na(http://ibchem.com/root_img/reaction_arrow.GIF)Al steady increase Increasing availability of electrons in the metallic bonding associated with greater charge density of the metal ion Si massive increase Si giant macromolecular structure P large decrease P4 molecules S small increase S8 crown shaped molecules Cl (http://ibchem.com/root_img/reaction_arrow.GIF) Ar decrease Cl2 molecules and Ar atoms

4 of 11

Physical Properties IV

Group 1:

CharacteristicTrend (descending group 1)Reason Atomic radius increases in size top to bottom The number of electron shells increases from Li to Cs Ionic radius increases from Li to Cs The number of electron shells increases from Li to Cs Electronegativity decreases Attracting power of the nucleus is sheilded by the inner electron shells increasingly as the group is descended Ionisation energy Decreases descending the group Sheilding effect of the inner electron shells increases as we descend the group and so the outer electron is more easily removed Melting point Decreases from Li to Cs The larger ions have weaker metallic bonding as their charge density (charge/volume ratio)is smaller

5 of 11

Physical Properties V

Group 7:

CharacteristicTrend (descending group 7)Reason Atomic radius increases in size from F to I The number of electron shells increases from F to I Ionic radius increases from F to I The number of electron shells increases from F to I Electronegativity decreases Attracting power of the nucleus is sheilded by the inner electron shells increasingly as the group is descended Ionisation energy Decreases descending the group Sheilding effect (repusion caused by the inner electrons) of the inner electron shells increases as we descend the group and so the outer electron is more easily removed Melting point Increases from F to I The larger halogens have greater Van der Waals forces holding the molecules together as they have more electrons

6 of 11

Physical Properties VI

The most electronegative element is Fluorine with the highest value on the Pauling Scale - 4.0.

(http://www.chemguide.co.uk/atoms/bonding/pteneg.GIF)

7 of 11

Chemical Properties

 

Reactions of group 1 and 7

Element

reagent

example equation

conditions (if any)

Group 1(Li...Cs)

water

2Na + 2H2O --> 2NaOH + H2

violent reaction

Group 1(Li...Cs)

halogen

2Na + Cl2 --> 2NaCl

heat needed

Group 7 (halogen)

water

Cl2 + H2Description: http://ibchem.com/root_img/doublearrow.gif HCl + HClO

 

8 of 11

Chemical Properties II

Displacement Reactions of the Halogens:

Reactivity of the halogens decreases going down the group and the more reactive halogen will displace a less reactive halogen from a solution of its ions. This is also a redox reaction.

 

Cl-(aq)

Br-(aq)

I-(aq)

Cl2

Colorless / no reaction

turns red due to formation of bromine

turns brown due to formation of iodine

Br2

no reaction

no reaction

turns brown due to formation of iodine

I2

no reaction

no reaction

no reaction

9 of 11

Chemical Properties III

The reactions of Halide ions with Silver ions

 Cl-(aq)Br-(aq)I-(aq) Ag+

white ppt

cream ppt

yellow ppt

reason

insoluble AgCl formed

insoluble AgBr formed

insoluble AgI formed

equation

Ag+ + Cl- (http://ibchem.com/root_img/reaction_arrow.GIF)AgCl

Ag+ + Br- (http://ibchem.com/root_img/reaction_arrow.GIF)AgCl

Ag+ + I- (http://ibchem.com/root_img/reaction_arrow.GIF)AgI

Metallic character of the elements:

Elements on the left are metallic...right are non-metals...Si is a metalloid.

Acidic character of the oxides:

·        Metal oxides are basic

·        Aluminium oxide is amphoteric (reacts with both acids and bases)

·        Non-metal oxides are acidic

10 of 11

Chemical Properties IV

Acidic character of the oxides:

 

Na2O

MgO

Al2O3

Adding H2O

Na2O + H2O -> 2NaOH

MgO + H2O -> Mg(OH)2

Insoluble

Adding HCl

Na2O + H+ -> 2Na+ + H2O

MgO + 2H+ -> Mg2+ + H2O

Al2O3 + 6H+ -> 2Al3+ + 3H2O

Adding NaOH

No reaction

No reaction

Al2O3 + 2OH- + 3H2O -> 2Al(OH)4

Nature

Basic Oxide

Basic Oxide

Amphoteric Oxide

 

SiO2

P4O10 (or P4O6)

SO(or SO2)

Cl2O7

Adding H2O

Insoluble

P4O10 + 6H2O -> 4H3PO4

SO3 + H2O -> H2SO4

Cl2O7 + H2O -> HClO4

Adding HCl

No reaction

No reaction

No reaction

No reaction

Adding NaOH

SiO2 + 2OH- -> SiO32- + H2O

P4O10 + 12OH- -> 4PO43- + 6H2O

SO3 + OH- -> SO42- + H2O

Cl2O7 + OH- -> 2ClO4- + H2O

Nature

Acidic Oxide

Acidic Oxide

Acidic Oxide

Acidic Oxide

11 of 11

Comments

No comments have yet been made

Similar Chemistry resources:

See all Chemistry resources »See all resources »