Monday, 16 July 2018

Periodic table: periodic law, groups, periods

Periodic Table
Table of Contents
1) What is periodic table?
2) What is the periodic law?
3) What are Groups?
4) What are periods?
5) Families of Elements
6) Group 0 to 7 properties.









Periodic table
The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number and electron configuration. The periodic table is divided into eight (8) vertical columns known as "Groups" and eight (8) horizontal columns known as "Periods".



What is the periodic law?
The periodic law states that;
  1. The physical and chemical properties of the elements recur in a systematic and predictable way when the elements are arranged in order of increasing atomic number. 
  2. Many of the properties recur at intervals. When the elements are arranged correctly, the trends in element properties become apparent (as proved by Lothar Meyer and Dmitri Mendeleev) and can be used to make predictions about unknown or unfamiliar elements, simply based on their placement on the table. 


Groups
The vertical column of element (groups) are numbered from 0-7.

Group One Elements are called "Alkali Metals". 
Group Two Elements are called "Alkali Earth Metals". 
Group Three Elements are called "Icosagens". 
Group Four Elements are called "Crystallogens". 
Group Seven Elements are called "Halogens". 
Group Zero Elements are called "noble gases



    • Elements on the same group have the same number of electrons in the outermost shell of the atom. i.e. they have the same number of valence electrons. For example, Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), which are in group one the periodic table, have (1) as their valence electron. Their electronic configuration is given below:       
      Li 2,1
      Na 2,8,1
      k 2,8,8,1
                                                                                                 
    • Hydrogen does not fit into any groups but it is placed in group one because of the single electrons.




Periods
The elements in the horizontal rows (periods) are numbered from 0-7.
  • ·   The elements in the same period have the same number of electron shell. For example, elements in period 2 (Li, Be, F and so on) have two electron shells, while elements in period 3 (Na , mg , Si and so on) have three electron shells. 
  •     The valence electrons of the elements in the same period increase progressively across.

Rows and columns periodic Table



Families of element

Changes in the properties of an element down the group are gradual and less marked from those across the period. The similarities in chemical behavior characterizes the elements in the group. Therefore, elements in the same group are said to belong to one family. The gradual change in the properties of an element down a group and across the period is known as Periodic Trend.


Periodic Table Elements

Group One Elements.
There are six (6) elements in group one of the periodic table. These includes: Lithium(Li), Sodium(Na), Potassium(K), Rubidium(Rb), Caesium(Cs), Francium(Fr).


Group 1 elements periodic Table

Properties of elements in group one.
1)They are univalent because they have one valence electron.
2) They are reducing agents because they donate one electron during chemical reaction.
3) They are good conductors of electricity.
4) They are alkali metals; that is, they react with cold water easily to form hydrogen gas and produce an alkali compound.
2K + 2H2O --> 2KOH + H2
5) There are the most highly reactive metals. 


Group Two Elements
These includes; beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

·         Calcium reacts very slowly in cold water to liberate hydrogen gas, while magnesium only reacts with steam to liberate hydrogen gas. Ca + 2H2O --> Ca(OH)2 + H2

·         Calcium oxide dissolves slightly in water to form calcium hydroxide solution, which is a weak acid, while magnesium oxide is practically insoluble in water.


Group 2 elements periodic Table


Properties of elements in Group 2

1) They are alkali metals.
2) The trioxonitrate(v) salt of group two elements decompose readily on heating to liberate; metallic oxide, oxygen and nitrogen
3) They are less metallic in character than the Group 1 elements.
4) All the elements in Group 2 have two electrons in their valence shells, giving them an oxidation state of +2.


Group four elements
These includes; carbon, silicon, germanium, tin, lead and so on. 

Properties of elements in Group 4
1) They are tetravalent elements; that is, each of the atoms have four valence electrons.
2) C, Si, Ge are all giant covalent, Sn and Pb are metallic
2) The sudden decrease in electronegativity of  between C and Si due to the increased shielding effect and weaker attraction for the outer bonding electrons, makes it exhibit two oxidation states; +2 and +4. The stability of +2 compounds increase down the group, and that of +4 decreases down the group. 


Group Seven elements

The elements in group seven are known as halogens. This is synonymous to salt formation. They are the most reactive non-metals in the periodic table. These includes: fluorine, chlorine, bromine, iodine, astatine, manganese (Mn), technetium (Tc), rhenium (Re), and bohrium (Bh). All known elements of group 7 are transition metals. 



Group 7 elements periodic Table



 Properties of elements in Group 7

1)They are all non-metals.
2) They exist as a diatomic molecule.
3) They react with metallic ion to form elecrovalent compounds.
4) They are coloured.
5) Their hydrides are covalent at room temperature.


Group eight or Zero elements.
These are known as noble gases.
Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) and Radon (Rn).


Group 8 elements periodic Table


 Properties of elements in Group 0
1) They have no bonding electrons in their outermost shell.
2) They are chemically Inert (hence, they are non-reactive)
3) Noble gases exhibit a degradation in their physical properties as the atomic number increases.
4) They have very low boiling and melting points.
5) They are all gases at room temperature.

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