PERIODIC TABLE

 

 PERIODIC TABLE 

- Periodic Law

Many Chemist contributed to the periodic classification of elements. Notable among them are Dobereiner (1829), he observed that there is similarities in the chemical properties of the groups of three elements such as Lithium, Sodium and potassium or sulphur, selenium and Tellenium. He also found out that the atomic mass of the middle element is approximately the average of the other two elements in the group.

Mendeleef (1896) proposed a periodic table, he arranged elements in order of increasing atomic weight (mass number) wherever he found out that an element cannot fit a place, he left a space, because he believed that there are more elements to be discovered. This periodic table could not stand the test of time because of the discovery of isotopes of elements.

Moseley (1913) discovered that each element has a characteristic number and this number is the atomic number of element which is the same for all isotopes of an element. When the chemist now arranged  the element discovered in order of increasing atomic number they found out that the problem encountered in Mendeleef  periodic table varnished.

The basis for periodic classification (Periodic law) of element in the periodic table is that elements are arranged in order of their increase in atomic number.

The most important form of periodic table is the one which the elements are arranged in s,p,d,f orbital block.

The vertical arrangement of elements in the periodic table is known as GROUP while the horizontal arrangement of elements in the periodic table is known as PERIOD. It will be noticed that all the elements in the same group have the same number of electron in their outermost shell, and this outermost shell electron donate their group number. The elements in the same group have the same chemical properties but with different reactivity. Also, elements in the same period have the same number of shell and their number of shell predict their period number, take for instance hydrogen and helium have one shell, this shows that they are in period one.

The first-twenty elements in the periodic table are arranged as shown below:

             S- block                                                                                                                                             P- block

 IA                                                                                                                                                                                                                                                                                                                                                 VIIIB

1

IIA

 

IIIB              IVB               VB             VIB              VIIB

2

2,1

2,2

 

 

 

      dblock

      

 

2,3

2,4

 2,5

2,6

2,7

2,8

 

2,8,1

2,8,2

2,8,3

2,8,4

2,8,5

 2,8,6

 
2,8,7

 

2,8,8

 

2,8,8,1

 

2,8,8,2

 

 

- Blocks Of Element, Metals, Non- Metals, Metalloids And Transition Metals 

The periodic table shows different block of elements which are:

1.        Metal: metal elements are usually good conductors of both electricity and heat. The group I and II are usually metals.

2.        Non-metals: the terms is used to classify hydrogen, carbon, phosphorous, oxygen, sulphur and selenium. Even the halogen are also a subset of the non-metals.

3.        Metalloid: these elements are called semi-metals or poor metals. They usually behave as semi-conductors ( Boron, silicon, germanium, arsenic, antimony, tellurium and polonium rather than as conductors.

4.        Transition metals: these are metals that have a partially filled d-subshell and comprises group 3 to 12 and the lanthanides and actinides.

5.        Post-transition metal: these elements have some of the characteristics of the transition metal, but they tend to be softer and conduct more poorly than transition metals. Examples aluminium, gallium, indium, thallium, tin, lead and bismuth.

6.        Noble gases: they are generally very stable chemically and exhibit similar properties of being colourless and odourless

- Families; (s-p-d-f) According To Groups  I-Vii I.E. Group IA- Alkalis Metals, Groups And  IIA-Alkali Earth And The Other Family

Groups and general names of the families in the periodic table

Group number

Name by element

Trivial name

IA

Lithium group

Alkali metal

IIA

Beryllium group

Alkaline earth metal

IIIB

Boron group

Icosagens (is not IUPAC recommended)

IVB

Carbon group

Crystallogen( is not IUPAC recommended)

VB

Nitrogen group

Pnicogen

VIB

Oxygen group

Chalcogen

VIIB

Fluorine group

Halogen

VIIIB

Helium or Neon group

Noble gas / Inert gas

 

Properties, Change in size, changes down the Group, Across Periods And Accompany Changes In Properties.

ATOMIC RADII: this deals with the size of the atom, and it depends on the number of the electronic shell present in the atom.

Down the group: increases                                     Across a period: increases

IONIC RADII: This is a measure of inter ionic distances between two nearest positively charged ionic species e.g Na+ Cl-. Ionic radii depend on atomic size and effective nuclear charge.

Down a group- The effect of nuclear charge of an atom is to shrink (reduce the size) of the atom, but down a group the atomic increases due to an increase in the number of electronic shell, the increament in the electronic shell superceed the effect of nuclear charge, therefore down a group the ionic radii increases.

Across a period- The effective nuclear charge increases (from +1, +2 ….) across a period and this result into a magnified impact on the atomic size, hence, as we go across a period the size of the ionic species keeps on diminishing. There are some anomalous along the line but for this level, it is generally accepted that across a period the radii decreases due to an increase in the effective nuclear charge.

ELCTRONEGATIVITY- this is the ability of an atom to attract or accept electron from other atoms. According  to Milikan electronegativity of an atom can be calculated by finding the average of the I.E and E.A ie      Electronegativity=  

Down a group - decreases                                                      Across a group- increases

ELECTROPOSITIVITY- this is the ability of an tom to loose electron(s) to the other atom(s). this is a characteristics feature of metal.

Down a group- increases                                                        Across a period-decreases

                         

WK 10   PERIODIC TABLE - III

DIAGONAL RELATIONSHIP

In the periodic table, particularly for the elements Li and Mg; Be and  Al; B and Si, there is a diagonal resemblance. This is to be expected, since in moving from left to right across the periodic table, the metallic properties gradually decrease, whilst on descending a group, they increase. Hence, elements diagonally below one another have similar properties.

Li             Be            B              C

                                                 

                               

Na           Mg           Al             Si

IONIZATION AND ELECTRON AFFINITY

IONIZATION ENERGY: This is the energy required to remove the most loosely bound electron from a neutral gaseous atom.

X(g)  + Energy                           X+(g)   +  e-(g)

Ionization energy depends on atomic radii and effective nuclear charge.

Down a group: As we go down a particular group the effective nuclear charge remain the same , while the atomic radii increases due to an increase in number of shells, the increament in the numbers of shells make the outermost shell electrons far away from the nucleus and this reduce the effect of nuclear poll on the electron in the outermost shell thereby making it easy  for the outermost electron to be removed. i.e as we go down the group ionization energy decreases.

Across a period: As we move across a period, the effective nuclear charge on the atom increases, the consequence of this is that the atom will be shielded, and to remove electron from this shielded atom will require more energy.

As we go across the period the stability of the atoms increase from group I to the noble gas and to remove electrons from stable atom will be very difficult, therefore greater amount of energy will be required. Generally across a period ionization energy increases.

Ionization energy is dependent on three factors. They are:

 i. The distance between the outermost electron and the nucleus.

 ii. The screening or the shielding effect of the inner electrons.

 iii. The size or the strength of the positive nuclear charge.

Ionization potential is the ability of the atom to loose electron.                                                                                                                

ELECTRON AFFINITY- is defined as the change in energy when one mole of electron is added to one mole of gaseous atom to form a univalent element of negative ions.

Down a group- electron affinity decreases down the group due to a decrease in the electronegativity of the atom.

Across a period- E.A increases across a period.

Summary of the properties change within the rows and periods

Properties

Down a group

Across a period

Atomic radii

Increases

Increases

Ionic radii

Increases

Decreases

Electronegativity

Decreases

Increases

Electropositivity

Increases

Decreases

Ionization energy

Decreases

Increases

Electron affinity

Decreases

Increases

 

 

 

Comments

Post a Comment

Popular posts from this blog

POST HARVESTING PROCESSES

CHAPTER TWELVES POST HARVESTING PROCESSES 12.1             CONCEPTS AND PHILOSPHY OF POST HARVEST TECHNOLOGY Post-harvest fisheries entails all steps, process and or activities immediately after catch handling and transportation processing and distribution of fish and fishery product where if control is not applied post-harvest losses will occur.         Post –harvest fish losses are a major concern and occur in most fish distribution chains throughout the world. Not only do losses constitute lost income to fishers, processors and traders, they also contribute food insecurity i.e a loss of fish means less fish available for the consumer. POST HARVEST PROCESSES:         Fish are highly perishable. A central concern of fish processing is to prevent fish from deteriorating . Causatic factors of fish spoilage 1. High moisture content.   ...
Read more

NICOM SAT 1

TOPIC: - NICOM-SAT 1    INSTRUCTIONAL MATERIALS: -         Satellite dish REFERENCES BOOK: -     1.      FARINDE O. E e tal, ESSENTIAL PHYSICS FOR SSS, Tonad Publishing Limited. 2.      M. W. ANYAKOHA (2011), NEW SCHOOL PHYSICS FOR SENIOR SECONDARY SCHOOLS, Africana first publishers.    3.      INTERNET PREVIOUS KNOWLEDGE: -     Students have been taught Niger-sat 1 INSTRUCTIONAL OBJECTIVES: - At the end of the lesson students should be able to: - 1.        Explain the concept of NICOM-SAT 1 2.        State the features of NICOM-SAT 1 3.        Uses of NICOM-SAT 1 CONTENT: - NICOM- SAT 1 NigComSat-1 is a Nigerian Communication Satellite. It was launched on 14 may, 2007 in China by China Great Wall Industry...
Read more

FISH SEED PRODUCTION

CHAPTER THIRTEEN FISH SEED PRODUCTION BROOD STOCK SELECTION             Brood stock means a group of sexually mature individuals of a culture species that is kept separate for  breeding purpose. 13.1     DIFFERENCES  BETWEEN MALE  AND FEMALE SEXUALLY MATURED FISHES             Male and female breeders may be easily differentiated by the shape of the body and the relative position of genital papilla. In females, the body is plump and the genital opening is situated above the genital papilla. In males, the body is slender and the genital opening is found behind the genital papilla. External signs of the brood stock A male brood stock will release milt under a slight abdominal pressure: Its belly is not blown up but rather slim; it sometimes has callosities on the head. A female brood stock has a well-rounded and soft  or semi...
Read more