Periodic Table and Periodicity of Properties || Periods and Groups || Atomic Size and Atomic radius || Ionization Energy, Electron Affinity and Electronegativity

Atomic size and atomic radius

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Introduction to Periodic Table
Periods
Groups
Atomic size and Atomic radius
Shielding effect
Ionization Energy
Electron Affinity
Electronegativity

Introduction to Periodic Table:

The periodic table is based on the arrangement of elements according to their increasing proton number. When elements are arranged in the periodic table according to their increasing proton number, it has been observed that their properties were found similar after regular intervals so those elements having similar properties were placed in the same group.

It has been observed in the periodic table that after every eighth element, ninth element shows similar properties as first element and after every eighteenth element, nineteenth element was also showing similar properties so the long rows of periodic table were cut down into eight and eighteen elements and placed on each other so that a table of horizontal rows and vertical columns was obtained.

In the periodic table, periods can be defined as the horizontal rows of elements present in the periodic table and the elements in a period have continuously changing(increasing) atomic number that's why the properties of elements in a period are different.

The number of electrons present in the outermost shell that is valence shell of an atom decides the position of an element in the periodic table such as those elements having only one electron in their outermost shell(valence shell) are placed in the first group of the periodic table and are known as alkali metals while those elements having two electrons in their outermost shell(valence shell) are placed in the second group of the periodic table and are known as alkaline earth metals.

In the periodic table, groups can be defined as the vertical columns of elements present in the periodic table. In a group of the periodic table, elements do not have continously increasing atomic numbers rather their atomic numbers are increased with irregular gaps.

In a group of the periodic table, all elements present in the same group have same electronic configuration as all elements in a group have same number of electrons in the outermost shell or valence shell such as elements of first group have only one electron in their outermost shell while elements of second group have two electrons in their outermost shell.

In a periodic table their are seven horizontal rows of elements called periods while eighteen vertical columns of elements that are groups. First period have only two elements, second and third period have eight elements, fourth and fifth period have eighteen elements, sixth period have thirty two elements while seventh period has twenty three elements and is incomplete.

Periods:

There are only two elements in the first group of the periodic table which are hydrogen and helium and this first group of periodic table is also known as short period. Their are eight elements in the second and third period of the periodic table and these second and third periods are also known as normal periods.

Elements present in the second period are lithium, beryllium, boron, carbon, nitrogen, oxygen, fluorine and neon. Their are eighteen elements in the fourth and fifth period of the periodic table and these fourth and fifth periods of the periodic table are also known as long periods. 

Sixth and seventh periods of the periodic table are also known as very long periods and in these periods after atomic numbers fifty seven and eighty nine two series of elements known as lanthanides and actinides starts. Both of these two series of elements(lanthanides and actinides) have fourteen elements in each of them.

Groups:

In the periodic table, elements of group one are hydrogen, lithium, sodium, potassium, rubidium, caesium and francium. Elements of a group are also known as a family because in a group all elements have similar electronic configuration as all elements have same number of electrons in the outermost shell or valence shell.

In periodic table, groups one, two, thirteen and seventeen have normal elements and this means that all inner shells are completely filled with electrons of these normal elements but their valence shells are incomplete such as group seventeen elements which are known as halogens have seven electrons in their outermost shell.

Atomic size and Atomic radius:

In simple words atomic size is the size of an atom and atomic radius can be defined as half of the distance between the nuclei of two bonded atoms. We all know that atoms are very small and we cannot measure the size of a single atom so we take two atoms of the same element that is two same atoms and let them to form a bond. After that they approach each other and when they touch each other or form a bond we calculate the distance between the nuclei of these atoms by using different techniques and this distance is said to be the atomic size of one of those atoms while half of this distance is said to be the atomic radius of that atom.

The atomic number increases continously across the period but atomic size reduces gradually because of the addition of more and more protons in the nucleus and electrons in the same shell are increasing so their is more nuclear pull towards electrons and hence atom will shrink a little bit and the size of atom reduces.

On the other hand, in a group atomic size or atomic radius increases because of the addition of more and more shells in the atom that is one shell is added after every period and hence the effective nuclear charge decreases so atomic size increases.

Shielding Effect:

Because of the inner electrons of an atom, the valence electrons experiences less attractive force or nuclear force as these inner electrons shield or screen this nuclear force, this is called shielding effect. With the increase in the number of electrons in an atom their is an increase in the shielding effect.

If we move from left to right in a period shielding effect decreases while on the other hand shielding effect increases down the group in the periodic table.

Ionization Energy:

The term ionization energy can be defined as the amount of energy required to remove an electron from the outermost shell or valence shell of an isolated gaseous atom. 

If we move from left to right in a period of the periodic table the value of ionization energy increases and this is because atomic size reduces, effective nuclear charge increases and valence electrons are held strongly by the electrostatic force of nucleus, hence it is more difficult to remove an electron from the right side of the periodic table.

On the other hand if we move from top to bottom in a group the value of ionization energy decreases because atomic size increases, more and more shells lie between the nucleus and the valence shell of the atom and hence electrostatic force of nucleus on the valence electrons reduces, as a result to remove an electron from the outermost shell becomes easier. 

Electron Affinity: 

The term electron affinity can be defined as the amount of energy released when an electron is added in the valence shell or outermost shell of an isolated gaseous atom.

Electron affinity increases in a group because as atomic size reduces the attraction of the nucleus for the incoming electron increases and hence more energy will be released.

While on the other hand, electron affinity decreases from top to bottom in a group because atomic size increases and shielding effect increases which results in the poor attraction for the incoming electrons.

Electronegativity:

The term electronegativity can be defined as the ability of an atom to attract the bonded pair of electrons towards itself.

If we move from left to right in a period of the periodic table, electronegativity increases because atomic size reduces and distance between the nucleus and valence electrons decreases and hence this enhances the power to attract shared pair of electrons.

On the other hand, if we move from top to bottom in a group, electronegativity generally decreases as atomic size increases and thus the attraction for the shared pair of electrons weakens.

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Introduction to Periodic Table
Periods
Groups
Atomic size and Atomic radius
Shielding effect
Ionization Energy
Electron Affinity
Electronegativity