Groups of Periodic Table and Trends in Periodic Table

Periodic Table:

It is a table in which the elements arranged according to their atomic numbers.

Groups of periodic table are 18 groups and also periodic table contain 7  periods.

Groups of periodic table:

The periodic table consists of 18 groups some of periodic table groups have common names such as:

• Group 1 or IA called alkali metals (except hydrogen)
• Group 2 or IIA called alkaline earth metals.
• Transition metals or d-block elements,
• Group 8 called Noble gases group
• Lanthanides    (4f)
• Actinides         (5f)

The periodic table consist of 4 blocks:

• s-block (metals) and p-block (non-metals) elements called representative elements
• d-block elements called transition elements
• f-block elements called inner transition elements

The outer shell electronic configuration of the representative element groups are:

-         Group 1: their outermost shell is ended by S¹

-         Group 2: their outermost shell is ended by S²

-         Group 3: their outermost shell is ended by S² P¹

-         Group 4: their outermost shell is ended by S² P²

-         Group 5: their outermost shell is ended by S² P³

-         Group 6: their outermost shell is ended by S² P⁴

-         Group 7: their outermost shell is ended by S² P⁵

-         Group 8: their outermost shell is ended by S² P⁶

 

Periodic Trends in Atomic Properties:

In studying the properties of elements we will study the trend of these properties through the periodic table

(1) - Atomic size or radius:

In the groups:

The atomic radius increase from top to bottom due to the increase in atomic number(increase the number of electrons in new main energy level)

In the periods:

The atomic radius decrease from left to right due to the increase of attraction of nucleus while the number of electrons increase in the same energy level.

The size of positive and negative ions:

In s-block elements the ionic size is smaller than the atomic size

Positive ion: is smaller than its atom because it losses electrons and the attraction force of the nucleus increase so, the size decrease.

Negative ion: is larger than its atom because it gains an electron and the attraction force of the nucleus decrease so, the size increase.

Penetration and Shielding (or screening)

In an atom each electron acts as a shield for electrons farther out from the nucleus, reducing the attraction between the nucleus and the distant electrons.

Penetration describes the proximity of electrons in an orbital to the nucleus. Electrons closer to nucleus have greater penetration and have less shielding and therefore have a larger Effective Nuclear Charge (Z_eff)

The penetrating power and shielding of an electron follows this trend in subshells: 

s>p>d>f

Effective Nuclear Charge (Z_eff): is the net positive charge experienced by an electron in a multi-electron atom.

Z_{eff = Z - S}

where:

Z is the atomic number

S is the number of electrons between the nucleus and the electron in question

 

(2)– Ionization energy:

It is the energy required to remove one electrons from the outermost orbital of  atom.

Atoms can loss one, two, or three electrons so there are first, second and third ionization energies.

In periods:

The ionization energy increases from left to right because the atomic radius decrease and the attraction of nucleus to the outer electrons increase.

In groups:

Ionization energy decrease from top to bottom due to the increase in atomic radius and the decrease of attraction of nucleus to the outer electrons (this make electrons need low energy to be removed).

(3)-Electronaffinity:

It is the energy change associated with the addition or gain of electron to a gaseous atom.

The electron affinity of nonmetals is higher than electron affinity of metals.

The more the electronaffinity the more easily ability of atom to form negative ion.

In periods:

The electronaffinity increase from left to right due to the  decrease in the atomic radius.

In groups:

The electronaffinity decrease from top to bottom due to the  increase in the atomic radius.

(4)-Electronegativity:

It is the ability of atom to attract electrons of the bond.

In periods:

Increase from left to right due to the decrease in the atomic radius.

In groups:

Decrease from top to bottom due to the increase in the atomic radius.

 

(5)-Electrical Conductivity:

Elements are classified into metals, nonmetals and semi metals according to their electrical properties as follow:

Metals: are good conductors of electricity. but their conductivity decrease slowly with increase in temperature.

Nonmetals: are electrical insulator(the ability to conduct electricity is undetectable)

Semi metals: they called semi conductors and their conductivity is small but measurable and their conductivity increase with increase in temperature.