Periodicity

Periodic table

The periodic table is a tabular arrangement of all known elements, ordered by increasing atomic numbers. This arrangement reflects the elements' electronic configuration and periodicity of their properties.

Mendeleev's and Lothar Meyer (1869)

The first comprehensive classification of elements was made independently by Mendeleev in Russia and Lothar Meyer in Germany in 1869. They tabulated all known elements based on relative atomic mass. The arrangement of elements in the early periodic table followed the "ordinary periodic law," which states that "The properties of elements are periodic functions of their relative atomic masses."

When elements were arranged in increasing atomic mass, elements with similar properties recurred at regular intervals. This recurrence of elements with similar properties is known as periodicity.

Mendeleev and Lothar Meyer placed elements in horizontal rows (periods), causing elements with similar properties to appear in the same vertical columns (groups). However, some elements were not yet discovered (e.g., noble gases, gallium, germanium).

In the early periodic table, there were three anomalies caused by isotopes. For example:

1. Potassium (39.1) and Argon (39.9) had discrepancies in their placements.
2. Cobalt (58.94) and Nickel (58.69) positions were also in conflict.
3. Tellurium (127.6) and Iodine (126.9) had similar issues.

These anomalies were due to the isotopic nature of elements, which caused variations in atomic masses. For example, Argon has a higher abundance of its heavier isotope (atomic mass of 39.9), while Potassium has a lighter isotope (atomic mass of 39.1).

ELEMENTS	ISOTOPE	PROTONS	NEUTRONS	RELATIVE ATOMIC MASS
Argon	1st isotope	18	18	36
	2nd isotope	18	22	40
Potassium	1st isotope	19	20	39
	2nd isotope	19	22	41
	3rd isotope	19	21	40

Moseley's discovery

Moseley discovered that the atomic number was the proper criterion for arranging elements in the periodic table. Atomic number determines the number of electrons in an atom, which in turn determines the element's arrangement and properties.

When atomic numbers were used, the anomalies observed in potassium, argon, cobalt, nickel, tellurium, and iodine disappeared. Today, the classification of elements in the periodic table is based on the Modern Periodic Law: "The properties of elements are periodic functions of their atomic numbers."

Structure of the periodic table

The periodic table is essential in the study of inorganic chemistry. The relationship between atomic number and element properties provides an overview of various facts in inorganic chemistry.

The periodic table consists of boxes containing elements. Each box includes the element's symbol, atomic number, and sometimes its atomic mass. Additional data like electronegativity, boiling point, melting point, and oxidation states may also be included. There are various layouts for the periodic table, but here we focus on the long form.

The periodic table is divided into groups (vertical columns) and periods (horizontal rows). Elements with similar properties are found in the same group, while each period has elements with the same number of electron shells.

The periodic table is divided into four major blocks, which depend on the sub-shell in which the elements fill their electrons:

1. S-Block Elements: Elements that fill their outermost electrons in the s-sub shell. These include Group IA and IIA elements like Li, Na, K, and Mg.
2. P-Block Elements: Elements that fill their outermost electrons in the p-sub shell. This block consists of Groups IIIA to VIIA, including elements like Carbon, Sulphur, Phosphorus, Nitrogen, Oxygen, Chlorine, and noble gases like Neon and Argon.
3. D-Block Elements: These are transition metals (e.g., Fe, Cu, Zn), and they fill electrons in the d-sub shell of the penultimate shell. They use both s- and d-sub shell electrons for bonding.
4. F-Block Elements: Known as inner transition elements, they fill electrons in both (n-1)d and (n-2)f sub-shells. Examples include Lanthanides and Actinides like La, U, and Th.

Key notes

1. Periodicity: Similar properties recur at regular intervals due to the arrangement of electrons in the outermost shells.
2. Group Number: The group number reflects the number of electrons in the outermost shell of the elements.
3. Period Number: The period number corresponds to the principal quantum number (n) of the outermost shell and the total number of electron shells in a given period.

Summary of periodic table blocks

1. S-Block: Includes Groups 1A and 2A (alkali metals and alkaline earth metals).
2. P-Block: Includes Groups 3A to 8A, including nonmetals, metalloids, and halogens.
3. D-Block: Transition metals that fill d-orbitals.
4. F-Block: Lanthanides and actinides that fill f-orbitals.