1. Introduction to the Periodic Table:
   • The periodic table is a tabular arrangement of chemical elements based on their atomic number and properties.
   • Dmitri Mendeleev is credited with the first widely accepted periodic table in 1869.
   • Modern periodic table is organized based on atomic number (number of protons) rather than atomic mass.
2. Arrangement of Elements:

1. Elements are arranged in rows called periods and columns called groups/families.
2. Elements within a group share similar chemical properties due to their similar electronic configurations.
3. Periods and Groups:

1. The periodic table has 7 periods (rows) and 18 groups (columns).
2. Elements in the same period have the same number of electron shells.
3. Elements in the same group have the same number of valence electrons.
4. Metals, Nonmetals, and Metalloids:
   • Elements are classified as metals, nonmetals, or metalloids (semi-metals) based on their properties.
   • Metals are typically shiny, conductive, and malleable.
   • Nonmetals are generally non-conductive and have a wide range of properties.
   • Metalloids exhibit properties intermediate between metals and nonmetals.
5. Periodic Trends:
   • Atomic radius decreases across a period (left to right) and increases down a group (top to bottom).
   • Ionization energy and electronegativity generally increase across a period and decrease down a group.
   • Metallic character increases down a group and decreases across a period.
6. Main Group and Transition Elements:
   • Main group elements include Groups 1, 2, and 13-18.
   • Transition elements are found in Groups 3-12 and have partially filled d orbitals.
   • Transition metals are known for their colorful compounds and variable oxidation states.
7. Noble Gases:

1. Group 18 elements are noble gases, characterized by their low reactivity and full valence electron shells.
2. Noble gases are used in various applications, such as lighting and cryogenics.
3. Periodic Trends in Reactivity:
   • Reactivity of elements is influenced by their position in the periodic table.
   • Alkali metals (Group 1) are highly reactive due to their tendency to lose one electron.
   • Halogens (Group 17) are also highly reactive, seeking to gain one electron.
4. Uses of the Periodic Table:
   • The periodic table is a valuable tool for predicting element properties, chemical reactions, and trends.
   • It aids in understanding the behavior of elements and compounds in various applications.
5. Contributions and Ongoing Research:
   • Scientists continue to study and refine the periodic table.
   • New elements are being discovered and added to the table.
   • The periodic table remains a fundamental cornerstone of chemistry and our understanding of the elements.

Remember, these key notes provide a concise overview of the modern periodic table. You can expand on each point, include relevant examples, and use visual aids to enhance your understanding.

In the modern periodic table, elements are arranged in order of their increasing atomic numbers. Explanation of Modern Periodic Table: Elements are arranged in order of their increasing atomic numbers. The vertical columns are known as groups and horizontal columns are known as periods; in the modern periodic table.

In the famous atomic theory of John Dalton (1805), it was suggested that the atoms of an element have a characteristic mass. So, attempts were made to classify elements on the basis of their atomic masses.

Dobereiner found that when elements are arranged into groups of three in the order of their increasing atomic mass, the atomic mass of the element; which comes in the middle; is the arithmetic mean of rest of the two. On this basis, he arranged three elements in one group which is known as ‘Triad’. This arrangement of elements is known as Dobereiner’s Triads.

Newlands found that every eighth element has similar physical and chemical properties when they are arranged in increasing order of their relative masses. This law is known as Newland’s Law of Octaves.

Mendeleev classified the then known 56 elements on the basis of their physical and chemical properties in the increasing order of the atomic masses, in the form of a table.

Law of Modern Periodic Table states that properties of elements are the periodic function of their atomic numbers. In the modern periodic table, elements are arranged in order of their increasing atomic numbers.

Ionization potential or ionization energy is the amount of energy required to remove one or more electrons from the outermost shell of an isolated atom in the gaseous state.

Ionization potential or ionization energy is measured in the units of electron volts (eV) per atom or kilo joules per mole of atoms or kJ mol^-1.

Metals usually have low ionization potential whereas non-metals have high ionization potential. Metalloid’s have intermediate ionization potential.

The inert gases have very high ionization potential, due to the stability of the outer shell. Helium has the highest ionization potential.

Electron affinity is the ability of an atom to hold an additional electron. If the atom has more tendency, to accept an electron then the energy released will be large and consequently the electron affinity will be high. Electron affinities can be positive or negative. It is taken as positive when an electron is added to an atom. It is expressed as electron volts per atom (eV per atom) or kilo joules per mole.

Electronegativity is the tendency of an atom to attract electrons towards itself in a molecule of a compound.

Atomic size increases on moving from top to bottom in a group and decreases on moving from left to right in a period.

Atomic radius increases on moving from top to bottom in a group and decreases on moving from left to right in a period.

Metallic character decreases on moving from left to right in a period.

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