periodic table

What is the periodic table?

It is a table that classifies all known elements based on their properties, grouping similar elements in the same vertical column and separating dissimilar ones.

How are the 115 known elements arranged in the periodic table?

They are arranged in order of increasing atomic number.

What are the vertical columns in the periodic table called?

Groups.

What are the horizontal rows in the periodic table called?

Periods.

What is Dobereiner’s Triads?

Dobereiner classified elements into groups of three (triads) where the atomic mass of the middle element is the average of the other two.

What is Newlands’ Law of Octaves?

Newlands noticed that elements showed similar properties every eighth element when arranged by atomic mass, similar to the octaves in music.

What is Lother Meyer’s Law?

Lother Meyer proposed that atomic volume is a periodic function of atomic mass.

What is Mendeleev’s Periodic Law?

Mendeleev stated that the properties of elements are periodic functions of their atomic masses. Elements with similar properties recur at regular intervals.

What are the anomalies in Mendeleev’s table?

Position of hydrogen, rare earths, isotopes, noble gases, anomalous pairs of elements, and causes of periodicity.

What is the Modern Periodic Law?

The physical and chemical properties of elements are periodic functions of their atomic numbers.

How is the long form of the periodic table organized?

It is based on the modern periodic law, where elements are arranged by increasing atomic number.

What are the periods in the periodic table?

First period has 2 elements; second and third have 8 each; fourth and fifth have 18 each; sixth has 32; seventh is incomplete.

How many groups are in the modern periodic table?

There are 18 vertical columns called groups, arranged from IA to XVIII.

What determines a group in the periodic table?

A group is determined by the number of electrons in the outermost shell of an element.

What are the different types of elements in groups?

Groups 1, 2, and 13–17: Normal elements; Groups 3–12: Transition elements; Group 18: Noble gases.

Where are reactive metals and non-metals placed?

Reactive metals: Groups 1 and 2; Transition metals: Middle of the table; Non-metals: Upper right corner.

What is periodicity?

It refers to the repetition of properties of elements at regular intervals in the periodic table.

What are periodic properties?

Properties like atomic size, ionization energy, electron affinity, and electronegativity that show regular variation in the periodic table.

What are shells or orbits?

Electrons revolve around the nucleus in fixed circular paths called shells or orbits, which are associated with specific energy levels.

What is valency?

It is the combining capacity of an atom, equal to the number of electrons an atom can lose, gain, or share.

How does valency change in a group and period?

Down a group: Valency remains the same; Across a period: Valency increases from 1 to 8.

Which elements show variable valency?

Transition metals like Cu, Fe, Ag, and Au.

What is atomic size?

The distance between the nucleus and the outermost shell of an atom.

What is metallic character?

The tendency of an element to lose valence electrons and form a positive ion (e.g., Na → Na⁺).

What is non-metallic character?

The tendency of an element to gain electrons to attain an octet (e.g., Cl + e⁻ → Cl⁻).

What determines chemical reactivity in metals and non-metals?

Metals: Greater tendency to lose electrons = higher reactivity; Non-metals: Greater tendency to gain electrons = higher reactivity.

What is ionization energy (IE)?

The energy required to remove an electron from a neutral gaseous atom.

What is electron affinity (EA)?

The energy released when a neutral atom gains electrons to form a negatively charged ion.

What is electronegativity?

The tendency of an atom to attract shared electrons in a molecule.

What is atomic number (Z)?

The number of protons in the nucleus of an atom, unique to each element.

What is mass number (A)?

The sum of protons and neutrons in the nucleus of an atom.

How does atomic size vary in a group and period?

Increases down a group; Decreases across a period.

How does ionization energy vary in a group and period?

Decreases down a group; Increases across a period.

How does electron affinity vary in a group and period?

Decreases down a group; Increases across a period.

How does electronegativity vary in a group and period?

Decreases down a group; Increases across a period.

How does metallic character vary in a group and period?

Increases down a group; Decreases across a period.

How does non-metallic character vary in a group and period?

Decreases down a group; Increases across a period.

How does the basic nature of oxides vary in a group and period?

Increases down a group; Decreases across a period (becomes acidic).

How does chemical reactivity vary in a group and period?

Metals: Reactivity increases down a group; Non-metals: Reactivity decreases down a group; Across a period: Reactivity first decreases and then increases.