- Atomic radius is the distance from the nucleus to the outermost shell.
- Over time, atomic size decreases due to a stronger nuclear pull.
- Down a group, atomic size increases as new shells are added.
- Atomic size depends on the number of shells and the nuclear charge.
- Cations are smaller, anions are larger, and in isoelectronic ions, size decreases with more protons.
Definitions [22]
Definition: Modern Periodic Table
A tabular arrangement of elements in groups (vertical columns) and periods (horizontal rows), highlighting the regular trends in properties of elements, is called a Periodic Table.
OR
The classification of elements resulting from an arrangement of the elements in an increasing order of their atomic numbers is the modern periodic table.
Definition: Elements
Elements are pure substances made up of one type of atom.
Define periods of modern periodic table.
The horizontal rows are called periods. The table consists of 7 periods, numbered from 1 to 7 from top to bottom.
Define:
Periodic table
The periodic table is a tabular arrangement of elements in horizontal rows, called periods, and vertical columns, called groups, to classify elements and facilitate their systematic study.
Define groups of modern periodic table.
In the modern periodic table, groups (also known as families) are the 18 vertical columns that organize chemical elements by shared properties. Unlike periods, which are horizontal rows representing electron shells, groups are vertical columns of elements with similar chemical properties.
Definition: Periods
There are seven horizontal rows in the modern periodic table. They are known as Periods.
Definition: Typical Elements
The third period elements, Na, Mg, Al, Si, P, S and Cl, summarise the properties of their respective groups and are called typical elements.
Definition: Groups
The modern periodic table has eighteen vertical columns. Each vertical column accommodates elements with the same number of electrons in the outermost shell. These vertical columns are known as Groups.
Definition: Periodicity
The properties that reappear at regular intervals, or in which there is gradual variation (i.e. increase or decrease) at regular intervals, are called 'periodic properties' and the phenomenon is known as the periodicity of elements.
Definition: Valency
Valency denotes the combining capacity of the atom of an element. It is equal to the number of electrons an atom can donate or accept or share.
Definition: Orbits
Electrons revolve around the nucleus in certain definite circular paths called orbits or shells.
Definition: Periodic Properties
The properties of elements which are directly or indirectly related to their electronic configurations and show a regular gradation as we move across a period, from left to right or down the group from top to bottom, are called Periodic Properties.
Definition: Atomic Size (Atomic Radius)
It is the distance between the centre of the nucleus of an atom and its outermost shell.
Definition: Metals
Those elements, which have a tendency to lose their valence electrons (electrons of the outermost orbit) and form a positive ion, are considered metals.
Definition: Non-Metallic Character
Those elements which have a tendency to gain electrons, in order to attain octet in their outermost orbit, are considered as non-metals.
Define the term ‘ionisation potential`.
The energy required to remove an electron from a neutral isolated gaseous atom and convert it into a positively charged gaseous ion is called Ionization energy or ionization potential.
Definition: Ionisation Energy
The energy required to remove an electron from a neutral isolated gaseous atom and convert it into a positively charged gaseous ion is called ionisation potential (l.P) or ionisation energy (I.E.) or first ionisation energy (IE1).
Definition: Electron Affinity
The amount of energy released while converting a neutral gaseous isolated atom into a negatively charged gaseous ion (anion) by the addition of electron is called Electron Affinity (E.A.)
Define the term ‘electron affinity’.
Electron affinity is the energy released when an isolated gaseous atom acquires an electron to form an anion.
\[\ce{X (g) + e- -> \underset{(anion)}{X-(g)}+ E.A.}\]
X is any element taken in its gaseous state.
Definition: Electronegativity
The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is called its electronegativity.
Definition: Mass Number
The mass number of an element is the sum of the number of protons and neutrons in the nucleus of the atom of that element.
Mass number (A) = No. of protons (p)
+ No. of neutrons (n)
Definition: Atomic Number
The atomic number of an element is equal to the number of protons in the nucleus.
Atomic number (Z) = Number of protons.
= Number of electrons.
Key Points
Key Points: Modern Periodic Table
- Dobereiner grouped elements in threes (triads) with similar properties and a pattern in atomic masses.
- Newlands found that every 8th element shared similar properties (the Law of Octaves).
- Mendeleev arranged elements by atomic mass and predicted new elements, but couldn’t explain isotopes and rare earths.
- Moseley fixed the flaws by arranging elements by atomic number, forming the modern periodic table.
- Bohr proposed the long-form periodic table based on electron arrangement.
Key Points: Atomic Size
Key Points: Metallic Character
- Metals lose electrons to form positive ions (cations).
- Bigger atoms lose electrons easily — more metallic.
- Metallic character increases down a group.
- Metallic character decreases across a period.
- Metals are good reducing agents — they give away electrons.
Key Points: Non-metallic Character
- Non-metals gain electrons to complete their octet and form negative ions.
- Non-metallic character increases across a period and decreases down a group.
- Metals lose electrons easily and act as reducing agents.
- Non-metals are oxidising agents as they readily gain electrons.
- Melting and boiling points of non-metals increase down the group, while those of metals decrease.
Key Points: Ionisation Potential
- Ionisation energy is the energy needed to remove an electron from a neutral gaseous atom to form a positive ion.
- Larger atomic size → lower ionisation energy because outer electrons are farther from the nucleus.
- Higher nuclear charge → higher ionisation energy due to stronger attraction of electrons.
- Across a period, ionisation energy increases from left to right as atomic size decreases.
- Down a group, ionisation energy decreases with increasing atomic size; metals have low I.E., non‑metals have high I.E.
Key Points: Electron Affinity
- Smaller atoms and higher nuclear charge → higher (more negative) electron affinity due to stronger attraction for electrons.
- Over time, E.A. becomes more negative (increases), with the largest increase for halogens (Group 17).
- Down a group, E.A. becomes less negative (decreases) due to increased atomic size and electron repulsion.
- Exceptions: Fluorine < Chlorine and Oxygen < Sulphur in E.A. due to strong electron repulsions in very small atoms.
Key Points: Electronegativity
- Electronegativity is the ability of an atom to pull shared electrons; it is highest for fluorine (4.0).
- It increases across a period (left to right) and decreases down a group (top to bottom).
- Non-metals have high electronegativity (gain electrons), while metals have low electronegativity (lose electrons).
Important Questions [25]
- An element with the largest atomic radius among the following is ______.
- In Period 3 of the Periodic Table, element B is placed to the left of element A. On the basis of this information, choose the correct word from the option to complete the following statement:
- Arrange the following as per the instruction given in the bracket: Mg, Cl, Na, S, Si (decreasing order of atomic size).
- Arrange the following as per the instruction given in the brackets: Na, K, Li (Increasing atomic size)
- Arrange the following as per the instruction given in the bracket: Carbon, Fluorine, Beryllium (decreasing order of atomic size).
- The Energy Required to Remove an Electron from a Neutral Isolated Gaseous Atom and Convert It into a Positively Charged Gaseous Ion is Called
- Arrange the Following as per the Instruction Given in the Brackets: Na, Li, K (Increasing Ionisation Energy)
- The Ionization Potential of Potassium is _________________ that of Sodium.
- Choose the Correct Answer from the Options Given Below: Ionisation Potential Increases Over a Period from Left to Right Because of the
- Give One Word Or Phrase for the Following: Formation of Ions from Molecules
- Process of Formation of Ions from Molecules Which Are Not in Ionic State
- Give a Reason For Ionisation Potential Increases Across a Period, from Left to Right
- Li, K, Na, H (In the Decreasing Order of Their Ionization Potential)
- Give reason for the following: Ionisation potential decreases down a group.
- Arrange the following as per the instruction given in the bracket: Potassium, Lithium, Sodium (increasing order of ionization potential).
- Draw an Electron Dot Diagram to Show the Formation of Each of the Following Compounds: Methane
- An element in period 3, whose electron affinity is zero:
- Arrange the Following as per the Instruction Given in the Brackets: He, Ar, Ne (Increasing Order of the Number of Electron Shells)
- Element X is a Metal with a Valency 2, Y is 3 Non- Metal with a Valency 3. Write an Equation to Show How Y from an Ion. If Y is a Diatomic Gas, Write an Equation for the Direct Combination of X and Y to Form a Compound.
- F, B, N, O (In the increasing order of electron affinity)
- Choose the Correct Answer from the Options Given Below: If an Element a Belongs to Period 3 and Group Ii, Then It Will Have
- Draw an Electron Dot Diagram to Show the Formation of Each of the Following Compounds: Magnesium Chloride
- Give One Word Or Phrase for the Following: the Amount of Energy Released When an Atom in the Gaseous State Accepts an Electron to Form an Anion
- The Energy Released When an Electron is Added to a Neutral Gaseous Isolated Atom to Form a Negatively Charged Iron.
- In Period 3 of the Periodic Table, element B is placed to the left of element A. On the basis of this information, choose the correct word from the option to complete the following statement:
Concepts [14]
- The Modern Periodic Table
- Salient Features of the Modern Periodic Table
- Periodicity
- Shells and Valency
- Periodic Properties
- Atomic Size
- Metallic Character
- Non-metallic Character
- Ionisation Potential (Ionisation Energy)
- Electron Affinity
- Electronegativity
- Summary Periodic Properties
- Atomic Number and Mass Number
- Comparison of Alkali Metals and Halogens
