- Mendeleev corrected atomic masses to correctly place elements.
- He predicted new elements like Sc, Ga, and Ge with correct properties.
- He later added a zero group for noble gases.
- Co and Ni have similar masses, which can cause confusion about their order.
- Isotopes couldn’t be placed due to different masses.
- Atomic mass gaps are uneven, so new elements couldn’t be predicted.
- Hydrogen's position is unclear—it’s like both alkali metals and halogens.
Definitions [11]
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.
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.
Define the atomic size.
Atomic size is the distance between the center of an atom i.e., from the nucleus to the outermost shell (valence shell) of that atom.
Definition: Elements
Elements are pure substances made up of one type of atom.
Definition: Ionic Compounds
The compounds formed in this manner by the transfer of electrons from a metal to a non-metal are known as ionic compounds or electrovalent compounds.
Define electronegativity.
Electronegativity is defined as the relative tendency of an element present in a covalently bonded molecule, to attract the shared pair of electrons towards itself.
Definition: Electronegativity
The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is called its electronegativity.
Definition: Atomic Size (Atomic Radius)
It is the distance between the centre of the nucleus of an atom and its outermost shell.
Definition: Electronegativity
The tendency of an atom in a molecule to attract the shared pair of electrons towards itself is called its electronegativity.
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: Insights into Mendeleev’s Periodic Table
Key Points: Electronic Configurations
- Metals react by losing electrons to form positively charged ions (cations), while non-metals gain electrons to form negatively charged ions (anions), in order to attain a stable electronic configuration (octet or duplet).
- Ionic compounds consist of aggregates of oppositely charged ions held together by strong electrostatic forces of attraction, and do not exist as molecules.
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).
Key Points: Structure of the Modern Periodic Table
- The modern periodic table has 7 periods, 18 groups, and 118 elements.
- It has 4 blocks: s, p, d, and f (with d-block as transition elements).
- A zig-zag line separates metals, metalloids, and nonmetals.
Key Points: Atomic Size
- 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.
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).
Concepts [30]
- Significance of Classification of Elements
- Genesis of Periodic Classification
- The Modern Periodic Table
- Insights into Mendeleev’s Periodic Table
- Modern Periodic Law and the Present Form of the Periodic Table
- Nomenclature of Elements with Atomic Number Greater than 100
- Electric Configurations of Elements and the Periodic Table
- Electronic Configurations and Types of Elements: S-, P-, D-, F- Blocks
- The s-Block Elements
- The p-Block Elements
- The d-Block Elements (Transition Elements)
- The f-Block Elements (Inner-transition Elements)
- Metals, Non-metals and Metalloids
- Periodic Trends in Properties of Elements
- Trends in Physical Properties
- Atomic Radius
- Ionic Radius
- Ionization Enthalpy or Ionization Energy (IE) or Ionization Potential (IP)
- Electron Gain Enthalpy
- Electronegativity
- Valency
- IUPAC Nomenclature of Elements
- Periodicity of Valence or Oxidation States
- Anomalous Properties of Second Period Elements
- Periodic Trends and Chemical Reactivity
- Structure of the Modern Periodic Table
- Study of Specific Groups in Periodic Table
- Physical Properties of Halogen Derivatives
- Atomic Size
- Electronegativity
