Definitions [2]
Define modern periodic law.
The modern periodic law states that “The physical and chemical properties of the elements are a periodic function of their atomic numbers.”
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.
Key Points
Key Points: Classification of Elements
- Around 1800, only about 30 elements were known, whereas today the number has increased to 118.
- To manage the growing volume of information, scientists began identifying patterns in element properties to facilitate systematic classification.
- Elements were initially grouped as metals and nonmetals, and later, a third category called metalloids was recognised.
Key Points: Classification of Elements
- Around 1800, only about 30 elements were known, whereas today the number has increased to 118.
- To manage the growing volume of information, scientists began identifying patterns in element properties to facilitate systematic classification.
- Elements were initially grouped as metals and nonmetals, and later, a third category called metalloids was recognised.
Key Points: Periodic Trends in Properties
- Periodic trends are regular changes in properties across periods and down groups.
- These trends depend on atomic number and electronic configuration.
- Across a period, the effective nuclear charge increases.
- Down a group, the number of shells increases.
- Important trends include atomic radius, ionic radius, ionisation enthalpy, electron gain enthalpy and electronegativity.
- Periodic trends help predict chemical reactivity.
