Periodic Table and Periodicity

Electronegativity, metallic and non-metallic character

Electronegativity is the ability of an atom to attract shared electrons in a chemical bond.
Measured on the Pauling scale, where fluorine has the highest value (4.0).
Electronegativity increases across a period from left to right due to increasing nuclear charge and a smaller atomic radius.
Electronegativity decreases down a group as atomic size increases, reducing the pull on shared electrons.
Non-metals like oxygen, nitrogen, and fluor

The atomic radius is the distance from the nucleus to the outermost shell of an atom.
Atomic radius decreases across a period due to increased nuclear charge, which pulls electrons closer to the nucleus.
Atomic radius increases down a group because of the addition of new electron shells.
Cations (positively charged ions) have smaller radii than their parent atoms due to the loss of electrons and reduced electron-electron re

Proposed by Dmitri Mendeleev in 1869.
Based on the periodic recurrence of properties of elements when arranged in order of increasing atomic mass.
Contained 63 known elements at the time.
Mendeleev organized elements into rows and columns to form the periodic table.
He left gaps in the table for undiscovered elements and predicted their properties accurately, such as gallium (eka-aluminum) and g