Chemistry - Periodic Table

Periodic Table: A table that organizes elements according to their chemical properties. Group: A vertical column in the periodic table; elements in the same group share similar chemical characteristics. Period: A horizontal row in the periodic table; elements in the same period have the same number of electron shells. Octet Rule: A rule stating that atoms tend to gain, lose, or share electrons to achieve a full outer shell of eight valence electrons, which is considered a stable state. However, starting from the 4th period where transition metals appear, the outer shell expands, extending to the 18-electron rule. Orbital: A theory that explains the shape of atomic orbitals. Each orbital can hold a maximum of two electrons. Period 1: Uses the 1s orbital and can only hold 2 electrons. Contains only two elements: H and He. Periods 2 & 3: Have 8 valence electrons (s(2)p(6)). Periods 4 & 5: Have 18 valence electrons (s(2)p(6)d(10)). Periods 6 & 7: Have 32 valence electrons (s(2)p(6)d(10)f(14)).