The Periodic Table & Periodic Law

Meyer & Mendeleev In 1869, published almost identical versions with the elements in order of increasing atomic mass and in columns with similar properties.

Periodic Law There is a periodic repetition of chemical and physical properties of the elements when they are arranged in order of increasing atomic number

Arrangement of the Periodic Table Groups/Families 18 vertical columns (↑↓) Two Labeling Systems Number-and-letter system 1A through 8A columns (representative elements) 1B through 8B short columns (transition elements) 2. Number system, Group 1 to Group18 Periods 7 horizontal rows (↔)

Non-Metals Metalloid Non-Metals Metals Metals

Metals - Properties Shiny Solid at room temperature Good conductors of heat and electricity Malleable Ductile

Nonmetals & Metalloids Dull Generally gases or brittle solids at room temperature Poor conductors of heat and electricity Metalloids Elements with physical and chemical properties of both metals and nonmetals Rest on the “stair-step” B Si As Te At Ge Sb Po ←Metals

Periodic Trends

Atomic Radius Half the distance between two nuclei of identical atoms that are chemically bonded together Down the group atomic radius increases, because… Across the period atomic radius decreases, becauses….

Ionization Energy The amount of energy required to remove an electron from the atom (how tightly an atom holds on to its electrons) A general term for the energy required to remove an electron from an orbital in an atom. Think of it also as the energy required to make a cation. Down a group ionization energy decreases, because… Across a period ionization energy increases, because…

Electron Affinity The electron affinity of an element is the energy given off when a neutral atom in the gas phase gains an extra electron to form a negatively charged ion. The attraction to additional electrons A fluorine atom in the gas phase, for example, gives off energy when it gains an electron to form a fluoride ion. Down the group electron affinity decreases, because Across the period electron affinity increases, because

Electronegativity The attraction an atom has for electrons in a covalent bond. The ability of an atom to attract electrons in a chemical bond. Down the group Electronegativity values decrease, because Across the period Electronegativity values increase, because *Noble gases are the exception to this rule.