The Modern Periodic Table

Early Periodic Table – Atomic Number In 1913 Henry Mosley discovered that each element contained a unique number of protons in the nuclei Arranged elements in order of atomic number. Resulted in a clear periodic pattern of properties.

Periodic Law There is a periodic repetition of chemical and physical properties of elements when arranged in increasing atomic number (increasing number of protons) called the periodic law

Modern Periodic Table Organized in columns called groups or families Rows are called periods Group A – representative elements (1A-8A) Group B - transition elements (1B-8B) Transition Elements (Group B) Representative Elements (Group A) Representative Elements (Group A)

Classification of Elements metals nonmetalsmetalloidssemimetals Three classifications for elements metals, nonmetals, and metalloids (semimetals).

Metals Properties of Metals – shiny, smooth, solids (except mercury) – Good conductors of heat and electricity – High densities – High melting and boiling points – Malleable – bended or pounded into sheets – Ductile – drawn into wires

Groups of Metals Alkali metals – group 1A except H Alkaline earth metals – group 2A – Alkali metals and alkaline earth metals are chemically reactive Transition metals – group B elements Inner transition metals – Lanthanide – Actinide

Transition Metals (B group elements) Alkali Metals Alkaline Earth Metals Inner Transition Metals Metals

Organizing by Electron Configuration Group number for group A elements represents the number of valence electrons Atoms in the same group have similar chemical properties because they have the same number of valence electrons

Alkali Metals Electron configurations for alkali metals Lithium 1s 2 2s 1 [He]2s 1 Sodium 1s 2 2s 2 2p 6 3s 1 [Ne]3s 1 Potassium 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 [Ar]4s 1 Rubidium 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 3d 10 4p 6 5s 1 [Kr]5s 1 What do the four configurations have in common? They have a single electron in their outermost energy level They all have one valence electron, thus similar chemical properties

Alkaline Earth Metals Electron configuration for alkaline earth metals Beryllium [He]2s 2 Magnesium [Ne]3s 2 Calcium [Ar]4s 2 Strontium[Kr]5s 2 All alkaline earth metals have two valence electrons, thus similar chemical properties.

Nonmetals Gases or brittle, dull looking solids Poor conductors of heat and electricity Usually have lower densities, melting point, and boiling point than metals. Groups of nonmetals – Halogens 7A – Noble gases 8A sulfur

Noble Gases Halogens Nonmetals

Noble Gases Noble gases – Group 8A Called inert gases because they rarely take part in a reaction He – 1s 2 Ne – 1s 2 2s 2 2p 6 Ar – 1s 2 2s 2 2p 6 3s 2 3p 6 Kr - 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 Because noble gases have completely filled s and p sublevels, they do not react with other elements

Metalloids (Semimetals) Physical and chemical properties similar to both metals and nonmetals – They are metallic-looking brittle solids – Relatively good electrical conductivity. Used in glasses, alloys, and semiconductors The six elements commonly recognized as metalloids are boron, silicon, germanium, arsenic, antimony, and tellurium. Polonium and astatine are sometimes classified as metalloids

Metalloids (Semimetals)