Classification of Elements • Three classifications for elements metals, nonmetals, and metalloids (semimetals). 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) Representative Elements Representative Elements (Group A) (Group A) Transition Elements (Group B) Classification of Elements • 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 Metals (blue) Alkali Metals Alkaline Earth Metals Transition Metals (B group elements) Inner Transition 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 1s22s1 [He]2s1 • Sodium 1s22s22p63s1 [Ne]3s1 • Potassium 1s22s22p63s23p64s1 [Ar]4s1 • Rubidium 1s22s22p63s23p64s23d104p65s1[Kr]5s1 • 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]2s2 • Magnesium [Ne]3s2 • Calcium [Ar]4s2 • Strontium [Kr]5s2 • All alkaline earth metals have two valence electrons, thus similar chemical properties. Nonmetals Noble (yellow) Gases Halogens Nonmetals • Gases or brittle, dull looking solids • Poor conductors of heat and electricity • Usually have lower densities, melting point, and boiling point than metals. sulfur • Groups of nonmetals – Halogens 7A – Noble gases 8A Noble Gases • Noble gases – Group 8A • Called inert gases because they rarely take part in a reaction He – 1s2 Ne – 1s22s22p6 Ar – 1s22s22p63s23p6 Kr - 1s22s22p63s23p63d104s24p6 • 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 aka Semi-metals (pink) .