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The Periodic Table During the nineteenth century, chemists began to categorize the elements according to similarities in their physical and chemical properties. The end result of these studies was our modern periodic table. Dmitri Mendeleev In 1869 he published a table of the elements organized by increasing atomic mass. 1834 - 1907 Lothar Meyer At the same time, he published his own table of the elements organized by increasing atomic mass. 1830 - 1895 Henry Moseley In 1913, through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements*. He rearranged the elements in order of increasing atomic number. *“There is in the atom a fundamental quantity which increases by regular steps as we pass from each element to the next. This quantity can only be the charge on the central positive nucleus.” 1887 - 1915 Periodic Table Geography Periodic Table • Columns called Families/Groups – Family # indicates # valence (outer shell) electrons – Elements in same family have similar properties • Rows called Periods – Row # indicates # energy levels in atom The horizontal rows of the periodic table are called PERIODS. The elements in any group of the periodic table have similar physical and chemical properties! The vertical columns of the periodic table are called GROUPS, or FAMILIES. Metals/Nonmetals/Semiconductors • Metals: excellent conductors of heat & electricity; have luster, are ductile/malleable • Nonmetals: poor conductors of heat & electricity; are dull & brittle • Semiconductors(Metalloids): elements that under certain conditions conduct heat & electricity Families of Elements • • • • • • • • • • Family 1: Alkali Metals Family 2: Alkaline Earth Metals Families 3 to 12: Transition Metals Family 13: Boron Family Family 14: Carbon Family Family 15: Nitrogen Family Family 16: Oxygen Family Family 17: Halogens Family 18: Noble Gases Three general groups: metals, nonmetals, & semiconductors(metalloids) Periodic Table Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties. Alkali Metals Alkaline Earth Metals Transition Metals Metals • Alkali metals (Family 1) – Very reactive – Has 1 valence electron – When ionized has charge of 1+ • Alkaline Earth metals (Family 2) – Reactive – Has 2 valence electrons – When ionized has charge of 2+ • Transition metals (Families 3 to 12) – Somewhat reactive – Valence electron number varies – Ionized charge varies These elements are also called the rare-earth elements. InnerTransition Metals Halogens Noble Gases Nonmetals • Include H, some elements from families 13 to 16, all elements from families 17 & 18. Zig-zag line divides metals from nonmetals. • Inert gases are unreactive; contain 8 valence electrons • Halogens are very reactive; contain 7 valence electrons; gain electrons becoming negatively charged • Elements in other families gain electrons to become negatively charged • These elements plentiful on Earth Semiconductors (aka Metalloids) • Located along the zig-zag line • Includes: – Boron (B); Silicon (Si), Germanium (Ge), Arsenic (As), Antimony (Sb), Tellurium (Te), Polonium (Po) • Notice that Al is not considered a metalloid, it is considered a metal • Conduct heat & electricity under certain conditions • B is hard & added to steel to increase hardness; Sb is bluish-white and shin, Te is silvery-white & electrical conductivity increases with light exposure, Si important in solar cells & integrated circuits Periodic Table Trends #1. Atomic Size - Group trends • As we increase the atomic number (or go down a group). . . • each atom has another energy level, • so the atoms get bigger. H Li Na K Rb #1. Atomic Size - Period Trends • Going from left to right across a period, the size gets smaller. • Electrons are in the same energy level. • But, there is more nuclear charge. • Outermost electrons are pulled closer. Na Mg Al Si P S Cl Ar #2. Trends in Ionization Energy • Ionization energy is the amount of energy required to completely remove an electron (from a gaseous atom). • Removing one electron makes a 1+ ion. • The energy required to remove only the first electron is called the first ionization energy. Ionization Energy • The second ionization energy is the energy required to remove the second electron. – Always greater than first IE. • The third IE is the energy required to remove a third electron. – Greater than 1st or 2nd IE. #3. Trends in Electronegativity • Electronegativity is the tendency for an atom to attract electrons to itself when it is chemically combined with another element. • They share the electron, but how equally do they share it? • An element with a big electronegativity means it pulls the electron towards itself strongly! Electronegativity Group Trend • The further down a group, the farther the electron is away from the nucleus, plus the more electrons an atom has. • Thus, more willing to share. • Low electronegativity. Electronegativity Period Trend • • • • Metals are at the left of the table. They let their electrons go easily Thus, low electronegativity At the right end are the nonmetals. • They want more electrons. • Try to take them away from others • High electronegativity. The periodic table is the most important tool in the chemist’s toolbox!