Periodic Table Chapter 4

History of the Periodic Table Dmitri Mendeleev wrote the first periodic table. He arranged elements in order of atomic mass. He noticed repeating properties.

Mendeleev’s periodic table

Moseley’s periodic table Moseley rearranged the elements by atomic number.

Organization of the p.t. There are 18 groups or families (columns). All elements in a group have the same number of outer level (valence) electrons. There are 7 periods (rows). All elements in a period have electrons on the same energy level.

Why? Group 1 metals Called alkali metals. They all react violently with nonmetals. They have 1 valence electron which they lose very easily. Li is the least reactive, Fr is the most reactive They are all soft They are not found in nature because they are so reactive. Why?

Group 2 metals Called Alkaline Earth Metals They have 2 valence electrons. They are harder and less reactive than group 1 metals.

Why? Group 17 Called halogens Most reactive nonmetals They all have 7 valence electrons They react with metals to form “salts” Why?

Why? Group 18 Noble gases They don’t react They have 8 valence electrons (except Helium) This is a full outer level Why?

Metals Most elements are metals Metals are good conductors of heat and electricity Metals are ductile (can be squeezed into a wire) Metals are malleable (can be hammered or bent)

Transition Metals Groups 3 – 12 They have many different properties Less reactive than alkaline earth metals Some are fairly non-reactive (Cu, Ag, Au) Tungsten has the highest melting point Mercury is a liquid with high density Metals can be mixed together (alloy) to produce desirable properties.

F - Block Lanthanides (group 4f) Actinides (group 5f) #58 – 71 #90 - 103

Ions An ion is an atom that has lost or gained electrons. Lose electrons – (+ ion) Called cation Gain electrons – (- ion) Called anion

Ionization Energy The energy required to remove an electron. If an electron is easy to remove, it takes little energy. Period Trend As you go from left to right across the period, it is harder to remove an electron – I.E. increases Group Trend As you go down a group, it is easier to remove an electron – I.E. decreases

Atomic Radius Size of an atom Half the distance between 2 adjacent nuclei

Atomic Radius Period Trend Group Trend As you go from left to right across a period, atomic radius decreases Group Trend As you go down a group, atomic radius increases.

Electron Affinity Energy change when an atom gains an electron. Period Trend As you go from left to right across a period, electron affinity increases. Group Trend As you go down a group, electron affinity decreases.

Electronegativity Ability to attract electrons Period Trend 0 – 4 Period Trend As you go from left to right across a period, electronegativity increases. Group Trend As you go down a group, electronegativity decreases.