1 Unit 4 – The Periodic Table

2 Mendeleev (1869) arranged elements in order of atomic mass Certain properties Ex.) unreactive gas Ex.) reactive metal that combines 1:1 with chlorine Each element was placed below the preceding one with similar properties noble gases.....re-appeared periodically

3 Elements are now arranged by atomic number Vertical columns are called groups --contain elements with similar chemical properties Horizontal rows are called periods --properties of the elements change predictably because they have similar electron arrangements same group = same number of valence electrons same period = same number of electron energy levels (period no. = no. of levels)

4 Periodic Properties -- change in a predictable way as you move across or down the table 1. Atomic Radius:half the distance between nuclei -- measured in picometers (pm) = meter Related to: a. number of e - energy levels Li small Fr large b. strength of attraction between nucleus and outer e - number of protons (nuclear charge) Li large Ne small

5

6 Ionic Radius – radius after electron gain or loss metals lose electrons + charge attracts electrons to nucleus, radius gets smaller non-metals gain electrons – charge repels electrons, radius gets larger

7 Periodic Properties, continued 2. Ionization Energy --the amount of energy required to remove the most loosely held electron from an atom -- measured in kilojoules per mole (kJ/mol) [see ref table S] -- depends on radius a. large radius = weak attraction for outer e - = low ionization energy b. small radius = strong attraction for outer e - = high ionization energy 3. Electronegativity -- the tendency to gain electrons in a bond -- arbitrary scale (no units) [see ref table S] -- depends on radiuslarge radius = low electronegativity small radius = high electronegativity

8 Periodic Properties, continued 4. Metallic Character -- ease of electron loss -- depends on radius large radius = high metallic character small radius = low metallic character

9 Trends in Periodic Properties As the atomic number increases, within a: Group 1. Atomic radius 2. Ionization energy 3. Electronegativity 4. Metallic character Period

10 Types of Elements 1. Metals -- luster --malleable --good conductors Metals have a weak hold on their electrons -- low ionization energy and electronegativity -- react with non-metals by losing electrons, forming + ions --metallic solids (except Hg) 2. Non-Metals no luster, brittle, poor conductors Non-metals have a strong hold on their electrons -- high ionization energy and electronegativity -- react with metals by gaining electrons, forming - ions --react with other non-metals by sharing electrons to form covalent bonds

11 Non-metals can be: a. molecular solids -- C P S Se I 2 At b. liquids -- Br 2 c. gases -- N 2 O 2 F 2 Cl 2 H 2 3. Metalloids -- properties midway between the above -- used as semiconductors -- all solids: B Si Ge As Sb Te 4. Noble Gases -- do not easily gain, lose, or share electrons -- all gases: He Ne Ar Kr Xe Rn

12 The Elements by Group 1 and 2-- very reactive metals (except H) -- not found pure in nature -- 1 more reactive than 2 -- within each group, reactivity increases as you move down the group -- atoms lose e - easily: easiest for larger elements ( group 1, lower elements) -- usually form ionic compounds Transition elements -- less reactive metals -- many found pure -- have incomplete inner e - shell: : similar properties :ions can have several different charges

13 13 – less reactive metals (except B, metalloid) Al – self protective metal 14 – increasing metallic character as you move down the group C Si Ge Sn Pb non-metal metalloids metals C – basis of life; organic chemistry -- 2 allotropes (different forms of the same element) DiamondGraphite

14 Allotropes have different properties due to their different structures Diamond Graphite Si + Ge – used in computer circuits Pb – easily worked metal subtly toxic; formerly used in pipes, paint, gasoline, solder 15 Metallic character as you the group N 2 – very unreactive; found pure N N strong triple bond found in protein; used in fertilizers and explosives must react (“fix”) nitrogen before it can be used

15 16 mostly nonmetals O 2 -- reactive gas; found pure due to photosynthesis -- allotropes O 2 and O 3 ozone in the atmosphere absorbs harmful UV energy O 2  O + O O 2 + O  O 3 chlorofluorocarbons like Freon (CF 2 Cl 2 ) reach the ozone layer and destroy it CF 2 Cl 2  CF 2 Cl + Cl light Cl + O 3  ClO + O 2 light (ozone) map showing ozone depletion over Earth’s southern hemishpere

16 S – less reactive than O 2 -- an impurity in fossil fuels and metal ores S + O 2  SO 2 SO 2 is an irritating pollutant that combines with moisture in the air to produce acid rain: SO 2 + H 2 O  H 2 SO 3

17 17 – The Halogens -- all are diatomic, reactive, not found pure -- reactivity decreases as you the group (easier for small atoms to gain e - ) melting and boiling points increase as you the group Fluorine gas Chlorine gas Bromine liquid Iodine solid

18 18 – The Noble Gases --very stable; full outer electron levels He Ne Ar -- no compounds Kr Xe Rn -- can react with F 2 or O 2 -- used when reactions are undesirable He – non-flammable; for balloons and blimps Ar – to fill light bulbs heliumhydrogen