The periodic table of elements A closer look The periodic table might seem confusing at first so let’s look at its main features Each box contains information about a single element such as hydrogen or oxygen You will not find water or any other compound in the periodic table This is because compounds are made from two or more elements chemically joined together For example water is a compound made up of two hydrogen atoms and one oxygen atom Chemical symbols Each element has its own chemical symbol made from one two or sometimes three letters The first letter is always a capital letter and any others are lower case Some symbols are easy to understand such as H for hydrogen and C for carbon Others such as Cu for copper are not so obvious THAT’S A FACT The ancient Romans had copper mines on Cyprus an island in the Mediterranean Sea They called the metal aes Cyprium which became shortened to cuprum That is why the symbol for copper is Cu and not Co which is the symbol for cobalt group 1 1 1 H hydrogen 7 3 Li lithium Na sodium 23 39 11 19 K potassium 37 85 Rb rubidium 133 55 Cs cesium group 2 4 9 Be beryllium 24 12 Mg Ca Sr strontium 137 56 Ba barium 223 87 226 88 Fr francium Ra radium relative atomic mass name Example 2 4 He helium atomic number symbol group 8 26 56 Fe iron group 9 27 59 Co cobalt group 7 25 55 Mn magnesium 20 40 group 3 21 45 group 4 22 48 group 5 23 51 group 6 24 52 calcium 88 38 scandium 39 89 titanium 40 91 chromium 96 42 manganese 98 43 zirconium 178 72 niobium 73 181 molybdenum 74 184 technetium 75 186 ruthenium 76 190 rhodium 77 192 Tc 101 44 103 45 Ru Rh V vanadium 93 41 Nb hafnium tantalum tungsten 266 106 Sg Re rhenium Os osmium Bh Hs 261 104 262 105 264 107 277 108 268 109 rutherfordium dubnium seaborgium bohrium hassium meitnerium Sc Y yttrium lanthanides 57-71 actinides 89-103 139 57 140 58 141 59 144 60 145 61 150 62 152 63 157 64 La lanthanum 227 89 Ac Ce cerium 232 90 Th praseodymium 91 231 neodymium 238 92 promethium 237 93 samarium 244 94 europium 243 95 gadolinium 247 96 Sm Pu Eu Am actinium thorium protactinium uranium neptunium plutonium americium Ti Zr Hf Rf Pr Pa Cr Mo W Pm Np Ta Db Nd U Ir iridium Mt Gd Cm curium period 1 period 2 period 3 period 4 period 5 period 6 period 7 8
The numbers Atoms are not only very small they are also very light They are so light that it makes little sense to use their actual masses in grams Instead their relative atomic mass is used This is the mass of the atom compared to the mass of a carbon atom Hydrogen atoms are the lightest Their relative atomic mass is just 1 The relative atomic mass of carbon is 12 so a carbon atom weighs 12 times more than a hydrogen atom The top left number in each box of the periodic table is the relative atomic mass of the element The top right one is the atomic number the number of protons in that element’s atoms arranged in order of increasing atomic number As you go from left to right across a period the atomic number on the right increases by one each time Groups A vertical column in the periodic table is called a group The elements in a group have similar chemical properties For example the elements in group 1 are very reactive metals The elements in group 18 are very unreactive nonmetals You are going to find out more about elements like these and how understanding them helped in the invention of the periodic table Periods A horizontal row in the periodic table is called a period The elements are The periodic table of elements The number on the left in each box is the element’s relative atomic mass The number on the right is its atomic number proton number group 13 group 14 group 15 group 16 group 17 9 11 14 16 12 19 5 6 7 8 27 13 28 B boron Al aluminum 31 70 Ga gallium C carbon Si silicon 14 32 73 Ge germanium 119 50 Sn tin Pb lead Fl 82 114 nitrogen 15 31 N P phosphorus 75 33 As arsenic 122 51 Sb Bi bismuth 288 115 Uup O oxygen S sulfur 32 79 16 34 Se Te Po Lv polonium 116 293 fluorine 35 17 chlorine 35 80 F Cl Br I iodine 210 85 At astatine Uus selenium 128 52 bromine 53 127 204 81 207 antimony 83 209 tellurium 84 209 metals non-metals metalloids 47 112 48 115 49 group 10 group 11 group 12 59 30 63 5 29 65 28 Ni nickel 106 46 Pd palladium 78 195 Pt platinum Ds Tb terbium 247 97 Bk Cu copper 108 Ag silver 197 Au gold 79 111 Rg Dy Cf cadmium 80 201 Hg mercury Zn zinc Cd Cn Ho Es indium In Tl thallium Uut ununtrium Er erbium Fm group 18 4 2 He helium Ne neon Ar argon 20 40 84 10 18 36 Kr krypton 54 86 131 Xe xenon 222 Rn radon Uuo ununoctium period 1 period 2 period 3 period 4 period 5 period 6 period 7 9 271 110 272 285 112 284 113 289 294 117 294 118 darmstadtium roentgenium copernicium flerovium ununpentium livermorium ununseptium 159 65 162 66 165 67 167 68 169 69 173 70 175 71 dysprosium 98 251 holmium 99 252 257 100 258 101 Tm thulium Md Yb ytterbium 102 259 No Lu lutetium 262 103 Lr berkelium californium einsteinium fermium mendelevium nobelium lawrencium
A glow in the dark Ancient elements It was difficult to do complex experiments thousands of years ago In those days philosophers thought carefully about the world and came up with ideas to explain what they saw Aristotle was a Greek philosopher who was born in 384 B C E He thought that everything on Earth was made from four elements These were air earth fire and water Aristotle could not prove this but people thought highly of him so his ideas influenced science for almost 2,000 years This began to change in the 17th century Unlucky for some Just 13 elements were known in the 1660s These included nonmetals such as carbon and sulfur and metals such as gold copper and iron But because everybody still believed in Aristotle’s idea of four elements no one recognized these substances for what they were true elements Alchemy In 1669 German alchemist Hennig Brand tried to make gold from urine Instead he discovered the element phosphorus Alchemy was a strange mixture of chemistry religion and mystery One of its aims was to make gold from cheaper substances As Brand thought Urine is golden colored so it might contain gold This 1771 painting by Joseph Wright shows an alchemist making phosphorus 10
Red phosphorus is a form of phosphorus that catches fire at a higher temperature than white phosphorus It is used in matches Bringer of light Brand collected fifty buckets of urine He left them to stand for several days and then heated the stinky sludge to concentrate it He heated the remaining ghastly goo to evaporate some of it and then cooled the vapor In this way Brand used distillation to collect a pure waxy white solid Once in the air this gave off a green glow in the dark and it could suddenly burst into flames It was called phosphorus after the Greek words meaning bringer of light Brand had discovered that phosphorus is an element found naturally in the body Our bones contain most of it and any extra comes out in our urine THAT’S A FACT Brand was lucky Had he collected his phosphorus in the open air instead of water he could have been seriously hurt White phosphorus does not react with water but it is very dangerous in air It can set itself on fire and then burn violently Today it is used in incendiary bombs which cause damage by starting fires Breakthrough Brand never made his fortune from his discovery Even though he tried to keep his methods secret other people worked out how to make phosphorus and became rich Brand’s discovery of phosphorus encouraged the search for other new elements There was a good chance that if a new element could be found through experiments others could also be found 11
