Page 17 - The Periodic Table Book

KEY Reading the table

Hydrogen The Boron Group Element symbol
Every element has a unique symbol of one or two
Alkali Metals The Carbon Group letters. These symbols ensure that scientists who
speak different languages do not get confused while
Alkaline Earth Metals The Nitrogen Group describing the same element.

Transition Metals The Oxygen Group
3 The atomic number is the number of protons Introduction
in the nucleus of this element’s atoms.
Lanthanides The Halogen Group The first letter of a symbol is always
Actinides Noble Gases Li a capital, but the second is lower case.
6.941 The atomic mass number is the average of all the
atoms of the element. It is not a whole number
because there are different isotopes (forms) of each
element, each with a different number of neutrons.
Elements of this group
are semi-metals (elements
with the properties of Periods
metals and non-metals): This group contains 2 Elements in the same period, or row, have the same
they are shiny like metals the noble gases, which
but crumble easily never form bonds with other He number of electron shells in their atoms. So elements
like non-metals. elements, and are unreactive. in period one have one electron shell, while those in
4.0026 period six have six electron shells.
5 6 7 8 9 10
B C N O F Ne Periods run from
left to right.
10.811 12.011 14.007 15.999 18.998 20.180

13 14 15 16 17 18
Al Si P S Cl Ar Groups run from

26.982 28.086 30.974 32.065 35.453 39.948 top to bottom.

31 32 33 34 35 36 Groups
Ga Ge As Se Br Kr Members of a group, or column, all
have the same number of electrons
69.723 72.64 74.922 78.96 79.904 83.80 in their outermost shell. For example,
group one elements have one outer
49 50 51 52 53 54 electron, while group eight elements
In Sn Sb Te I Xe have eight outer electrons.

114.82 118.71 121.76 127.60 126.90 131.29
DMITRI MENDELEEV
81 82 83 84 85 86
Tl Pb Bi Po At Rn The periodic table was

204.38 207.2 208.96 (209) (210) (222) developed by the Russian
chemist Dmitri Mendeleev in
113 114 115 116 117 118 1869. Others had tried before,
Nh Fl Mc Lv Ts Og but his table was periodic,
or repeating, because the
284 289 288 293 294 294 characteristics of elements
follow a pattern. The table was
66 67 68 69 70 71 incomplete as some elements
Dy Ho Er Tm Yb Lu had not yet been discovered.
However, Mendeleev predicted
162.50 164.93 167.26 168.93 173.04 174.97 the positions of the missing
elements, and was proved right
98 99 100 101 102 103 when they were finally isolated
Cf Es Fm Md No Lr many years later.

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