The Periodic Table Introduction to the Periodic Table The periodic tab

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The Periodic Table
 
Introduction to the Periodic Table 
The  periodic  table  of  elements  is  one  of  the  most  important  tools  of  chemistry.  Through  its  ingenious
organization,  the  table  provides  concise  and  fundamental  information  not  only  about  every  individual
element, but also about general trends across all the elements. Mastering  the vagaries of the periodic  table
now will save you work later. 
This (www.forum.ysapak.com) Note on the Periodic Table will begin with a discussion of the table's history and
then move into a description of how to read the table and describe some general periodic trends. In the next
(www.forum.ysapak.com) Note on the basics of atomic structure, we will also cover a number of periodic trends
the comprehension of which demand some knowledge of atomic structure. 
Terms and Definitions 
Atom  -  The smallest unit of matter that can exist of an element. 
Compound  -  A molecule containing two or more different atoms bound together. 
Element  -  A fundamental substance that has a unique atomic number on the periodic table. 
Gas  -  A form of matter that has mass but no definite shape, and can be either compressed or expanded to
fill an infinite volume. 
Isotope  -  A different form of an element that varies by the number of neutrons in the nucleus. 
Liquid   -   A  form  of  matter  which  has  mass,  occupies  a  volume,  and  flows  to  adopt  the  shape  of  its
container. 
Solid  -  A form of matter which has a definite shape and volume. 
 
A Short History of the Periodic Table 
In  1789,  building  upon  the  work  of  precursors  and  contemporaries  alike,  the  French  chemist  Antoine
Laurent  Lavoisier  first defined  an  element  as a fundamental substance  that could  not be  broken down  by
any  chemical means  then  known.  In  the  same  Treatise  on  Chemical  Elements,  he  compiled  a  list  of  33
elements (a number of which were not actually elements) and devised a naming system for the discovery of
new elements. 
Lavoisier's definition and list of elements helped spur an attempt by chemists to systematize and understand
the elements. In 1803, the English chemist John Dalton used the general scientific recognition that elements
combined with each other according to different ratios by weight to create an atomic theory that claimed all
elements were built out of variable numbers of hydrogen atoms. As a  part of this theory, Dalton created a
scale of atomic weight based on the hydrogen atom (the  weight of hydrogen was  set equal to 1). In 1869,
the  Russian  chemist  Dmitry  Mendeleyev  organized  the  elements  in  a  table  according  to  their  atomic
weights  (the  German  chemist  Julius  Lothar  Meyer  independently  struck  upon  the  same  organization  in
1870). 
In the sixty-seven  years from Dalton's formulation  of  atomic weight to  Mendeleyev's periodic table many
scientists had  tried  to  create  a  working  organizational  structure  for  the  elements.  Mendeleyev  succeeded
where others failed because he realized that there existed a number of as yet unknown elements with atomic
weights  between  the  weights  of  already  known  elements.  By  leaving  vacancies  for  those  elements  he
believed were undiscovered, he hit upon an organizational scheme that seemed to vertically group elements
with  similar  properties.  Among  elements  with  low  atomic  weights,  he  found  that  similar  chemical
characteristics  recurred  every  seven  elements.  Among  heavier  elements,  he  found  that  characteristics
resurfaced every seventeen elements.  This phenomenon  in which physical and chemical characteristics  of
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elements are periodic  functions  of their  atomic weight is  called  the periodic  law  (and gives  the  periodic
table its name). In 1879, Mendeleyev's periodic table received a powerful boost in general acceptance when
it predicted the existence of the elements gallium, germanium, and scandium. 
Through time, Mendeleyev's periodic table has undergone some small changes. Many, many new elements
have been added. The discovery of the inert gases raised the number of elements between similar elements
to eight  for the  lighter  elements  and  eighteen for the darker elements.  In a  few  instances,  scientists have
discovered  that  organization  along  atomic  weights  does  not  coincide  with  vertical  similarities.  In  such
instances,  as  in  the  case  of  tellurium  (Te)  and  iodine  (I),  similarity  wins  out  over  atomic  weight  in
determining organization. 
The next section will describe how to read the periodic table. 
Reading the Periodic Table 
Once again, here is a link to view a full-size periodic  table: To see the periodic table, click here. Once the
window appears, roll your mouse over the  elements to see their specific  information. You can also access
the periodic table by going into the (www.forum.ysapak.com) Notes reference section that resides at the top of
every (www.forum.ysapak.com) Notes page. 
General Structure of the Periodic Table 
As stated last section, the periodic table organizes the elements according to general patterns of similarity.
Below  is  a  very  small  image  of  the  periodic  table.  It  is  basically  unreadable  in  terms  of  specific
information, but it allows us to easily look at the periodic tables structure general trends. 
 
Figure %: A very small periodic table 
The vertical columns of the periodic table (marked by yellow  stripes in the figure) are called groups. The
horizontal rows are called periods. There are 18 groups and 7 periods. In discussing the periodic table from
here  on  out  we  will  use  the  terms group and  period. Down a  group  means  moving  from  top  to  bottom;
across a period means moving from left to right. 
Reading the Periodic Table: Carbon 
To describe the information contained within each individual box we will use a specific example: carbon. 
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Figure %: Description of Carbon on the Periodic Table 
Element Name 
The  purpose  of  the  element  name  is  obvious.  However,  many  Periodic  Tables  do  not  include  element
names. For those situations you must memorize the symbols that accord to each element name. 
Element Symbol 
Each  element has  a  specific  one  or  two letter  symbol  that  is  used  interchangeably  with  its  name.  These
should  be  memorized.  Most  of  the  time,  symbols  quite  clearly  accord  to  the  name  of  the  element  they
represent, as C accords to carbon. Occasional, however, an element's name and symbol have little relation.
For example, the symbol for mercury is Hg. 
Atomic Number 
As  you  move  across  a  period  the  atomic  number  increases.  Similarly,  as  you  move  down  a  group  the
atomic number increases. In this way, the atomic number represents exactly where in the periodic table an
element stands. 
More  importantly,  and  the reason  why  the  ordering  of  the  elements  according  to  atomic number  yields
elements in  groups  with similar  chemical  and  physical  properties,  the  atomic  number  is  the  same  as  the
number of protons in  the nucleus of an atom of an element, and also the same as the  number of  electrons
surrounding the nucleus in a neutral state. Carbon, for example, has six protons and six electrons. (Protons
and electrons will be discussed in more detail in the Atomic Structure (www.forum.ysapak.com) Note) 
(atomicmass) Atomic Mass 
Along  with protons,  an  atom  also  contains neutrons  in  its  nucleus.  The atomic  mass  (also  called  atomic
weight) of an element is the combined number of protons and neutrons in the nucleus. 
Atoms of  particular elements generally have  different  "versions," meaning  that elements have atoms with
different numbers  of  neutrons  in  their nucleus. These  different  versions  are  called  isotopes.  The  atomic
weight displayed is actually the weighted average of the mass numbers of the various isotopes. The atomic
weight for Carbon is 12.01 because around 99% of all carbon is the carbon-12 isotope. 
Simple Periodic Trends 
Atomic Number 
The Atomic  number  increases from  the  top  left  to  the  bottom  right. It ascends  sequentially across  each
period. 
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Atomic Weight 
Weight The  atomic  weight of  the  elements  generally  increases  as  you move down a group and  across  a
period.  Hydrogen,  at  the  top  left  of  the  table,  is  the  lightest  element.  The  unnamed  element  112  is  the
heaviest. There are some instances when this rule does not hold true, however. For instance, because it has
a high percentage of  isotopes  with many neutrons, the atomic  weight of tellurium  (Te) is  higher  than that
for iodine (I), even though iodine has a higher atomic number. 
Types of Elements 
Elements  can  be  organized  by  group  or  period,  but  they  also  can  be  placed  into  three  distinct  groups:
metals, semi-metals, and non-metals. 
Metals 
Metals  are  the  pink  section  on  the  left  side  of  .  Metals  are  generally  lustrous  solids,  often  deformable
(though  mercury  (Hg)  is  a  liquid  at  room  temperature).  Metals  are  highly  conducive  to  both  heat  and
electricity. 
Nonmetals 
Nonmetals  are the  blue  boxes  on  the  upper  right  hand  of the  periodic  table.  More  than  half  of  the non-
metals are gaseous at normal temperatures. 
Semimetals 
Semimetals  are  the  green  boxes  on  the  periodic  table.  As  their  transitory  name  and  placement  on  the
periodic table suggest, they exist in between the distinctions of metals and nonmetals. 
Metals and Nonmetals 
Most chemical compounds are formed by the interactions between metals and non- metals. 
Further Periodic Trends 
Beyond  those  trends  described  here,  there  are  a  number  of  further  periodic  trends  such  as atomic  size,
ionization  energy,  electron  affinity,  and  electronegativity.  We  will  discuss  these  trends  in  the  atomic
structure (www.forum.ysapak.com) Note, since we must have a better understanding of atomic structure  before
getting into their specifics. 
 
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