Solved Problems & Examples:

Solved problems and examples will usually be given after each section of expository material.  This is in contrast to how earlier versions of this web page were done.  Students have said that they'd rather things were done this way; so, I hope this is what you really wanted.

Please note that some of the material discussed with the problems is not discussed in the main exposition.  This is done mainly for reasons of convenience in the presentation.  You should read all the material in any case.

Problem 1.28:  How many elements are presently known?  About how many occur naturally?

To get started on this, look at the periodic table:

Elements 1-112 are all there along with 114 and 116.  Thus, 114 are known at present.

U (uranium), element #92, is the highest known element.  However Tc (#43) and Pm (#61) are manmade and do not occur naturally.  Thus there are only 90 naturally-occurring elements.

Problem 1.30:  How many groups are there in the periodic table?  How are they labeled?

There 18 groups or, possibly, 32 if you look at things from another point of view.  The reason for this ambiguity is because of the lanthanides and actinides and are often put into group 3B.  Now we look at group numberings:

Problem 1.34:  What is a semimetal and where in the periodic table are semimetals found?

You are probably getting tired of this by now, but here is our little periodic table again!


The semimetals are those shown in sky blue. The actual elements are B, Si, Ge, As, Sb, Te, and At (Boron, Silicon, Germanium, Arsenic, Antimony, Tellurium, and Astatine, respectively).  Most of these are metallic in appearance in the free state.  However, their chemistries are often more nonmetallic than metallic.  Also, some of these (Si and Ge in particular) are semiconductors and are the heart and soul of modern electronics (e.g.,  transistors).  All these (except for At) have numerous uses and have extensively studied chemistries.

Problem 1.40:  What are the symbols of the following elements?
 
  a) Gadolinium (used in color TV screens)
  b)  Germanium (used in semiconductors)
  c)  Technetium (used in biomedical imaging)
  d)  Arsenic (used in pesticides and many murder mysteries)

This is fairly easy!  I would strongly suggest that you memorize all symbols in any event!  Anyway, here are the answers (note that there is alphabetical listing in the front of the text).
 

Element
Symbol
Gadolinium
Gd
Germanium
Ge
Technetium
Tc
Arsenic
As

Problem 1.42:  Give the names corresponding the the following symbols:

     a)  Te     b)  Re     c)  Be     d)  Ar     e)  Pu

With little discussion (other than to harass you into knowing these), we give the answers.
 

Symbol
Element
Te
tellurium
Re
rhenium
Be
beryllium
Ar
argon
Pu
plutonium

Problem 1.43:  Give the names corresponding to the following symbols:

     a)  B     b)  Rh     c)  Cf     d)  Os     e)  Ga

More of the same.  However, in an "exam from heck" you can bet that a professor would mix things such a Mg and Mn, Re and Rh, and As and Ar!
 

Symbol
Element
B
boron
Rh
rhodium
Cf
californium
Os
osmium
Ga
gallium

Problem 1.44:  What is wrong with each of the following statements?

Here we shall put the problems in black and put the answers in blue in the same table.  This is to save space and speed up the writing!
 
 
Statement
Answer
  a) The symbol for tin is Ti. The symbol is actually Sn (from the Latin name).
  b)  The symbol for manganese is Mg. Mn is the proper symbol.  Mg and Mn were actually confused with each other at the start and that is the reason for the similar names and symbols.
  c)  The symbol for potassium is Po. The proper symbol is K.  Please do not make this mistake on an exam!  (Po is "polonium," incidentally.)
  d)  The symbol for helium is HE. He is the symbol.  The second letter is always lower case.