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U-1
EXPERIMENT U: BONDING AND
CHEMICAL PROPERTIES
OBJECTIVE
In this experiment, you will examine how inter and intramolecular bonding affects the physical and chemical
properties of compounds. In the process, you will familiarize yourself with the concepts of bonding and
periodicity.
THEORETICAL CONSIDERATIONS
The modern form of the periodic table was developed independently by J.L. Meyer and
D.I. Mendeleev during the latter half of the nineteenth century as a means of grouping together elements with
similar chemical and physical properties. The periodic table was arranged so that vertical columns (groups)
contained elements with similar chemical properties. At the time of their work, there were many blank spaces in
the periodic table (i.e. yet to be discovered elements). However, by using their newly devised system of periodic
classification, Mendeleev and Meyer were able to accurately forecast the existence of several elements and
predict some of their intrinsic physical properties well before they were actually isolated. Modern periodic tables
show atomic symbols, atomic numbers (number of protons in the nucleus), average atomic masses (in atomic mass
units, A.M.U.) and quite frequently, the number of valence electrons. Valence or outer shell electrons are those
electrons that are most likely to participate in chemical reactions. The periodic table is thus an indispensable tool
for chemists because it allows important physical and chemical properties for the elements to be correlated with
their their positions in the table.
Elements combine to form compounds via the formation of chemical bonds. A chemical bond is a strong
interaction between atoms in a molecule or a crystal lattice. There are two principal types of chemical bonds:
ionic and covalent. An ionic bond is an electrostatic attraction between a positively charged and a negatively
charged ion. Most commonly, ionic bonds form when electrons are transferred from the atoms of a metal to the
atoms of a non-metal or grouping of non-metals. A covalent bond consists of a pair of electrons that is shared
between two atoms and attracted by both nuclei. Generally, covalent bonds are formed between identical non-
metal atoms (pure covalent bond) or non-metal atoms with similar electronegativities (electron-attracting
tendencies). Electronegativity, “
”, increases from left to right and decreases from the top to the bottom in the
periodic table. Thus, the most electronegative element is fluorine, while the most electropostive naturally occuring
