The Foundations of Chemistry

168 CHAPTER 4: Some Types of Chemical Reactions

Exercises

The Periodic Table

1.State the periodic law. What does it mean?

2.What was Mendeleev’s contribution to the construction of

the modern periodic table?

3.Consult a handbook of chemistry, and look up melting

points of the elements of Periods 2 and 3. Show that melt-

ing point is a property that varies periodically for these

elements.

*4.Mendeleev’s periodic table was based on increasing atomic

weight. Argon has a higher atomic weight than potassium,

yet in the modern table argon appears before potassium.

Explain how this can be.

5.Estimate the density of antimony from the following den-

sities (g/cm^3 ): As, 5.72; Bi, 9.8; Sn, 7.30; Te, 6.24. Show

how you arrived at your answer. Using a reference other

than your textbook, look up the density of antimony. How

does your predicted value compare with the reported

value?

6.Given the following melting points in °C, estimate the

value for CBr 4 : CF 4 , 184; CCl 4 , 23; CI 4 , 171 (decom-

poses). Using a reference other than your textbook, look

Metal An element below and to the left of the stepwise division
(metalloids) of the periodic table; about 80% of the known ele-
ments are metals.
Metalloids Elements with properties intermediate between met-
als and nonmetals: B, Si, Ge, As, Sb, Te, Po, and At.
Metathesis reaction A reaction in which the positive and neg-
ative ions in two compounds “change partners,” with no change
in oxidation numbers, to form two new compounds.
Net ionic equation An equation that results from canceling
spectator ions from a total ionic equation.
Neutralization reaction The reaction of an acid with a base to
form a salt. Often, the reaction of hydrogen ions with hydrox-
ide ions to form water molecules.
Noble (rare) gases Elements of Group VIIIA in the periodic
table.
Nonelectrolyte A substance whose aqueous solutions do not
conduct electricity.
Nonmetals Elements above and to the right of the metalloids in
the periodic table.
Oxidation An increase in oxidation number; corresponds to a
loss of electrons.
Oxidation numbers Arbitrary numbers that can be used as
mechanical aids in writing formulas and balancing equations;
for single-atom ions they correspond to the charge on the ion;
less metallic atoms are assigned negative oxidation numbers in
compounds and polyatomic ions.
Oxidation–reduction reaction A reaction in which oxidation
and reduction occur; also called a redox reaction.
Oxidation states See Oxidation numbers.
Oxidizing agent The substance that oxidizes another substance
and is reduced.
Period The elements in a horizontal row of the periodic table.
Periodic law The properties of the elements are periodic func-
tions of their atomic numbers.
Periodic table An arrangement of elements in order of increas-
ing atomic number that also emphasizes periodicity.
Periodicity Regular periodic variations of properties of elements
with atomic number (and position in the periodic table).

Precipitate An insoluble solid that forms and separates from a

solution.

Precipitation reaction A reaction in which a solid (precipitate)

forms.

Pseudobinary ionic compound A compound that contains

more than two elements but is named like a binary compound.

Redox reaction See Oxidation–reduction reaction.

Reducing agent The substance that reduces another substance

and is oxidized.

Reduction A decrease in oxidation number; corresponds to a

gain of electrons.

Reversible reaction A reaction that occurs in both directions;

described with double arrows ( 34 ).

Salt A compound that contains a cation other than H
and an

anion other than OHor O^2 .

Semiconductor A substance that does not conduct electricity at

low temperatures but does so at higher temperatures.

Spectator ions Ions in solution that do not participate in a chem-

ical reaction. They do not appear in net ionic equations.

Strong acid An acid that ionizes (separates into ions) completely,

or very nearly completely, in dilute aqueous solution.

Strong electrolyte A substance that conducts electricity well in

dilute aqueous solution.

Strong base Metal hydroxide that is soluble in water and disso-

ciates completely in dilute aqueous solution.

Ternary acid A ternary compound containing H, O, and another

element, usually a nonmetal.

Ternary compound A compound consisting of three elements;

may be ionic or molecular.

Total ionic equation An equation for a chemical reaction writ-

ten to show the predominant form of all species in aqueous

solution or in contact with water.

Weak acid An acid that ionizes only slightly in dilute aqueous

solution.

Weak base A molecular substance that ionizes only slightly in

water to produce an alkaline (base) solution.

Weak electrolyte A substance that conducts electricity poorly

in dilute aqueous solution.