ELEMENTS AND BINARIES.
13. About Seventy Different Elements are now recognized, half of
which have been discovered within little more than a century.
These differ from one another in (1) atomic weight, (2) physical
and chemical properties, (3) mode of occurrence, etc. Page 12
contains the most important elements.
The symbol of an element is usually the initial letter or letters
of its Latin name, and stands for one atom of the element. C is
the symbol for carbon, and represents one atom of it. O means one
atom of oxygen.[The symbols of elements will also be used in this
book to stand for an indefinite quantity of them; e.g. O will be
used for oxygen in general as well as for one atom. The text will
readily decide when symbols have a definite meaning, and when
they are used in place of words.] Write, explain, and memorize
the symbols of the elements in heavy type.
14. The Atomic Weight of an element is the weight of its atom
compared with that of hydrogen. H is taken as the standard
because it has the least atomic weight. The atomic weight of O is
16, which means that its atom weighs 16 times as much as the H
atom. Every symbol, then, stands for a definite weight of the
element, i.e. its atomic weight, as well as for its atom.
How much bromine by weight does Br stand for? What do these
symbols mean--As, Na, N, P? If O represents one atom, how much
does O2 or 2 O stand for? How much by weight? Most elements have
two atoms in the molecule. How many molecules in 6 H? 10 N? S8?
I20?
The symbol of a compound is formed by writing in succession the
symbols of the elements of which it is composed. How many atoms
in the following molecules, and how many of each element: C2H60?
HNO3? PbSO4? MgCl2? (Hg2(NO3)2?)
15. The Simplest Compounds are Binaries.--A binary is a substance
composed of two elements; e.g. common salt, which is a compound
of sodium and chlorine. Its symbol is NaCl, its chemical name
sodium chloride. The ending ide is applied to the last name of
binaries. How many parts by weight of Na and of Cl in NaCl? What
is the molecular weight, i.e. the weight of its molecule? Name
KCl. How many atoms in its molecule? Parts by weight of each
element? Molecular weight? Does the symbol stand for more than
one molecule? How many molecules in 4 NaCl? How many atoms of Na
and of Cl? Name these: HCl, NaBr, NaI, KBr, AgCl, AgI, HBr, HI,
HF, HgO, ZnO, ZnS, MgO, CaO. Compute the proportion by weight of
each element in the last three.
A coefficient before the symbol of a compound includes all the
elements of the symbol, and shows the number of molecules. How
many in these: 6 KBr? 3 Sn0? 12 NaCl? How many atoms of each
element in the above?
An exponent, always written below, applies only to the element
after which it is written, and shows the number of atoms. Explain
these: AuCl3, ZnCl2, Hg2Cl2.
Write symbols for four molecules of sodium bromide, one of silver
iodide (always omit coefficient one), eight of potassium bromide,
ten of hydrogen chloride; also for one molecule of each of these:
hydrogen fluoride, potassium iodide, silver chloride.
In all the above cases the elements have united atom for atom.
Some elements will not so unite. In CaCl2 how many atoms of each
element? Parts by weight of each? Give molecular weight. Is the
size of the molecule thereby changed? Name these, give the number
of atoms of each element in the molecule, and the proportion by
weight, also their molecular weights: AuCl3, ZnCl2, MnCl2, Na2O,
K2S, H3P, H4C.
Principal Elements.
Name. Sym. At. Wt. Valence. Vap.D. At.Vol. Mol.Vol. State.
Aluminium Al 27. II, IV ... ... ... Solid
Antimony Sb 120. III, V. ... ... ... "
Arsenic As 75. III, V 150. "
Barium Ba 137. II ... ... ... "
Bismuth Bi 210. III, V ... ... ... "
Boron B 11. III ... ... ... "
Bromine Br 80. I, (V) 80. Liquid
Cadmium Cd 112. II 56. Solid
Calcium Ca 40. II ... ... ... "
Carbon C 12. (II), IV ... ... ... "
Chlorine Cl 35.5 I, (V) 35.5 Gas
Chromium Cr 52. (II),IV,VI ... ... ... Solid
Cobalt Co 59. II, IV ... ... ... Gas
Copper Cu 63. I, II ... ... ... "
Fluorine F 19. I, (V) ... ... ... Gas
Gold Au 196. (I), III ... ... ... Solid
Hydrogen H 1. I 1. Gas
Iodine I 127. I, (V) 127. ... ... Solid
Iron Fe 56. II,IV,(VI) ... ... ... "
Lead Pb 206. II, IV ... ... ... "
Lithium Li 7. I ... ... ... "
Magnesium Mg 24. II ... ... ... "
Manganese Mn 55. II, IV, VI ... ... ... "
Mercury Hg 200. I, II 100. Liquid
Nickel Ni 59. II, IV ... ... ... Solid
Nitrogen N 14. (I),III,V 14. Gas
Oxygen O 16. II 16. "
Phosphorus P 31. (I),III, V 62. Solid
Platinum Pt 197. (II), IV ... ... ... "
Potassium K 39. I ... ... ... "
Silicon Si 28. IV ... ... ... "
Silver Ag 108. I ... ... ... "
Sodium Na 23. I ... ... ... "
Strontium Sr 87. II ... ... ... "
Sulphur S 32. II,IV,(VI) 32(96) "
Tin Sn 118. II, IV ... ... ... "
Zinc Zn 65. II 32.5 "
If more than one atom of an element enters into the composition
of a binary, a prefix is often used to denote the number. SO2 is
called sulphur dioxide, to distinguish it from SO3, sulphur
trioxide. Name these: CO2, SiO2, MnO2. The prefixes are: mono or
proto, one; di or bi, two; tri or ter, three; tetra, four; pente,
five; hex, six; etc. Diarsenic pentoxide is written, As2O5.
Symbolize these: carbon protoxide, diphosphorus pentoxide,
diphosphorus trioxide, iron disulphide, iron protosulphide. Often
only the prefix of the last name is used.
16. An Oxide is a Compound of Oxygen and Some Other Element, as
HgO. What is a chloride? Define sulphide, phosphide, arsenide,
carbide, bromide, iodide, fluoride.
In Experiment 6, where S and Fe united, the symbol of the product
was FeS. Name it. How many parts by weight of each element? What
is its molecular weight? To produce FeS a chemical union took
place between each atom of the Fe and of the S. We may express
this reaction, i.e. chemical action, by an equation:--
Iron + Sulphur = Iron Sulphide
Or, using symbols Fe + S = FeS
Using atomic weights, 56 32 = 88.
These equations are explained by saying that 56 parts by weight
of iron unite chemically with 32 parts by weight of sulphur to
produce 88 parts by weight of iron sulphide. This, then,
indicates the proportion of each element which combines, and
which should be taken for the experiment. If 56 g. of Fe be used,
32 g. of S should be taken. If we use more than 56 parts of Fe
with 32 of S, will it all combine? If more than 32 of S with 56
of Fe? There is found to be a definite quantity of each element
in every chemical compound. Symbols would have no meaning if this
were not so.
Write and explain the equation for the experiment with copper and
sulphur, using names, symbols, and weights, as above.