Microsoft word - chemistry_naming_compounds.docx

Teaching innovatively (with focus on ICT) and its impact on the quality of

Teacher: Fazilet TURNA
Level: 9th Grade
Unit: Substance and Its Features
Topic: Naming Compounds
Time: 40 Minutes
Materials: Publications, software, slide
1. To be able to write the name of the ionic compound the formula of which 2. To be able to write formula of the ionic compound the name of which is 3. To be able to write the name of the covalent compound the formula of 4. To be able to write the formula of the covanlent compound the name of 5. To use ICT as a successful tool when learning. 1. Teacher teach the subject trough someslıdes 2. Students name the compounds on the prepared software
Evaluation: Solving the problems of naming compounds on the software
Click on to play the game.

Chemical formulae
Chemists use a kind of shorthand to describe elements and compounts. All
elements have characteristic symbols. These symbols sometimes consist of the first
letter(s) of the name of the element; for example, hydrogen is given the symbol H,
whereas the chemical symbol for bromine is Br. Some symbols, however, are not
derived from the modern or English name of the element: gold has the chemical
symbol Au (from the Latin Aurum), whereas tungsten is denoted by W (from Wolfram,
a German word). Note that the first letter only of a chemical symbol is written as a
capital letter
. Box 2.4 gives the symbols of some elements.
Extensive and
Classify the following
properties as extensive or
(i) length (ii) colour
(iii) mass (iv) density.
Exercise 2C
Physical and
chemical properties
Classify the following as
physical or chemical
(i) the hardness of
(ii) the low density of
(iii) wood burns in air
(iv) arsenic is poisonous
(v) milk goes sour.
Exercise 2B
Using symbols and formulae
1. Use Information Box 2.4 to name the following elements:
(i) Ba (ii) Si (iii) Ar (iv) F (v) Li (vi) Hg (vii) Sn (viii) Ag (ix) B (x) Ti.
2. Name the elements in the following compounds and state how many atoms of each element
are present:
(i) CsBr (ii) CuCl2 (iii) Fe3O4 (iv) CH4 (v) PbSO4 (vi) K2Cr2O7 (vii) Na3PO4 (viii) MnO2.
Exercise 2D

The formulae for elements and compounds are constructed using these symbols. The
symbol for the element oxygen is written as O. Since oxygen is normally found as
oxygen gas, in which the smallest particles are diatomic molecules, the chemical formula
for oxygen gas, or dioxygen, is written as O2. Compounds are written using a
collection of different symbols. For example, water is H2O (indicating that two
hydrogen atoms have joined with one oxygen atom to form a molecule of water),
whereas sodium chloride is written as NaCl (this compound is formed when sodium
reacts with chlorine in a ratio of 1 atom to 1 atom). Chemical formulae therefore
give us two important pieces of information:
1. the elements that are present in a substance;
2. the relative number of atoms that make up that substance.
Note that ‘2H2O’ refers to two separate molecules of water.
Writing chemical formulae
Although it is necessary for a chemist to learn the symbols of the common
elements, it is possible to work out the chemical formulae of common substances
BOX 2.4
Some symbols for elements (you are strongly advised to learn
Element Symbol
Aluminium Al
Argon Ar
Arsenic As
Barium Ba
Boron B
Bromine Br
Caesium Cs
Calcium Ca
Carbon C
Chlorine Cl
Chromium Cr
Element Symbol
Cobalt Co
Copper Cu
Fluorine F
Gold Au
Helium He
Hydrogen H
Iodine I
Iron Fe
Lead Pb
Lithium Li
Magnesium Mg
Element Symbol
Manganese Mn
Mercury Hg
Neon Ne
Nitrogen N
Oxygen O
Phosphorus P
Platinum Pt
Potassium K
Radon Rn
Silicon Si
Silver Ag
Element Symbol
Sodium Na
Sulfur S
Tin Sn
Titanium Ti
Tungsten W
Uranium U
Vanadium V
Xenon Xe
Zinc Zn

Main elements in
the human body
Can you identify the main
elements in the human body
from Fig. 2.4?
Exercise 2E
Fig. 2.4 Main elements in
the human body (diagram
from F. C. Hess, Chemistry
Made Simple
, W. H. Allen).

Symbols of elements
1. Using library books at your disposal, find out from what names the symbols of the
elements were derived:
(i) sodium (Na) (ii) iron (Fe) (iii) lead (Pb) (iv) tin (Sn) (v) potassium (K) (vi) silver (Ag).
2. Some of the latest elements discovered derive their names from famous scientists. See if
you can find out the main contributions to our knowledge made by the following scientists:
(i) meitnerium (Mt) named after Lise Meitner;
(ii) seaborgium (Sg) named after Glenn Seaborg;
(iii) bohrium (Bh) named after Niels Bohr;
(iv) rutherfordium (Rf) named after Ernest Rutherford.
Exercise 2F
A good place to eat.
take it with a grain of:
without having to learn them parrot fashion. Different elements have atoms with
different combining powers. The combining power of an atom is known as its
valency, and these valencies can be used to find out how many atoms of one
element will combine with another. A table of the valencies of common elements
and groups is shown on page 464. Again, these need to be learned.
To obtain a clearer picture of how a chemical formula is constructed, imagine that
the valencies of atoms are ‘arms’, which link up with the arms of other elements’ atoms.
Some elements have more than one valency, but the name of the compound
should help you work out the formula. For example, in the compound iron(III)
chloride, the iron atoms have a valency of three and its formula is FeCl3, whereas in
iron(II) chloride, the iron combines with a valency of two and the formula is FeCl2.
BOX 2.5

Naming compounds
1. When a compound consists of a
metal and a non-metal, the metal is
written and named first. The Periodic
Table will help you to distinguish whether
an element is a metal or non-metal.
Metals are shown to the left of the table,
whereas non-metals are found to the
right. The border between the two is
shown as a zig-zag line. The non-metal
part is named by putting ‘ide’ at the end,
thus chlorine becomes chloride and
oxygen becomes oxide.
MgO magnesium oxide
Na2O sodium oxide
AlCl3 aluminium chloride
CaS calcium sulfide
2. If a compound is composed of two nonmetals,
the non-metal that is the closest
to being a metal (closer to the metal–nonmetal
border in the table) is written first. If
more than one compound of the same two
non-metals exist then the prefixes mono(1),
di(2), tri(3), tetra(4), penta(5), hexa(6) and
so on are put in front of the non-metal to
indicate the number of its atoms present in
the compound.
Some examples:
CO carbon monoxide
CO2 carbon dioxide
N2O3 dinitrogen trioxide
N2O dinitrogen monoxide
P4O6 tetraphosphorus hexaoxide*
P4O10 tetraphosphorus decaoxide*
* Often written hexoxide and decoxide (for ease
of pronunciation).
Example 2.1
Construct the formula of magnesium oxide (a compound of
magnesium and oxygen).
The symbol for magnesium is Mg and it has a valency of two. Imagine it as:
Similarly, oxygen could be thought of as:
When magnesium combines with oxygen, the arms link up with one another and
there are no free arms left over. Therefore, one atom of magnesium combines with
one atom of oxygen to form magnesium oxide:
Mg O
The formula is written as MgO. (Leave out the arms, they are only used to help you to
construct the formula!)

Example 2.2
What is the formula of aluminium chloride?
Aluminium chloride is a compound of aluminium and chlorine. The symbols and
valencies for atoms of both these elements are
Al and Cl
When they combine together,
aluminium has two ‘arms’ left over, so another two chlorine atoms, with one ‘arm’
each, must be added:
Al Cl
The formula of aluminium chloride is therefore AlCl3. The subscript after Cl shows
that three chlorine atoms combine with one atom of aluminium. There is no
after Al, meaning that only one atom of aluminium is involved in the

More simple formulae
Write formulae for the following compounds (in (i)–(x), the valencies of the metals atoms are
shown in brackets after the name of the metal; you should be able to work out the formulae of
(xi)–(xx) just by looking at their names!):
Exercise 2H
(i) copper(I) oxide
(ii) copper(II) oxide
(iii) lead(IV) oxide
(iv) chromium(III) sulfide
(v) manganese(IV) oxide
(vi) chromium(VI) fluoride
(vii) cobalt(III) sulfide
(viii) chromium(III) oxide
(ix) vanadium(V) oxide
(x) titanium(III) fluoride
(xi) nitrogen monoxide
(xii) arsenic trichloride
(xiii) sulfur hexafluoride
(xiv) dinitrogen
(xv) disulfur dichloride
(xvi) dinitrogen pentoxide
(xvii) dioxygen difluoride
(xviii) tellurium trioxide
(xix) dichlorine hexaoxide (hexoxide)
(xx) silicon tetrachloride.
Simple formulae
Write formulae for the following compounds, using the valency table on page 464.
(i) calcium oxide (v) aluminium fluoride (viii) lithium bromide
(ii) hydrogen sulfide (vi) aluminium oxide (ix) magnesium sulfide
(iii) magnesium fluoride (vii) hydrogen chloride (x) magnesium nitride.
(iv) magnesium chloride
Exercise 2G
Groups of atoms
For the purposes of writing formulae, sometimes groups of atoms act as if they have
a valency of their own. Their valencies are also shown on page 464.
Example 2.3
Write the formula of ammonium sulfate
The ammonium group is a combination of one nitrogen atom and four hydrogen
atoms, but together they act as if the group has a valency of one:
Similarly, sulfate has a valency of two:
Two ammonium groups therefore combine with one sulfate group:
The formula is written as (NH4)2SO4.
Note that if more than one group of atoms are to be represented, the group is
enclosed in brackets and the number of groups present is written as a subscript
outside the brackets.
Formulae involving groups of atoms
Write formulae for the following compounds:
Exercise 2I
(i) copper(II) sulfate
(ii) copper(II) nitrate (iii) ammonium chloride (iv) sodium phosphate (v) calcium phosphate (vi) sulfuric acid (dihydrogen sulfate) (vii) nitric acid (hydrogen nitrate) (viii) aluminium nitrate (ix) lithium carbonate (x) ammonium carbonate (xi) calcium hydroxide (xii) potassium hydrogencarbonate (xiii) calcium hydrogencarbonate (xiv) sodium hydrogensulfate (xv) iron(III) hydroxide.


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