1. Lead-in

a. What can you see in the picture above? Do you know how to say these elements and compounds in English?

b. Match the words in A with the words in B to form word combinations. Then complete the following sentences using these word combinations.

A. Latin, atomic, chemical, initial, definite

B. symbol, quantity, name, weight, letter

1. A shorthand interpretation of an element, molecule, or a compound is a ……

2. An ……….. is the average mass of an atom of an element usually expressed in relation to the atomic mass of carbon 12.

3. An ……………. is the first letter of a name.

4. In most cases, the symbols of metals are taken from their ……………..

5. The chemical symbol means not only the element but a ………….. of the element.

II. Reading

a. Read the text and translate it.

Text A

Chemical symbols used today

Chemists have found it convenient to represent various elements by chemical symbols. A chemical symbol is an abbreviation or short representation of the name of a chemical element, generally assigned in relation to its Latin name. It is usually the first letter, capitalized, of the name of the element. Examples are: C for carbon, H for hydrogen, O for oxygen and S for sulphur. In many cases, where two or more elements have the same initial letter, another letter that is prominent in the name is added but not capitalized. Such are Cl for chlorine, Br for bromine, Si for silicon and Mg for magnesium. In other cases, such as metals known to the ancients, the symbol is taken from the Latin name. Thus Cu stands for copper (cuprum), Fe for iron (ferrum), Ag for silver (argentum) and Au for gold (aurum).

The symbols are not used only as shortened signs of the elements. Each one also stands for an atom of the element. For example, the symbol O stands for one atom of oxygen and the symbols H, N, Na, Fe represent one atom of hydrogen, nitrogen, sodium and iron respectively. More exactly, they are atomic symbols and not only abbreviations of the names of the elements. We know that every atom has a definite weight. Therefore the symbol means not only the element but a definite quantity of the element. O always means 16 parts by weight of oxygen, C always means 12 parts by weight of carbon and H always means 1.008 parts by weight of hydrogen. Since we usually express the weights in grams, we often speak of the gram atomic weight of an element. Thus, the gram atomic weight of carbon is 12 grams.

b. Scan the text and fill in the gaps. The first letter of each missing word is given.

1. Each symbol stands for an a… of the element.

2. A chemical symbol is an a… or short representation of the name of a chemical element.

3. The symbol means a definite q… of the element.

4. Every atom has a definite w….

5. Chemists have found it c……… to represent various elements by chemical symbols.

III. Speaking

Make a short summary of the text.

IV. Reading

a. Guess if the following statements are true or false. If they are false correct them.

1. When a chemical reaction occurs, at least one product is formed that is different from the substances present before the change occurred. T/F

2. A chemical equation tells us what happens in a chemical reaction. T/F

3. Any chemical change involves four sets of substances. T/F

4. Chemical equations are represented by means of chemical reactions. T/F

5. Products are the substances that react to form the new compound. T/F

6. Oxidation-reduction is the type of a chemical reaction when one or more elements in the reaction changes its oxidation state during the reaction. T/F

Text B

Chemical reactions and equations

A chemical reaction is a process that leads to the interconversion of chemical substances. When it occurs, at least one product is formed that is different from the substances present before the change occurred. Any chemical change involves two sets of substances: reactants and products. A reactant is an element or compound present before a chemical change takes place. A product is an element or compound formed as a result of the chemical reaction. Most chemical reactions can be categorized into one of five general types:

a) synthesis - two substances combine to form one new substance

for example: 2 Na + Cl ₂ → 2 NaCl or CaO + H 2 O → Ca(OH) ₂

b) decomposition - one substance breaks down to form two new substances

for example: 2 H ₂ O → 2 H ₂ + O ₂

c) single replacement - an element and a compound react such that the element replaces one other element in the compound

for example: Mg + 2 HCl → MgCl ₂ + H ₂

d) double replacement - two compounds react with each other in such a way that they exchange partners with each other

for example: NaBr + HCl → NaCl + HBr

e) oxidation-reduction - one or more elements in the reaction changes its oxidation state during the reaction

for example: Cr ³⁺ → Cr ⁶⁺

Chemical reactions are represented by means of chemical equations. A chemical equation is a shorthand method for representing the changes that take place during a chemical reaction. In describing the formation of water from its elements, a chemist could say, for example, that "two molecules of hydrogen gas combine with one molecule of oxygen to form two molecules of water." Or she could write the following chemical equation that contains the same information in a much more compact form: 2 H ₂ + O ₂ → 2 H ₂ O. A chemical equation contains the chemical symbols and formulas for the elements and compounds involved in the reaction and the + and → (the arrow (or yields)) signs indicate reactants and products. The term reactant refers to the substances present at the beginning of the reaction, and the term product refers to the substances formed in the reaction. In the example above, the reactants are represented by the symbols H for hydrogen and O for oxygen. The product is represented by the formula H ₂O for water. The + sign indicates that hydrogen has combined with oxygen in the reaction. The arrow indicates that the two have reacted with each other to form water.

b. Fill in the blanks with the words listed: reactant, synthesis, chemical equation, interconversion, product.

1. A chemical reaction is a process that leads to the … of chemical substances.

2. A … is a substance produced from one or more other substances as a result of chemical change.

3. A … contains the chemical symbols and formulas for the elements and compounds involved in the reaction

4. A … is a substance that changes when it is combined with another substance in a chemical reaction.

5. … is the production of a substance by the union of chemical elements, groups, or simpler compounds or by the degradation of a complex compound.

c. Fill in the missing prepositions into the gaps.

1. Chemical reactions are represented ……….. means of chemical equations.

2. A chemical equation contains the chemical symbols and formulas for the elements and compounds involved ………….. the reaction.

3. The term reactant refers ………….. the substances present at the beginning of the reaction.

4. A chemical reaction is a process that leads ………….. the interconversion of chemical substances.

5. Most chemical reactions can be categorized ………. one of about five general types.

d. Find 22 special words and terms in the crossword puzzle.

i

n

t

e

r

c

o

n

v

e

r

s

i

o

n

m

s

i

q

e

s

x

i

l

l

e

y

f

c

i

o

u

r

u

a

i

y

c

y

e

p

m

o

o

t

l

b

e

a

c

o

g

k

a

m

l

b

r

b

r

e

s

a

t

t

w

e

e

m

e

a

o

m

a

o

c

t

c

i

a

t

n

l

i

n

c

l

u

l

g

u

a

t

o

n

a

c

i

d

t

e

c

l

t

e

l

n

i

n

t

g

a

u

r

u

m

g

a

s

n

e

c

o

p

p

e

r

a

o

w

e

i

g

h

t

y

e

n

r

v

a

u

q

u

a

n

t

i

t

y

d

e

f

i

n

i

t

e

s

e

t

y

p

e

w