The Birth of Chemical Formulas and Equations

8.5DF: Chemical Formulas and Equations

Matter and Energy

The Birth of Chemical Formulas and Equations

(Lexile 990L)

1 Around 2,000 years ago, the Roman poet

Lucretius said, ¡°Things cannot be born from

nothing.¡± Even then, people knew that all the

matter that we see is all the matter we would

ever have. It wasn't until the 1700s that several

scientists proved the theory.

NH3

H

N

H

H

2 In the 1700s, several scientists made chemical

compounds and formulas easier to understand.

In 1748, Russian scientist Mikhail Lomonosov

first came up with the idea of the Law of Conservation of Mass. In 1789, French scientist

Antoine Lavoisier proved this law. His experiments showed how two reactants (tin and lead)

combined with oxygen. Swedish scientist J?ns Jacob Berzelius and British scientist John

Dalton also get credit. They created a simpler way to explain how chemical reactions happen.

3 Because Berzelius worked with chemical compounds with several different elements, he

needed a way to simplify chemical notations and make them easier to manipulate. He worked

up a system of one- or two-letter symbols along with a smaller-sized number (subscript). The

chemical formula pictured above is NH3 (1 nitrogen and 3 hydrogen atoms.) It would be much

harder to write if chemical symbols and subscripts were not used.

4 John Dalton came up with his atomic theory, which scientists still use. The theory explains

chemical formulas and has four major points:

?

?

?

?

All matter is made of atoms that cannot be divided or destroyed.

All atoms of a given element are the same in mass and properties.

New compounds are formed when two or more elements combine.

A chemical reaction changes how atoms are arranged.

He and other scientists knew that the chemical properties of a molecule are related to the

arrangements of the atoms in that molecule.

5 Without the early work of chemists from many different countries, chemical formulas would be

hard to work with. Their methods give us an easy way to represent complex chemicals by using

formulas and subscripts.

1

8.5DF: Chemical Formulas and Equations

Matter and Energy

1

Complete the following analogy:

Mikhail Lomonosov: Law of Conservation of Mass as John Dalton:_____

2

3

A

atomic theory

B

subscripts

C

chemical compounds

D

formulas

What is the purpose of subscripts in chemical formulas?

A

so the chemist can multiply the chemical formula by that number

B

to let the chemist know that the element is a noble gas

C

to indicate that the element has an isotope

D

to indicate an element's proportions within a formula

Ammonium carbonate has the chemical formula (NH4)2CO3. How many

hydrogen atoms (H) are in ammonium carbonate?

A

8

B

4

C

3

D

2

2

8.5DF: Chemical Formulas and Equations

Matter and Energy

4

5

Which of the following is one component of John Dalton's atomic theory?

A

All matter can be divided by chemical reactions.

B

All matter is made of indivisible, indestructible atoms.

C

Chemical reactions can only occur by means of a particle accelerator.

D

Elements cannot be combined to form new compounds.

What is the meaning of the word manipulate in paragraph 3?

A

chance

B

confuse

C

work with

D

free

3

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