Slide 1 of 27 chemistry. Slide 2 of 27 © Copyright Pearson Prentice Hall The Laws Governing Formulas and Names > The Laws of Definite and Multiple Proportions.

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chemistry

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© Copyright Pearson Prentice Hall

The Laws Governing Formulas and Names

> The Laws of Definite and Multiple Proportions

The Laws of Definite and Multiple Proportions

There are laws in chemistry that determine how chemicals combine and how reactions occur. These laws provided the experimental support for Dalton’s Atomic Theory.

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The rules for naming and writing formulas for compounds are possible only because compounds form from the elements in predictable ways.

These ways are summed up in two laws: the law of definite proportions and the law of multiple proportions.


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The Law of Definite Proportions

The law of definite proportions states that in samples of any chemical compound, the masses of the elements are always in the same proportions.


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Water obeys the law of definite proportions. In every sample of water, the mass ratio of oxygen to hydrogen is always 8:1.


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Hydrogen peroxide obeys the law of definite proportions. The mass ratio of oxygen to hydrogen is always 16:1.


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The Law of Multiple Proportions

The law of multiple proportions: Whenever the same two elements form more than one compound, the different masses of one element that combine with the same mass of the other element are in the ratio of small whole numbers.


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> The Laws of Definite and Multiple Proportions

Two compounds formed from carbon and oxygen are:

•CO – carbon monoxide – the mass ratio of O to C is 4/3

•CO2 – carbon dioxide – the mass ration of O to c is 8/3

For the same amount of C there is twice as much O in CO2. Ratio 2/1 (simple whole numbers)


SAMPLE PROBLEM

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SAMPLE PROBLEM

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Practice Problems for Sample Problem 9.1

Problem Solving 9.34 Solve Problem 34 with the help of an interactive guided tutorial.


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Follow the arrows and answer the questions on the flowchart to write the correct name for a compound.

Practicing Skills: Naming Chemical Compounds

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> Practicing Skills: Naming Chemical Compounds

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CuSO4 is an example from the flowchart. The compound will end in -ite or -ate. Cu is not part of Group A, so you must name the ions and use a Roman numeral to identify the charge of the transition metal. The name is copper(II) sulfate.


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Practicing Skills: Writing Chemical Formulas

What four guidelines should you follow to write the formula of a chemical compound?

9.4 Practicing Skills: Naming Chemical Compounds

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In writing a chemical formula from a chemical name, it is helpful to remember the following guidelines.

An -ide ending generally indicates a binary compound.

An -ite or -ate ending means a polyatomic ion that includes oxygen is in the formula.


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Prefixes in a name generally indicate that the compound is molecular.

A Roman numeral after the name of a cation shows the ionic charge of the cation.


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> Practicing Skills: Naming Chemical Compounds

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END OF SHOW

Slide 1 of 27 chemistry. Slide 2 of 27 © Copyright Pearson Prentice Hall The Laws Governing Formulas and Names > The Laws of Definite and Multiple Proportions.

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