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Unit 5

Chapter Overview
During this unit, students are introduced to the law of definite proportions and the law of multiple proportions as the foundations of chemistry. Students “speak
and write chemistry” by learning how to represent compounds with formulas and to name compounds given their formulas (using the rules of the International
Union of Pure and Applied Chemistry [IUPAC]). Students identify formulas and names of ionic substances by implementing comparative investigations using

Main Ideas
Scientists use a system of naming compounds so that their formulas may be easily derived.
    *What is the process for naming compounds?
    *What is the process for deriving a chemical formula from a compound name?

***Students may not understand that elements can form compounds with different atomic ratios, such as carbon monoxide and carbon dioxide.

Law of Definite Proportions – in a given compound, elements are combined in proportions by mass and thus by atoms that do not vary; also called Proust’s Law
Law of Multiple Proportions – when different compounds are formed by a combination of the same two elements, different masses of one element combine with the same fixed mass of the other element in a ratio of small whole numbers; also called Dalton’s Law
International Union of Pure and Applied Chemistry (IUPAC)the recognized authority  or chemical standards of nomenclature, measurements, and atomic mass values
Chemical Formula – the kind and number of atoms in a representative unit of a substance
Subscripta number that is smaller than the other text, and below the normal text line, showing multiple atoms
Chemical Nomenclaturea set of rules to generate systematic names for chemical compounds
Mono – prefix that means one
Di – prefix that means two
Tri – prefix that means three
Molecular Compoundcompound where the atoms share electrons through covalent bonds, also called covalent compound
Ionic Compoundchemical compound composed of ions held together by electrostatic forces termed ionic bonding
Ionan electrically charged atom or group of atoms formed by the loss or gain of one or more electrons
Monatomic Ionan ion consisting of a single atom
Polyatomic Ion – an ion that contains more than one atom, even if these atoms are of the same element
Anion – any ion with a negative charge
Cation – any ion with a positive charge
Acid – substance that dissociates (breaks apart) and donates protons in an aqueous solution
Base – substance that dissociates (breaks apart) donates hydroxide ions in a solution.
Oxidation Numbera number assigned to an element in chemical combination that represents the number of electrons lost (or gained, if the number is negative) by an atom of that element in the compound


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