sample: re-write of chemistry textbook

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Textbook of Basic Chemistry

Seese and Daub 3rd Ed.

Prentice Hall (1981)

pgs  3, 57

(from pg 3: introductory)

      Chemistry can be described as being concerned with the composition of matter and the changes that it undergoes.  As an example, chemistry would be concerned with (1) the component parts of water (composition) and (2) the reactions of water with other matter and the conditions required to effect such reactions (transformations).

(from pg 57: compounds)

      In (Section 3-3 prior) we defined compounds as pure substances that can be broken down into two or more different simpler substances by various chemical means.  Compounds may be composed of charged particles (ions) or molecules.

     In the case of an ionic compound, it is convenient to represent the compound with a formula unit in which the opposite charges of ions present balance each other so that the formula unit representing the compound as an overall charge of zero.  Generally, the simplest formula unit possible is used.  For example, sodium chloride is composed of sodium ions (Na+1) and chloride ions (Cl-1) in equal numbers, and a formula unit of this compound is NaCl. 

     For those compounds existing as molecules, a molecular formula is used to represent the compound. The molecule is the smallest particle of the compound that can exist and still retain the physical and chemical properties of the compound.  Molecules, like atoms, are the particles that undergo chemical changes in a reaction.  These molecules are composed of atoms of elements, held together by chemical bonds (Chapter 6); hence these small particles called atoms are fundamental to all compounds.  Molecules may be composed of two or more nonidentical atoms - that is, atoms from different elements, which are the smallest particles of a compound.  Water molecules are composed of the nonidentical atoms of hydrogen and oxygen.  Molecules may also be composed of one or more identical atoms, that is, atoms from the same element.  Oxygen molecules are composed of two identical atoms of oxygen.  For now, we shall consider only molecules of compounds.  Later, in Chapter 6 when we discuss bonding, we shall again refer to formula units and molecules from nonidentical and identical atoms. 

     An atom of an element is represented by a symbol, and a molecule of a compound is represented by a formula - more precisely, a molecular formula.  Such a formula is composed of an appropriate number of symbols of elements representing one molecule of the given compound. For example, the molecular formula for water is H2O (read H-two 0). The subscripts represent the number of atoms of the respective elements in one molecule of the compound. Where no subscript is given, the number of atoms is one. Hence, in one molecule of water there are 2 atoms of the element hydrogen and 1 atom of the element oxygen, resulting in a total of 3 atoms in one molecule of water.

An Introduction to Chemistry

      One of our most basic ideas about the world is that there are two kinds of things that you see in it, or at least see going on in it; these being matter and energy.  Matter is the stuff that makes up the things of the world.  Concerning matter, there are two basic sciences out there that deal with it: physics and chemistry.  On one hand, physics is about the motion of matter.  On the other hand, chemistry is about the interactions of matter.  

      How pieces of matter interact with other pieces of matter, and even how it acts in its own itself, includes facts about what makes it up and how it reacts in special ways with other pieces of matter.  This means that chemistry is about both how matter is put together and how it changes, its composition and its transformations.

On Compounds

      In (Section 3-3 prior) we defined compounds as pure substances that can be broken down into two or more different simpler substances by various chemical means.  In order to understand compounds, we should review the basic terminology that is used to talk about chemical substances.

      On one hand there are the particles that are called atoms, which are the smallest pieces of matter that have unique characteristics and that can undergo chemical changes.  Basically, they are the smallest pieces of matter that can be called a substance.  On the other hand there are elements, which are types or kinds of substances.  So atoms are the pieces of basic things and elements are the kinds of basic things.  Every atom is an atom of some kind, the kind being the element. For example, there are atoms out there of the kind that is called hydrogen, atoms of the kind oxygen, and so on.

      Every element has a symbol to represent it.  For example, the symbol for hydrogen is H, the symbol for oxygen is O.  With symbols for every element, we can write formulas for every compound.  These formulas show not only the kind of atoms in a compound but also the number of each kind of atoms in it.  For example, the formula for the common compound that we all know as water is H2O (read H-two-O).  The subscripts in a formula represent the number of atoms of the respective elements.  Note that where no subscripts are given, the number atoms is one.  So this formula means that in the smallest piece of the compound water, there are two atoms of the element hydrogen and one atom of the element oxygen, making a total of three atoms in that one smallest piece of water.

      There are two types of compounds: ionic compounds and molecular compounds.  These two types differ in how the compounds are held together as a group.  How they are held together is an issue that we will cover later in Chapter 6 with a discussion of chemical bonding.  For now, we will only be concerned with molecular compounds.

      The best way to understand a molecule is by comparison to atoms.  Like atoms, the molecule is the smallest particle of a compound that can exist and still retain the physical and chemical properties of that compound.  Also like atoms, molecules are the particles that undergo chemical changes in a reaction.  Simply put, atoms occur in the kinds that are elements, while molecules occur in the kind that are their compounds.  For example: There are atoms of the kind hydrogen, and molecules of the kind water.