Chapter 2



CHE101- 2

Tom Douwes 6/25/04

Dr. Rahni Chemistry 101

The second chapter of “Fundamentals of general, organic and biological chemistry,” deals with five main topics. The first topic is matter which deals with the all the substance from which the universe is composed. The next concept introduced is the symbols and formulas used to express matter in a quantitative manner, making it simpler to manipulate matter. Dalton’s atomic theory, which was later shown to not be entirely correct, but is an incredible theory, is also examined. Different forms of energy are explored including the most basic forms, those being kinetic and potential energies. Finally heat energy is specifically explored. Heat energy demonstrates how all these concepts bind to each other. These five concepts are, as the book states in its title, fundamental to the science of chemistry.

Matter is anything that can occupy space and has mass. This means that matter is essentially any and every physical thing in the universe. I am composed of matter as is the paper this report is printed on. Matter can be assembled in three ways and has three states in which it can exist. The states, which are discussed in chapter one are solid, liquid, and gas. The ways that matter can be assembled are elements, compounds and mixtures.

An element is a “pure substance that can not be broken down into simpler pure substances.”(1, pg. 30) There are a total of “one hundred eighteen” (4.) elements. “Ninety elements occur naturally;” (1, pg. 30). Elements have special characteristics that individuate each one from the others. One such characteristic is radioactivity. Radioactivity is “the emission of one or more kinds of radiation,” (1, pg. 30). These special qualities come from each elements unique subatomic structure. This structure is based on how the three different types of subatomic particles protons, neutrons, and electrons. How they affect the chemical properties of the element will be discussed in later chapter.

When “at room temperature,” (1, pg 31) each element is in the state that it is most frequently recognized at. “Two elements are liquid,” (pg. 31); these elements are mercury (Hg) and bromine (Br). “Eleven [elements] are gas,” (1, pg. 31); these elements are hydrogen (H), helium (He), nitrogen (N), oxygen (O), fluorine (F), neon (Ne), chlorine (Cl), argon (Ar), krypton (Kr), xenon (Xe), and radon (Rn). The remaining elements from solids at room temperature. These solid elements form metals, metalloids, and other nonmetals. Metals are “good conductors of heat and electricity,” (1, pg 31). The external surfaces of metals shine when they are polished and metals can be shaped in a number of useful ways. For example they “can be hammered into sheets and drawn into wires,” (1, pg. 31). The shape of wire allows us to take advantage of metals conducting properties. We use it to conduct electricity from power plants to our homes, for example. Metalloids only have some of the properties of metals depending upon the element being referred to and nonmetals, which are all of the other solid elements and some of the gas elements, have none of metals properties.

The next kind of matter is a compound. “Compounds are pure substances made from two or more elements always combined in a proportion by mass that is both definite and unique for the compound,” (1, pg. 31) This means that in a particular type of compound the same ration of different elements will always be found. For example table salt or sodium chloride will always have a ratio of one sodium atom and one chlorine atom. Compounds being matter are also in one of the three states; solid, liquid, or gas.

Mixtures are the final type of matter. “A mixture consists of two or more pure substances that are present in a proportion that can vary considerably,” (1, pg. 32). A mixture’s properties are derived from the substances that make it up. For example chocolate can be considered a mixture. Its make up of milk, sugar, and coco beans. The proportion of all of these different substances can very and the end result will still be chocolate. Another example of a mixture is alloys. Alloys are produced when two or more metals are heated and fused together. The resulting alloy has the properties in some proportion of the two or more metals that went into its creation. Bronze is an example of an alloy. Copper is heated and has other metals added to it. The result is a stronger metal that holds a better edge.

Some might say that there seems to be a similarity between mixtures and compounds. That it is rather difficult to tell them apart because the only difference seems to be that one requires definite proportions while the other does not. But they are very different. One way to understand this difference is by understanding how the two different types of matter form. Compounds are created from chemical reactions. Mixtures are made by simply changing there physical structure. This makes the two types of matter very different.

Chemical reactions are “events in which substances called reactants change into different substances called products,” (1, pg. 32). So what you are getting from a chemical reaction is something entirely new. It has entirely different chemical and physical properties then the initial substances. For example when iron and sulfur are put through a chemical reaction the “product” no longer has the color of sulfur (physical property) or responds to magnetism (chemical property) like iron does. In a “sugar and water,” (1, pg. 32) mixture you can still detect the properties of both of the mixtures components. You can still taste the sweetness of the sugar and the water remains a liquid. You also require very little effort to separate the components. For example all you have to do is put out some of the mixture so that the water evaporates away leaving sugar crystals. Mixtures and compounds are also different in another way. Of the two types of matter only compounds obey the law of definite proportions.

An element and a compound are pure substances. A mixture while being made of a pure substance is not. Elements and compounds are pure substances because they obey the law of definite proportions. The law of definite proportions states that “in a given chemical compound, the elements are always combined in the same proportions by mass,” (1, pg. 32). A substance is considered a pure substance if it obeys the law of definite proportions. This means that a compound is always a pure substance because it, by definition, is made of elements that are always united in the same proportion. Elements must, therefore, also be pure substances because they are always made up of exactly “one hundred percent,” (1, pg 32) of themselves.

The rest of this section in chapter two discusses one of the fundamental laws of nature. It is the law of conservation of mass. It must be brought up because it deals closely with the law of definite proportions. It is why when you initiate or revere a chemical reaction the new substance or substances have the same mass as the initial substance or substances. The law of conservation of mass states that “in any chemical reaction the sum of the masses of the reactants always equal the sum of the masses of the products,” (1, pg. 33). This is so fundamental because it is stating that matter can not be created spontaneously nor can it be destroyed utterly. Matter can be changed in a number of different fashions but not in the amount that exists, ever!

The next section of this chapter deals with atoms, the symbols that represent elements called chemical symbols and how to use these symbols in chemical equations. The chapter also features heavily a scientist named John Dalton who reinvented the idea of the atom and defined it in a much deeper and a more concrete manner then did the Greek philosopher that originally came up with the concept.

John Dalton created theories in an attempt to explain the laws of definite proportions and conservation of mass. He believed that chemical changes occurred because of incredibly small pieces of matter. These pieces would not them selves change and could not be destroyed. He took the name that the Greeks used for the “not cuttable,” (1, pg. 33) pieces of matter, reviving the idea of the atom. Dalton’s atomic theory had five main points. They were,

“1. Matter consists of definite particles called atoms,” (1, pg. 33).

He meant by this that they were separate and distinct particles. This means that Dalton state that the atom is the smallest single unit of matter that was possible. This portion of the theory was later shown to be wrong by the discovery of subatomic particles.

“2. Atoms are indestructible,” (1, pg. 33).

This was also shown to be incorrect because an atom can be broken down into its subatomic particles.

“3. All atoms of one particular element are identical in mass,” (1, pg. 33).

Atoms of the same element do in some cases have different mass as was discovered later. These element sub-groups are referred to as isotopes and have a different mass because they have different amounts of neutrons in them. Atoms of the same type of element might also have different masses if one is converted into an ion. That is the number of electrons in the atom changes.

“4. Atoms of different elements have different masses,” (1, pg. 33).

“5. By becoming bound together in different ways, atoms form compounds in definite rations by atoms,” (1, pg 33)

While not all of Dalton’s theory proved to be correct it did explain enough to advance the science of chemistry even further. Dalton’s theories also lead to the discovery of the third law of chemical reactions. This is the law of multiple proportions. It states that “whenever two elements form more then one compound the different masses of one that combine with the same mass of the other are in the ration of small whole numbers,”(1, pg 35). This meant that an atom combined in a chemical reaction as a single unit. This as well as other evidence has made the atom into the scientific fact we take it for today.

All elements have there own symbol. These symbols are recognized through out the scientific community and it allows physical scientists to instantly understand what elements are being referred to in any paper or study. They are usually one upper case letter or one upper case and one lower case letter. An elements symbol is called its atomic symbol. Besides being instantly recognizable by the scientific community at large it also allows for easier manipulation of elements by allowing scientists to put them in chemical formulas. These formulas allow one scientist to tell all his fellows exactly how to recreate a compound he has made because the formula tells the other scientists all the important information they need.

The simplest type of chemical formula is the empirical formula. An empirical formula is comprised of “the atomic symbols of the elements making up the compound (and) are displayed in the smallest possible whole number ratio that corresponds to the compound’s actual atom ratio,” (1, pg 36). An empirical formula is composed of formula units. Formula units are “particles that have the composition of the formula of a compound,” (1, pg. 37). An atom is one sort of formula unit. A molecule is another type of formula unit. A molecule is “a particle made from two or more atoms that are joined together and that then exist together as a single independent package,” (1, pg 37). Formula units are put into chemical equations to represent the reactants. Chemical equations are “shorthand descriptions of reactions that group the symbols of the reactants, separated by plus signs, on one side of an arrow and places the products, also separated by plus signs on the arrow head side of the arrow,” (1, pg 37). An example of a chemical formula is the formation of water.

2H + O (H2O

In the formula above, the number in front of the chemical symbol H is called a coefficient. Coefficients “specify the proportion of the formula units involved in the chemical reaction,” (1, pg. 38). The most important thing about a chemical equation though is that it be balanced. A balanced equation is one that has all atoms that were on the reactants side present on the products side. The term makes you think of a scale with weights on both sides. If the scale has the exact same amount of weight on both sides then the scale is balanced. Chemical equations are the same way. Chemical equations depict chemical reactions in a way that is both brief but delivers all the detail needed so that scientists can recreate the reaction again and again. All chemical reactions require energy to some extent. Some chemical reactions give off heat when they occur these reactions are called exothermic reactions. Other chemical reactions require constant heat energy to continue. These reactions are referred to as endothermic. Energy is the topic of the next section in this chapter.

Energy in the book is defined as “the ability to cause change,” (1, pg. 38). This does not mean that it is actively causing change only that it can at some point. Energy exists in two main states. It is either stored as in the case of potential energy or it is acting upon something as in the case of kinetic energy.

Kinetic energy is defined as the “energy associated with motion,” (1, pg 38). It is the energy involved when a car rolls down a hill or when a ball is thrown through the air.

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The Kinetic energy of an object in motion is calculated by this equation.

KE=1/2mv2

In the above equation KE stands for kinetic energy, m stands for mass and v stands for velocity. In this equation it is obvious that the component that affects the result the most is velocity. This is why a small bullet can have so much force when it hits its target. Even though its mass is very small the velocity is so great that it generates a huge amount of kinetic energy. Kinetic energy is measured in joules. The unit joule is based on the equation.

1J=1/2 x (2kg) x (1m/s)2

The above equation is meant to represent “an object with the mass of exactly two kilograms moving at a velocity of exactly 1 meter per second,” (pg 39). The other from of energy is potential energy.

Potential energy is defined as “stored energy,” (pg. 39). In the case of mechanical energy it can be seen when you wind up a string or stretch a rubber band.

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The picture above shows a rubber band before stretched. It has no potential energy because nothing is acting on it. Energy has to first be put into the object. It is like filling a bucket with water so that you can pour out the water some where else that you want it more.

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Here the rubber band is having energy stored in it. By putting mechanical energy into the rubber band like this the person in the picture is “filling the bucket.” Potential energy comes in more forms then just mechanical. There is the energy held by elements and compounds that chemistry studies. This sort of potential energy is referred to as chemical energy. The chapter defines chemical energy as the potential energy that chemicals have through “virtue of their compositions,” (pg 39). Chemical energy is what we use every day when we drive a car or cook our dinner. It is using the energy in gasoline or natural gas to do work. By causing chemical reactions we convert the potential energy inherent in the chemicals into kinetic energy. When we “use up” the gas in a car we have to refill the tank. So it appears that we use up all the chemical fuel. But as stated earlier in the chapter matter can not be destroyed only changed. This is also the case with energy.

Just as there is a law of conservation for matter there is also one for energy. It states that “the total energy of the universe is constant and can neither be created nor destroyed; it can only be transformed,” (pr. 40). The law of conservation is also known as the “first law of thermodynamics,” (pg 40). The total energy in the universe is the sum of all the kinetic and potential energy that exists. The last topic of this chapter is heat energy.

Heat energy is gone into in great detail in this chapter. The first definition of heat is that it is the “energy that transfers from one object to another when the two are at different temperatures and in some kind of contact,” (pg. 40). Heat is also defined as “a temperature changing capacity possessed by and object,” (pg. 40). It is also broadened to be defined as a “physical state-changing capacity,” (pg 40). Heat is thus an energy that moves between objects that can if intense enough change the matter-state that said object or objects are in. An example of heats state changing properties can be seen in a block of ice. As more heat moves to the ice it melts becoming water, a liquid. The point at which the amount of heat in an object is sufficient to melt it from solid to liquid is called its melting point. Then as the now liquid water is heated it begins to convert into steam, a gas. The point at which a liquid has enough heat to become gas is referred to as that liquids boiling point.

A thermal property is one of the physical properties that were mentioned earlier on in this paper and in the book. The book defines something’s thermal properties as being the properties of matter that are related to “the ability of a substance to handle heat without undergoing a chemical change,” (pg. 41). The specific heat of an object is one thermal property that is used to show the differences between the thermal properties in different sorts of matter. Specific heat is defined as the “quantity of energy required to change the temperature of one gram sample of something by one degree Celsius. Heat is measured in calories and so this is part of the equation for measuring specific heat. “One calorie is the amount of heat that, when added to one gram of water at fourteen and five tenths degrees Celsius, makes the temperature increase to fifteen and five tenths degrees Celsius,” (pg 41). To figure out a substances specific heat you must divide the number of calories put into the substance by the number of grams that make up the substance times the change of temperature in the substance using the Celsius scale. Heat is not an energy that flows from one object to another like a liquid. Heat is actually a form of molecular energy.

Heat is generated by the movement of molecules and other particles. The sum total of these movements being referred to as “molecular kinetic energy,” (pg 43). This means that the measure of an objects temperature is actually the measure of its kinetic energy. Like the marbles in the picture below bouncing off one another in a random fashion.

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This definition of heat though means that when there is no heat energy at all there is no molecular kinetic motion. So if you could lower an object to 0 Kelvin you would have an object with no molecular movement at all.

Bibliography

1) Fundamentals of General, Organic, and Biological Chemistry. Holum, John R. John Wiley & Sons, Inc. 1997.

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4) Lecture. Dr Rahni. Chemistry 101. 06/02/04.

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