economic english 7

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– SCIENCE AS INQUIRY – T he Scientific Method bility or job when hunting for food?” A question that is There are many ways to obtain knowledge. Modern sci- too general and not very useful is “Why do some people entists tend to obtain knowledge about the world by have better memories than others?” A better, more spe- making systematic observations. This principle is called ciﬁc question, along the same lines, is “What parts of the empiricism and is the basis of the scientiﬁc method. The brain and which brain chemicals are involved in recol- scientiﬁc method is a set of rules for asking and answer- lection of childhood memories?” ing questions about science. Most scientists use the scientific method loosely and often unconsciously. However, the key concepts of the scientiﬁc method are A good science question is very specific and the groundwork for scientiﬁc study, and we will review can be answered by performing experiments. those concepts in this section. The scientiﬁc method involves: T HE H YPOTHESIS asking a speciﬁc question about a process or phe- ■ After formulating a question, a scientist gathers the nomenon that can be answered by performing information on the topic that is already available or pub- experiments lished, and then comes up with an educated guess or a formulating a testable hypothesis based on obser- ■ tentative explanation about the answer to the question. vations and previous results Such an educated guess about a natural process or phe- designing an experiment, with a control, to test ■ nomenon is called a hypothesis. the hypothesis A hypothesis doesn’t have to be correct, but it should collecting and analyzing the results of the ■ be testable. In other words, a testable hypothesis can be experiment disproved through experiment, in a reasonable amount developing a model or theory that explains the ■ of time, with the resources available. For example, the phenomenon and is consistent with experimental statement, “Everyone has a soul mate somewhere in the results world,” is not a valid hypothesis. First, the term soul mate making predictions based on the model or theory ■ is not well deﬁned, so formulating an experiment to in order to test it and designing experiments that determine whether two people are soul mates would be could disprove the proposed theory difﬁcult. More importantly, even if we were to agree on what soul mate means and how to experimentally deter- T HE Q UESTION mine whether two people are soul mates, this hypothe- In order to understand something, a scientist must ﬁrst sis could never be proved wrong. Any experiment focus on a speciﬁc question or aspect of a problem. In conceived would require testing every possible pair of order to do that, the scientist has to clearly formulate the human beings around the world, which, considering the question. The answer to such a question has to exist and population and the population growth per second, is just the possibility of obtaining it through experiment must not feasible. exist. For example, the question “Does the presence of the moon shorten the life span of ducks on Earth?” is not valid because it can not be answered through experi- A hypothesis doesn’t need to be correct. It only ment. There is no way to measure the life span of ducks on has to be testable. Earth in the absence of the moon, since we have no way of removing the moon from its orbit. Similarly, asking a general question, such as “How do animals obtain food?” Disproving a hypothesis is not a failure. It casts away is not very useful for gaining knowledge. This question is illusions about what was previously thought to be true, too general and broad for one person to answer. and can cause a great advance, a thought in another Better questions are more speciﬁc—for example, direction that can bring about new ideas. Most likely, in “Does each member of a wolf pack have a set responsi- the process of showing that one hypothesis is wrong, a 220
– SCIENCE AS INQUIRY – scientist may gain an understanding of a better hypoth- T HE A NALYSIS Analysis of experimental results involves looking for esis. Disproving a hypothesis serves a purpose. Science trends in the data and correlation among variables. It and our understanding of nature often advance through also involves making generalizations about the results, tiny incremental pieces of information. Eliminating a quantifying experimental error, and correlating the potential hypothesis narrows down the choices, and variable being manipulated to the variable being tested. eliminating the wrong answers sometimes leads to ﬁnd- A scientist who analyzes results uniﬁes them, interprets ing the correct one. them, and gives them meaning. The goal is to ﬁnd a pat- tern or sense of order in the observations and to under- T HE E XPERIMENT stand the reason for this order. In an experiment, researchers manipulate one or more variables and examine their effect on another variable or variables. An experiment is carefully designed to test the M ODELS T HEORIES AND After collecting a sufﬁcient amount of consistently hypothesis. The number of variables in an experiment reproducible results under a range of conditions or in dif- should be manageable and carefully controlled. All vari- ferent kinds of samples, scientist often seek to formulate ables and procedures are carefully deﬁned and described, a theory or a model. A model is a hypothesis that is sufﬁ- as is the method of observation and measurement. ciently general and is continually effective in predicting Results of a valid experiment are reproducible, meaning facts yet to be observed. A theory is an explanation of the that another researcher who follows the same procedure general principles of certain observations with extensive should be able to obtain the same result. experimental evidence or facts to support it. A good experiment also includes one or more con- Scientiﬁc models and theories, like hypotheses, should trols. Experimental controls are designed to get an be testable using available resources. Scientists make pre- understanding of the observed variables in the absence of dictions based on their models and theories. A good the- the manipulated variables. For example, in pharmaceu- ory or model should be able to accurately predict an tical studies, three groups of patients are examined. One event or behavior. Many scientists go a step beyond and is given the drug, one is given a placebo (a pill contain- try to test their theories by designing experiments that ing no active ingredient), and one is not given anything. could prove them wrong. The theories that fail to make This is a good way to test whether the improvement in accurate predictions are revised or discarded, and those patient condition (observed variable) is due to the active that survive the test of a series of experiments aimed to ingredient in the pill (manipulated variable). If the prove them wrong become more convincing. Theories patients in the group that was given the placebo recover and models therefore lead to new experiments; if they sooner or at the same time as those who were given the don’t adequately predict behavior, they are revised drug, the effect of pill taking can be attributed patient through development of new hypotheses and experi- belief that a pill makes one feel better, or to other ingre- ments. The cycle of experiment-theory-experiment con- dients in the pill. If the group that was not given any pill tinues until a satisfactory understanding that is recovers faster or just as fast as the group that was given consistent with observations and predictions is obtained. the drug, the improvement in patient condition could be a result of the natural healing processes. An experimental control is a version of the experiment in which all conditions and variables are the same as in other versions of the exper- iment, but the variable being tested is elimi- nated or changed. A good experiment should include carefully designed controls. 221
CHAPTER 23 Physical Science PHYSICAL SCIENCE includes the disciplines of chemistry (the study of matter) and physics (the study of energy and how energy affects matter). The questions on the physical science section of the GED will cover topics taught in high school chemistry and physics courses. This chapter reviews the basic concepts of physical- science—the structure of atoms, the structure and properties of mat- ter, chemical reactions, motions and forces, conservation of energy, increase in disorder, and interactions of energy and matter. T he Structure of Atoms You and everything around you are composed of tiny particles called atoms. The book you are reading, the neu- rons in your brain, and the air you are breathing can all be described as a collection of various atoms. History of the Atom The term atom, which means indivisible, was coined by Greek philosopher Democritus (460–370 B.C.). He dis- agreed with Plato and Aristotle—who believed that matter could inﬁnitely be divided into smaller and smaller pieces—and postulated that matter is composed of tiny indivisible particles. In spite of Democritus, the belief that matter could be inﬁnitely divided lingered until the early 1800s, when John Dalton formulated a meaningful atomic theory. It stated: Matter is composed of atoms. ■ All atoms of a given element are identical. ■ Atoms of different elements are different and have different properties. ■ Atoms are neither created nor destroyed in a chemical reaction. ■ 223
– PHYSICAL SCIENCE – Compounds are formed when atoms of more Charges and Masses ■ than one element combine. of Atomic Particles A given compound always has the same relative ■ Proton Neutron Electron number and kind of atoms. Charge +1 0 –1 These postulates remain at the core of physical science 1 Mass 1 amu 1 amu amu 1800 today, and we will explore them in more detail in the fol- lowing sections. Isotopes Protons, Neutrons, and Electrons The number of protons in an element is always the same. An atom is the smallest unit of matter that has the prop- In fact, the number of protons is what deﬁnes an ele- erties of a chemical element. It consists of a nucleus sur- ment. However, the number of neutrons in the atomic rounded by electrons. The nucleus contains positively nucleus, and thus the atomic weight, can vary. Atoms charged particles called protons, and uncharged neu- that contain the same number of protons and electrons, trons. Each neutron and each proton has a mass of about but a different number of neutrons, are called isotopes. 1 atomic mass unit, abbreviated amu. An amu is equiv- The atomic masses of elements in the periodic table are alent to about 1.66 × 10−24 g. The number of protons in weighted averages for different isotopes. This explains an element is called the atomic number. Electrons are why the atomic mass (the number of protons plus the negatively charged and orbit the nucleus in electron number of neutrons) is not a whole number. For exam- shells. ple, most carbon atoms have 6 protons and 6 neutrons, Electrons in the outermost shell are called valence giving it a mass of 12 amu. This isotope of carbon is electrons. Valence electrons are mostly responsible for called “carbon twelve” (carbon-12). But the atomic mass the properties and reaction patterns of an element. The of carbon in the periodic table is listed as 12.011. The mass of an electron is more than 1,800 times smaller mass is not simply 12, because other isotopes of carbon than the mass of a proton or a neutron. When calculat- have 5, 7, or 8 neutrons, and all the isotopes and their ing atomic mass, the mass of electrons can safely be neg- abundance are considered when the average atomic mass lected. In a neutral atom, the number of protons and is reported. electrons is equal. The negatively charged electrons are attracted to the positively charged nucleus. This attrac- Ions tive force holds an atom together. The nucleus is held An atom can lose or gain electrons and become charged. together by strong nuclear forces. An atom that has lost or gained one or more electrons is called an ion. If an atom loses an electron, it becomes a positively charged ion. If it gains an electron, it becomes a negatively charged ion. For example, calcium (Ca), a Nucleus biologically important element, can lose two electrons to become an ion with a positive charge of +2 (Ca2+). Chlo- rine (Cl) can gain an electron to become an ion with a 3p e e 4n negative charge of −1 (Cl−). Electron shells The Periodic Table The periodic table is an organized list of all known ele- e ments, arranged in order of increasing atomic number, such that elements with the same number of valence A representation of a lithium atom (Li). It has 3 protons (p) and 4 neutrons (n) in the nucleus, and 3 electrons (e) in the electrons, and therefore similar chemical properties, are two electron shells. Its atomic number is 3 (p). Its atomic found in the same column, or group. For example, the mass is 7 amu (p + n). The atom has no net charge because last column in the periodic table lists the inert (noble) the number of positively charged protons equals the number gases, such as helium and neon—highly unreactive ele- of negatively charged electrons. ments. A row in the periodic table is called a period. 224
– PHYSICAL SCIENCE – Elements that share the same period have the same num- actions form the basis of chemical and physical ber of electron shells. reactions. Common Elements Molecules Some elements are frequently encountered in biologi- Molecules are composed of two or more atoms. Atoms cally important molecules and everyday life. Below you are held together in molecules by chemical bonds. will ﬁnd a list of common elements, their symbols, and Chemical bonds can be ionic or covalent. Ionic bonds common uses. form when one atom donates one or more electrons to another. Covalent bonds form when electrons are shared H—Hydrogen: involved in the nuclear process that between atoms. The mass of a molecule can be calculated produces energy in the sun by adding the masses of the atoms of which it is com- He—Helium: used to make balloons ﬂy posed. The number of atoms of a given element in a C—Carbon: found in all living organisms; pure car- molecule is designated in a chemical formula by a sub- bon exists as graphite and diamonds script after the symbol for that element. For example, the N—Nitrogen: used as a coolant to rapidly freeze glucose (blood sugar) molecule is represented as food C6H12O6. This formula tells you that the glucose mole- O—Oxygen: essential for respiration (breathing) cule is contains six carbon atoms (C), twelve hydrogen and combustion (burning) atoms (H), and six oxygen atoms (O). Si—Silicon: used in making transistors and solar cells Organic and Inorganic Molecules Cl—Chlorine: used as a disinfectant in pools and as Molecules are often classiﬁed as organic or inorganic. a cleaning agent in bleach Organic molecules are those that contain both carbon Ca—Calcium: necessary for bone formation and hydrogen. Examples of organic compounds are Fe—Iron: used as a building material; carries oxygen methane (natural gas, CH4), glycine (an amino acid, in the blood NH2CH2COOH), and ethanol (an alcohol, C2H5OH). Cu—Copper: a U.S. penny is made of copper; good Inorganic compounds include sodium chloride (table conductor of electricity salt, NaCl), carbon dioxide (CO2), and water (H2O). I—Iodine: lack in the diet results in an enlarged thy- roid gland, or goiter States of Matter Hg—Mercury: used in thermometers; ingestion can Matter is held together by intermolecular forces—forces cause brain damage and poisoning between different molecules. Three common states of Pb—Lead: used for X-ray shielding in a dentist matter are solid, liquid, and gas. Matter is an atom, a ofﬁce molecule (compound), or a mixture. Examples of mat- ter in solid form are diamonds (carbon atoms), ice Some elements exist in diatomic form (two atoms of (water molecules), and metal alloys (mixtures of differ- such an element are bonded), and are technically mole- ent metals). A solid has a ﬁxed shape and a ﬁxed volume. cules. These elements include hydrogen (H2), nitrogen The molecules in a solid have a regular, ordered arrange- (N2), oxygen (O2), ﬂuorine (F2), chlorine (Cl2), bromine ment and vibrate in place, but are unable to move far. (Br2), and iodine (I2). Examples of matter in liquid form are mercury (mer- cury atoms), vinegar (molecules of acetic acid), and per- fume (a mixture of liquids made of different molecules). S tructure and Properties Liquids have a ﬁxed volume, but take the shape of the of Matter container they are in. Liquids ﬂow, and their density (mass per unit volume) is usually lower than the density Matter has weight and takes up space. The building of solids. The molecules in a liquid are not ordered and blocks of matter are atoms and molecules. Matter can can move by sliding past one another through a process interact with other matter and with energy. These inter- called diffusion. 225