General Science and Basics of Matter for Nursing School Entrance Exam Study Guide
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- Quarks and Charges
- Essential Concepts
- Basic Forces
- Gravity attracts two masses toward each other. Newton wrote the main equation of gravity, and Einstein's general theory of relativity more completely explained gravity as a warping by matter of space-time. The force of gravity obeys an inverse-square law: The force falls off as the square of the distance from the source.
- Electromagnetism (EM) is the force that exists between charged particles. It is attractive when the charges are opposite (positive and negative) and repulsive when the charges are the same (both positive or both negative). Electromagnetism holds atoms together—the EM force in various forms is the secret to the chemical bond. The EM force, like gravity, obeys an inverse square law. Its main theoretical formulation is in Maxwell's equations.
- Weak nuclear force, which has a very short range and is responsible for certain kinds of interactions in the atom, governs a particular kind of radioactive decay called beta decay, in which a neutron converts to a proton plus an electron and antineutrino.
- Strong nuclear force is the major stabilizer of the atomic nucleus, governing interactions among the quarks that make up the protons and neutrons. Unlike forces such as gravity and EM that diminish with distance, strong nuclear force strengthens with distance. The more quarks are separated, the more strongly they are bound to each other. This is why free quarks have never been observed.
- Atoms and the Periodic Table
- Chemical Reactions
- States of Matter
- Organic and Inorganic Molecules
- First Law of Thermodynamics
- Second Law of Thermodynamics
- Types of Energy
Work is force times distance, which has the same units as energy. The metric unit of energy is the joule (J, therefore 1 J = 1 N– m). The unit is named after James Prescott Joule (1818–1889), one of the founders of the concept of the conservation of energy.
In the first law of thermodynamics, energy is neither created nor destroyed, but only transformed.
One of the amazing discoveries in the history of science was the gradual realization that types of energy can be equivalent in value (the manifestation of the first law). How can the warmth of our body or the strength of our arms come from the food we eat? Joule discovered the mechanical equivalent to heat—that, indeed, mechanical motion and heat could be put into equivalent terms as forms of energy. In heat, the unit is the calorie. In the mechanical equivalent of heat, 4.18 J = 1 calorie. One feature shared by all forms of energy is that they can be converted into heat, or work.
All forms of energy can be converted to heat; heat cannot be converted to all other forms of energy with equal efficiency. In a sense, heat is the most degraded form of energy, because it is least convertible into the other forms. This fact—that not all forms of energy are equal in "quality"—led to what is known today as the second law of thermodynamics.
The key property is entropy. This is often taken to mean "disorder." Indeed, there is a relationship between the order of matter and its entropy content. Thus, a gas has a higher entropy than a solid, because compared to the molecular chaos of a gas, the solid has atoms and molecules in relatively neat arrangements.
Physicist Ludwig Boltzman (1844–1906) worked out the relationship between entropy and the number of states possibly occupied by a state of matter. He had the equation for entropy put on his gravestone.
In general, entropy will increase over time. Disorder increases. A hot cup of tea placed in an ordinary room will cool off. Its energy went into the room's air. Thus, the tea cooled off by many degrees as the room warmed up a tiny amount of temperature (because it has a bigger mass). Because the heat, as energy, went from a more concentrated state (in the tea) to a more diffuse state (in the room's air), there was an increase in entropy of the tea-and room considered as a system. A concentrated amount of heat at a high temperature is not as degraded as a diffuse amount of heat at a lower temperature. In fact, the unit of entropy is the heat per unit degree Celsius, in other words, the . (Note from this definition that one calorie of heat at a lower temperature has a higher entropy than one calorie at a higher temperature.) A state of higher entropy is a more disorderly and a more degraded state of energy. These considerations are essential for the industrial world—for example, in the design and operation of the electrical power plants.
Entropy can sometimes decrease. Energy can become more useful (less degraded). For example, in plant photosynthesis, carbon dioxide and water are transformed into carbohydrates, which are food energy that we can eat. The carbon dioxide and water have a higher entropy than the same atoms arranged into the carbohydrate molecules. In this case, entropy decreased, an apparent violation of the second law. But photosynthesis takes sunlight—solar energy—which itself is a very low form of entropy. One can compute the efficiency of photosynthesis, which is the efficiency of the conversion of solar energy into chemical energy of food. The wasted light (this waste is an unavoidable part of the process) goes off as heat from the plant. This heat is an increase in entropy. When we combine the entropies for the two processes (1. some part of the sunlight, along with carbon dioxide and water go into carbohydrates in an entropy decrease, 2. the other part of sunlight goes into heat in an entropy increase), it turns out that the increase dominates.
Local decreases in entropy have always been found to co-occur with increases in entropy at a larger scale, when more factors are included. Therefore, some prefer to state the second law as the fact that in any process that transforms energy, the entropy of the universe always increases.
Heat (also called thermal energy), on a molecular scale, whether for a solid, liquid, or gas, is the motion of molecules. In a solid, the atoms or molecules do not go anywhere, they vibrate in place. In a gas, higher temperatures mean faster velocities for the molecules. As a cup of hot tea cools, the fast molecules of the tea hit the molecules of the tea cup, which causes them to vibrate faster; these, in turn, come in contact with the molecules of air around the cup, causing the air molecules to move faster. The air molecules that are faster collide into the slower ones, causing them to move. Thus, the heat moves outward as the cup cools. In addition to this conduction of heat, heat can also move by convection, as when waves of air waft upward from a hot highway during midday in summer. Heat can also move by radiation, which is why your hands held even to the sides of a campfire perimeter are warmed.
Mechanical energy is the energy of motion (for example, water in a waterfall that can turn a turbine). As a very high quality (low entropy) form of energy, mechanical motion can be easily converted into other high quality forms, such as electricity.
Light is an electromagnetic wave that travels in a vacuum at the universal constant velocity, the speed of light. The energy of an individual quantum packet of light in this wave (the photon) is higher for shorter wavelengths. Thus, a blue photon has higher energy than a red photon, and an ultraviolet photon has even higher energy. A very high energy photon would be the X-ray. A low energy photon is the microwave.
Electricity is moving electrons. In direct current (DC, as from a battery), electrons actually move from the negative pole to the positive pole. Eventually, the battery becomes dead when the electrons that can move have all done so. In alternating current (AC, 60 cycles per second here in the United States), electrons are vibrated back and forth, first toward one direction in the wire, then toward the other direction. So they do not actually travel. We use AC for most power needs, because it is safer at the high voltages needed for long distance transmission from the power plants to individual homes.
Nuclear energy is the energy inherent in the nuclei of certain atoms. For example, nuclear power plants use the nuclear energy of a uranium isotope (U-235), which can be split in a controlled chain reaction of nuclear fission. This source of energy turns water to steam to spin the turbine and thereby generates electricity. In the sun, the form of nuclear energy is nuclear fusion, in which hydrogen is fused to helium, with the release of energy.
Work is formally defined as force times distance. For example, to lift a heavy box from the ground is work. You exert a force, counter to that of gravity, to lift the mass through a distance. Work has the same units as energy. Work requires the expenditure of energy. Where has the energy gone? Some went into body heat as your muscles were used. Some went into lifting the box, now above the ground, and now a form of potential energy.
Gravitational and mechanical potential energy: There are many forms of potential energy, which usually means that energy is held in a static arrangement of matter in some form, with the potential to be released and turned into some other form of energy, such as kinetic or electrical or heat (thermal). An object lifted above the ground has potential energy (thus, every leaf on a tree has potential energy). Potential energy also resides in the mechanical tension of a pressed or stretched spring.
Chemical potential energy exists when any two or more substances are capable of undergoing a chemical reaction that could potentially release energy in an exothermic reaction. One example is food and the oxygen in the air. That pair has the chemical potential to "burn" together and release energy. We do this when consuming the food. Our cells convert the energy into other molecules that can store energy. This stored energy can then be used to construct the other molecules we need to live.
Kinetic energy is similar to mechanical energy and is called the energy of motion. It is proportional to the square of the velocity of an object.
Physics is the study of the constituents and forces that govern matter at its most elementary level.
The word atom comes from the ancient Greek, meaning "indivisible." Atoms are the most finely divided parts of matter that possess the characteristics of a particular element, such as copper, gold, carbon, or hydrogen.
Atoms are not actually indivisible. Atoms not in molecules or ions are electrically neutral and contain equal amounts of positive and negative electrical charges. The positive charge is concentrated in a tiny central massive region called the nucleus. The negative charge is in one or more tiny electrons, which "whir" around the nucleus, bound to it by electrical attraction.
The nucleus, too, has parts: protons and neutrons. Protons are positively charged, neutrons are neutral. Their masses are nearly (but not exactly) the same. The mass of a proton or neutron is about 2,000 times the mass of an electron.
Quantum theory made the picture of the atom more complete though more difficult to visualize. According to quantum mechanics, the electrons do not orbit the nucleus like planets around a star, but are more like clouds of probability, in which an electron can exist anywhere in its cloud (its range of possible places), popping in and out of existence in different sites within its cloud, which fades out with distance from the nucleus.
The atoms of a particular element all have the same number of protons in their nuclei (which determines the charge of the nucleus, thus the number of electrons around the nucleus, and thus the chemistry of the element). But atoms of elements can vary in the number of neutrons in their nuclei. Therefore atoms of an element can vary in their masses. These different atomic masses of the same element are called isotopes.
Most atoms of the element carbon contain 6 protons and 6 neutrons in their nuclei. This is carbon-12 (atomic number 6, atomic weight 12). About 1 in 100 atoms of carbon have 6 protons and 7 neutrons in their nuclei. This is carbon-13 (atomic number 6, atomic weight 13). An even smaller fraction of carbon is carbon-14. It has 6 protons and 8 neutrons in the nucleus. Also, it is radioactive, which means it is inherently unstable and will decay in the following manner. One neutron converts to a proton plus an electron that is shot out at great energy from the nucleus (note that the electron was created by the conversion, it was not "in" the nucleus.) This is beta decay, governed by the weak nuclear force. After beta decay, the atom is no longer carbon, it is nitrogen, with 7 protons and 7 neutrons, and now is perfectly stable. Other radioactive isotopes, such as those of uranium, can decay in another manner called alpha decay, when a bound particle of 2 protons and 2 neutrons is ejected.
From the discoveries of quantum mechanics, protons and neutrons were found to be made of quarks. The proton is made of two "up" quarks and one "down" quark. The neutron is one "up" quark and two "down" quarks. Other numbers of quarks create other kinds of particles in a quantum mechanical "zoo," such as mesons. This zoo also contains chargeless particles called neutrinos with much less mass than electrons. There are other types of quarks, too, such as strange and charm.
Velocity (v) is distance (s) covered per unit time (t): .
Acceleration is the change in velocity over an interval of time. It can be written as = difference, or, in the terms of calculus, derivative). If velocity is a change in position, acceleration is the change in velocity.
Newtonian concept of force (F): F = m × a. It takes force to accelerate a mass (m) (stepping on the gas pedal of a car, which causes more gasoline to be burned and converted into the car's forward motion). Honoring Newton, the metric unit of force is called a Newton (N). Its units are (the force it takes to accelerate one kilogram by one meter by second over the course of one second).
Momentum is mass times velocity. A car traveling at 60 mph has twice the momentum of a car of the same mass traveling at 30 mph.
Objects traveling not in straight lines but in curved paths have properties called angular, because in the governing equations one must also account for the change in the angle; thus, angular velocity, angular acceleration, and angular momentum. Earth has a huge angular momentum because of its huge mass.
Forces can be static as well as dynamic. Pressure (for example, the pressure that exists inside a balloon blown up with air) is expressed as force per area on the inner surface of the balloon. But once it is blown up, the balloon does not keep expanding. This is because there is an equal and opposite force exerted by the stretched skin of the balloon. The balloon remains at the same size (except for slowly leaking) because the two forces, from air and skin, exactly balance each other.
Electricity is an entire special topic in physics.
Voltage is the difference in electrical force that can drive electrons from one place to another; the unit is the volt.
Amperage is the actual amount of flow of electricity, or electrons; the unit is the amp or ampere.
Resistance is the resistance to the flow of electricity, which varies among materials; the unit is the ohm. The watt (W) is the amount of power that flows when 1 amp flows by an electrical force of 1 volt.
Another important topic in physics is waves. Waves are characterized by frequency (cycles per unit of time) and by wavelength (distance traveled by one cycle).Amplitude (strength) is another characteristic. For example, sound consists of traveling waves of compression and expansion in air (or water). Light waves (standing waves) are electromagnetic, which can travel in a vacuum.
Physicists recognize four forces that are ultimately fundamental.
Chemistry studies the interactions of atoms, how they form molecules, and the interactions of those molecules, which range from simple ions to complex organic molecules.
The naturally occurring elements contain from 1 proton (hydrogen) to 92 protons (uranium) in the nuclei of their atoms. Elements with more protons have been made artificially in experiments of high energy physics.
The electrons around each nucleus fill, in sequence, what are called shells. These shells, and the number of electrons in them, determine the chemical properties of the elements, such as crystal geometry, electrical conductivity, and, most important, their bonding properties with other atoms into molecules.
The first shell, K, can hold two electrons. The second shell, L, can hold eight electrons (in two subshells of s with two and p with six). The third shell, M, can also hold eight electrons (in two subshells of s with two and p with six), and so on. Things become more complicated as the elements move into higher atomic numbers (the number of protons in their nuclei),with, for example, phenomena such as a lower subshell filling after a more outer shell contains electrons. But basically, for most chemistry we need to consider, the outermost shell will have eight electrons when it is "full." (Note that the first shell only holds two electrons.)
These shells of electrons, and the fact that shells can be full or less than full, creates cycles in the properties of elements. For example, elements with full shells include helium, neon, and argon. These elements are in the family of elements called noble gases, which almost never combine with other elements (they don't need the other elements to create a full shell of electrons, because they already are full).
There is a tendency, driven by energy considerations, for atoms to achieve complete shells of electrons. They may do this by either losing or gaining electrons, depending on which direction makes creating the full shell "easier."
For example, elements with one electron in an outer shell will tend to give up that electron in a chemical bond with a different atom. Elements with seven electrons in the outer shell will tend to grab an electron in a chemical bond with another atom. An example is table salt, NaCl. By themselves, atoms of sodium (Na) have one outer electron, whereas those of chlorine (Cl) have seven outer electrons. In chemical contact, sodium gives up an electron to chlorine, thereby both achieving full shells. They bond into a solid crystal (salt) of an alternating, three-dimensional lattice of Na ions and Cl ions. The outer shell that is chemically active by virtue of this tendency to give up or gain electrons is called the valence shell of atoms.
Depending on the strength of the tendency to gain or lose electrons, and on the "needs" of chemical partners, chemical bonds can occur in different types. Ionic bonds are when one element gives up electrons and the other element gains. An example is table salt, where the sodium atoms, having lost electrons, become ions with a positive charge (of 1), and the chlorine atoms, having gained electrons, become ions with a negative charge (of –1). In another kind of bond, called a covalent bond, electrons are shared in pairs. In a covalent bond, the resulting atoms in the bond do not become ions, but still can have a slight charge polarization. The complexities of forces between atoms in chemical bonds and between molecules with charged surfaces create other types of bonds (for example, hydrogen bonds and the bonds from van der Waal forces).
Chemical reactions occur when chemical reactants change into products. Reactions can be as simple as salt dissolving its ions into water, or as complex as two organic molecules brought together into a larger one in the presence of an enzyme. In a chemical reaction, substances called reactants undergo a chemical change so that new chemical substances are formed. The new substances are called products. Chemical reactions can be expressed with chemical equations, in which the reactants are on the right side of the equation and products are on the left side. By convention, chemical equations are written with an arrow taking the reactants into the state of products.
Chemical reactions must be balanced according to the law of conservation of matter: Matter can be neither created nor destroyed. (Changes in the nucleus, for example, from nuclear fusion, nuclear fission, or radioactive decay, are not considered here in these ordinary chemical reactions that involve only the electrons of atoms, and not their nuclei.) For instance, the number of atoms of oxygen in the reactants has to equal the number of atoms of oxygen in the products.
Reactions can give off energy (exothermic). These tend to occur spontaneously (but not instantaneously). Some reactions require energy supplied from the environment—these are called endothermic.
Many important chemical reactions are known as oxidation-reduction reactions. One element gains electrons (is reduced). A different element loses electrons (is oxidized). The word reduced refers to the fact that the gain in electrons reduces the charge of the element to a more negative value.
Acids are substances whose dissolution in water creates hydrogen ions (H+) in water. Bases are substances whose dissolution accepts hydrogen ions (H+) ions in water. The pH scale is the measure of acidity or basicity, and it ranges from 0 to 14, with 7 being neutral, values below 7 being acidic, and those above 7 being basic.
Solid: the state of matter in which the atoms or molecules are bound tightly and move together as a unit. Some solids are mathematically regular in their atomic structure (such as crystals). Other solids can be more amorphous (such as coal).
Liquid: the state of matter in which the atoms or molecules can glide past each other, loosely bound but not attached to specific neighbors. However, in liquids, the molecules still have some degree of coherence to each other.
Gas: the state of matter in which atoms or molecules are totally free of each other. In air, for example, the molecules of nitrogen and oxygen travel as independent units, only bumping into other molecules (this bumping creates the gas pressure).
The different states of matter contain different amounts of energy. The energy required to change a substance from solid to liquid is called the heat of fusion (fusion here means melting). The energy required to change a substance from liquid to gas is called the heat of vaporization. The heats of fusion and vaporization occur at constant temperatures. It requires energy to heat water to the boiling point, but then more energy is needed—at that constant boiling point temperature—to turn the water into steam. Only after the water has become steam can more energy raise the temperature of the steam itself. These heats of fusion and vaporization are unique for all substances, as are the freezing and boiling temperatures.
For water, for example, the heat of vaporization is 549 calories per gram. This is the same amount of energy it takes to raise 10 grams of water by 54.9° C (or one gram by 549° C, but that is not possible, given that the freezing point is 0° C and the boiling point is 100° C).
When temperatures are extreme (as in the center of the sun), electrons are stripped from their nuclei. The resulting state of matter is called a plasma (often, plasma is called a fourth state of matter).
Basically, organic molecules contain a reduced form of carbon, in other words, carbon with a slightly negative charge from the stronger attraction (electron affinity) of electrons in sharing with other atoms, notably hydrogen. Carbon has four electrons in an outer energy level, thus requiring four more to complete the shell of eight. It is special. Carbon can bond with itself in chains, a virtually unique feature of its atomic structure (silicon also has this special characteristic). Pure forms of carbon include diamonds, graphite, and the recently discovered form of carbon in hollow spheres of 60 atoms called "buckyballs."
Organic molecules are the stuff of life. Therefore, organic chemistry is the chemistry of life itself. There are important classes of organic molecules in living things.
Proteins are organic molecules made from smaller organic components called amino acids. Amino acids contain the element nitrogen. Enzymes and many structural parts of cells are all types of proteins. Hemoglobin in our blood is a protein.
Carbohydrates are organic molecules of carbon in chains that are fairly short, with side groups that branch off the chains and consist of hydrogen and hydrogen-oxygen pairs. The chemical formulae for carbohydrates often look like they consist of carbon plus multiples of water (for example, C6H12O6)—thus, the name carbohydrates. Examples are sugars such as sucrose and lactose, and starch. The important structural molecule of plants—cellulose—is also a carbohydrate.
Lipids are very long chains of carbon atoms, with side groups that are primarily single hydrogen atoms. Other side groups also occur. Examples of lipids are the molecules in various kinds of oils (saturated versus unsaturated). Lipids are crucial in the membranes of cells, which all consist of complex lipids called phospholipids, because they have a phosphate group at one end. Most lipids are insoluble in water.
Nucleic acids, such as DNA and RNA, form important coding molecules inside cells for the genetics of living things.
Inorganic chemistry deals with the chemistry of everything that is not organic. This includes, for example, the chemical reactions between simple charged ions dissolved in water, and the structures of crystals, with their different planes of cleavage. Inorganic chemistry includes many kinds of reactions among molecules in Earth's atmosphere.
You Should Review
- laws of motion, gravitation, momentum
- light and magnetism
- structure of the atom
- periodic table
- chemical bonds
- forms of energy
- first and second laws of energy thermodynamics
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