Pima Medical Institute BIO 120 Hole’s Essentials of Human Anatomy & Physiology Chemical Bonds BIO 120 Anatomy & Physiology Lesson 2 David Shier, Jackie Butler, Ricki Lewis, Hole’s Essentials of Human Anatomy & Physiology, 10th Ed. CopyrightThe McGraw-Hill Companies, Inc. Created by Dr. Melissa Eisenhauer, Trevecca Nazarene University
Introduction: A. Chemistry deals with the composition of substances and how they change. B. A knowledge of chemistry is necessary for the understanding of physiology because of the importance of chemicals in body processes. Chemistry is the branch of science that deals with the composition of substances and the changes that take place in their composition. Understanding chemistry is essential for understanding anatomy and physiology because body structures and functions result from chemical changes within cells. The human body is composed of chemicals, including salts, water, proteins, carbohydrates, lipids, and nucleic acids. All of the food that we eat, liquids that we drink, and medications that we may take when we are sick, are chemicals. At the cellular level of organization, chemistry, in a sense, becomes biology. A cell’s working parts—its organelles—are intricate assemblies of macromolecules. Because the macromolecules that build the cells that build tissues and organs are themselves composed of atoms, the study of anatomy and physiology begins with chemistry.
1. Matter is anything that has weight and takes up space. Structure of Matter: A. Elements and Atoms: 1. Matter is anything that has weight and takes up space. 2. All matter is composed of elements, 90 of which occur naturally. Matter is anything that has weight and takes up space. This includes all the solids, liquids, and gases in our surroundings, as well as inside out bodies. Mass refers to the amount of a substance, whereas weight refers to how heavy it is. If your weight on earth is 150 pounds, on the moon it would be only 25 pounds, but you mass (in kilograms) would be the same in both places. That is, you take up the same volume of space, but weigh less on the moon, because the force of gravity is lower on the moon. All matter is composed of fundamental substances called elements. Examples include such common materials as iron, copper, silver, gold, aluminum, carbon, hydrogen, and oxygen. An element is a basic substance that other things are composed from. The four most abundant elements are oxygen (O), carbon (C), hydrogen (H), and nitrogen (N).
Elements in the Human Body As the table shows, a one-or-two-letter symbol represents each element.
Elements and Atoms: (continued) 3. Living organisms require about 20 elements, of which oxygen, carbon, hydrogen, and nitrogen are most abundant. 4. Elements are composed of atoms; atoms of different elements vary in size, weight, and interaction with other atoms. Living organism require about twenty elements. Of these, oxygen, carbon, hydrogen, and nitrogen make up more than 95% (by weight) of the human body. Each individual element is made up of tiny, invisible particles called atoms. The atom is the smallest complete unit of an element. Atoms vary in size, weight, and the ways they interact with other atoms. Some atoms can combine with atoms like themselves or with other atoms by forming attractions called chemical bonds.
Electrons are much smaller and bear a negative charge B. Atomic Structure: 1. An atom consists of a nucleus containing protons and neutrons, with electrons in orbit around the nucleus in shells. 2. Protons, with a positive charge, are about equal in size to neutrons, which have no charge. Electrons are much smaller and bear a negative charge Each atom is composed of a central portion, called a nucleus, and one or more electrons that are in constant motion around the nucleus. The nucleus contains one or more large particles called protons, and can also contain one or more similarly-sized particles called neutrons. The electron carries a single negative electric charge. The protons carry a single positive electric charge. Neutrons carry no charge, thereby making them electrically neutral.
An atom of the element Lithium An atom consists of subatomic particles. In an atom of the element Lithium, three electrons move around a nucleus that consists of three protons and four neutrons.
B. Atomic Structure: (continued) 4. An electrically neutral atom has equal numbers of protons and electrons. 5. The number of protons denotes the atomic number of an element; the number of protons plus the number of neutrons equals the atomic weight. The atom is electrically neutral because there is the exact same number of protons and electrons, which effectively cancel each other out. Atomic number tells you the number of protons in an atom of a particular element. For example, hydrogen whose atoms each have one proton, has the atomic number 1; carbon, whose atoms each have six protons, has the atomic number 6. Since atoms are electrically neutral, it also tells you the number of electrons. Atomic weight gives the number of protons plus the number of neutrons in an atom of a particular element. For example, the atomic weight of hydrogen, with one proton and no neutrons, is 1, whereas the atomic weight of carbon, with six protons and six neutrons, is 12 (see slide 9, Table 2.2, Atomic Structure of Elements 1 through 12). In other words, an atom of carbon weighs about twelve times more than an atom of hydrogen.
Atomic Structure of Elements 1 through 12 Table 2.2, p. 32, Atomic structure of elements 1 through 12. Please note Hydrogen’s atomic number, atomic weight, protons, and neutrons. Please note Carbon’s atomic number, atomic weight, protons, and neutrons.
2. Electrons are found in shells around the nucleus. C. Bonding of Atoms: 1. Atoms form bonds by gaining, losing, or sharing electrons. 2. Electrons are found in shells around the nucleus. a. The first energy shell holds a maximum of two electrons; the other energy shells each hold a maximum of eight electrons when on the outside. Atoms can attach to other atoms by forming chemical bonds. The chemical behavior of atoms results from interactions among their electrons. When atoms form chemical bonds they gain, lose, or share electrons. The electrons of an atom occupy one or more areas of space called shells, around the nucleus (see Table 2.2, slide 9) The electrons of an atom occur in one or more shells around the nucleus. The maximum number of electrons that each of the first three inner shells can hold is as follows: First shell ( closest to the nucleus) -- 2 electrons Second shell -------------------------- 8 electrons Third shell --------------------------- 8 electrons
Electrons orbit the atomic nucleus Electrons orbit the atomic nucleus. The single electron of a hydrogen atom is located in its first shell. The two electrons of a helium atom fill its first shell. Two of the three electrons of a lithium atom are in the first shell, and one is in the second shell. The above simplified diagram (Figure 2.2) depicts electron locations within the shells of atoms. The electrons in the outermost shell of an atom determine its chemical behavior. Atoms such as helium, whose outermost electron shells are filled, have stable structures and are chemically inactive, or inert (see Table 2.2, slide 9). Atoms such as hydrogen or lithium, whose outmost electron shells are incompletely filled, tend to gain, lose, or share electrons in ways that empty of fill their outer shells. This enables them to achieve stable structures. Figure 2.2
C. Bonding of Atoms: (continued) 3. Atoms with incompletely filled outer shells tend to be reactive to form stable outer shells of 8. 4. When atoms gain or lose electrons, they become ions with a charge. Whether they gain or lose will depend on how many electrons they have in the outer shell to start with. Atoms that gain or lose electrons becomes electrically charged and are called ions. An atom of sodium, for example, has eleven electrons: two in the first shell, eight in the second shell, and one in the third shell (Figure 2.3, slide 13).
A sodium atom This sodium atom tends to lose the electron from its outer shell, which leaves the second (now the outer-most) shell filled and the new form stable (see figure 2.4a, slide 14).
In the process, sodium is left with eleven protons (11+) in its nucleus and only ten electrons (10-). As a result, the atom develops a net electrical charge of 1+ and is called a sodium ion, symbolized by Na+ . A chlorine atom has seventeen electrons, with two in the first shell, eight in the second shell, and seven in the third shell. An atom of this type tends to accept a single electron, filling its outer shell and achieving stability (Figure 2.4a). In the process, the chlorine atom is left with seventeen protons (17+) in its nucleus and eighteen electrons (18-). The atom develops a net electrical charge of 1_ and is called a chloride ion, symbolized Cl - .
C. Bonding of Atoms: (continued) 5. Oppositely-charged ions attract each other and form an (electrovalent bond) ionic bond. 6. Covalent bonds are formed when atoms share electrons to become stable with filled outer shells. a. Two pairs of electrons shared between atoms form a double covalent bond. An ionic bond (electrovalent bond) is formed when atoms gain or lose electrons. Because oppositely-charged ions attract, sodium and chloride ions react to form a type of chemical bond call an ionic bond. Sodium ions (Na+) and chloride ions (Cl-) united in this manner form the compound sodium chloride (NaCl), or table salt (see Figure 2.4b, slide 14). Some ions have an electrical charge greater than 1—for example Calcium, (Ca++). Atoms may also bond by sharing electron, rather than by exchanging them. A hydrogen atoms, for example, has one electron in its first shell but requires two electrons to achieve a stable structure (Figure 2.5, slide 16). It may fill this shell by combining with another hydrogen atom in such a way that the two atoms share a pair of electrons. The two electrons then encircle the nuclei of both atoms, and each atom achieves a stable form. The chemical bond between the atoms that share electrons is called a covalent bond. If one pair of electrons is shared, the resulting bond is called a single covalent bond; if two pairs of electrons are shared, the bond is called a double covalent bond. Triple covalent bonds are also possible between some atoms.
A hydrogen molecule forms when two hydrogen atoms share a pair of electrons. A covalent bond forms between the atoms. Figure 2.5
C. Bonding of Atoms: (continued) The attraction of the positive hydrogen end of a polar molecule to the negative nitrogen or oxygen end of another polar molecule is called a hydrogen bond. Different types of chemical bonds share electrons to different degrees. At one extreme is the ionic bond in which atoms gain or lose electrons. At the other extreme is the covalent bond in which the electrons are shared equally. In between lies the covalent bond in which electrons are not shared equally, resulting in a molecule whose shape gives an uneven distribution of charges. Such a molecule is called polar. Unlike an ion, a polar molecule has an equal number of protons and electrons, but one end of the molecule has more than its share of electrons, becoming slightly negative, while the other end of the molecule has less than its share, becoming slightly positive. Typically, polar covalent bonds form where hydrogen atoms bond to oxygen or nitrogen atoms. Water is an important polar molecule (see Figure 2.6, slide 18). A hydrogen bond is a chemical bond formed between an electropositive atom (typically hydrogen) and a strongly electronegative atom, such as oxygen or nitrogen. Hydrogen bonds are responsible for the bonding of water molecules in liquid and solid states, and are weaker than covalent and ionic bonds.
Water is a polar molecule Hydrogen bonding connects water molecules Water molecules have equal numbers of electrons and protons but are polar because the electrons are shared unequally, creating slightly negative ends and slightly positive ends. Hydrogen bonding connects water molecules. Figure 2.6
D. Molecules and Compounds: 1. A molecule is formed when two or more atoms combine. 2. If atoms of different elements combine, the molecule can also be called a compound. a. Compounds always have a definite kind and number of atoms. When two or more atoms bond, they form a new kind of particle called molecule. If atoms of the same element bond, they produce molecules of that element. Gases of hydrogen, oxygen, and nitrogen consist of such molecules (see Figure 2.5, slide 16). When atoms of different elements bond, they form molecules called compounds. Two atoms of hydrogen for example, can bond with one atom of oxygen to produce a molecule of the compound water (H2O) (see Figure 2.7, slide 20).
Hydrogen molecules can combine with oxygen molecules Hydrogen molecules can combine with oxygen molecules, forming water molecules. The shared electrons represent covalent bonds. A molecule of a compound always consists of definite kinds and numbers of atoms. A molecule of water, for instance, always has two hydrogen atoms and one oxygen atom. If two hydrogen atoms bond with two oxygen atoms, the compound formed is not water, but hydrogen peroxide (H2O2). Figure 2.7
Table 2.3 summarizes the characteristics of the particles of matter discussed so far
E. Formulas: 1. A molecular formula represents the numbers and types of atoms in a molecule. Ex: Glucose = C6H12O6 2. Various representations, called structural formulas, can be used to illustrate molecules. Ex: Water = H H O A molecular formula consists of the symbols of the elements in the molecule together with numbers to indicate how many atoms of each element are present. It is the recipe. For example, the molecular formula for water is H2O, which means that each water molecule consists of two atoms of hydrogen and one atom of oxygen (see figure 2.8, slide 23). The molecular formula for the sugar glucose (see example slide 22) indicates that each glucose molecule consists of six atoms of carbon, twelve atoms of hydrogen, and six atoms of oxygen. A structural formula is drawn to represent how atoms are joined and arranged in various molecules. It is the blueprint. Single lines represent single bonds, and double lines represent double bonds.
Structural and molecular formulas Structural and molecular formulas for molecules of hydrogen, oxygen, water, and carbon dioxide. Note the double covalent bonds. (triple covalent bonds are also possible between some atoms). Figure 2.8
3-D molecular models Figure 2.9 Three-dimensional models of structural formulas use different colors for the different kinds of atoms. Three-dimensional molecular models depict spatial relationships of the constituent atoms. (Figure 2.9) Figure 2.9
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