8/24/2018. Bio 1101 Lecture 2 (guided) Chapters 2: Essential Chemistry. Chapter 2: Essential Chemistry for Biology

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1 Bio 1101 Lecture 2 (guided) Chapters 2: Essential Chemistry Chapter 2: Essential Chemistry for Biology Levels of biological organization Ecosystem (e.g. savanna) Community (e.g. the organisms in the savanna) Populations (e.g. a herd of zebra) Organism (e.g. one zebra) Organ System (e.g. circulatory system) Organ (e.g. heart) Tissues (e.g. cardiac muscle) Cells (e.g. one muscle cell) Chemicals (e.g. the DNA inside a muscle cell) Some terminology Matter = 3 physical states of matter: Elements = substances that cannot be broken down into other substances 92 naturally occurring elements Periodic Table 25 of these are essential to life Can you think of any examples of elements? carbon (C), oxygen (O), hydrogen (H), an nitrogen (N) make up about 96% of body weight of most living things Most of the remaining 4% consists of: calcium (Ca), phosphorous (P), potassium (K), sulfur (S), sodium (Na), chlorine (Cl), and magnesium (Mg) 14 trace elements are also essential for life, but make up only about 0.01% of your body weight are required in the diet of an organism in very small quantities Example is iodine, essential in functioning of thyroid gland 1

2 6 7 Elements combine to form, substances that contain two or more elements in a fixed ratio Can you think of any compounds? 8 Water: H 2 O Composed of two atoms and one atom It is a highly polar molecule, as we will see later Sodium Chloride (table salt): NaCl One molecule consists of one atom of and one atom of Atoms The periodic table shows some important pieces of information about each element 6 C 12 Top number = atomic number Bottom number = mass number Atomic Number: Number of in an atom; a critical aspect of an atom, as it determines which type of element it is Mass number: Number of and in an atom Atom: the smallest unit of matter that still retains the properties of an element Three main subatomic particles: Proton have a charge 2

3 Neutron have charge Electron have a charge Protons and neutrons are located in the of an atom Electrons are located outside of the nucleus Atomic structure of a helium atom ACTIVITY Part 1 A hydrogen atom has 1 proton, 0 neutrons, and 1 electron. What is its atomic number? What is its mass number? Helium has a mass number of 4, including 2 neutrons. What is its atomic number? If an element has 8 protons, 8 electrons, and 8 neutrons, what is its atomic number? What is its mass number? Elements may come in slightly different forms called isotopes: Ions are atoms with Number of electrons does not equal number of protons Cation = charged Anion = charged Isotopes have same number of protons and electrons, but have varying numbers of neutrons Example: Carbon-12 is the most common type (6 protons and 6 neutrons); two other isotopes are Carbon-13 and Carbon-14 Electron Arrangements & Bonding Electrons circle the nucleus at specific distances from the nucleus, called Electrons occur in pairs in these shells; these pairs are called Inner-most electron shell is full when it contains 2 electrons 3

4 Second shell is full when they contain 8 electrons (4 pairs) Third shell is stable when it contains 8 electrons Electrons begin filling orbitals beginning with inner-most electron shell and working outward Fill up like strangers boarding a bus 17 Chemical Bonding If the outermost shell (called the ) is full, the atom does not form bonds, and is said to be If the outermost electron shell is not full, the atom Atoms may either transfer or share electrons in their outer electron shells 18 If one atom donates an electron to another, it forms an (example: NaCl), with one atom becoming negative (Cl) and the other positive (Na) Results in formation of ions (electrically charged) When ions attach to each other, form If two atoms share electrons in their outer orbitals, they form a This results in formation of a Example: methane, CH 4 LE 2-11 A general rule of thumb: The number of covalent bonds an atom can form is equal to the number of additional electrons needed to fill its outer shell rule for atoms with atomic numbers between 1-18 (most of the elements we will be concerned with in this course) Sharing 1, 2, or 3 covalent bonds is fairly common; having 4 is rare and, as is the case with carbon, can result in compounds 4

5 23 ACTIVITY Part 2 1. Sodium has an atomic number of 11. a. How many electrons are in its outer-most (valence) electron shell? b. If a sodium atom lost one of its electrons, would it become positively or negatively charged? And therefore, would it become a cation or an anion? Hydrogen has one electron, one proton, and no neutrons. How many covalent bonds can hydrogen atom form? Nitrogen has 7 electrons. How many covalent bonds can nitrogen form? Phosphorus has an atomic number of 15. Assuming it is not charged (not an ion), how many electrons does it have? How many covalent bonds can it form? minute break Water H 2 O Oxygen and hydrogen are both reactive atoms Oxygen has 8 electrons and 8 protons, so it needs 2 more electrons to fill its outer shell Hydrogen has 1 electron and 1 proton, and needs one electron to fill its outer shell Therefore, oxygen readily forms bonds with two hydrogen atoms to make water After forming covalent bonds, the resulting water molecule is polar The polarity of water results in an attraction between adjacent molecules These attractions are called Hydrogen atoms of one molecule are slightly attracted to the oxygen end of another molecule Results in cohesion of water Water has some unusual properties that are beneficial to life For example, ice: Most liquids condense when they get cold, and freeze solid; they are more dense than their liquid form Water behaves in the opposite way; the molecules spread out, and ice is less dense than the liquid form 5

6 Benefits to life Ice floats Cohesion of water allows water to flow up through vascular tissue of trees Solutions are liquid mixtures of two or more substances The substance that dissolves another is the The substance that dissolves is the If the solvent is water, the solution is called an aqueous solution Acids, Bases, and ph ph = potential hydrogen; represents hydrogen ion concentration Acids are compounds that donate hydrogen ions (H + ) to a solution Bases are compounds that accept hydrogen ions (H + ) from a solution, or donating hydroxide (OH - ) ions A ph scale is used to describe the acidity of a solution A ph of 7 is neutral (H+ and OH- concentrations are ) A ph of 14 is the most (greater OH- than H+ concentration) A ph of 0 is the most (greater H+ than OH- concentration) A one-unit change is the ph scale is a tenfold change in actual hydrogen ions Biological solutions contain that can accept or donate hydrogen ions, to help stabilize ph Human blood, for example, has a typical ph of If ph starts to drop, as can occur during exercise, buffers remove the excess H + from the blood Important blood buffer: (HCO 3- ) Bicarbonate reacts with H + to produce carbonic acid, which then produces carbon dioxide and water; body can easily get rid of excess carbon dioxide and water 6

7 Acid Rain Pure rain is naturally somewhat acidic (ph around 5.5-6), but acid rain is more acidic A result of industrial air pollution forming acidic solutions in rain In North America, mostly a problem in the northeast Also a problem in many European countries Results in ecological damage to aquatic organisms, as well as terrestrial ones Also destroys architectural structures LE 3-9 Radiation Radiation is powerful form of that travels as or, and is produced by radioactive substances and nuclear reactions This energy can penetrate living tissues and cells, damaging DNA and potentially killing cells Can cause cancer, as in the case of UV rays causing skin cancer On the other hand, can be used to treat cancer Radiation beams aimed at a tumor deliver a strong dose of radiation to the cancerous cells, killing them We can also use naturally-occurring radioactive isotopes as a means of determining the age of fossils Carbon dating as an example Most abundant form of carbon is Carbon-14 forms in the atmosphere when cosmic rays bombard atoms and transform nitrogen into C-14 About 1 C-14 atom per trillion C-12 atoms Different isotopes of carbon (C-12, C-14) are used by plants and animals Carbon is taken in by plants from the atmosphere during The ratio of C-14 to C-12 ratio in an organism is thus equal to its ratio in When an organism dies, it stops taking in new carbon The C-12 in its remains is stable, but C-14 is radioactive and decays back into nitrogen The decay rate is stable and known Radioactive elements have specific the amount of time it takes half of the atoms in a specimen to decay back into the parent element (in this case, nitrogen) 7

8 Half-life of C-14 is years Thus, the ratio of C-14 to C-12 in an organism can be used like a clock to determine ages of fossils ACTIVITY Part 3 Imagine you re an anthropologist attempting to determine the age of a human skull using carbon dating. You find that the ratio of Carbon-14 to Carbon-12 in the skull is 1/16 th that of the environment, how old is it? When you re done, turn in your bonus activities All for today, except Random Animal of the Day! 8