BIO 213 Lecture 3 - Notes PDF

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BIO 213 Lecture 3 All mater is composed of atoms. Atoms are composed of :   

Electron: Negatively charged Proton: Positively charged Neutron: Neutrally Charged

Mass of one proton or one neutron = 1 dalton (Da) or 1.7*10-24 grams Generally, atoms are electrically neutral: number of electrons = number of protons. The mass of protons and neutrons are identical. On the other hand electrons are significantly lighter in mass than protons and neutrons. Element: Fundamental substance containing only one kind of atom. The number of protons (atomic number) identifies an element. Atomic # = protons Mass # = protons + neutrons Isotopes: Forms of an element with different numbers of neutrons, and thus different mass numbers. (differ in number of neutrons.)

Carbon atoms in biological molecules are mostly 12C , but some are 13C. The ratio of 13C: 12C varies with location and can be used to identify the origin of biological samples. Mass spectroscopy can determine differences between 13C and 12C. (figure 1.below)

Some isotopes are unstable: Radioisotopes give off energy in the form of alpha, beta, and gamma radiation from the nucleus (radioactive decay). The atom is transformed, sometimes to a different element. Molecule: A stable association of atoms. Orbital: Region where an electron is found at least 90% of the time. Orbitals are filled in a specific sequence, in a series of electron shells, or energy levels. First shell (innermost): 1 orbital; holds 2 electrons Second shell: 4 orbitals; holds 8 electrons Addition shells: 4 orbitals; each shell holds 8 electrons The farther a shell is from the nucleus, the higher the energy level of electrons in that shell The outermost electron shell (valence shell) determines how the atoms behave If the outermost shell is full, the atom is stable; it won’t react with other atoms. Reactive atoms have unpaired electrons in their outermost shell. Octet rule: Tendency of atoms to form stable molecules resulting in full valence shells. Chemical bond: Attractive force that links atoms together to form molecules. Covalent bond: Atoms share one or more pairs of electrons so that the outer shell are filled Compound : Pure substance made up of two or more different elements bonded together in a fixed ratio. Molecular weight of a compound = sum of atomic weights of all atoms in the molecule/.

Covalent bonds are very strong. Nonpolar covalent bond: Electrons are shared equally (atoms have similar electronegativity Polar covalent bonds: One atom has greater electronegativity, so electrons are drawn more to nucleus. Ions : Electrically charged particles formed when atoms lose or gain one or more electrons Complex ions : Groups of covalently bonded atoms that carry a charge . (ex: NH4+) Ionic bonds Formed by electrical attraction of positive and negative ions. (ex: salts ) In solids, ionic bonds are strong because ions are close together. In water they are far apart....