2_Principles of Atomic Structure.pdf

MBiol 112 Organic Molecules STRUCTURE AND BONDING Unit Objectives ◎ Demonstrate the concepts of general chemistry such as the electronic structure of the atom, Lewis structures and the octet rule, types of bonding, electronegativity, and formal charges. ◎ Predict patterns of covalent and i...

MBiol 112 Organic Molecules STRUCTURE AND BONDING Unit Objectives ◎ Demonstrate the concepts of general chemistry such as the electronic structure of the atom, Lewis structures and the octet rule, types of bonding, electronegativity, and formal charges. ◎ Predict patterns of covalent and ionic bonding involving C, H, O, N, and the halogens. ◎ Evaluate stabilized structures relative to their resonance forms. Unit Objectives ◎ Draw and interpret the types of structural formulas commonly used in organic chemistry, including condensed structural formulas and line–angle formulas. ◎ Predict the hybridization and geometry of organic molecules based on their bonding. ◎ Evaluate isomers based on their differences. Principles of Atomic Structure 4 Principles of Atomic Structure ◎ Atoms – consists of a dense, positively charged nucleus surrounded at a relatively large distance by negatively charged electrons 5 Principles of Atomic Structure ◎ nucleus consists of subatomic particles ◉ protons, positively charged ◉ neutrons, electrically neutral 6 7 Principles of Atomic Structure ◎ Nucleus -extremely small—about 10-14 to 10-15 meter (m) in diameter it contains essentially all the mass of the atom ◎ Electrons have negligible mass and circulate around the nucleus at a distance of approximately 10-10 m. the diameter of a typical atom is about 2 x 10-10 m, or 200 picometers (pm), where 1 pm = 10-12 m 8 A thin pencil line is about 3 million carbon atoms wide! 9 10 Isotopes of Carbon ◎ ◎ Atoms with the same atomic umber but different mass numbers are called isotopes. 11 Isotopes of Hydrogen 12 Atomic Mass ◎ The weighted average mass in atomic mass units (amu) of an element’s naturally occurring isotopes ○ Ex. 1.008 amu for hydrogen, 12.011 amu for carbon, 30.974 amu for phosphorus, etc. 13 Orbitals ◎ an orbital describes the volume of space around a nucleus that an electron is most likely to occupy, 90% to 95% of its time ◎ doesn’t have a sharp boundary 14 Kinds of orbitals Note: the two lobes of each orbital are separated by a region of zero electron density called a node 15  Orbitals ◎ The orbitals in an atom are organized into different electron shells (quantum number n), centered around the nucleus and having successively larger size and energy. ◎ Different shells contain different numbers and kinds of orbitals, and each orbital within a shell can be occupied by two electrons. 16 The energy levels of electrons in an atom 17 18 Electron Configuration ◎ also called the lowest-energy arrangement or ground-state electron configuration ◎ a listing of the orbitals occupied by its electrons 19 Electron Configuration: Rules ◎ Rule 1 ◎ The lowest-energy orbitals fill up first, according to the order 1s - 2s -2p - 3s - 3p - 4s - 3d..., a statement called the aufbau principle. Note that the 4s orbital lies between the 3p and 3d orbitals in energy. 20 Electron Configuration: Rules ◎ Rule 2 ◎ Electrons act in some ways as if they were spinning around an axis, somewhat as the earth spins. This spin can have two orientations, denoted as up (↑) and down (↓). Only two electrons can occupy an orbital, and they must be of opposite spin, a statement called the Pauli exclusion principle. 21 Electron Configuration: Rules ◎ Rule 3 ◎ If two or more empty orbitals of equal energy are available, one electron occupies each with spins parallel until all orbitals are half-full, a statement called Hund’s rule. 22 23 ◎ Valence Electrons – electrons in the outermost shell ◎ *Carbon has 4 valence electrons (Group 4A of the periodic table) 24 25