W1-Atomic structure & Bonding.pptx

PY4040 Lecture 1 Atomic Structure & Professor Fawaz Aldabbagh Bonding What is the Atomic Number? What is the mass number? Isotopes : Hydrogen he same atomic number (number of protons) but different numbers of ne The Three Naturally occurring Isotopes H (abundance: 99.98%, stable) D (abundanc...

PY4040 Lecture 1 Atomic Structure & Professor Fawaz Aldabbagh Bonding What is the Atomic Number? What is the mass number? Isotopes : Hydrogen he same atomic number (number of protons) but different numbers of ne The Three Naturally occurring Isotopes H (abundance: 99.98%, stable) D (abundance: 0.02%, stable) T (trace, radioactive, t1/2 = 12.32 years) g. Chloroform: CHCl3 (common organic solvent) & CDCl3 (common NMR solvent) Isotopes : Carbon e same atomic number (number of protons) but different numbers of ne C (abundance: 98.89%) & 13C (abundance: 1.11%) are stable 14 C (trace) has six protons and eight neutrons with t1/2 = 5730 years 14 C is used in carbon-dating 12 What is the atomic weight? ANS: Is the Average Mass of Atoms 889 X 12.000) + (0.0111 X 13.0034) = 12.011 amu is the atomic weight of carbo t is the molecular weight of CH4? Is the sum of atomic weights Electronic Structure is represented in the The Distribution of Electrons in First (row) shell consists of 1sAtoms (maximum number of valence electrons = 2) Second (row) shell consists of 1s2s2px2py2pz (maximum number of electrons = 8) ond and higher shells contain three degenerate p-orbitals third and higher shells – in addition to s and p orbitals contain five degenerate d i Exclusion Principle: Maximum of two electrons in each orbital of opposite spin d’s Rule: An electron will occupy an empty degenerate orbital before it will pair u closer the orbital is to the nucleus, the lower will be its energy E.g. Silicon (14) 1s22s22p63s23p13p13p03d03d03d03d03d0 Lewis Symbols Electrons in the Outermost shell are called Valence Electrons Represent the number of valence electrons as dots Valence number is the same as the Periodic Table Group Number Number of valence orbitals in a given Periodic Table Row is given by n2 n=1 n=2 Groups 1 For example, 2 3 4 5 6 7 8 Elements want to achieve the stable electron configuration of the nearest noble gas n=2 n=3 Atoms tend to gain, lose or share electrons until they are surrounded by 8 electrons Octet Rule Noble Gases (Inert Gases) Nobel Gas Has a Stable Electron Configuration Example of Ionic Bonding 11 9 10 Electronic configuration of Neon achieved in both cases Covalent versus Ionic Bonding Ionic Bonding refers to electrostatic forces between ions, usually a metal cation and a non-metal anion. The compounds created are highly crystalline with usually high melting points (e.g. NaCl melts at 801C). Covalent Bonding results from the sharing of two electrons between two atoms (usually non-metals) resulting in molecules. Molecules are usually gases, liquids or low melting point solids. Octet Rule applies Each Covalent Bond contains Two Electrons He and H2 have the same number of electrons Hydrogen molecule, H2 Concentration of negative charge between two nuclei occurs in a covalent bond Summarizing the Octet Rule: 7A elements (e.g. F) have one valence electron for covalent bonding, so to achieve octet 6A elements (e.g. O) use two valence electrons for covalent bonding, so to achieve octet 5A elements (e.g. N) use three valence electrons for covalent bonding, so to achieve octet 4A elements (e.g. C) use four valence electrons for covalent bonding, so to achieve octet Learning Outcomes n define atomic number and atomic mass. derstand that elements can exist as isotopes due to different numbers of neutron ow how to calculate molecular weight for a compound. derstand the distribution of electrons in atoms according to the Periodic Table. derstand the filling of the first three quantum shells of electrons in the Periodic T period number (Ƞ) identifies the number of orbitals in the valence shell = Ƞ2. ow valency is related to Group Number and Lewis structures of elements. ow elements react to form the stable electronic configuration of the nearest Nob ow ionic bonds are oppositely charged ions with Noble gas electronic configuratio ow C, N, O and F react to form an octet. derstand that molecules form covalent bonds through the sharing of a pair of ele