University of Texas, CH 318M

Excerpt: ... nfiguration of sodium cation is 1s22s2sp6, which is neon-like. The electronic configuration of fluoride anion is also 1s22s2sp6, which is neon-like. Thus, formation of our product is driven by the ability to achieve a filled electronic shell. In general, to assess reactivity only the valence electrons need be considered, i.e. you can ignore inner shell electrons. To draw the Lewis structure of an atom, ignore the inner shell electrons. Just draw the atomic symbol and depict the valence electrons as dots. Using this protocol, we drew Lewis structures for H2, F2 and HF. Note that bonding pairs of electrons are depicted as lines. Having drawn Lewis structures for H2, F2 and HF, we briefly reviewed the concept of bond polarity and dipole moment. Know the trends in electronegativity (and why) and be able to use this knowledge to predict bond dipoles and identify ionic bonds, pure covalent bonds and polar covalent bonds. Rules for drawing Lewis structures of more complex molecules. The ...

Iowa State, CHEM 155

Excerpt: ... Chem 155 Dec. 01 Lecture Notes Chapter 9 Chemical Bonding Lewis Dot Symbols/Structures means of representing atoms, molecules, and ions by showing their valence electrons and how they are involved in bonding Valence electrons = outer shell, the electrons with the highest principal quantum number (n) Why do we ignore the core electrons? Because they do not participate in bonding! (Chemical reactions are defined as those that make or break bonds, so all of chemistry reduces to bonding.) Lewis symbols for atoms: 1s1 H 2 1s He: 1s22s1 Li . 1s22s22p3 N (the dot represents the electron) (we only draw the valence electrons , so just 1 dot, not 3) (5 valence electrons ALL the electrons with the highest principal quantum number, both s and p) (7 valence electrons ) (8 valence electrons = stable octet) . :F: 1s 2s 2p 2 2 5 1s22s22p6 . :F . : Ne : Adding an electron to F gives it a stable octet: Removing an electron from Li makes it isoelectronic to He, which ...

Winthrop, CHEM 105

Excerpt: ... Lecture 15: Bonding and Molecular Structure (Chapter 8 Part 1) Chemical Bonds Lewis Structures Resonance Elements that are the exception to the octet rule Bonding and Molecular Structure As a structural biologist, the shape and structure of every molecule tells me something about it. What is does, how it reacts, etc. Structure: How the atoms are arranged in space Bonding: How are the atoms held together? Making a Chemical Bond When 2 atoms react to form a bond, their valence electrons interact and reorganize so that an attractive force holds them together. This attractive force is called a CHEMICAL BOND There are 2 types of chemical bonds: Ionic Covalent Ionic Bonds Direct transfer of a valence electron(s) from one atom to another This transfer creates cations and anions The electrostatic interaction of the 2 ions is called an IONIC BOND Covalent Bonds When 2 atoms share their valence electrons so that each has a full valence shell, a COVALENT BOND is formed Each chlori ...

FSU, BSC 2010

Excerpt: ... c arrangement and complexity of parts Example: NaCl Na = Cl = NaCl = = Atoms The atomic # = number of protons In an uncharged atom, the number of protons = number of electrons Atomic weight roughly = # protons + # neutrons Isotopes Same element, (ergo, same # protons) but different # neutrons Some isotopes are radioactive, in which the nucleus decays, giving off particles and energy These radioactive isotopes can be useful for scientific research Electrons H, C, N, O, P, S - important biological elements, you'll need to know for this class. Be able to recognize/draw the electron-shell diagrams given in the lecture notes! Valence electrons are those in the outermost shell. Chemical behavior of the atom is determined mostly by valence electrons , because they have the most energy and only the valence shell can be unfilled. Covalent Bonding When two atoms share a valence electron, a molecule is formed A single covalent bond is the sharing of a pair of electrons A ...

Vermont, CHEM 131

Excerpt: ... 8 Lecture 5, January 25, 2008 III. Why are Valence Electrons Important? A. Screening 1. Core electrons are closer to the nucleus, so more energy is required to separate them from the atom (since the nucleus has a positive charge, and energy is required to separate positive and negative charges). 2. Valence electrons don't experience as much positive charge, because the core electrons "block" some of it-they sit between the valence electrons and the nucleus, so they prevent the valence electrons from experiencing some of it. However, this blocking is not perfect, because the radial wavefunction (R2) does not go to zero until r (implying that the core electrons do not spend 100% of their time between the nucleus and the valence electrons ). B. Slater's rules 1. These are a set of rules used to calculate how much positive charge is experienced by each electron in an atom. It makes approximations about how effective the screening of each orbital is, based primarily on the quantum numbers n and l. 2. It uses a f ...

Washington, CHEM 152

Excerpt: ... r the unpaired electron in O and the corresponding one on H (at the ends of the dotted red line). We are going to let them pair up to form a polar covalent bond in which the two electrons are shared (not equally but close) by the two atoms. H O 8 valence electrons total H . H . Lone Pairs on Oxygen Note that each H has two electrons that it is involved with (obeys the duet rule), and the oxygen is surrounded by 8 electrons (obeys the octet rule) so all atoms are happy. The Octet Rule 1. Count the number of valence electrons for all the atoms in the molecule or ion (consider group number) -add n electrons for n- anions; -subtract n electrons for n+ cations. 2. Draw a skeleton structure and use a pair of electrons to form a bond between the central atom and each of the bound (terminal) atoms such as H, F, O etc. -central atom is usually the one that can form the most bonds -the number of possible bonds is usually suggested by group # 3. Arrange the remaining electrons to satisfy the octet rule (on ...

Berkeley, CHEM 3A

Excerpt: ... CHEM 3A Problem Set 1 (January, 24 2007) NOTE: No problem sets will be turned in for 3A lecture! Write out the ground-state electron configuration for the following atoms and identify how many valence electrons each has: a) Magnesium b) Calcium c) Bromine d) sulfur e) Boron f) Silicon Guess at what the most likely value for X is in the following molecules: a) AlClX b) NIX c) CClXF Lithium methoxide, LiOCH3, has both ionic and covelent bonds in it. Draw its Lewis structure and identify which bonds are ionic and which are covalent. ...

University of Texas, CH 53750

Excerpt: ... me other general things to remember about electronic shielding include: You should remember that the above discussion is only a rough approximation. Not all inner shell electrons will shield effectively. You must remember that, in terms of penetration to the nucleus, that s > p > d > f (this is because there is a greater probability of finding an s-electron at the nucleus than for a p-electron, etc). Atomic Radius We would like to use the P.T. to assign general trends. One trend we are interested in is the atomic radius, or the size of the atom. In general, atomic radius (A.R.) will increase as one goes down a group in the P.T., and it will decrease as you go across a period. The reasons for this: A.R. increases as you go down a group because the valence electrons will lie in higher principle quantum number shell n. Remember that n is a measure of both i) the energy of the electron in the atom, and ii) the average distance of the electron in the nucleus. Lithium would have a smaller A.R. than Cesium because L ...

IUP, CH 105

Excerpt: ... Chemistry 105 Lecture Lewis Structure & VSEPR Name_ 1. Summarize the following information concerning the atoms and electrons in the _ molecule: Elements Present Number of Valence Electrons Per Atom Number of Atoms Present Number of Valence Electrons On All Atoms _ _ _ _ _ _ _ _ Number of Electrons Added or Subtracted Due to Charge _ (-charge=add e, +charge=subtract e) Total Number of Valence Electrons _ 2. Which element is placed in the center of the Lewis diagram and why? 3. In the space below draw the element symbol for the center atom and the element symbols for the other atoms around it. 4. Draw a single bond from the center atom to each of the outer atoms in the sketch above. How many electrons did you use to create all the single bonds? _ How many of the "Total Number of Valence Electrons " are left when you subtract from it the number of electrons used for bonds? _ 5. Use some or all of the remaining electrons to ...

Laurentian, C 1000

Excerpt: ... Chemistry 1000 Lecture 16: Lewis structures Marc R. Roussel Covalent bonding Denition: a chemical bond in which electrons are shared between two atoms Contrast: Ionic bonding: material held together by electrostatic force (no sharing of electrons) Metallic bonding: electrons shared among all the metal atoms Typically formed between two non-metallic elements Lewis diagrams A convenient graphical accounting system for valence electrons in molecules A shared electron pair is represented by a line between the two atoms. Bond order: Number of shared electron pairs in a bond A nonbonding valence electron is represented by a dot. Dots are paired to represent their occupation of orbitals. The octet rule Typically, main-group elements in chemical compounds (except H) are surrounded by eight valence electrons (including any shared in covalent bonds). Guidelines for drawing Lewis diagrams 1. Count up the number of valence electrons in all the atoms. If the species is a cation, subtract the charge. If the s ...

LSU, APPL 003

Excerpt: ... rent atoms.) C. Isoelectronic Series a group of ions that contain the same number of valence electrons . E.g. Na+, Mg2+, Al3+, O2-, etc. In any isolectronic series, the anions will be larger than the neutral atom containing the same number of electrons as the ions in the series, and the cations will be smaller. The greater the negative charge, the larger the anion; the greater the positive charge, the smaller the cation. (See Sample Exercise 7.4 for practice with this.) Important note: Pay close attention to whether the problem asks you to arrange in order of increasing or decreasing size! Ionization Energy A. Definition of ionization energy The ionization energy is the energy required to remove an electron from the gaseous atom in the ground state. i.e. M + energy M+. The ionization energy increases from left to right when moving across the periodic table, V. VI. and decreases from top to bottom. These trends are due to the differences in the effective nuclear charge experienced by the electron being re ...

UWO, CHEM 020

Excerpt: ... that only electrons in the valence shell are involved in the formation of covalent bonds. Suppose we have two H atoms forming molecular hydrogen: H(g) + H(g) This is favourable because: o The two electrons in the bond are simultaneously attracted to both nuclei. o The pairing of electrons with opposite spin reduces the energy of the system We use electron-dot structures to show electrons and bonds: H2(g) H = Each bond contains two electrons (one electron pair). In order for bonds to form, orbital overlap must occur. In this case, the 1s orbital from each H atom overlaps. 13.3 Since each H atom has the configuration 1s1 (one electron in the valence shell), it can only form one bond. H H H Cl H O H What if there is more than one electron in the valence shell, for example, with oxygen in water above? Such atoms can form more than one bond, but the exact number of bonds formed is predicted by Lewis structures. o The number of valence electrons surrounding a nonmetal should be equal t ...