Documents about Valence Electrons

  • 2 Pages

    lecture 2

    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 ...

  • 2 Pages

    Lecture_2

    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 ...

  • 3 Pages

    Chem155Dec01chalkboard

    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 ...

  • 3 Pages

    Ch400Ch6LN1

    American River, CHEM 400-401

    Excerpt: ... Chem 400 Chapter 6 Lecture Notes Part 1 Ions and their Electron Configurations, and Radii You already learned how to write the electron configurations and the Noble Gas electron configurations for ions. Just remember that it is the valence electrons which get removed or added to first! So you always add to or remove from the highest energy level, or n value. Write the electron configurations and Noble Gas electron configurations for Cl-, Ca2+, and Mn2+. Can you see why metals tend to lose electrons and why nonmetals tend to gain electrons? What kind of electron configuration are they trying to obtain? And how many valence s and p electrons is this? Ionic Radii When a neutral atom of Li loses its valence 2s1 electron, what happens to the size of the Li+ cation? Is it smaller or larger than Li? Why is it smaller (think of Zeff, the effective nuclear charge and what shell the electron is lost from)? Likewise, if an oxygen atom gains 2 electrons to become O2-, what about the size of the ...

  • 28 Pages

    notes_lecture_notes_wk9_03_07

    Washington, CHEM 152

    Excerpt: ... he basic rule, then for elements other than H (which is happy with the [He] configuration or the so-called duet rule), most of the n=2 and n=3 atoms prefer to be surrounded by 4 electron pairs, the so-called octet rule. Atoms with configs of ns2 and ns2n'p1 are a problem. Applying the Octet Rule The Octet Rule rules. Rather than trying to say a lot more about it, we are probably best served by doing a bunch of examples. Let's try the water molecule. H O 8 valence electrons total H . The Octet Rule in Water Consider 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 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. H We prefer to draw the electr ...

  • 25 Pages

    Review Session 1

    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 ...

  • 46 Pages

    chapter1

    Mines, CHGN 222

    Excerpt: ... anic salt ammonium cyanate into organic substance "urea" 5 Organic chemistry is study of carbon compounds. Why is it so special? - 90% of more than 30 million chemical compounds contain carbon. - Examination of carbon in periodic chart answers some of these questions. - Formation of C-C bonds unique. - Carbon is group 4A element, it can share 4 valence electrons and form 4 covalent bonds. 6 Why this chapter? Review ideas from general chemistry: atoms, bonds, molecular geometry 7 1.1 Atomic Structure Structure of an atom Positively charged nucleus (very dense, protons and neutrons) and small (10-15 m) Negatively charged electrons are in a cloud (10-10 m) around nucleus Diameter is about 2 10-10 m (200 picometers (pm) [the unit angstrom () is 10-10 m = 100 pm] 8 Atomic Number and Atomic Mass The atomic number (Z) is the number of protons in the atom's nucleus The mass number (A) is the number of protons plus neutrons All the atoms of a given element ...

  • 3 Pages

    lecture5

    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 ...

  • 3 Pages

    Ch400Ch6LN3

    American River, CHEM 400-401

    Excerpt: ... to decompose the salt into the metal and chlorine gas. K, Rb, and Cs are produced at very high temperatures via single displacement rxns. The Alkaline Earth Metals The alkaline earth metals of Group 2 all have 2 valence electrons with the configuration ns2. Although they have low IE1 values, their IE2 values are much higher. However the Lattice energy for their ionic compounds is very high as their +2 cations are small and have a high + charge. So they lose their 2 valence electrons easily to form +2 cations. So they form ionic compounds readily and they are strong reducing agents. They are the second most reactive metal Group, and reactivity increases going down the Group. So actually Ca, Ba and Sr are more reactive than Na in most circumstances. Like the Alkali Metals they are strong metals with a silvery appearance, but they are generally harder than the Alkali Metals (but still softer than most metals). They also have low melting points and densities, but they are higher than the Alka ...

  • 6 Pages

    notes_Lecture_24(6spp)

    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 ...

  • 16 Pages

    notes_Lecture_24(2spp)

    Washington, CHEM 152

    Excerpt: ... er elements in the second row would prefer the [Ne] configuration and with the exception of B and Be (which have too few electrons) most of the others strive to achieve the [Ne] configuration. The Complications for n 3 When you get into the n=3 shell things can get a bit more complicated because now in contrast to B and Be where you have too few electrons available to get a complete shell, now you may have too many. However, we will deal with that by stuffing any extras into the 3d orbitals as we will see later. The basic rule, then for elements other than H (which is happy with the [He] configuration or the so-called duet rule), most of the n=2 and n=3 atoms prefer to be surrounded by 4 electron pairs, the so-called octet rule. Atoms with configs of ns1, ns2 and ns2n'p1 are special. 3 Applying the Octet Rule The Octet Rule rules. Rather than trying to say a lot more about it, we are probably best served by doing a bunch of examples. Let's try the water molecule. H O 8 valence electrons total ...

  • 2 Pages

    PS1

    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. ...

  • 4 Pages

    Lecture 6 NotesThe Periodic Table and Atomic Co...

    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 ...

  • 8 Pages

    16

    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 ...

  • 18 Pages

    me3344_call_ch2_landscape

    TAMU Kingsville, MEEN 3344

    Excerpt: ... be determined by the way that atoms interact with each other. However, we must understand atoms before we can understand how they interact. MEEN 3344 MATERIALS SCIENCE Atomic model of Zinc: The outer shell of electrons are the valence electrons MEEN 3344 MATERIALS SCIENCE Bohr Model MEEN 3344 MATERIALS SCIENCE Electron configurations and orbits: p, d, and f subshells are directional. Useful to know for later MEEN 3344 MATERIALS SCIENCE This periodic table is good for basic stuff Which are the most electro-negative elements (take electrons)?right side. Electropositive give up electrons MEEN 3344 MATERIALS SCIENCE Which are the gases? Liquids? Metals? What is the atomic number? Atomic mass? Valence electrons ? Which want to keep their electrons? Loose them? MEEN 3344 MATERIALS SCIENCE Energy-related or dependent processes Thermodynamics study of relationships between thermal properties and system variables Kinetics determines how fast chemical / other re ...

  • 16 Pages

    Bonding

    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 ...