Dots Lewis Structures

LANL2DZbasis.setl01,133 adding diffuse functions 134 Lewis dot structure 131 Link 0 commands 295 Link 0 section xl Linkl command 295 LOGlN.COM file xxxiii LUMO 19,112... 

Covalent bonds form between atoms with similar electronegativities. In these reactions, electrons do not migrate from one atom to another as they do in ionic bonds they are shared by the atoms in the molecule. A good way to visualize this was proposed by Gilbert Lewis, a chemist at the University of California, Berkeley. His representations of molecular bonds are called Lewis dot structures. These structures use dots to denote the valence electrons of an element or molecule. 

The Lewis dot structure and the molecular formula for the simplest molecule, H2, are... 

Lewis was an American scientist bom in 1875 in Massachusetts, USA. He started his academic career in 1912 and proposed the theory of electron sharing in 1916 which as we have seen is of great importance to chemists. Because of this theory, electron dot representation is also named Lewis dot structure . 

These are extensions of Lewis dot structures, where bonding electrons associated with each bond are shown as dots. In our simple structures, bonding is associated with eight electrons in the valence shell of the atom, unless it is hydrogen, when two electrons are required for bonding. Whilst we have almost completely abandoned putting in electron dots for bonds, we still routinely show some pairs of electrons not involved in bonding (lone pairs) because these help in our mechanistic rationalizations of chemical reactions. 

The Lewis dot structure for BF3 shows the central boron atom being surrounded by only six electrons, which violates the octet rule. This illustrates that the octet rule, while providing general guidelines, has exceptions. 

Geometry Number of lone pairs Number of bonding pairs Lewis dot structure Shape ... 

All Br0nsted-Lowry acids are Lewis acids, but in practice, the term Lewis acid is generally reserved for Lewis acids that don t also fit the Bronsted-Lowry definition. The best way to spot a Lewis acid-base pair is to draw a Lewis dot structure of the reacting substances, noting the presence of lone pairs of electrons. (We introduce Lewis structures in Chapter 5.) For example, consider the reaction between ammonia (NH3) and boron trifluoride (BFj) ... 

At first glance, neither the reactants nor the product appears to be an acid or base, but the reactants are revealed as a Lewis acid-base pair when drawn as Lewis dot structures as in Figure 16-1. Ammonia donates its lone pair of electrons to the bond with boron trifluoride, making ammonia the Lewis base and boron trifluoride the Lewis acid. 

Sometimes you can identify the Lewis acid and base in a compound without drawing the Lewis dot structure. You can do this by identifying reactants that are electron rich (bases) or electron poor (acids). A metal cation, for example, is electron poor and tends to act as a Lewis acid in a reaction, accepting a pair of electrons. 

Identify the Lewis acid and base in each reaction. Draw Lewis dot structures for the first two, and determine the Lewis acid and base in the third reaction without a dot structure. 

To identify Lewis acids and bases, track the movement of electron pairs. Draw a Lewis dot structure to locate the atom with a lone pair available to donate. This is the Lewis base. 

Structural formulae are representations of molecules on paper. The MCAT may use any or all of the various formulae so you should be familiar with all of them. The most basic form of structural formula is tire Lewis dot structure. 

There are three rules for forming Lewis dot structures. 

Lewis dot structures/diagrams are a method for keeping track of each atom s valence electrons in a molecule. Drawing Lewis structures is a three-step process ... 

To select the most probable Lewis dot structure for a compound or molecule that follows the octet rule, review the structures and compare to the method for constructing Lewis dot structures from the previous page. 

Which of the following is a proper Lewis dot structure of CHCIO ... 

Although most chemistry students know about Lewis dot structures, few of them know much about the man who invented those dotty structures. Fewer still can identify his most important contribution to valence bond theory. 

The Lewis dot structures for hydrogen, oxygen, and water are shown below. 

Lewis dot structures These structures use dots to represent the valance electrons of an atom either standing alone or in a molecule. 

Resonance Structures Molecules with two or more valid Lewis dot structures are said to be resonant. The actual structure is neither of the alternatives but rather a lower-energy molecule with delocalized valence electrons. Benzene with its alternating double and single bonds is an example of a resonant structure. Benzene actually has no single or double bonds. Its real structure lies somewhere between the two possibilities. 

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