Chemical reactions involve the making and breaking of bonds. It is essential that we know what bonds are before we can understand any chemical reaction. To understand bonds, we will first describe several of their properties. The bond strength tells us how hard it is to break a bond. Bond lengths give us valuable structural information about the positions of the atomic nuclei. Bond dipoles inform us about the electron distribution around the two bonded atoms. From bond dipoles we may derive electronegativity data useful for predicting the bond dipoles of bonds that may have never been made before.
From these properties of bonds we will see that there are two fundamental types of bonds--covalent and ionic. Covalent bonding represents a situation of about equal sharing of the electrons between nuclei in the bond. Covalent bonds are formed between atoms of approximately equal electronegativity. Because each atom has near equal pull for the electrons in the bond, the electrons are not completely transferred from one atom to another. When the difference in electronegativity between the two atoms in a bond is large, the more electronegative atom can strip an electron off of the less electronegative one to form a negatively charged anion and a positively charged cation. The two ions are held together in an ionic bond because the oppositely charged ions attract each other as described by Coulomb's Law.
Ionic compounds, when in the solid state, can be described as ionic lattices whose shapes are dictated by the need to place oppositely charged ions close to each other and similarly charged ions as far apart as possible. Though there is some structural diversity in ionic compounds, covalent compounds present us with a world of structural possibilities. From simple linear molecules like H2 to complex chains of atoms like butane (CH3CH2CH2CH3), covalent molecules can take on many shapes. To help decide which shape a polyatomic molecule might prefer we will use Valence Shell Electron Pair Repulsion theory (VSEPR). VSEPR states that electrons like to stay as far away from one another as possible to provide the lowest energy (i.e. most stable) structure for any bonding arrangement. In this way, VSEPR is a powerful tool for predicting the geometries of covalent molecules.
The development of quantum mechanics in the 1920's and 1930's has revolutionized our understanding of the chemical bond. It has allowed chemists to advance from the simple picture that covalent and ionic bonding affords to a more complex model based on molecular orbital theory.
middle of paper ... ... The Web. 22 Feb. 2014. http://www.chemheritage.org/discover/online-resources/chemistry-in-history>.
Rasmussen, T.; Jensen, J. F.; Ostergaard, N.; Tanner, D.; Ziegler, T.; Norrby, P. Chem. Eur. J., 2002, 8, 177.
Covalent compounds are formed when two or more non-metals react together. The covalent compound is actually made of molecules, and the name given depends on the structure of these molecules. Prefixes, like di- for two, tri- for three, tetra- for four, and so forth, are frequently used. Thus, NO2 is nitrogen dioxide and N2O4 is dinitrogen
Throughout history, the curiosities of obtaining knowledge of facts that show the operation of general laws have resulted into the improvements of today’s society. Such curiosity of chemical reactions coiled in the minds of John Dalton in the atomic theory, Rosalind Franklin with genetics, and most importantly Antoine Lavoisier the father of modern chemistry. All who, worked extensively to acquire the understanding that fascinated them most, chemistry. Another chemist who sought after the same knowledge was Stanislao Cannizzaro. Studying organic chemistry Cannizzaro explained how certain elements lacked the hydrogen atom in what is know n as the Cannizzaro Reaction.
Chemistry dictates the structure of DNA. DNA is a polymer of monomers called nucleic acids. These are made of a nitrogenous base, a phosphate group and a sugar. It is the negative charge on the phosphate group that makes DNA an acid. There are 4 different bases: adenine, thymine, guanine and cytosine. In groups of three, these four bases can code for any protein coded for in an organism’s genome. Two strands of nucleic acids stack on top of each other in a double helix. The backbone of the nucleic acids consists of the interaction between phosphate groups and the hydroxide groups of nucleic acids. These are held together by covalent bonds called phosphodiester bonds. The helix itself is held together by hydrogen bonds. Although h...
Quantum Mechanics developed over many decades beginning as a set of controversial mathematical explanations of experiments that the math of classical mechanics could not explain. It began in the turn of the 20th century, a separate mathematical revolution in physics that describes the motion of things at high speeds. The origins of Quantum Mechanics cannot be credited to any one scientists. Multiple scientists contributed to a foundation of three revolutionary principles that gradually gained acceptance and experiment verification from 1900-1930 (Coolman). Quantum Mechanics is
This chemistry book report is focus on a book called “Napoleon's buttons: How 17 molecules changed history” by Penny Le Couteur and Jay Burreson. The publisher of this book is Tarcher Putnam, the book was published in Canada on 2003 with 17 chapters (hey the number match the title of the book!) and a total of 378 pages. The genre of this book is nonfiction. “Napoleon's Buttons” contain a fascinating story of seventeen groups of molecules that have greatly changed the course of history and continuing affect the world we live in today. It also reveal the astonishing chemical connection among some unrelated events, for example: Chemistry caused New Amsterdamers to be renamed New Yorkers and one little accident of detonating cotton apron in a minor housekeeping mishap lead to the development of modern explosives and the founding of the movie industry.
One of these classes is DNA binding agents. They form a covalent bond with the DNA or stick to it noncovalently very tightly. A covalent bond is a chemical bond. It involves sharing of electron pairs in the middle of atoms. These electron pairs are known as shared pairs or bonding
In particular, the forces exerted on a nucleus in a molecule by the other nuclei and by the electronic charge density may be rigorously calculated and interpreted in terms of classical electrostatics. Thus, given the molecular charge distribution, the stability of a chemical bond may be discussed in terms of the electrostatic requirement of achieving a zero force on the nuclei in the molecule. A chemical bond is the result of the accumulation of negative charge dens...
23. S. Alwarappan, S. Boyapalle, A. Kumar, C.-Z. Li and S. Mohapatra, J. Phys. Chem. C, 2012, 116, 6556–6559
Stemming from the first years of the 20th century, quantum mechanics has had a monumental influence on modern science. First explored by Max Planck in the 1900s, Einstein modified and applied much of the research in this field. This begs the question, “how did Einstein contribute to the development and research of quantum mechanics?” Before studying how Einstein’s research contributed to the development of quantum mechanics, it is important to examine the origins of the science itself. Einstein took much of Planck’s experimental “quantum theory” research and applied it in usable ways to existing science. He also greatly contributed to the establishment of the base for quantum mechanics research today. Along with establishing base research in the field, Einstein’s discoveries have been modified and updated to apply to our more advanced understanding of this science today. Einstein greatly contributed to the foundation of quantum mechanics through his research, and his theories and discoveries remain relevant to science even today.
The alkaline earth metals form many compounds that are commonly found in nature. The ionic bonds these metals form with the halogen family are called metal halides. These bonds are not solely ionic; they can be a covalent bond in the case of beryllium. Additionally, all of the alkaline metals, except beryllium, can react with water to form alkaline hydroxides, compounds containing the hydroxide ion. However,...
Bond making is an exothermic process. However if a certain bond in a molecule is broken and then reformed, then the same amount of energy must be involved. During a chemical reaction bonds in the reactants are broken and new bonds are made in the products.
...ubstances that have different properties than the properties of the reactants (blue book). Most atoms form bonds with valence electrons only, which means the number of valence electrons determines if an atom will form a bond (eight electrons are usually unreactive, while fewer than eight tend to bond more often). Atoms bond to fill their outermost energy level. They would either lose share or gain an electron. In baking soda and vinegar, you may be wondering what bonding has to do with a chemical reaction. Well, in order for a chemical reaction to take place a bond must be broken. This happens because molecules are always moving which means if they bump with enough energy, the bond will break. The atoms then rearrange and new bonds form to make new substances (blue book). So behind the aesthetic view of the “white fizz,” there is always a scientific explanation.
Bonds have a number of characteristics that differentiate one issue from another. We are going to define and describe a number of characteristics in detail below.