ELECTRONEGATIVITY

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.The Pauling scale is the most commonly used. Fluorine (the most electronegative element) is assigned a value of 4.0, and values range down to caesium and francium which are the least electronegative at 0.7.

What happens if two atoms of equal electronegativity bond together?

Consider a bond between two atoms, A and B. Each atom may be forming other bonds as well as the one shown - but these are irrelevant to the argument. If the atoms are equally electronegative, both have the same tendency to attract the bonding pair of electrons, and so it will be found on average half way between the two atoms. To get a bond like this, A and B would usually have to be the same atom. You will find this sort of bond in, for example, H₂ or Cl₂ molecules. This sort of bond could be thought of as being a "pure" covalent bond - where the electrons are shared evenly between the two atoms.

What happens if B is slightly more electronegative than A?

B will attract the electron pair rather more than A does. That means that the B end of the bond has more than its fair share of electron density and so becomes slightly negative. At the same time, the A end (rather short of electrons) becomes slightly positive. In the diagram, "" (read as "delta") means "slightly" - so + means "slightly positive".

Defining polar bonds

This is described as a polar bond. A polar bond is a covalent bond in which there is a separation of charge between one end and the other - in other words in which one end is slightly positive and the other slightly negative. Examples include most covalent bonds. The hydrogen-chlorine bond in HCl or the hydrogen-oxygen bonds in water are typical.

What happens if B is a lot more electronegative than A?

In this case, the electron pair is dragged right over to B's end of the bond. To all intents and purposes, A has lost control of its electron, and B has complete control over both electrons. Ions have been formed. In this case, the electron pair is dragged right over to B's end of the bond. To all intents and purposes, A has lost control of its electron, and B has complete control over both electrons. Ions have been formed.

Lithium iodide, on the other hand, would be described as being "ionic with some covalent character". In this case, the pair of electrons hasn't moved entirely over to the iodine end of the bond. Lithium iodide, for example, dissolves in organic solvents like ethanol - not something which ionic substances normally do.

CHEMICAL BOND

Ionic bond
Ionic bonds arise from elements with low electronegativity(almost empty outer shells) reacting with elements with high electronegativity (mostly full outer shells). In this case there is a complete transfer of electrons.

A well known example is table salt, sodium chloride. Sodium gives up its one outer shell electron completely to chlorine which needs only one electron to fill its shell. Thus, the attraction between these atoms is much like static electricity since opposite charges attract.

Covalent bond

Covalent bonds involve a complete sharing of electrons and occurrs most commonly between atoms that have partially filled outer shells or energy levels. Thus if the atoms are similar in negativity then the electrons will be shared. Carbon forms covalent bonds. The electrons are in hybrid orbitals formed by the atoms involved as in this example: ethane. Diamond is strong because it involves a vast network of covalent bonds between the carbon atoms in the diamond.

Polar covalent bond

These bonds are in between covalent and ionic bonds in that the atoms share electrons but the electrons spend more of their time around on atom versus the others in the compound. This type of bond occurs when the atoms involved differ greatly in electronegativity. The most familiar example is water. Oxygen is much more electronegative than hydrogen, and so the electrons involved in bonding the water molecule spend more time there. The fact that water is a polar covalently bonded moleccule has a number of implications for molecules that are disolved in water. In particular, molecules with polar covalent bods can break apart when they encounter water molecules. They are broken apart because of the electrical attraction between the dissimilar charges of the molecules. Also, since ionically bonded molecules involve ions with opposite charges, water with its polar covalent bonds can separate ions from each other and then surround the ions which prevents them from recombining. The properties of water all relate to this polar covalent bonding. Indeed the sorts of so called hydrophilic and hydrophobic interactions water has with varios organic compounds depend on the nature of the polar covalent bond in water.

Hydrogen bond

The fact that the oxygen end of a water molecule is negatively charged and the hydrogen end positively charged means that the hydrogens of one water molecule attract the oxygen of its neighbor and vice versa. This is because unlike charges attract. This largely electrostatic attraction is called a hydrogen bond and is important in determining many important properties of water that make it such an important liquid for living things. Water can also form this type of bond with other polar molecules or ions such as hydrogen or sodium ions. Further, hydrogen bonds can occurr within and between other molecules. For instance, the two strands of a DNA molecule are held together by hydrogen bonds. Hygrogen bonding between water molecules and the amino acids of proteins are involved in maintaining the protein's proper shape.

from http://staff.jccc.net/pdecell/chemistry/bonds.html

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http://library.thinkquest.org/04oct/00206/text_pti_blood_analysis.htm#pti_thetest
http://library.thinkquest.org/04oct/00206/text_tte_bloodstain_analysis.htm

WHAT IS INORGANIC CHEMISTRY

Inorganic is a branch of chemistry that deals with the properties and behavior of inorganic compounds. Inorganic compounds are generally those that are not biological, and characterized by not containing any hydrogen and carbon bonds. It is almost easier to discuss inorganic chemistry in terms of what it is not: organic chemistry. Organic chemistry is the study of any chemical reaction that involves carbon, which is the element that all life is based on. It if often said that inorganic chemistry is any type of chemistry that is not organic chemistry.

The term organic has traditionally referred only to animal or plant matter. Therefore, there is a common misconception that organic chemistry always refers to life processes, or that inorganic chemistry applies to everything that does not. This assumption is inaccurate. Many chemical processes veer away from this line of thinking. There are many chemical life processes that depend on inorganic chemical processes.

There are exceptions to every rule. Although carbon is the main common element in organic chemistry, inorganic chemical compounds can contain carbon, too. For example, carbon monoxide and carbon dioxide both contain carbon, but are inorganic compounds. Carbon dioxide, in particular, is also very important to chemical processes necessary for life, especially plant life. The truth is that the lines between inorganic and organic chemistry are often blurred.

There are many branches of inorganic chemistry available for specialization. Geochemistry is the study of the chemicals of the Earth and other planets. It covers the chemical compositions of rocks and soil. Within the field of geochemistry, there are several subfields. These subfields include isotope geochemistry, cosmochemistry and biogeochemistry.

Another type of inorganic chemistry is physical chemistry, which relates to the concept of physics in chemical systems. This field is also sometimes called physicochemistry. It uses the principles of thermodynamics, quantum chemistry and kinetics as its basis.

On the other hand, bioinorganic chemistry is the study of compounds containing metal-carbon bonds within biological systems. This is a particularly interesting branch of inorganic chemistry because it also incorporates aspects of organic chemistry into it. Bioinorganic chemistry focuses on the pretense of metal ions in biochemical processes.

Inorganic chemistry lends itself to many different industries, including education, environmental science, and government agencies. A scientist who focuses on inorganic chemistry might create or improves formulas for household cleansers. He may also work in chemical research, coming up with new ways to manipulate the properties of metallic elements into useful functions.

FROM http://www.wisegeek.com/what-is-inorganic-chemistry.htm

WHAT IS ANALYTICAL CHEMISTRY

Analytical chemistry is the study of matter in order to reveal its composition, structure, and extent. Because these understandings are fundamental in just about every chemical inquiry, analyticalanalyticalanalytical chemistrychemistrychemistry is used to obtain information, insure safety, and solve problems in many different chemical areas, and is essential in both theoretical and applied chemistrychemistrychemistry.
Early analytical chemistry was mainly focused on identifying elements and compounds and discovering their attributes. Discovery gave way to systematic analysis, which took a giant step forward with the invention in the 1850’s of the first instrument for chemical analysis—flame emissive spectrometry—by Robert Bunsen, a German chemist who is better known for his invention of the Bunsen burner, and his colleague Gustav Kirchoff, a German physicist who is known for his 1862 coining the name "black body" radiation for an object that absorbs all of the electromagnetic radiation that reaches it.

Other separation processes were developed, including various kinds of chromatography such as paper, gas, and liquid; electrophoresis; crystallography; microfiltration; and other spectrometers, including atomic absorption spectrometers, infrared spectrometers, and mass spectrometers. Other changes in the field took place, for example, the extension of analytical chemistry allowing for bioanalytical chemistry to develop. Bioanalytics includes areas such as genomics, lipidomics, metabolomics, peptidomics, proteomics, and transcriptomics.

The traditional subdivisions of analytical chemistry followed the same paradigm as in statistical analysis: a qualitative approach that was focused on determining what elements and/or compounds were present and a quantitative approach that aimed to establish the precise amount of an element or compound in a given sample. Either, or both, of these approaches to analytical chemistry can be applied to materials in a variety of fields, including the food and beverage industry, the pharmaceutical industry, synthetic materials such as polymers, and natural materials, such as minerals and water samples. As the field grew, analytical chemistry also broadened to embrace applications of its techniques in forensics, and medicine.

Analytical chemists today use a wide variety of techniques in their analyses, including some involving robotics, digital microscopes, a Fourier transform infrared spectophotometers, chip-based technology, and chemometrics, for example. They also use techniques in which technologies are combined, resulting in approaches referred to as hyphenated or hybrid techniques, characteristically referred to by initials. Examples include CE-MS—capillary electrophoresis-mass spectrometry; GC-MS—gas chromatography-mass spectrometry; CE-UV—capillary electrophoresis-ultraviolet; and HPLC/ESI-MS—high performance liquid chromatography/electrospray ionization-mass spectrometry.

FROM http://www.wisegeek.com/what-is-analytical-chemistry.htm

WHAT IS PHYSICAL HEMISTRY

Physical chemistry is an empirical science. A science is a set of constructs, called theories, that link fragments of experience into a consistent description of natural phenomena. The adjective “empirical” refers to the common experiences from which the theories grow, that is, to experiments. Simple working hypotheses are guessed by imaginative insight or intuition or luck, usually from a study of experiments. This repetitive interplay in time leads to the formulation of theories that correlate the accumulated experimental information and that can predict new phenomena with accuracy. (Berry, Rice and Ross)

Traditionally, there are three principal areas of physical chemistry: thermodynamics (which concerns the energetics of chemical reactions), quantum chemistry (which concerns the structures of molecules), and chemical kinetics (which concerns the rates of chemical reactions). (McQuarrie and Simon)

Physical chemistry is the branch of chemistry that establishes and develops the principles of the subject. Its concepts are used to explain and interpret observations on the physical and chemical properties of matter. Physical chemistry is also essential for developing and interpreting the modern techniques used to determine the structure and properties of matter, such as new synthetic materials and biological membranes. (Atkins)

Physical chemistry is the study of the physical basis of phenomena related to the chemical composition and structure of substances. It has been pursued from two levels, the macroscopic and the molecular. Knowledge in physical chemistry available today provides a rich, comprehensive view of the world of atoms and molecules that connects their nature with macroscopic properties and phenomena of materials and substances. A starting point for an introduction to physical chemistry is the concept of energy levels in atoms and molecules, distributions among these energy levels, and something familiar, temperature. (Dykstra)

Physical chemistry is the study of the underlying physical principles that govern the properties and behavior of chemical systems. (Levine)

Physical chemistry, like a table with four legs, is built upon four major theoretical areas: thermodynamics, kinetics (or, more generally, transport processes), quantum mechanics, and statistical mechanics This is not all of physical chemistry, no more than a table is only legs. Physical chemistry is a widely diverse subject that cannot be summarized adequately in any brief definition, and there are important parts of physical chemistry that do not fit neatly into this quadrivium. (Noggle)

Physical Chemistry is a fascinating field of study. It can reasonably be claimed that many parts of physics and all parts of chemistry are included within physical chemistry and its applications. Furthermore, it is the course in which most chemistry students first have the opportunity to synthesize what they have learned in mathematics, physics, and chemistry courses into a coherent pattern of knowledge. (Mortimer)

We see it as the quantitative interpretation of the macroscopic world in terms of the atomic-molecular world. To achieve this interpretation, we must organize our observations of macroscopic phenomena, as we do in thermodynamics and in parts of kinetics. We must advance our studies of atoms and molecules, as we do, for example, in quantum mechanics and spectroscopy. Then we must bring these studies together. This coming together is woven into much of the fabric of a modern physical chemistry course. (Barrow)

Physical chemistry is the application of the methods of physics to chemical problems. It includes the qualitative and quantitative study, both experimental and theoretical, of the general principles determining the behavior of matter, particularly the transformation of one substance into another. Although the physical chemist uses many of the methods of the physicist, he applies them to chemical structures and chemical processes. Physical chemistry is not so much concerned with the description of chemical substances and their reactions-this is the concern of organic and inorganic chemistry-as with theoretical principles and with quantitative problems. (Laidler & Meiser)

It is said that there are more than four million chemical compounds. If you add to this list composite materials like alloys and minerals and intermediate species like the free radicals, it becomes truly staggering. The list of properties that interest scientists, even though modest compared to the above list, is also vast. The fascinating aspect of science is that only a few principles are needed to understand the behavior of the huge number of substances and their properties. Physical chemistry is the study of these principles. (Vemulapalli)

FROM http://www.depauw.edu/acad/chemistry/bgourley/Reseach/what_is_physical_chemistry.htm

WHAT IS BIOCHEMISTRY

Biochemistry is the application of chemistry to the study of biological processes at the cellular and molecular level. It emerged as a distinct discipline around the beginning of the 20th century when scientists combined chemistry, physiology and biology to investigate the chemistry of living systems.
The study of life in its chemical processes

Biochemistry is both a life science and a chemical science - it explores the chemistry of living organisms and the molecular basis for the changes occurring in living cells. It uses the methods of chemistry,

"Biochemistry has become the foundation for understanding all biological processes. It has provided explanations for the causes of many diseases in humans, animals and plants."

physics, molecular biology and immunology to study the structure and behaviour of the complex molecules found in biological material and the ways these molecules interact to form cells, tissues and whole organisms.

Biochemists are interested, for example, in mechanisms of brain function, cellular multiplication and differentiation, communication within and between cells and organs, and the chemical bases of inheritance and disease. The biochemist seeks to determine how specific molecules such as proteins, nucleic acids, lipids, vitamins and hormones function in such processes. Particular emphasis is placed on regulation of chemical reactions in living cells.

FROM http://www.mcgill.ca/biochemistry/information/biochemistry/

WHAT IS ORGANIC CHEMISTRY

Organic chemistry is a branch of chemistry that involves the study of organic carbon compounds. It encompasses the structures, composition, and synthesis of carbon-containing compounds. In understanding organic chemistry, it is important to note that all organic molecules consist not only of carbon, but also contain hydrogen. While it is true that organic compounds can contain other elements, the bond between carbon and hydrogen is what makes a compound organic.

Originally, organic chemistry was defined as the study of compounds created by living organisms. However, its definition has been enlarged to include artificially synthesized substances as well. Before 1828, all organic compounds were obtained from living organisms. Scientists didn’t believe it was possible to synthesize organic compounds from inorganic compounds. Many attempted to do so and failed. However, in 1828, urea was synthesized from inorganic substances, paving the way for a new definition of organic chemistry.

There are more than six million known organic compounds. In addition to being plentiful, organic compounds are also unique. This is because carbon atoms have the ability to form strong bonds with many different elements. Carbon atoms are also able to bond covalently to other carbon atoms, while simultaneously forming strong bonds with other nonmetal atoms. When carbon atoms bond together, they can form chains consisting of thousands of atoms. They can also form rings, spheres, and tubes.

Many individuals consider organic chemistry to be very complicated and unrelated to daily life. Though the study of organic chemistry may be complex, it is very important to everyday life. In fact, organic compounds are a part of everything, from the foods we eat to the products we use. They are important in the creation of clothing, plastics, fibers, medications, insecticides, petroleum-derived chemicals, and a long list of products used to support life and to make it more convenient.

The study of organic chemistry is important, not only to those who are interested in science-related careers, but to every individual alive today and to those who will be born in the future. Organic chemistry is key in developing new products and improving those on which we’ve become dependent. Each year, organic chemists make discoveries that are helpful in improving medicines, aiding agricultural growth, understanding the human body, and performing countless tasks important to the average person.

FROM http://www.wisegeek.com/what-is-organic-chemistry.htm

Why Study Chemistry?

Because understanding chemistry helps you to understand the world around you. Cooking is chemistry. Everything you can touch or taste or smell is a chemical. When you study chemistry, you come to understand a bit about how things work. Chemistry isn't secret knowledge, useless to anyone but a scientist. It's the explanation for everyday things, like why laundry detergent works better in hot water or how baking soda works or why not all pain relievers work equally well on a headache. If you know some chemistry, you can make educated choices about everyday products that you use.

FROM http://chemistry.about.com/od/chemistry101/a/basics.htm

CHEMISTRY

Chemistry (from Arabic: كيمياء Latinized: chem (kēme), meaning "value")is the science of matter and the changes it undergoes. The science of matter is also addressed by physics, but while physics takes a more general and fundamental approach, chemistry is more specialized, being concerned with the composition, behavior, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.It is a physical science for studies of various atoms, molecules, crystals and other aggregates of matter whether in isolation or combination, which incorporates the concepts of energy and entropy in relation to the spontaneity of chemical processes.

Disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study. These include inorganic chemistry, the study of inorganic matter; organic chemistry, the study of organic matter; biochemistry, the study of substances found in biological organisms; physical chemistry, the energy related studies of chemical systems at macro, molecular and submolecular scales; analytical chemistry, the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e.g. neurochemistry the chemical study of the nervous system