Atomic Spectroscopy

Atomic spectroscopy is the study of the electromagnetic radiation absorbed and emitted by atoms. Since unique elements have characteristic (signature) spectras, atomic spectroscopy, specifically the electromagnetic spectrum or mass spectrum, is applied for determination of elemental compositions. It can be divided by atomization source or by the type of spectroscopy used. In the latter case, the main division is between optical and mass spectrometry. Mass spectrometry generally gives significantly better analytical performance, but is also significantly more complex. This complexity translates into higher purchase costs, higher operational costs, more operator training, and a greater number of components that can potentially fail. Because optical spectroscopy is often less expensive and has performance adequate for many tasks, it is far more commonAtomic absorption spectrometers are one of the most commonly sold and used analytical device.

Optical spectroscopy

Electrons exist in energy levels (i.e. atomic orbitals) within an atom. Atomic orbitals are quantized, meaning they exist as defined values instead of being continuous (see: atomic orbitals). Electrons may move between orbitals, but in doing so they must absorb or emit energy equal to the energy difference between their atom's specific quantized orbital energy levels. In optical spectroscopy, energy absorbed to move an electron to a higher energy level (higher orbital) and/or the energy emitted as the electron moves to a lower energy level is absorbed or emitted in the form of photons (light particles). Because each element has a unique number of electrons, an atom will absorb/release energy in a pattern unique to its elemental identity (e.g. Ca, Na, etc.) and thus will absorb/emit photons in a correspondingly unique pattern. The type of atoms present in a sample, or the amount of atoms present in a sample can be deduced from measuring these changes in light wavelength and light intensity.

Optical spectroscopy is further divided into Atomic absorption spectroscopy, Atomic Emission Spectroscopy, and Fluorescence Spectroscopy.

In atomic absorption spectroscopy, light of a predetermined wavelength is passed through a collection of atoms. If the wavelength of the source light has energy corresponding to the energy difference between two energy levels in the atoms, a portion of the light will be absorbed. The difference between the intensity of the light emitted from the source (e.g., lamp) and the light collected by the detector yields an absorbance value. This absorbance value can then be used to determine the concentration of a given element (or atoms) within the sample. The relationship between the concentration of atoms, the distance the light travels through the collection of atoms, and the portion of the light absorbed is given by the Beer–Lambert law.

The energy stored in the atoms can be released in a variety of ways. When it is released as light, this is known as fluorescence. Atomic fluorescence spectroscopy measures this emitted light. Fluorescence is generally measured at a 90° angle from the excitation source to minimize collection of scattered light from the excitation source, often such a rotation is provided by a Pellin–Broca prism on a turntable which will also separate the light into its spectrum for closer analysis. The wavelength once again tells you the identity of the atoms. For low absorbances (and therefore low concentrations) the intensity of the fluoresced light is directly proportional to the concentration of atoms. Atomic fluorescence is generally more sensitive (i.e. it can detect lower concentrations) than atomic absorption.

Strictly speaking, any measurement of the emitted light is emission spectroscopy, but atomic emission spectroscopy usually does not include fluorescence and rather refers to emission after excitation by thermal means. The intensity of the emitted light is directly proportional to the concentration of atoms.

Mass spectrometry

Atomic mass spectrometry is similar to other types of mass spectrometry in that it consists of an ion source, a mass analyzer, and a detector. Atoms' identities are determined by their mass-to-charge ratio (via the mass analyzer) and their concentrations are determined by the number of ions detected. Although considerable research has gone into customizing mass spectrometers for atomic ion sources, it is the ion source that differs most from other forms of mass spectrometry. These ion sources must also atomize samples, or an atomization step must take place before ionization. Atomic ion sources are generally modifications of atomic optical spectroscopy atom sources.

Ion and atom sources

Sources can be adapted in many ways, but the lists below give the general uses of a number of sources. Of these, flames are the most common due to their low cost and their simplicity. Although significantly less common, inductively-coupled plasmas, especially when used with mass spectrometers, are recognized for their outstanding analytical performance and their versatility.

For all atomic spectroscopy, a sample must be vaporized and atomized. For atomic mass spectrometry, a sample must also be ionized. Vaporization, atomization, and ionization are often, but not always, accomplished with a single source. Alternatively, one source may be used to vaporize a sample while another is used to atomize (and possibly ionize). An example of this is laser ablation inductively-coupled plasma atomic emission spectrometry, where a laser is used to vaporize a solid sample and an inductively-coupled plasma is used to atomize the vapor.

With the exception of flames and graphite furnaces, which are most commonly used for atomic absorption spectroscopy, most sources are used for atomic emission spectroscopy.

Liquid-sampling sources include flames and sparks (atom source), inductively-coupled plasma (atom and ion source), graphite furnace (atom source), microwave plasma (atom and ion source), and direct-current plasma (atom and ion source). Solid-sampling sources include lasers (atom and vapor source), glow discharge (atom and ion source), arc (atom and ion source), spark (atom and ion source), and graphite furnace (atom and vapor source). Gas-sampling sources include flame (atom source), inductively-coupled plasma (atom and ion source), microwave plasma (atom and ion source), direct-current plasma (atom and ion source), and glow discharge (atom and ion source).

Real Defination Of Chemistry

Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry is chiefly concerned with atoms and molecules and their interactions and transformations, for example, the properties of the chemical bonds formed between atoms to create chemical compounds. As such, chemistry studies the involvement of electrons and various forms of energy in photochemical reactions, oxidation-reduction reactions, changes in phases of matter, and separation of mixtures. Preparation and properties of complex substances, such as alloys, polymers, biological molecules, and pharmaceutical agents are considered in specialized fields of chemistry.

Chemistry is sometimes called the central science because it bridges other natural sciences like physics, geology and biology.Chemistry is a branch of physical science but distinct from physics..

The etymology of the word chemistry has been much disputed. The history of chemistry can be traced to certain practices, known as alchemy, which had been practiced for several millennia in various parts of the world.

Comparison of Chemistry and Physics

Chemistry and physics are branches of science that both study matter. The difference between the two lies in their scope and approach. Chemists and physicists are trained differently, and they have different professional roles, even when working in a team. The division between chemistry and physics becomes diffuse at the interface of the two branches, notably in fields such as physical chemistry,chemical physics, quantum mechanics, nuclear physics/chemistry, material science, spectroscopy, solid state physics, crystallography, and nanotechnology.

Scope

Physics and chemistry may overlap when the system under study involves matter commonly encountered on earth, composed of electrons and nuclei made of protons and neutrons. On the other hand, chemistry is not concerned with other forms of matter such as quarks, mu and tau leptons and dark matter, which do not participate in the transformation of one kind of substance into another, and which we do not observe under typical terrestrial conditions.

Although fundamental laws that govern the behavior of matter apply both in chemistry and physics, the disciplines of physics and chemistry are distinct. Physics is concerned with nature from a very large scale (the entire universe) down to a very small scale (subatomic particles). All natural (or man-made) phenomena that are measurable follow some behavior that is in accordance with the most basic principles studied in physics.

Physics is involved with the fundamental principles of physical phenomena and the basic forces of nature, and also gives insight into the aspects of space and time. Physics also deals with the basic principles that explain matter and energy, and may study aspects of atomic matter by following concepts derived from the most fundamental principles.

Chemistry focuses on how substances interact with each other and with energy (for example heat and light). The study of change of matter (chemical reactions) and synthesis lies at the heart of chemistry, and gives rise to concepts such as organic functional groups and rate laws for chemical reactions. Chemistry also studies the properties of matter at a larger scale (for example, astrochemistry) and the reactions of matter at a larger scale (for example, technical chemistry), but typically, explanations and predictions are related back to the underlying atomic structure, giving more emphasis on the methods for the identification of molecules and their mechanisms of transformation than any other science.

Chemistry is not a sub-discipline of physics because chemistry differs from physics in aspects such as approach, emphasis (scope) and training of its practitioners. The knowledge obtained from studying either chemistry or physics can be used in a more direct way (as an applied science) or can be used to further our understanding of some aspect of nature.

Approach

Although both physics and chemistry are concerned with matter and its interaction with energy, the two disciplines differ in approach. In physics, it is typical to abstract from the specific type of matter, and to focus on the common properties of many different materials. In optics, for example, materials are characterized by their index of refraction, and materials with the same index of refraction will have identical properties. Chemistry, on the other hand, focuses on what compounds are present in a sample, and explores how changing the structure of molecules will change their reactivity and their physical properties.

The two sciences differ in the role that theory plays within the discipline. Physics can be divided into experimental and theoretical physics. Historically, theoretical physics has correctly predicted phenomena that were out of experimental reach at the time, and could be verified only after experimental techniques caught up. In chemistry, the role of theory historically has been a retrospective one, summarizing experimental data and predicting the outcome of similar experiments. However, with the increasing power of computational methods in chemistry, it has become possible to predict whether a hypothetical compound is stable or not before experimental data is available.

Training

In a typical undergraduate program for physics majors, required courses are in the sub-disciplines of physics, with additional required courses in mathematics. Because much of the insight of physics is described by differential equations relating matter, space and time (for example Newton's law of motion and the Maxwell equations of electromagnetism), students have to be familiar with differential equations. In a typical undergraduate program for chemistry majors, emphasis is placed on laboratory classes and understanding and applying models describing chemical bonds and molecular structure. Emphasis is also placed in the methods for analysis and the formulas and equations used when considering the chemical transformation. Students take courses in math, physics, chemistry and often biochemistry. Between the two programs of study, there is a large area of overlap (calculus, introductory physics, quantum mechanics, thermodynamics). However, physics places a larger emphasis on fundamental theory (with its deep mathematical treatment) while chemistry places more emphasis in combining the most important mathematical definitions of the theory with the approach of the molecular models. Laboratory skills may differ in both programs, as students may be involved in different technologies, depending on the program and the institution of higher education (for example, a chemistry student may spend more laboratory time dealing with glassware for distillation and purification or on a form of chromatography-spectroscopy instrument, while a physics student may spend much more time dealing with a laser and non-linear optics technology or some complex electrical circuit).

Careers in chemistry and physics

According to Bureau of Labor Statistics (United States Department of Labor), there are 80,000 chemists and 17,000 physicists working in the United States as of May 2010. In addition, 21,000 chemists and 13,500 physicists teach in high school. Chemistry is the only science that has an entire industry, the chemical industry, named after it, and many chemists work in this industry, in research and development, production, training or management. Other industries employing chemists include the petroleum, pharmaceutical, and food industry. While there is no industry named after physics, many industries have grown out of physics research, most notably the semiconductor and electronics industry. Physicists are also employed outside of science, for example in finance, because of their training in modeling complex systems.