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Top 10 Movie Couples with the Worst Chemistry
It is often seen as linked to the quest to turn lead or another common starting material into gold,  though in ancient times the study encompassed many of the questions of modern chemistry being defined as the study of the composition of waters, movement, growth, embodying, disembodying, drawing the spirits from bodies and bonding the spirits within bodies by the early 4th century Greek-Egyptian alchemist Zosimos. The current model of atomic structure is the quantum mechanical model. This matter can be studied in solid, liquid, or gas states , in isolation or in combination. The interactions , reactions and transformations that are studied in chemistry are usually the result of interactions between atoms, leading to rearrangements of the chemical bonds which hold atoms together. Such behaviors are studied in a chemistry laboratory. The chemistry laboratory stereotypically uses various forms of laboratory glassware. Solutions of substances in reagent bottles, including ammonium hydroxide and nitric acid , illuminated in different colors A chemical reaction is a transformation of some substances into one or more different substances. It can be symbolically depicted through a chemical equation , which usually involves atoms as subjects. The number of atoms on the left and the right in the equation for a chemical transformation is equal. When the number of atoms on either side is unequal, the transformation is referred to as a nuclear reaction or radioactive decay. The type of chemical reactions a substance may undergo and the energy changes that may accompany it are constrained by certain basic rules, known as chemical laws. Energy and entropy considerations are invariably important in almost all chemical studies. Chemical substances are classified in terms of their structure , phase, as well as their chemical compositions. They can be analyzed using the tools of chemical analysis , e. Scientists engaged in chemical research are known as chemists. Several concepts are essential for the study of chemistry; some of them are: Matter In chemistry, matter is defined as anything that has rest mass and volume it takes up space and is made up of particles. The particles that make up matter have rest mass as well — not all particles have rest mass, such as the photon. Matter can be a pure chemical substance or a mixture of substances. Atom A diagram of an atom based on the Bohr model The atom is the basic unit of chemistry. It consists of a dense core called the atomic nucleus surrounded by a space occupied by an electron cloud. The nucleus is made up of positively charged protons and uncharged neutrons together called nucleons , while the electron cloud consists of negatively charged electrons which orbit the nucleus. In a neutral atom, the negatively charged electrons balance out the positive charge of the protons. The nucleus is dense; the mass of a nucleon is appromixately 1, times that of an electron, yet the radius of an atom is about 10, times that of its nucleus. Chemical element A chemical element is a pure substance which is composed of a single type of atom, characterized by its particular number of protons in the nuclei of its atoms, known as the atomic number and represented by the symbol Z. The mass number is the sum of the number of protons and neutrons in a nucleus. Although all the nuclei of all atoms belonging to one element will have the same atomic number, they may not necessarily have the same mass number; atoms of an element which have different mass numbers are known as isotopes. For example, all atoms with 6 protons in their nuclei are atoms of the chemical element carbon , but atoms of carbon may have mass numbers of 12 or The periodic table is arranged in groups , or columns, and periods , or rows. The periodic table is useful in identifying periodic trends. Chemical compound A compound is a pure chemical substance composed of more than one element. The properties of a compound bear little similarity to those of its elements. Organic compounds are named according to the organic nomenclature system. When a compound has more than one component, then they are divided into two classes, the electropositive and the electronegative components. In this scheme each chemical substance is identifiable by a number known as its CAS registry number. A molecule is the smallest indivisible portion of a pure chemical substance that has its unique set of chemical properties, that is, its potential to undergo a certain set of chemical reactions with other substances. However, this definition only works well for substances that are composed of molecules, which is not true of many substances see below. Molecules are typically a set of atoms bound together by covalent bonds , such that the structure is electrically neutral and all valence electrons are paired with other electrons either in bonds or in lone pairs. Thus, molecules exist as electrically neutral units, unlike ions. When this rule is broken, giving the "molecule" a charge, the result is sometimes named a molecular ion or a polyatomic ion. However, the discrete and separate nature of the molecular concept usually requires that molecular ions be present only in well-separated form, such as a directed beam in a vacuum in a mass spectrometer. Charged polyatomic collections residing in solids for example, common sulfate or nitrate ions are generally not considered "molecules" in chemistry. Some molecules contain one or more unpaired electrons, creating radicals. Most radicals are comparatively reactive, but some, such as nitric oxide NO can be stable. A 2-D skeletal model of a benzene molecule C6H6 The "inert" or noble gas elements helium , neon , argon , krypton , xenon and radon are composed of lone atoms as their smallest discrete unit, but the other isolated chemical elements consist of either molecules or networks of atoms bonded to each other in some way. Identifiable molecules compose familiar substances such as water, air, and many organic compounds like alcohol, sugar, gasoline, and the various pharmaceuticals. However, not all substances or chemical compounds consist of discrete molecules, and indeed most of the solid substances that make up the solid crust, mantle, and core of the Earth are chemical compounds without molecules. These other types of substances, such as ionic compounds and network solids , are organized in such a way as to lack the existence of identifiable molecules per se. Instead, these substances are discussed in terms of formula units or unit cells as the smallest repeating structure within the substance. Examples of such substances are mineral salts such as table salt , solids like carbon and diamond, metals, and familiar silica and silicate minerals such as quartz and granite. One of the main characteristics of a molecule is its geometry often called its structure. While the structure of diatomic, triatomic or tetra atomic molecules may be trivial, linear, angular pyramidal etc. Substance and mixture Examples of pure chemical substances. From left to right: A chemical substance is a kind of matter with a definite composition and set of properties. Examples of mixtures are air and alloys. Mole The mole is a unit of measurement that denotes an amount of substance also called chemical amount. The mole is defined as the number of atoms found in exactly 0. Phase In addition to the specific chemical properties that distinguish different chemical classifications, chemicals can exist in several phases. For the most part, the chemical classifications are independent of these bulk phase classifications; however, some more exotic phases are incompatible with certain chemical properties. A phase is a set of states of a chemical system that have similar bulk structural properties, over a range of conditions, such as pressure or temperature. Physical properties, such as density and refractive index tend to fall within values characteristic of the phase. The phase of matter is defined by the phase transition , which is when energy put into or taken out of the system goes into rearranging the structure of the system, instead of changing the bulk conditions. Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions. The most familiar examples of phases are solids , liquids , and gases. Many substances exhibit multiple solid phases. For example, there are three phases of solid iron alpha, gamma, and delta that vary based on temperature and pressure. A principal difference between solid phases is the crystal structure , or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution that is, in water. Less familiar phases include plasmas , Bose—Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology. Chemical bond An animation of the process of ionic bonding between sodium Na and chlorine Cl to form sodium chloride , or common table salt. Ionic bonding involves one atom taking valence electrons from another as opposed to sharing, which occurs in covalent bonding Atoms sticking together in molecules or crystals are said to be bonded with one another. A chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them. A chemical bond can be a covalent bond , an ionic bond , a hydrogen bond or just because of Van der Waals force. Each of these kinds of bonds is ascribed to some potential. These potentials create the interactions which hold atoms together in molecules or crystals. In many simple compounds, valence bond theory , the Valence Shell Electron Pair Repulsion model VSEPR , and the concept of oxidation number can be used to explain molecular structure and composition. An ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non-metal atom, becoming a negatively charged anion. The two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them. The ions are held together due to electrostatic attraction, and that compound sodium chloride NaCl , or common table salt, is formed. In the methane molecule CH4 , the carbon atom shares a pair of valence electrons with each of the four hydrogen atoms. Thus, the octet rule is satisfied for C-atom it has eight electrons in its valence shell and the duet rule is satisfied for the H-atoms they have two electrons in their valence shells. In a covalent bond, one or more pairs of valence electrons are shared by two atoms: Atoms will share valence electrons in such a way as to create a noble gas electron configuration eight electrons in their outermost shell for each atom. Atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. However, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration; these atoms are said to follow the duet rule, and in this way they are reaching the electron configuration of the noble gas helium , which has two electrons in its outer shell. Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes , valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used. See diagram on electronic orbitals. Energy In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic , molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants. A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions , the reaction absorbs heat from the surroundings. Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. The speed of a chemical reaction at given temperature T is related to the activation energy E, by the Boltzmann's population factor e.
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