Chemistry is a branch of natural science that deals principally with the properties of substances, the changes they undergo, and the natural laws that describe these changes. The more qualitative chemist might work on synthesizing a new compound used in medicine, for example, while the more quantitative work can seem much like physics applied to the microscopic level of atoms and molecules.
The atomic composition of a molecule is given by its formula. However, the fact that we can write a formula for a compound does not imply the existence of molecules having that composition.
Gases and most liquids consist of molecules, but many solids exist as extended What is chemistry of atoms or ions electrically charged atoms or molecules. For example, there is no such thing as What is chemistry "molecule" of ordinary salt, NaCl see below.
Confused about the distinction between molecules and compounds? Maybe the following will help: A molecule but not a compound - Ozone, O3, is not a compound because it contains only a single element. This well-known molecule is a compound because it contains more than one element.
It is built from interpenetrating lattices of sodium and chloride ions that extend indefinitely. Structure and properties Composition and structure lie at the core of Chemistry, but they encompass only a very small part of it.
It is largely the properties of chemical substances that interest us; it is through these that we experience and find uses for substances, and much of chemistry-as-a-science is devoted to understanding the relation between structure and properties.
For some purposes it is convenient to distinguish between chemical properties and physical properties, but as with most human-constructed dichotomies, the distinction becomes more fuzzy as one looks more closely. Take some time to look it over and make sure you understand all the terms and the relations between them.
For a more in-depth treatment of much of the material covered here, please see The basics of atoms, moles, formulas equations, and nomenclature.
On a microscopic basis it can be thought of as a re-arrangement of atoms. As with most human-created dichotomies, this begins to break down when examined closely.
This is largely because of some ambiguity in what we regard as a distinct "substance". Elemental chlorine exists as the diatomic molecule Cl2 in the gas, liquid, and solid states; the major difference between them lies in the degree of organization. In the gas the molecules move about randomly, whereas in the solid they are constrained to locations in a 3-dimensional lattice.
In the liquid, this tight organization is relaxed, allowing the molecules to slip and slide around each other.
Since the basic molecular units remain the same in all three states, the processes of melting, freezing, condensation and vaporization are usually regarded as physical rather than chemical changes. Because the ions in the solid, the hydrated ions in the solution, and the molecule Na2Cl2 are really different chemical species, the distinction between physical and chemical change becomes a bit fuzzy.
Most chemical reactions proceed to some inermediate point that yields a mixture of reactants and products. For example, if the two gases phosphorus trichloride and chlorine are mixed together at room temprature, they will combine until about half of them have changed into phosphorus pentachloride: The result, in any case, will be an equilibrium mixture of reactants and products.
The most important question we can ask about any reaction is "what is the equilibrium composition"? If the answer is "all products and negligible quantities of reactants", then we say the reaction can takes place and that it "goes to completion ". If the answer is "negligible quantities of products", then we say the reaction cannot take place in the forward direction, but that the reverse reaction can occur.
If the answer is "significant quantities of all components" both reactans and products are present in the equilibrium mixture, then we say the reaction is "reversible" or "incomplete".
The aspect of "change" we are looking at here is a property of a chemical reaction, rather than of any one substance.
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|Chemistry - Wikipedia||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.|
|It’s Everywhere||Definition[ edit ] While the actual definition of chemistry, its components, and its manifestations are fairly vague, this is a well documented concept. Some people describe chemistry in metaphorical terms, such as "like cookie dough and vanilla ice cream", or "like a performance".|
But if you stop to think of the huge number of possible reactions between the more than 15 million known substances, you can see that it would be an impossible task to measure and record the equilibrium compositions of every possible combination.
One or two directly measurable properties of the individual reactants and products can be combined to give a number from which the equilibrium composition at any temperature can be easily calculated.
There is no need to do an experiment! This is very much a macroscopic view because the properties we need to directly concern ourselves with are those of the reactants and products.
Similarly, the equilibrium composition— the measure of the extent to which a reaction takes place— is expressed in terms of the quantities of these substances.
Chemical Thermodynamics Virtually all chemical changes involve the uptake or release of energy, usually in the form of heat. It turns out that these energy changes, which are the province of chemical thermodynamicsserve as a powerful means of predicting whether or not a given reaction can proceed, and to what extent.
Moreover, all we need in order to make this prediction is information about the energetic properties of the reactants and products; there is no need to study the reaction itself.
Because these are bulk properties of matter, chemical thermodynamics is entirely macroscopic in its outlook. Does the reaction take place in a single step, or are multiple steps and intermediate structures involved?
Mechanism of chemical change These details constitute what chemists call the mechanism of the reaction. For example, the reaction between nitric oxide and hydrogen identified as the net reaction at the bottom leftis believed to take place in the two steps shown here.Chemistry is the study of matter: its composition, properties, and reactivity.
This material roughly covers a first-year high school or college course, and a good understanding of algebra is helpful. Learn for free about math, art, computer programming, economics, physics, chemistry, biology, medicine, finance, history, and more. Chemistry, like all the natural sciences, begins with the direct observation of nature— in this case, of matter.
But when we look at matter in bulk, we see only the "forest", not the "trees"— the atoms and molecules of which matter is composed— whose properties ultimately determine the nature and behavior of the matter we are looking at.
Chemistry is a branch of natural science that deals principally with the properties of substances, the changes they undergo, and the natural laws that describe these changes.
Chemistry is frequently defined as the study of matter and the reactions that matter undergoes. Actually, physicists, geologists, and biologists also study matter, but only chemists study the .
Chemistry is the study of matter, its properties, how and why substances combine or separate to form other substances, and how substances interact with energy. Many people think of chemists as being white-coated scientists mixing strange liquids in a laboratory, but the truth is we are all chemists.
Organic chemistry is known as the “Chemistry of Life” because all of the molecules that make up living tissue have carbon as part of their makeup.