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- Most molecular compounds (i.e. involving chemical bonds) contain only non-metallic elements . Molecular, Empirical, and Structural Formulas
- Structural formulas
- In general, metal atoms tend to lose electrons, and nonmetal atoms tend to gain electrons.
Molecules and Ions Although atoms are the smallest unique unit of a particular element, in nature only the noble gases can be found as isolated atoms. Most matter is in the form of ions, or compounds. Molecules and chemical formulas A molecule is comprised of two or more chemically bonded atoms. The atoms may be of the same type of element, or they may be different. Many elements are found in nature in molecular form - two or more atoms (of the same type of element) are bonded together. Oxygen, for example, is most commonly found in its molecular form "O2" (two oxygen atoms chemically bonded together). Oxygen can also exist in another molecular form where three atoms are chemically bonded. O3 is also known as ozone. Although O2 and O3 are both compounds of oxygen, they are quite different in their chemical and physical properties. There are seven elements which commonly occur as diatomic molecules. These include H, N, O, F, Cl, Br, I. An example of a commonly occurring compound that is composed of two 400 different types of atoms is pure water, or "H2O". The chemical formula for water illustrates the method of describing such compounds in atomic terms: there are two atoms of hydrogen and one atom of oxygen (the "1" subscript is omitted) in the compound known as "water". There is another compound of Hydrogen and Oxygen with the chemical formula H2O2 , also known as hydrogen peroxide. Again, although both compounds are composed of the same types of atoms, they are chemically quite different: hydrogen peroxide is quite reactive and has been used as a rocket fuel (it powered Evil Kenievel part way over the Snake River canyon). Most molecular compounds (i.e. involving chemical bonds) contain only non-metallic elements. Molecular, Empirical, and Structural Formulas Empirical vs. Molecular formulas Molecular formulas refer to the actual number of the different atoms which comprise a single molecule of a compound. Empirical formulas refer to the smallest whole number ratios of atoms in a particular compound.
Molecular formulas provide more information, however, sometimes a substance is actually a collection of molecules with different sizes but the same empirical formula. For example, carbon is commonly found as a collection of three dimensional structures (carbon chemically bonded to carbon). In this form, it is most easily represented simply by the empirical formula "C" (the elemental name). Structural formulas Sometimes the molecular formulas are drawn out as structural formulas to give some idea of the actual chemical bonds which unite the atoms. 
Structural formulas give an idea about the connections between atoms, but they don't necessarily give information about the actual geometry of such bonds. Ions The nucleus of an atom (containing protons and neutrons) remains unchanged after ordinary chemical reactions, but atoms can readily gain or lose electrons. If electrons are lost or gained by a neutral atom, then the result is that a charged particle is formed - called an ion. 401
For example, Sodium (Na) has 11 protons and 11 electrons. However, it can easily lose 1 electron. The resulting cation has 11 protons and 10 electrons, for an overall net charge of 1+ (the units are electron charge). The ionic state of an atom or compound is represented by a superscript to the right of the chemical formula: Na+, Mg 2+ (note the in the case of 1+, or 1-, the '1'is omitted). In contrast to the Na atom, the Chlorine atom (Cl) easily gains 1 electron to yield the chloride ion Cl- (i.e. 17 protons and 18 electrons). In general, metal atoms tend to lose electrons, and nonmetal atoms tend to gain electrons. Na + and Cl- are simple ions, in contrast to polyatomic ions such as NO3- (nitrate ion) and SO42- (sulfate ion). These are compounds made up of chemically bonded atoms, but have a net positive or negative charge. The chemical properties of an ion are greatly different from those of the atom from which it was derived. жүктеу/скачать 18,66 Mb. Достарыңызбен бөлісу:
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