A chemical substance is made up of several similar molecules composed of atoms from more than one element bound together by chemical bonds. There are four kinds of compounds, depending on how the component atoms are held together:
• molecules held together by covalent bonds
• ionic compounds held together by ionic bonds
• intermetallic compounds held together by metallic bonds
• Specific complexes held together by coordinate covalent bonds.
A chemical formula is a mode of conveying information about the parts of atoms that constitute a certain chemical compound, with the help of the standard abbreviations for the chemical elements, and subscripts to specify the number of atoms involved. For instance, water is made up of two hydrogen atoms bonded to one oxygen atom: the chemical formula is written as H2O. Several chemical compounds have an exclusive numerical identifier allocated by the Chemical Abstracts Service (CAS): A compound can be transformed into a different chemical conformation by interaction with a second chemical compound through a chemical reaction. In this method, bonds between atoms are broken-down in both interacting compounds, and then bonds are restructured so that new links are made between atoms.
Any material containing two or more different kinds of atoms (chemical elements) in a fixed stoichiometric ratio can be called as a chemical compound; the idea is most readily understood when considering pure chemical materials. It follows from their being made of a fixed ratio of two or more kinds of atoms that chemical compounds can be transformed, through a chemical reaction, into compounds or materials each having fewer atoms. The proportion of each element in the compound is expressed in a proportion in its chemical formula. A chemical formula is a mode of expressing information about the parts of atoms that constitute a specific chemical compound, using the standard acronyms for the chemical elements, and subscripts to show the number of atoms is involved. For instance, water is made up of two hydrogen atoms bonded to one oxygen atom: the chemical formula is written as H2O. In the example compounds which are non-stoichiometric, the ratio can be reproducible about their production, and give a fixed ratio of their component elements, but proportions that are not essential [e.g., for palladium hydride, PdHx (0.02 < x < 0.58)].
Chemical compounds contain a unique and defined chemical configuration bind together in a definite three-dimensional arrangement by chemical bonds. Chemical compounds might be molecular compounds which are held together by covalent bonds, salts that are held together by ionic bonds, intermetallic compounds which are held together by metallic bonds, or the subset of chemical complexes that are bound together by coordinate covalent bonds. Chemical elements which are in pure form are usually not as considered chemical compounds, failing into having two or more atom requirement, though they often contain molecules made up of multiple atoms. Several chemical compounds have a distinct numerical identifier assigned by the Chemical Abstracts Service (CAS):
1. Molecular compound
Molecules bind together by covalent bonds.
A molecule is a neutral group (electrically) of two or more atoms seized together by chemical bonds. Molecules are separated from ions by their shortage of electrical charge. Nevertheless, in quantum organic chemistry, physics, and biochemistry, the word molecule is often used less severely, also being applied to polyatomic ions (having more than one atom). In the kinetic theory of gases, the word molecule is often used for some gaseous particle regardless of its constituent. Giving to this definition, noble gas atoms are thought as molecules which are monatomic molecules.
A molecule can be homonuclear, that is, it only consists of atoms of one chemical element, as in case of with oxygen (O2); or it could be heteronuclear, a chemical compound made of more than one element, example water (H2O). Atoms and complexes linked by non-covalent interactions, like hydrogen bonds or ionic bonds, are usually not considered as single molecules.
A covalent bond develops H2 (right) where two hydrogen atoms share the two electrons.
A covalent bond is a chemical bond that contains the distribution of electron pairs among atoms. These electron pairs are called bonding pairs or shared pairs, and the stable equilibrium of attractive and repulsive forces among atoms, when they distribute electrons, is called covalent bonding.
2. Ionic compound
Ionic compounds that are held together by ionic bonds are called an ionic compound. In chemistry, an ionic compound is a chemical compound that is made up of ions which are held together by electrostatic forces called ionic bonding. The compound is completely neutral but be made of positively charged ions named cations and negatively charged ions termed as anions. These can be just ions such as in sodium chloride, the sodium (Na+) and chloride (Cl−) or polyatomic class such as in ammonium carbonate the ammonium (NH4+) and carbonate (CO2−3) ions. Individual ions within an ionic compound usually have multiple closet neighbors, so are not be the part of molecules, but as an alternative a part of a continuous 3-d network, typically in a crystalline structure.
Ionic compounds comprising of hydrogen ions (H+) are categorized as acids, and those having basic ions oxide (O2−) or hydroxide (OH−) are categorized as bases. Ionic compounds without these ions are also called salts and that can be formed by acid-base reactions. Ionic compounds may also be formed from their constituent ions by vaporization of their freezing, precipitation, solvent, the electron transfer reaction or a solid-state reaction, of reactive metals with reactive non-metals, like halogen gases.
Ionic compounds normally have high boiling and melting points and are hard and weak. As solids, they are electrically insulating, but when liquefied or dissolved they become extremely conductive since the ions are mobilized.
3. intermetallic compounds
An intermetallic also recognized as an intermetallic compound, which is bound together by metallic bonds is a type of metallic alloy that forms a solid-state compound displaying distinct stoichiometry and ordered crystal structure.
4. Coordinate compound
Certain complexes that are held together by coordinate covalent bonds. A coordination complex which is commonly metallic and is so-called the coordination center and a near array of bound molecules or ions, which are in turn, called complexing agents or ligands. Many metal-containing compounds, mainly those of transition metals, are coordination complexes. A coordination complex whose center is a metal atom is known as a metal complex.
A compound can be transformed into different chemical constituents by interaction with a second chemical compound via a chemical reaction. In this method, bonds between atoms are broken down in both of the relating compounds, and then bonds are transformed so that new links are created between atoms.
This reaction could be called as AB + CD → AD + CB, where A, B, C, and D are each distinct atom; and AB, AD, CD, and CB are each unique compound.