A-Level化学-结构和成键Structure and Bonding

A-Level化学-结构和成键Structure and Bonding

　　Revision: Structure and Bonding

　　Ionic bonding

　　Ionic bonds are a type of chemical bond based on electrostatic forces between two oppositely-charged ions. In ionic bond formation, a metal donates an electron, due to a low electronegativity to form a positive ion or cation. Often ionic bonds form between metals and non-metals. The non-metal atom has an electron configuration just short of a noble gas structure. They have high electronegativity, and so readily gain electrons to form negative ions or anions. The two or more ions are then attracted to each other by electrostatic forces. Such bonds are stronger than hydrogen bonds, but similar in strength to covalent bonds.

　　Ionic bonding occurs only if the overall energy change for the reaction is favorable when the bonded atoms have a lower energy than the free ones. The larger the resulting energy change the stronger the bond.

　　Pure ionic bonding is not known to exist. All ionic bonds have a degree of covalent bonding or metallic bonding. The larger the difference in electronegativity between two atoms, the more ionic the bond. Ionic compounds conduct electricity when molten or in solution. They generally have a high melting point and tend to be soluble in water.

　　Covalent Bonding

　　Covalent bonding is a description form of chemical bonding that is characterized by the sharing of one or more electrons between two atoms. In general bonds are defined by a mutual attraction that holds the resultant molecule together. Often bonding occurs in such a way that the the outer electron shells of the participating atoms becomes filled. Such bonds are always stronger than the intermolecular hydrogen bond and similar in strength to or stronger than the ionic bond.

　　In contrast to the ionic and metallic bond, the covalent bond is directional, i.e. the bond angles have a great impact on the strength of the interaction. This impact arises because covalent bonds are formed by the overlap of atomic orbital, with greater overlap producing a greater strength of interaction. Atomic orbital all have highly directional character, resulting in a highly directionally-dependent interactions in bonding.

　　Covalent bonding most frequently occurs between atoms with similar electronegativities. For this reason, non-metals tend to engage in covalent bonding more readily since metals have access to metallic bonding.

　　Metallic bonding

　　Metallic bonding is the bonding within metals. It involves the delocalized sharing of free electrons among a lattice of metal atoms. Thus, metallic bonds may be compared to molten salts.

　　Metal atoms typically contain a high number of electrons in their valence shell compared to their period or energy level. These become delocalized and form a sea of electrons surrounding a giant lattice of positive ions. The surrounding electrons and the positive ions in the metal have a strong attractive force between them. This means that more energy is required to negate these forces. Therefore metals often have high melting or boiling points. The principle is similar to that of ionic bonds.

本文来源：https://www.2haoxitong.net/k/doc/b44e1b101fd9ad51f01dc281e53a580216fc50bf.html