The Ionic Lattice

Topics: Ion, Atom, Electric charge Pages: 7 (2166 words) Published: August 23, 2013
The Ionic Lattice
In most ionic compounds, the anions are much larger than the cations, and it is the anions which form the crystal array. The smaller cations reside in the holes between the anions. Basic Concepts:

1. Ions are assumed to be charged, incompressible, nonpolarizable spheres. 2. Ions try to surround themselves with as many ions of opposite charge as closely as possible. Usually in the packing arrangement, the cation is just large enough to allow te anions to surround it without touching one another. 3. The cation to anion ratio must reflect the stoichiometry of the compound. For MgCl2 the lattice must be an array of chloride anions with only half that number of magnesium ion.

An ionic lattice is a structure of millions of atomic formations of an ionic substance, structured like building blocks into one three-dimensional formation.

Ionic Bond

A chemical bond is a mutual attraction between the nuclei and valence electrons of two different atoms. This attraction results in the two atoms binding together. An ionic bond, also called an electron-transfer bond, is a type of chemical bond that is a result of the electromagnetic attraction between ions of opposite charges, i.e., a cation (a positively charged ion) and an anion (a negatively charged ion). An ion is an atom or group of atoms that has acquired an electrical charge due to the loss or gain of electrons. In an ionic bond, an atom gives or receives electrons from another atom. This is in contrast to covalent bonding, where two atoms share electron pairs between them. An ionic compound consists of anions and cations combined such that the total charge of the molecule is zero. All salts are ionic compounds.

One characteristic that both ionic and covalent compounds share is that they adhere to the octet rule. The octet rule is the principle that describes the bonding in atoms. Individual atoms are unstable unless they have an octet of electrons in their highest energy level. The electrons in this level are called valence electrons. When atoms gain, lose, or share electrons with other atoms, they satisfy the octet rule and form chemical compounds.

Ionic bonding occurs when one atom transfers electrons to another atom. In doing so, the atoms may achieve a complete outer energy level, satisfying the octet rule. During the formation of an ionic bond, one atom gains electrons and the other atom loses electrons. As a result, the atoms gain an electric charge. The atom that gains electrons gains a negative charge, becoming an anion. The atom that loses electrons gains a positive charge, becoming a cation. An example of this is the ionic bond that is formed between sodium (Na) and fluorine (F) to make sodium fluoride, NaF. A fluorine atom has seven valence electrons. It needs one more to have a complete outer energy level and satisfy the octet rule. If it gains this electron, it will become a negatively charged fluorine anion (F-). A sodium atom has only one valence electron. If it loses this electron, it is left with a complete outermost energy level that satisfies the octet rule. At the same time, it becomes a positively charged sodium cation (Na+). As the sodium atom loses its electron, the fluorine atom picks it up. The two ions now have opposite charges and attract each other. This electromagnetic attraction is quite strong and holds the ions together, forming sodium fluoride. This binding of the two ions is called an ionic bond.

Energy is required for an atom to lose an electron. The process of losing an electron and forming an ion is called ionization. The energy that is needed for ionization to occur is called the ionization energy. The ionization energy needs to be sufficient to overcome the attraction between the positively charged nucleus and the negatively charged electron. If an atom has only a few valence electrons, the ionization energy is low. The removal of a small number of electrons does not require much energy. Atoms...
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