Electrons are shared differently in ionic and covalent bonds. Covalent bonds can be non-polar or polar and react to electrostatic charges. This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. Types of Covalent Bonds: Polar and Nonpolar. In unit two, we compared atoms to puppies and electrons to bones in our analogy of how bonding works.
Now one puppy has two electron bones and one puppy has none. Because the electron bones in our analogy have a negative charge, the puppy thief becomes negatively charged due to the additional bone.
The puppy that lost its electron bone becomes positively charged. Because the puppy who lost his bone has the opposite charge of the thief puppy, the puppies are held together by electrostatic forces, just like sodium and chloride ions!
In our analogy, each puppy again starts out with an electron bone. An atom that loses one or more valence electrons to become a positively charged ion is known as a cation, while an atom that gains electrons and becomes negatively charged is known as an anion. This exchange of valence electrons allows ions to achieve electron configurations that mimic those of the noble gases, satisfying the octet rule. The octet rule states that an atom is most stable when there are eight electrons in its valence shell.
Atoms with less than eight electrons tend to satisfy the duet rule, having two electrons in their valence shell. By satisfying the duet rule or the octet rule, ions are more stable. An anion is indicated by a negative superscript charge - something to the right of the atom. Similarly, if a chlorine atom gains an extra electron, it becomes the chloride ion, Cl —. Both ions form because the ion is more stable than the atom due to the octet rule.
Once the oppositely charged ions form, they are attracted by their positive and negative charges and form an ionic compound. Ionic bonds are also formed when there is a large electronegativity difference between two atoms. This difference causes an unequal sharing of electrons such that one atom completely loses one or more electrons and the other atom gains one or more electrons, such as in the creation of an ionic bond between a metal atom sodium and a nonmetal fluorine.
Formation of sodium fluoride : The transfer of electrons and subsequent attraction of oppositely charged ions. To determine the chemical formulas of ionic compounds, the following two conditions must be satisfied:.
This is because Mg has two valence electrons and it would like to get rid of those two ions to obey the octet rule. Fluorine has seven valence electrons and usually forms the F — ion because it gains one electron to satisfy the octet rule. Therefore, the formula of the compound is MgF 2. The subscript two indicates that there are two fluorines that are ionically bonded to magnesium.
On the macroscopic scale, ionic compounds form crystalline lattice structures that are characterized by high melting and boiling points and good electrical conductivity when melted or solubilized.
Fluorine has seven valence electrons and as such, usually forms the F — ion because it gains one electron to satisfy the octet rule. Covalent bonds are a class of chemical bonds where valence electrons are shared between two atoms, typically two nonmetals.
The formation of a covalent bond allows the nonmetals to obey the octet rule and thus become more stable. For example:. Covalent bonding requires a specific orientation between atoms in order to achieve the overlap between bonding orbitals. A rule of thumb is that covalent compounds are more difficult to change than ionic compounds.
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Types of Bonds. Learning Objective Describe the types of bonds formed between atoms. If these colorless gases are allowed to mix, a thick white smoke of solid ammonium chloride is formed.
The hydrogen's electron is left behind on the chlorine to form a negative chloride ion. Once the ammonium ion has been formed it is impossible to tell any difference between the dative covalent and the ordinary covalent bonds. Although the electrons are shown differently in the diagram, there is no difference between them in reality. In simple diagrams, a coordinate bond is shown by an arrow.
The arrow points from the atom donating the lone pair to the atom accepting it. Something similar happens. In an introductory chemistry course, whenever you have talked about hydrogen ions for example in acids , you have actually been talking about the hydroxonium ion.
A raw hydrogen ion is simply a proton, and is far too reactive to exist on its own in a test tube. When it reacts with something an alkali, for example , the hydrogen ion simply becomes detached from the water molecule again. Note that once the coordinate bond has been set up, all the hydrogens attached to the oxygen are exactly equivalent.
When a hydrogen ion breaks away again, it could be any of the three. Boron trifluoride is a compound that does not have a noble gas structure around the boron atom a notorious "octet violator". The boron only has three pairs of electrons in its bonding level, whereas there would be room for four pairs.
The lone pair on the nitrogen of an ammonia molecule can be used to overcome that deficiency, and a compound is formed involving a coordinate bond. The second diagram shows another way that you might find coordinate bonds drawn.
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