Ionic bonds are formed between two or more atoms by the transfer of one or more electrons between atoms. From: Organic Chemistry, 2014 Ever feel overwhelmed with tests and homework? Do you wish you could balance all the things in your life a little better? We all need some stability in our lives. Atoms need stability, too. Atoms are constantly trying to complete their outer shell (find balance), and they will lose, gain, or even share electrons in order to achieve maximum stability. In order to complete their outer shell, some atoms give electrons, some atoms share electrons, and some atoms steal electrons. An atom's placement in the periodic table dictates what kind of personality that atom is likely to have (a giver, sharer, or a stealer). Exactly what types of bonds are formed between atoms to create compounds? Metals + Nonmetals → Ionic BondsNonmetal + Nonmetal → Covalent Bonds Metal + Metal → Metallic Bonds Ionic BondingAn ionic bond is held together by the electrostatic attraction between ions that are near one another. Electrostatic attraction is the attraction between atoms that have opposite charge and holds the atoms together in ionic bonds. Think of it as an atomic glue. In this type of bond, one atom gives up electrons and becomes a positively charged ion (cation). Another atom dons a ski mask and steals the electrons to become a negatively charged ion (anion). Okay, maybe steals is a bit harsh. The atom actually "accepts" or "takes" the electrons that the other atom is giving up. (We don't want to be accused of name-calling.) Some of our favorite foods have a bunch of ionic bonds sprinkled all over them. Is anyone up for some chips, fries, pretzels, or peanuts? Notice a pattern? #yumsalt Salts, including table salt, are held together by ionic bonds. Table salt is made of sodium chloride, or NaCl. Take a look at the periodic table. Notice that sodium is in the first column of the periodic table. That means it has only one valence electron in its outer shell. Chlorine, on the other hand, is in the seventh column. It has seven valence electrons. Cl only needs one more electron to complete its outer shell. Did you play matchmaker in your head? Sodium gladly gives up its extra valence electron to chlorine, which gobbles it up faster than Takeru Kobayashi eats hotdogs. The sodium atom becomes a cation and the chlorine atom because an anion, and the two atoms are held together by the positive and negative charges of the ions.  According to Coulomb's law, more highly charged ions form stronger bonds than less highly charged ions. Ionic bonds tend to be fairly strong and therefore have relatively high melting and boiling points. Ionic solids are poor conductors of electricity because each electron is localized around a particular atom. Their electrons aren't swimming in the electron pool. As a result, they don't move around the lattice. Ionic liquids do conduct electricity, however, because the ions are free to move around in the liquid phase. Covalent BondingIn the case of covalent bonds, electrons are neither lost nor gained. No ions are formed. Instead, the electrons are shared. This group of atoms must have watched Sesame Street as a kid. Covalent bonding is the sharing of one or more pairs of electrons between nonmetals. Covalent bonds in a molecule are often depicted as a dash. The dash represents the two electrons shared between the atoms. The atoms can have a:
The second type of covalent bond is the polar covalent bond. This is where the two atoms in the covalent bond are not the same and the attraction to the electron pair is not equal. The atom with the greater attraction pulls the bonding electrons towards them. As a result, the atom takes on a partial negative charge. The other atom has less attraction for the bonding electrons, and it will take on a partial positive charge. An example of this is HCl. The chlorine atom has a much greater attraction for the bonding pair of electrons and will therefore take on a partial negative charge. This type of bond is sometimes depicted as: Instead of using a single line to indicate the covalent bond, an arrow pointing towards the atom that has the greater attraction for the electron pair is used. The attractive force an atom has on a bonding pair of electrons is referred to as the atom's electronegativity. It's a measure of how badly the atom wants an electron. Atoms like chlorine and fluorine in that second to the last column on the right are desperate for electrons to complete their octet. In fact, electronegativity values have been calculated for all the atoms (see table below) so we can see which ones are more desperate than others for that extra electron. A general rule, as we go from left to right on the periodic table the electronegativity increases, as seen with the H and Cl atoms above. The electronegativity values can also be used to predict whether two atoms will likely undergo ionic, polar covalent, or non-polar covalent bonds. Refer to this video to get a better idea of how to tell if two atoms are likely to contain covalent versus ionic bonds as a result of their electronegativity. Brain SnackVisit the self-proclaimed most exciting/boring website in the world. Yes, you can find anything on the Internet. There are many types of chemical bonds and forces that bind molecules together. The two most basic types of bonds are characterized as either ionic or covalent. In ionic bonding, atoms transfer electrons to each other. Ionic bonds require at least one electron donor and one electron acceptor. In contrast, atoms with the same electronegativity share electrons in covalent bonds, because neither atom preferentially attracts or repels the shared electrons. Ionic bonding is the complete transfer of valence electron(s) between atoms. It is a type of chemical bond that generates two oppositely charged ions. In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion. Ionic bonds require an electron donor, often a metal, and an electron acceptor, a nonmetal. Ionic bonding is observed because metals have few electrons in their outer-most orbitals. By losing those electrons, these metals can achieve noble gas configuration and satisfy the octet rule. Similarly, nonmetals that have close to 8 electrons in their valence shells tend to readily accept electrons to achieve noble gas configuration. In ionic bonding, more than 1 electron can be donated or received to satisfy the octet rule. The charges on the anion and cation correspond to the number of electrons donated or received. In ionic bonds, the net charge of the compound must be zero. This sodium molecule donates the lone electron in its valence orbital in order to achieve octet configuration. This creates a positively charged cation due to the loss of electron. This chlorine atom receives one electron to achieve its octet configuration, which creates a negatively charged anion. The predicted overall energy of the ionic bonding process, which includes the ionization energy of the metal and electron affinity of the nonmetal, is usually positive, indicating that the reaction is endothermic and unfavorable. However, this reaction is highly favorable because of the electrostatic attraction between the particles. At the ideal interatomic distance, attraction between these particles releases enough energy to facilitate the reaction. Most ionic compounds tend to dissociate in polar solvents because they are often polar. This phenomenon is due to the opposite charges on each ion.
Example \(\PageIndex{1}\): Chloride Salts In this example, the sodium atom is donating its 1 valence electron to the chlorine atom. This creates a sodium cation and a chlorine anion. Notice that the net charge of the resulting compound is 0. In this example, the magnesium atom is donating both of its valence electrons to chlorine atoms. Each chlorine atom can only accept 1 electron before it can achieve its noble gas configuration; therefore, 2 atoms of chlorine are required to accept the 2 electrons donated by the magnesium. Notice that the net charge of the compound is 0.
Covalent bonding is the sharing of electrons between atoms. This type of bonding occurs between two atoms of the same element or of elements close to each other in the periodic table. This bonding occurs primarily between nonmetals; however, it can also be observed between nonmetals and metals. If atoms have similar electronegativities (the same affinity for electrons), covalent bonds are most likely to occur. Because both atoms have the same affinity for electrons and neither has a tendency to donate them, they share electrons in order to achieve octet configuration and become more stable. In addition, the ionization energy of the atom is too large and the electron affinity of the atom is too small for ionic bonding to occur. For example: carbon does not form ionic bonds because it has 4 valence electrons, half of an octet. To form ionic bonds, Carbon molecules must either gain or lose 4 electrons. This is highly unfavorable; therefore, carbon molecules share their 4 valence electrons through single, double, and triple bonds so that each atom can achieve noble gas configurations. Covalent bonds include interactions of the sigma and pi orbitals; therefore, covalent bonds lead to formation of single, double, triple, and quadruple bonds.
Example \(\PageIndex{2}\): \(PCl_3\) In this example, a phosphorous atom is sharing its three unpaired electrons with three chlorine atoms. In the end product, all four of these molecules have 8 valence electrons and satisfy the octet rule.
Ionic and covalent bonds are the two extremes of bonding. Polar covalent is the intermediate type of bonding between the two extremes. Some ionic bonds contain covalent characteristics and some covalent bonds are partially ionic. For example, most carbon-based compounds are covalently bonded but can also be partially ionic. Polarity is a measure of the separation of charge in a compound. A compound's polarity is dependent on the symmetry of the compound and on differences in electronegativity between atoms. Polarity occurs when the electron pushing elements, found on the left side of the periodic table, exchanges electrons with the electron pulling elements, on the right side of the table. This creates a spectrum of polarity, with ionic (polar) at one extreme, covalent (nonpolar) at another, and polar covalent in the middle. Both of these bonds are important in organic chemistry. Ionic bonds are important because they allow the synthesis of specific organic compounds. Scientists can manipulate ionic properties and these interactions in order to form desired products. Covalent bonds are especially important since most carbon molecules interact primarily through covalent bonding. Covalent bonding allows molecules to share electrons with other molecules, creating long chains of compounds and allowing more complexity in life. References
1. Are these compounds ionic or covalent? 2. In the following reactions, indicate whether the reactants and products are ionic or covalently bonded. a) b) Clarification: What is the nature of the bond between sodium and amide? What kind of bond forms between the anion carbon chain and sodium? c) Solutions
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In what type of bonds do atoms join together because their opposite charges attract each other?
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