To dissolve an ionic compound, the water molecules must be able to stabilize the ions that result from breaking the ionic bond. They do this by hydrating the ions. Water is a polar molecule. It has a permanent dipole. The #"O"# atom has a partial negative charge, and the #"H"# atoms have a partial positive charge.  When you place an ionic substance in water, the water molecules attract the positive and negative ions from the crystal. The particles are then free to move around within the solution. (from 2012books.lardbucket.org) The positive ions have several water molecules around them, all with their #"O"# atoms close to the positive ion. The negative ions have several water molecules around them, all with their #"H"# atoms close to the negative ion. The "shell" of water molecules reduces the attractions between the ions. The ions are hydrated. Here's a video that shows the process in action.
Updated May 11, 2018 By Claire Gillespie
A chemical compound is made up of many identical molecules formed from atoms from more than one element, attached by chemical bonds. However, not all compounds are created equally. Different things happen to ionic compounds and covalent compounds when they dissolve in water.
When ionic compounds dissolve in water they go through a process called dissociation, splitting into the ions that make them up. However, when you place covalent compounds in water, they typically do not dissolve but form a layer on top of the water.
Ionic compounds are molecules consisting of oppositely charged ions, which are ions with both negative and positive charges. Covalent compounds are non-metals bound together, made up of two electrons shared between two atoms. Ionic compounds have a high melting and boiling point, but covalent compounds have a comparatively lower melting and boiling point. This is because ionic compounds need a very large amount of energy to break their ionic bonds and separate the positive and negative charges. Because covalent compounds are made of distinct molecules that don’t mix with each other, they separate more easily. Sodium bromide, calcium chloride and magnesium oxide are examples of ionic compounds, while ethanol, ozone, hydrogen and carbon dioxide are examples of covalent compounds.
When ionic compounds dissolve in water, they break apart into the ions that make them up through a process called dissociation. When placed in water, the ions are attracted to the water molecules, each of which carries a polar charge. If the force between the ions and the water molecules is strong enough to break the bonds between the ions, the compound dissolves. The ions dissociate and disperse in solution, each ringed by water molecules to prevent reattachment. The ionic solution turns into an electrolyte, meaning it can conduct electricity.
When covalent compounds dissolve in water they break apart into molecules, but not individual atoms. Water is a polar solvent, but covalent compounds are usually nonpolar. This means covalent compounds typically don't dissolve in water, instead making a separate layer on the water's surface. Sugar is one of the few covalent compounds that does dissolve in water because it is a polar covalent compound (i.e., parts of their molecules have a negative side and a positive side), but it still doesn't separate into ions the way ionic compounds do in water. Oil is a non-polar covalent compound, which is why it doesn't dissolve in water. 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
|
Which response provides the best explanation as to why ionic compounds easily dissociate in water?
Postagens relacionadas
direito autoral © 2024 aprendervalor Inc.
