The nature of the attractive forces that hold atoms or ions together within a compound is the basis for classifying chemical bonding. When electrons are transferred and ions form, ionic bonds result. Ionic bonds are electrostatic forces of attraction, that is, the attractive forces experienced between objects of opposite electrical charge in this case, cations and anions.
Covalent bonds are the attractive forces between the positively charged nuclei of the bonded atoms and one or more pairs of electrons that are located between the atoms. Compounds are classified as ionic or molecular covalent on the basis of the bonds present in them. When an element composed of atoms that readily lose electrons a metal reacts with an element composed of atoms that readily gain electrons a nonmetal , a transfer of electrons usually occurs, producing ions.
The compound formed by this transfer is stabilized by the electrostatic attractions ionic bonds between the ions of opposite charge present in the compound. A compound that contains ions and is held together by ionic bonds is called an ionic compound. The periodic table can help us recognize many of the compounds that are ionic: When a metal is combined with one or more nonmetals, the compound is usually ionic. This guideline works well for predicting ionic compound formation for most of the compounds typically encountered in an introductory chemistry course.
However, it is not always true for example, aluminum chloride, AlCl 3 , is not ionic. You can often recognize ionic compounds because of their properties. Ionic compounds are solids that typically melt at high temperatures and boil at even higher temperatures.
When molten, however, it can conduct electricity because its ions are able to move freely through the liquid Figure 3.
Figure 3. Watch this video to see a mixture of salts melt and conduct electricity. Note that the video has no narration. You can access the audio description using the widget below the video. In every ionic compound, the total number of positive charges of the cations equals the total number of negative charges of the anions. Thus, ionic compounds are electrically neutral overall, even though they contain positive and negative ions.
We can use this observation to help us write the formula of an ionic compound. The formula of an ionic compound must have a ratio of ions such that the numbers of positive and negative charges are equal. What is the formula of this compound? Figure 4. Although pure aluminum oxide is colorless, trace amounts of iron and titanium give blue sapphire its characteristic color. Because the ionic compound must be electrically neutral, it must have the same number of positive and negative charges.
The formula would be Al 2 O 3. Many ionic compounds contain polyatomic ions Table 1 as the cation, the anion, or both. The other fluoride of tin is SnF 4 , which was previously called stannic fluoride but is now named tin IV fluoride. Name the following ionic compounds, which contain a metal that can have more than one ionic charge:. These charges are used in the names of the metal ions:.
Write the formulas of the following ionic compounds:. Chromium compounds are widely used in industry, such as for chrome plating, in dye-making, as preservatives, and to prevent corrosion in cooling tower water, as occurred near Hinckley.
Cr III , an ingredient of many vitamin and nutritional supplements, forms compounds that are not very soluble in water, and it has low toxicity. Cr VI , on the other hand, is much more toxic and forms compounds that are reasonably soluble in water.
Exposure to small amounts of Cr VI can lead to damage of the respiratory, gastrointestinal, and immune systems, as well as the kidneys, liver, blood, and skin. Despite cleanup efforts, Cr VI groundwater contamination remains a problem in Hinckley and other locations across the globe. A study by the Environmental Working Group found that of 35 US cities tested, 31 had higher levels of Cr VI in their tap water than the public health goal of 0.
The bonding characteristics of inorganic molecular compounds are different from ionic compounds, and they are named using a different system as well. The charges of cations and anions dictate their ratios in ionic compounds, so specifying the names of the ions provides sufficient information to determine chemical formulas. However, because covalent bonding allows for significant variation in the combination ratios of the atoms in a molecule, the names for molecular compounds must explicitly identify these ratios.
When two nonmetallic elements form a molecular compound, several combination ratios are often possible. For example, carbon and oxygen can form the compounds CO and CO 2. Since these are different substances with different properties, they cannot both have the same name they cannot both be called carbon oxide.
To deal with this situation, we use a naming method that is somewhat similar to that used for ionic compounds, but with added prefixes to specify the numbers of atoms of each element. When only one atom of the first element is present, the prefix mono - is usually deleted from that part. When two vowels are adjacent, the a in the Greek prefix is usually dropped. There are a few common names that you will encounter as you continue your study of chemistry. For example, although NO is often called nitric oxide, its proper name is nitrogen monoxide.
Similarly, N 2 O is known as nitrous oxide even though our rules would specify the name dinitrogen monoxide. And H 2 O is usually called water, not dihydrogen monoxide. You should commit to memory the common names of compounds as you encounter them. Because these compounds consist solely of nonmetals, we use prefixes to designate the number of atoms of each element:.
Some compounds containing hydrogen are members of an important class of substances known as acids. If the compound is a binary acid comprised of hydrogen and one other nonmetallic element :.
Many compounds containing three or more elements such as organic compounds or coordination compounds are subject to specialized nomenclature rules that you will learn later. However, we will briefly discuss the important compounds known as oxyacids , compounds that contain hydrogen, oxygen, and at least one other element, and are bonded in such a way as to impart acidic properties to the compound you will learn the details of this in a later chapter. Typical oxyacids consist of hydrogen combined with a polyatomic, oxygen-containing ion.
To name oxyacids:. There are some exceptions to the general naming method e. Metals particularly those in groups 1 and 2 tend to lose the number of electrons that would leave them with the same number of electrons as in the preceding noble gas in the periodic table. By this means, a positively charged ion is formed. Similarly, nonmetals especially those in groups 16 and 17, and, to a lesser extent, those in Group 15 can gain the number of electrons needed to provide atoms with the same number of electrons as in the next noble gas in the periodic table.
Thus, nonmetals tend to form negative ions. Positively charged ions are called cations, and negatively charged ions are called anions. Ions can be either monatomic containing only one atom or polyatomic containing more than one atom. Compounds that contain ions are called ionic compounds.
Ionic compounds generally form from metals and nonmetals. Compounds that do not contain ions, but instead consist of atoms bonded tightly together in molecules uncharged groups of atoms that behave as a single unit , are called covalent compounds.
Covalent compounds usually form from two or more nonmetals. Chemists use nomenclature rules to clearly name compounds. Ionic and molecular compounds are named using somewhat-different methods. Binary ionic compounds typically consist of a metal and a nonmetal. 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. But inside the NO3 - entity, you have true chemical bonds, so NO3 - can be considered a molecule with a net charge If one would split off an oxygen or a nitrogen, then it is not nitrate ion anymore.
One can even have compounds in which both the positive and negative ion consists of charged 'molecules'. Quote: Originally posted by dolimitless. I was reading on a website that ionic compounds are not considered to be "molecules. The difference in 'my model' of chemistry is that in ionic bonding the atoms don't share the electron, one just takes it, leaving the other one naked, and both with a net electrical charge.
It is more of a partnership between un-equals. This leaves the atoms free to move away from each other under many circumstances. Think of square dancing Thus they are not referred to as molecules. A covalent bond is more between equals and the electrons are shared, keeping the nuclei closer together and attached under most circumstances.
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