AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |
Back to Blog
The anion, O 2−, has the same number of electrons as the next noble gas – neon. This results in an anion with 8 protons, 10 electrons, and a 2− charge, and is symbolized as O 2−. For example, a neutral oxygen atom, with 8 protons and 8 electrons, readily gains two electrons. That is, atoms of group 17 gain one electron and form anions with a 1− charge atoms of group 16 gain two electrons and form ions with a 2− charge, and so on. Moving from the far right to the left on the periodic table, nonmetal elements often gain electrons to form anions with the same number of electrons as an atom of the next noble gas in the periodic table, and a negative charge equal to the number of groups moved left from the noble gases. The compound formed by this transfer is stabilized by the electrostatic attractions (ionic bonds) between the oppositely charged ions. There are two ways to recognize ionic compounds.An element composed of atoms that readily lose electrons (a metal) can react with an element composed of atoms that readily gain electrons (a nonmetal) to produce ions through complete electron transfer. Thus, the formula for this ionic compound is Fe 2O 3. To balance the positive and negative charges, we look to the least common multiple-6: two iron 3+ ions will give 6+, while three 2− oxygen ions will give 6−, thereby balancing the overall positive and negative charges. The oxygen atom has a 2− charge as an ion. Iron can form two possible ions, but the ion with a 3+ charge is specified here.Three fluorine 1− ions are needed to balance the 3+ charge on the aluminum ion. The aluminum ion has a 3+ charge, while the fluoride ion formed by fluorine has a 1− charge.Rather than writing the formula as NaNaS, we shorten it by convention to Na 2S. Two sodium 1+ ions are needed to balance the 2− charge on the sulfur ion. To obtain a valence shell octet, sodium forms an ion with a 1+ charge, while the sulfur ion has a 2− charge.Write the chemical formula for an ionic compound composed of each pair of ions. The formula Mg 2Cl 4 has balanced charges with the ions in a 1:2 ratio, but it is not the lowest whole number ratio. Rather, it exists as two individual chloride ions.) By convention, the lowest whole number ratio is used in the formulas of ionic compounds. Chlorine does not exist as a diatomic element in this compound. (Do not read the “Cl 2” part of the formula as a molecule of the diatomic elemental chlorine. This chemical formula says that there are one magnesium ion and two chloride ions in this formula. We could write the chemical formula for this ionic compound as MgClCl, but the convention is to use a numerical subscript when there is more than one ion of a given type-MgCl 2. Now the positive and negative charges are balanced. The easiest way to balance these charges is to assume the presence of two chloride ions for each magnesium ion: A magnesium ion has a 2+ charge, while a chlorine ion has a 1− charge:Ĭombining one ion of each does not completely balance the positive and negative charges. Now consider the ionic compound formed by magnesium and chlorine. Therefore, the proper formula for this ionic compound is MgO. Although both of these ions have higher charges than the ions in lithium bromide, they still balance each other in a one-to-one ratio. When an ionic compound is formed from magnesium and oxygen, the magnesium ion has a 2+ charge, and the oxygen atom has a 2− charge. Only one ion of each is needed to balance these charges. If we look at the ionic compound consisting of lithium ions and bromide ions, we see that the lithium ion has a 1+ charge and the bromide ion has a 1− charge. This rule is ultimately based on the fact that matter is, overall, electrically neutral.īy convention, assume that there is only one atom if a subscript is not present. To determine the proper formula of any combination of ions, determine how many of each ion is needed to balance the total positive and negative charges in the compound. Finally, the proper formula for an ionic compound always obeys the following rule: the total positive charge must equal the total negative charge. Remember that in an ionic compound, the component species are ions, not neutral atoms, even though the formula does not contain charges. Second, charges are not written in a formula. Because most metals form cations and most nonmetals form anions, formulas typically list the metal first and then the nonmetal. First, the cation is written before the anion. The formula for an ionic compound follows several conventions. A crystal of sodium chloride, shown here, is a collection of alternating sodium and chlorine ions. The precise pattern depends on the compound. A crystal contains a three-dimensional array of alternating positive and negative ions.
0 Comments
Read More
Leave a Reply. |