Each ion has a single charge, one positive and one negative, so we need only one ion of each to balance the overall charge. It is conventional to use the lowest ratio of ions that are needed to balance the charges.įor example, consider the ionic compound between Na + and Cl −. This formula merely indicates that sodium chloride is made of an equal number of sodium and chloride ions. An ionic formula, like NaCl, is an empirical formula. In the solid state, ionic compounds are in crystal lattice containing many ions each of the cation and anion. Because the charges on the ions are characteristic, sometimes we have to have more than one of a cation or an anion to balance the overall positive and negative charges. Ionic compounds do not exist as molecules. Molecules are the simplest unit of a covalent compound, and molecules can be represented in many different ways. The key to writing proper ionic formulas is simple: the total positive charge must balance the total negative charge. Compounds can be classified as ionic or covalent. A Ca 2+ cation has twice as much charge as a Cl - anion, so it will be able to attract and cancel out the charge on two Cl - anions. Two ions with opposite charges will be attracted to each other as being close to one another allows them to cancel out the additional charge they are carrying. Two ions with the same charge will push away from each other. Ions behave the same way on the atomic scale. When the magnets push away from each other we're trying to force two like charges together. One side of each of our magnets is positive and one side of each of our magnets is negative. If you've ever tried to force two refrigerator magnets together you'll remember that there was one side of each magnet that clicked together and there was one side of each magnet that pushed against the other. A proper ionic formula has a cation and an anion in it an ionic compound is never formed between two cations only or two anions only. An element symbol without a charge written next to it is assumed to be the uncharged atom.Ĭhemical formulas for ionic compounds are called ionic formulas. If the charge is a single positive or negative one, the number 1 is not written if the magnitude of the charge is greater than 1, then the number is written before the + or − sign. The magnitude of the charge is listed as a right superscript next to the symbol of the element. Note the convention for indicating an ion. In ionic compounds and polyatomic ions charges. Group of ions with the lowest ratio of ions in an ionic compound. Unfortunately, there is little understanding which two charges a metal atom may take, so it is best to just memorize the possible charges a particular element can have. B) contains a group of two or more atoms with a positive charge. Cobalt (Co) is another element that can form more than one possible charged ion (2+ and 3+), while lead (Pb) can form 2+ or 4+ cations. For example, iron (Fe) atoms can form 2+ cations or 3+ cations. A few elements, all metals, can form more than one possible charge. Examination of the table in the link given shows that there are some exceptions to the previous point. A more complete table of ions and their charges can be found at Monotomic Ions of Various Charges. the ions formed are negative, because they have more electrons than protonsįor elements in groups 6 and 7, the charge on the ion is equal to (8 minus group number).\) is helpful in determining the charge on a large number of our cations and anions it's hardly complete. IONIC COMPOUNDS versus MOLECULAR COMPOUNDS ionic compound: consist of cations (positive ions) and anions (negative ions).The outer shells of non-metal atoms gain electrons when they form ions: A sodium atom loses one electron to form a sodium ion Forming negative ions the ions have the electronic structure of a noble gas (group 0 element), with a full outer shellįor elements in groups 1, 2 and 3, the number of electrons lost is the same as the group number.the ions are positive, because they have more protons than electrons Nomenclature, a collection of rules for naming things, is important in science and in many other situations.This module describes an approach that is used to name simple ionic and molecular compounds, such as NaCl, CaCO 3, and N 2 O 4.Metal atoms lose electrons from their outer shell when they form ions: non-metal atoms gain electrons to form negatively charged ions.metal atoms lose electrons to form positively charged ions.Ions form when atoms lose or gain electrons to obtain a full outer shell: An ion is an atom or group of atoms with a positive or negative charge.
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