The positive and negative charges must balance, and this ionic compound must be electrically neutral. We designate this by enclosing the formula for the dihydrogen phosphate ion in parentheses and adding a subscript 2. The formula is Ca H 2 PO 4 2. Because an ionic compound is not made up of single, discrete molecules, it may not be properly symbolized using a molecular formula.
Instead, ionic compounds must be symbolized by a formula indicating the relative numbers of its constituent cations. However, the formulas for some ionic compounds containing polyatomic ions are not empirical formulas. Many compounds do not contain ions but instead consist solely of discrete, neutral molecules. These molecular compounds covalent compounds result when atoms share, rather than transfer gain or lose , electrons.
Covalent bonding is an important and extensive concept in chemistry, and it will be treated in considerable detail in a later module of this text. We can often identify molecular compounds on the basis of their physical properties. Under normal conditions, molecular compounds often exist as gases, low-boiling liquids, and low-melting solids, although many important exceptions exist. Whereas ionic compounds are usually formed when a metal and a nonmetal combine, covalent compounds are usually formed by a combination of nonmetals.
Thus, the periodic table can help us recognize many of the compounds that are covalent. 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 charge 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 nonmetals.
Skip to main content. Module 2: Atoms, Molecules, and Ions. Search for:. Molecular and Ionic Compounds Learning Outcomes Define ionic and molecular covalent compounds Predict the type of compound formed from elements based on their location within the periodic table Determine formulas for simple ionic compounds. Example 1: Composition of Ions An ion found in some compounds used as antiperspirants contains 13 protons and 10 electrons.
Show Solution Because the number of protons remains unchanged when an atom forms an ion, the atomic number of the element must be Example 2: Formation of Ions Magnesium and nitrogen react to form an ionic compound. Show Solution Because the ionic compound must be electrically neutral, it must have the same number of positive and negative charges.
Show Solution Na 2 S. Show Solution The positive and negative charges must balance, and this ionic compound must be electrically neutral. Show Solution Li 2 O 2. Ionic Bonding Ionic bonds form between metals and nonmetals. Example 5: Predicting the Type of Bonding in Compounds Predict whether the following compounds are ionic or molecular: KI, the compound used as a source of iodine in table salt H 2 O 2 , the bleach and disinfectant hydrogen peroxide CHCl 3 , the anesthetic chloroform Li 2 CO 3 , a source of lithium in antidepressants Show Solution Potassium group 1 is a metal, and iodine group 17 is a nonmetal; KI is predicted to be ionic.
Hydrogen group 1 is a nonmetal, and oxygen group 16 is a nonmetal; H 2 O 2 is predicted to be molecular. Carbon group 14 is a nonmetal, hydrogen group 1 is a nonmetal, and chlorine group 17 is a nonmetal; CHCl 3 is predicted to be molecular. For example, the formula for calcium phosphate, one of the minerals in our bones, is Ca 3 PO 4 2.
The compound is electrically neutral, and its formula shows a total count of three Ca, two P, and eight O atoms. Solution The positive and negative charges must balance, and this ionic compound must be electrically neutral. We designate this by enclosing the formula for the dihydrogen phosphate ion in parentheses and adding a subscript 2.
The formula is Ca H 2 PO 4 2. Because an ionic compound is not made up of single, discrete molecules, it may not be properly symbolized using a molecular formula.
Instead, ionic compounds must be symbolized by a formula indicating the relative numbers of its constituent ions. For compounds containing only monatomic ions such as NaCl and for many compounds containing polyatomic ions such as CaSO 4 , these formulas are just the empirical formulas introduced earlier in this chapter.
However, the formulas for some ionic compounds containing polyatomic ions are not empirical formulas. The subscripts in this formula are not the smallest-possible whole numbers, as each can be divided by 2 to yield the empirical formula, NaCO 2. Many compounds do not contain ions but instead consist solely of discrete, neutral molecules. These molecular compounds covalent compounds result when atoms share, rather than transfer gain or lose , electrons.
Covalent bonding is an important and extensive concept in chemistry, and it will be treated in considerable detail in a later chapter of this text. We can often identify molecular compounds on the basis of their physical properties. Under normal conditions, molecular compounds often exist as gases, low-boiling liquids, and low-melting solids, although many important exceptions exist.
Whereas ionic compounds are usually formed when a metal and a nonmetal combine, covalent compounds are usually formed by a combination of nonmetals. Thus, the periodic table can help us recognize many of the compounds that are covalent. Predicting the Type of Bonding in Compounds Predict whether the following compounds are ionic or molecular:. Solution a Potassium group 1 is a metal, and iodine group 17 is a nonmetal; KI is predicted to be ionic. Check Your Learning Using the periodic table, predict whether the following compounds are ionic or covalent:.
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 nonmetals. Skip to content Chapter 2. Atoms, Molecules, and Ions. Learning Objectives By the end of this section, you will be able to: Define ionic and molecular covalent compounds Predict the type of compound formed from elements based on their location within the periodic table Determine formulas for simple ionic compounds.
Example 1 Composition of Ions An ion found in some compounds used as antiperspirants contains 13 protons and 10 electrons. Example 2 Formation of Ions Magnesium and nitrogen react to form an ionic compound.
In general, metallic elements tend to form ionic compounds, and non-metallic elements tend to form covalent bonds. Ionic compounds are a result of ionic bonds ; ionic bonds are formed through the electrostatic forces between atoms that attract them towards each other due to opposite electrical charges.
Each element tries to achieve a stable electronic configuration, i. The atoms that have already achieved a noble gas electronic configuration are not reactive since they are already stable. But the elements that have not gained a stable electronic configuration tend to give away or receive the required number of electrons to achieve the closest noble gas configuration. Ions are formed by this principle. When in liquid form, they become excellent conducting materials as the ions are free to travel.
Ions can be atomic or molecular in nature. CO 3 2- is a molecular anion. Few examples of ionic compounds are NaCl, MgCl 2, etc. Covalent bonds are much weaker than ionic bonds and, therefore, most of the molecular compounds exist in the gaseous phase.
0コメント