Quick Review: Ionic Compounds and Ionic Bond (Quick Review Notes Book 1)

Sections: Two Types of Bonding. Ions. Electron Transfer. Lewis Diagrams. Covalent Bonding and Simple Molecular Compounds. Covalent Bonds.
Table of contents

Need a Chemistry Tutor? Is Study Abroad Right for You? Is Study Abroad Affordable? College Credit in High School. This content can also be downloaded as a PDF file. For the interactive PDF, adobe reader is required for full functionality. This text is published under creative commons licensing, for referencing and adaptation, please click here. There are only known chemical elements but tens of millions of known chemical compounds. Compounds can be very complex combinations of atoms, but many important compounds are fairly simple. Table salt, as we have seen, consists of only two elements: Nevertheless, the compound has properties completely different from either elemental sodium a chemically reactive metal or elemental chlorine a poisonous, green gas.

We will see additional examples of such differences in section 3. Atoms can join together by forming a chemical bond, which is a very strong attraction between two atoms.

Ionic Bonds

Chemical bonds are formed when electrons in different atoms interact with each other to make an arrangement that is more stable than when the atoms are apart. What causes atoms to make a chemical bond with other atoms, rather than remaining as individual atoms? A clue comes by considering the noble gas elements, the rightmost column of the periodic table.

These elements—helium, neon, argon, krypton, xenon, and radon—do not form compounds very easily, which suggests that they are especially stable as lone atoms. What else do the noble gas elements have in common? Except for helium, they all have eight valence electrons. Chemists have concluded that atoms are especially stable if they have eight electrons in their outermost shell. This useful rule of thumb is called the octet rule , and it is a key to understanding why compounds form. There are two ways for an atom that does not have an octet of valence electrons to obtain an octet in its outer shell.

One way is the transfer of electrons between two atoms until both atoms have octets.

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Because some atoms will lose electrons and some atoms will gain electrons, there is no overall change in the number of electrons, but with the transfer of electrons the individual atoms acquire a nonzero electric charge. Those that lose electrons become positively charged, and those that gain electrons become negatively charged.

Charged atoms are called ions. Because opposite charges attract while like charges repel , these oppositely charged ions attract each other, forming ionic bonds. The resulting compounds are called ionic compounds. The second way for an atom to obtain an octet of electrons is by sharing electrons with another atom. These shared electrons simultaneously occupy the outermost shell of both atoms. The bond made by electron sharing is called a covalent bond. Most atoms do not have eight electrons in their valence electron shell. Some atoms have only a few electrons in their outer shell, while some atoms lack only one or two electrons to have an octet.

Atoms, compounds, and ions | Chemistry | Science | Khan Academy

In cases where an atom has three or fewer valence electrons, the atom may lose those valence electrons quite easily until what remains is an octet in the next lower shell. Atoms that lose electrons acquire a positive charge as a result because they are left with fewer negatively charged electrons to balance the positive charges of the protons in the nucleus. Positively charged ions are called cations. Most metals become cations when they make ionic compounds. Some atoms have nearly eight electrons in their valence shell and can readily gain additional valence electrons until they have an octet.

When these atoms gain electrons, they acquire a negative charge because they now possess more electrons than protons. Negatively charged ions are called anions. Most nonmetals become anions when they make ionic compounds. We can use valence electrons and the octet rule to illustrate the electron transfer process between sodium atoms and chlorine atoms.

As demonstrated in Example 1 below , sodium is likely to achieve an octet in its outermost shell by losing its one valence electron. The outermost shell of the sodium ion is the second electron shell, which has eight electrons in it. The octet rule has been satisfied. The Formation of a Sodium Ion. On the left, a sodium atom has 11 electrons.

Note that the sodium ion now has an outer electron shell that has eight electrons, fulfilling the octet rule. In table salt, NaCl, this electron comes from the sodium atom. The Formation of a Chloride Ion. On the left, a chlorine atom has 17 electrons. Note that the chloride ion has now filled its outer shell and contains eight electrons, satisfying the octet rule. In this case, the ion has the same outermost shell as the original atom, but now that shell has eight electrons in it. Once again, the octet rule has been satisfied.

With two oppositely charged ions, there is an electrostatic attraction between them because opposite charges attract. The resulting combination is the ionic compound sodium chloride. Notice that there are no leftover electrons. In macroscopic samples of sodium chloride, there are billions and billions of sodium and chloride ions, although there is always the same number of cations and anions. In many cases, elements that belong to the same group vertical column on the periodic table form ions with the same charge, because they have the same number of valence electrons.

Thus, the periodic table becomes a tool for remembering the charges on many ions. Note the convention of first writing the number and then the sign on a multiply-charged ion. The Octet Rule can be used to help you predict how many electrons an element must gain or lose to achieve an electron configuration similar to the Noble Gases.

Note that the first 3 Main Group Columns typically lose electrons to achieve the octet, while columns typically gain electrons to reach the octet.

Notice column 4, it is right in the middle and is left blank. Elements in column 4 contain 4 electrons in their valence shell. The valence electrons are most distant from the nucleus; thus, they are weakly held by the electrostatic attraction of the protons and, consequently, are easily stripped from atoms of the metals. By contrast, the nonmetallic elements on the right side of the periodic table have fewer electrons than that of a stable configuration and can most readily attain the stable configuration of the inert gases by gaining electrons.


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The negative charge on the resulting nonmetal ion is due to the atom possessing more orbital electrons than nuclear protons. Table 2 compares three nonmetals to the inert gas argon. Because metallic elements tend to lose electrons and nonmetallic elements tend to gain electrons, a pair of contrasting elements will exchange electrons so that both achieve stable electronic configurations. The resulting ions of opposite charge have a strong force of electrostatic attraction, which is called an ionic bond. This bond forms through the complete transfer of electrons from one atom to another, in contrast to the electron sharing of the covalent bond.

The force of attraction between two points of opposite electrical charge is given by Coulomb's law: This law of electrostatic attraction can be used to measure the distance between two spherical ions because the charges can be considered to be located at the center of each sphere.

Notice that the distance between the centers of the two ions is the sum of radii of the ions. The appropriate electrostatic force then is calculated from the equation. The strength of ionic bonding, therefore, depends on both the charges and the sizes of the two ions. Higher charges and smaller sizes produce stronger bonds.

Table 3 shows the approximate radii of selected ions, which have the electronic configuration of an inert gas. The radii are in. For ions of the same charge, the ionic radius increases as you go down any column because the elements of higher atomic number have a greater number of electrons in a series of electronic shells progressively farther from the nucleus. The change in ionic size along a row in the chart just above shows the effect of attraction by protons in the nucleus.

For continuity, the neutral Ne atom is also in the chart, with its atomic radius. As you proceed to the right in Table 4, the greater number of protons attracts the electrons more strongly, producing progressively smaller ions. Metals tend to lose electrons, so they become cations and have a net positive charge.


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Nonmetals tend to gain electrons, forming anions that have a net negative charge. Just like opposite poles of a magnet attract, so do opposite ionic charges. Ions of opposite charge are held together by very strong ionic bonds within the compound. These bonds form a unique crystal lattice structure, making them difficult to break. However, put these compounds in a polar substance like water, and the opposite charges that surround it are able to break apart the ions and dissolve them into the liquid. Ionic compounds must be balanced - the sum of the positive and negative charges must equal zero.

But while the charges of an ionic compound are the sum of their parts, the substance that is formed is quite different. Separately, you would not want to eat sodium as a metal or chlorine as a gas. But put them together in salt, and they make a tasty addition to that order of fries you had for lunch! To unlock this lesson you must be a Study. Did you know… We have over college courses that prepare you to earn credit by exam that is accepted by over 1, colleges and universities.


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What Are Ionic Compounds? In this video lesson, you will learn about their formation and structure and see examples of compounds formed by ions. An error occurred trying to load this video. Try refreshing the page, or contact customer support. You must create an account to continue watching. Register to view this lesson Are you a student or a teacher? I am a student I am a teacher. What teachers are saying about Study.

Quiz: Ionic Bonds

Are you still watching? Your next lesson will play in 10 seconds. Add to Add to Add to. Want to watch this again later? Formation, Lattice Energy and Properties. Writing Ionic Compound Formulas: Predicting Formation, Charge, and Formulas of Ions. Rules for Naming Ionic Compounds. What is a Metallic Bond? Holt McDougal Modern Biology: Ionic compounds are a common, yet special type of chemical compound. Ionic Compounds Each atom is unique because it is made of a specific number of protons, neutrons, and electrons.

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Ionic Compounds Are Balanced Table salt is an example of an ionic compound. Structure of Ionic Compounds Ionic compounds are special because they form lattice or crystalline structures. Try it risk-free No obligation, cancel anytime. Want to learn more? Select a subject to preview related courses: Lesson Summary Ionic compounds are compounds made up of ions.

Learning Outcomes Once you've completed this lesson, you'll be able to: Define ions, ionic compounds, anions and cations Summarize how ionic compounds are formed Explain why the charges on ionic compounds must be balanced Describe the structure of ionic compounds. Unlock Your Education See for yourself why 30 million people use Study. Become a Member Already a member? Earning College Credit Did you know… We have over college courses that prepare you to earn credit by exam that is accepted by over 1, colleges and universities.

Ionic Bonds

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