ionic bonding

how ionic bonds form

An ionic bond is the force of attraction that holds together positive and negative ions. It forms when atoms of a metallic element give up electrons to atoms of a nonmetallic element. The Figure 1.1 shows how this happens. In row 1 of the Figure 1.1, an atom of sodium (Na) donates an electron to an atom of chlorine (Cl). By losing an electron, the sodium atom becomes a sodium ion. It now has more protons than electrons and a charge of +1. Positive ions such as sodium are given the same name as the element. The chemical symbol has a plus sign to distinguish the ion from an atom of the element. The symbol for a sodium ion is Na+ . By gaining an electron, the chlorine atom becomes a chloride ion. It now has more electrons than protons and a charge of -1. Negative ions are named by adding the suffix -ide to the first part of the element name. The symbol for chloride is Cl . Sodium and chloride ions have equal but opposite charges. Opposite electric charges attract each other, so sodium and chloride ions cling together in a strong ionic bond. You can see this in row 2 of the Figure 1.1. (Brackets separate the ions in the diagram to show that the ions in the compound do not actually share electrons.) When ionic bonds hold ions together, they form an ionic compound. The compound formed from sodium and chloride ions is named sodium chloride. It is commonly called table salt.

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why ionic bonds form

Ionic bonds form only between metals and nonmetals. Thats because metals want to give up electrons, and nonmetals want to gain electrons. Find sodium (Na) in the Figure 1.2. Sodium is an alkali metal in group 1. Like all group 1 elements, it has just one valence electron. If sodium loses that one electron, it will have a full outer energy level, which is the most stable arrangement of electrons. Now find fluorine (F) in the periodic table Figure gains one electron, it will also have a full outer energy level and the most stable arrangement of electrons. Q: Predict what other elements might form ionic bonds. A: Metals on the left and in the center of the periodic table form ionic bonds with nonmetals on the right of the periodic table. For example, alkali metals in group 1 form ionic bonds with halogen nonmetals in group 17.

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energy and ionic bonds

It takes energy to remove valence electrons from an atom because the force of attraction between the negative electrons and the positive nucleus must be overcome. The amount of energy needed depends on the element. Less energy is needed to remove just one or a few valence electrons than many. This explains why sodium and other alkali metals form positive ions so easily. Less energy is also needed to remove electrons from larger atoms in the same group. For example, in group 1, it takes less energy to remove an electron from francium (Fr) at the bottom of the group than from lithium (Li) at the top of the group (see the Figure 1.2). In bigger atoms, valence electrons are farther from the nucleus. As a result, the force of attraction between the valence electrons and the nucleus is weaker. Q: What do you think happens when an atom gains an electron and becomes a negative ion? A: Energy is released when an atom gains an electron. Halogens release the most energy when they form ions. As a result, they are very reactive elements.

instructional diagrams

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questions

how do ionic bonds form?

-->  a) atoms of metallic elements give up electrons to atoms of nonmetallic elements.

b) atoms of nonmetallic elements give up electrons to atoms of metallic elements.

c) atoms of metallic elements accept electrons from atoms of nonmetallic elements.

d) two of the above

in an ionic bond, the metallic ion is always a positive ion.

-->  a. true

b. false

positive ions are named by adding the suffix ide to the first part of the element name.

a. true

-->  b. false

ionic bonds form only between metals and nonmetals.

-->  a. true

b. false

atoms of the element sodium want to give up an electron because sodium atoms

a) already have seven valence electrons.

b) do not need any electrons.

-->  c) have just one valence electron.

d) form negative metal ions.

metals in group 2 of the periodic table form ionic bonds with nonmetals in group

a) 15.

-->  b) 16.

c) 17.

d) 18.

diagram questions

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