Molecular Compounds Sharing Electrons

LEARNIH6 GOAL Write the name and formula for an ionic compound containing a polyatomic ion. 

633 Write the formula including the charge for the following polyatomic ions  

37 Complete the following table with the formula and name of the compound that forms between each pair of ions  

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Chapter 6, Ionic and Molecular Compounds, describes the formation of ionic and covalent bonds. Chemical formulas are written, and ionic compounds—including those with polyatomic ions—and molecular compounds are named. Section 6.1 is now titled Ions Transfer of Electrons, 6.2 is titled Writing Formulas for Ionic Compounds, 6.3 is titled Naming Ionic Compounds, and 6.5 is titled Molecular Compounds Sharing Electrons. ... 

Ionic compounds are made up of positively charged ions (usually metal ions) and negatively charged ions (usually non-metal ions or polyatomic anions) held together by electrostatic forces of attraction. Molecular compounds are made up of discrete units called molecules. Generally they consist of a small number of nonmetal atoms held together by covalent bonds (sharing of electrons). 

If a nonmetal reacts with another nonmetal no electrons are lost or gained, but are shared. We call such compounds covalent (molecular) compounds. These compounds contain small units we call molecules. Ammonia, NH3, water, H20, and methane, CH4, are examples of covalent compounds. 

It is possible to have more than two electrons shared between two atoms, and Figure 6.18 shows a few examples. Molecular oxygen, 02, which is what we breathe, consists of two oxygen atoms connected by four shared electrons. This arrangement is called a double covalent bond or, for short, a double bond. As another example, the covalent compound carbon dioxide, C02, which is what we exhale, consists of two double bonds connecting two oxygen atoms to a central carbon atom. 

An oxidation-reduction reaction has to be accompanied by a change in the oxidation state of the reactants. Sometimes, these changes aren t that obvious. It helps if you learn how to follow the oxidation states of an element during a chemical reaction. In ionic compounds, it is very obvious where the electrons have been transferred. However, in molecular compounds, electrons are being shared. Oxidation numbers are really fictitious creations that help us better understand atomic behavior. If you remember back to Chapter 6 when we discussed covalent bonds, you may recall that electrons are being shared between atoms in a covalent bond. In many cases, one atom is more electronegative than the other, resulting in a polar... 

A molecular compound is formed when a non-metal and metal combine to form a covalent bond. Covalent bonds are the type of bonds formed when two atoms share one or more pairs of electrons to achieve an octet of electrons. A polar covalent bond is formed when the atoms unequally share paired electrons. 

In other situations, the neutral oxygen atom may share electrons with one or more other atoms, in order to act as though it has a complete valence shell part of the time. These shared electrons represent covalent bonds and result in the formation of molecular compounds, as shown here ... 

Finally, we must discuss the fact that many compounds contain both ionic and covalent bonds. This occurs when compounds contain special ions called polyatomic ions. Polyatomic ions are simply ions that are made up of more than one atom. How do such ions form Think back to the example of oxygen, with six valence electrons. If an atom of oxygen steals two additional electrons to complete its valence shell, it becomes the oxide (O2 ) ion. If it shares two pairs of electrons with two hydrogen atoms, it becomes part of a neutral molecule of water (HzO). However, if it steals one electron and shares one pair with an atom of hydrogen, you get a molecular compound, which is also an ion, the polyatomic ion called hydroxide (OH ). A polyatomic ion can then attach to another ion with an opposite charge, forming an ionic compound such as sodium hydroxide (NaOH), which contains both ionic and covalent bonds. 

The Covalent Bond Atoms of many elements become more stable by sharing electrons. The chemical bond that forms between nonmetal atoms when they share electrons is called a covalent (koh VAY luhnt) bond. Shared electrons are attracted to the nuclei of both atoms. They move back and forth between the outer energy levels of each atom in the covalent bond. So, each atom has a stable outer energy level some of the time. Covalently bonded compounds are called molecular compounds. 

The atoms in a covalent bond form a neutral particle, which contains the same numbers of positive and negative charges. The neutral particle formed when atoms share electrons is called a molecule (MAH lih kyewl). A molecule is the basic unit of a molecular compound. You can see how molecules form by sharing electrons in Figure 16. Notice that no ions are involved because no electrons are gained or lost. Crystalline solids, such as sodium chloride, are not referred to as molecules, because their basic units are ions, not molecules. 

Molecular Compounds when certain atoms form compounds, they share electrons. Sharing electrons is called covalent bonding. Compounds that contain covalent bonds are called molecular compounds, or molecules. 

Atomic hydrogen has the electron configuration. It reacts with metals and with other nonmetals to form binary compounds called hydrides. These can be (a) ionic hydrides, which contain hydride ions, H, formed when hydrogen gains one electron per atom from an active metal or (2) molecular hydrides, in which hydrogen shares electrons with an atom of another nonmetal. 

It is seen that, every time a compound may be described by a unique Lewis formula, the latter corresponds quite well to the picture given by the centroid of charge distribution. Each dot plays the same role as a line in the Lewis formula, but we must emphasize that a dot is the centroid of charge of a doubly occupied localized orbital and not a localized shared electron pair. In other words, the presence of a centroid of charge in a given molecular region does not necessarily imply that two electrons are confined in the same region. This remark can be illustrated by two typical... 

Another way that atoms can achieve stability is by sharing electrons with other atoms to form molecules. A compound formed by electron sharing is a covalent compound, also called a molecular compound. 

The bonding pi orbital 71) follows regions separate from a line drawn between the two atoms in a bond. Two overlapping p orbitals will form n bonds to contain the additional shared electrons in molecules with double or triple bonds, n bonds prevent atoms from rotating about the central axis between them. The atomic orbitals that form the compound C2H4 are shown above to the left. Each H atom contains one electron in an s orbital and each C atom contains 4 valence electrons in three hybrid sp2 orbitals and one p orbital. The compound itself contains the molecular orbitals shown below to the left. There are five a bonds (white ovals) and one n bond (the shaded shapes). For additional examples of n bonds in carbon compounds, see Skill 6.1a. 

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