chapter 6 covalent compounds section 1 – covalent bonds sharing electrons you learned that...

Chapter 6 Covalent CompoundsSection 1 – Covalent Bonds

Sharing Electrons

You learned that electrons are rearranged when an ionic bond forms.When this happens, electrons transfer from one atom to another to formcharged ions. Covalent bonds are different because electrons are not transferred from one atom to another, they are shared between two atoms.

Summary:Ionic Bonds: a metal will lose an electron and a nonmetal will gain an electron forming ions that are ionicly bonded.

Covalent Bonds: atoms will share a pair of electrons between them forming a covalent bond.


Atoms Share Electrons Equally or UnequallyYour reference table lists the electronegativity values for several elements. In a molecule such as H2, the values of the two atoms in the bond are equal. Becauseeach one attracts the bonding electrons with the same force, they sharethe electrons equally. A non polar covalent bond is a covalent bond in which the bonding electrons are shared equally.

If the values differ significantly, the two atoms form a different type of covalentbond. Think about a carbon atom bonding with an oxygen atom. The Oatom has a higher electronegativity and attracts the bonding electrons morethan the C atom does. As a result, the two atoms share the bonding electrons,but unequally. This type of bond is a polar covalent bond. In a polarcovalent bond, the shared electrons are more likely to be found nearer to the atom whose electronegativity is higher.

If the difference in electronegativity values of the two atoms is greatenough, the atom with the higher value may remove an electron from theother atom. An ionic bond will form.


Polar Molecules Have Positive and Negative EndsThe difference between the electronegativity values of hydrogen and fluorine shows that H and F atoms form a polar covalent bond. The word polar suggests that this bond has ends that are in some way opposite one another, like the two poles of a planet, a magnet, or a battery. In fact, the ends of the HF molecule have opposite partial charges.

The electronegativity of fluorine (4.0) is much higher than that ofhydrogen (2.2). Therefore, the shared electrons are more likely to befound nearer to the fluorine atom. For this reason, the fluorine atom inthe HF molecule has a partial negative charge. In contrast, the sharedelectrons are less likely to be found nearer to the hydrogen atom.

As a result, the hydrogen atom in the HF molecule has a partial positivecharge. A molecule in which one end has a partial positive charge and theother end has a partial negative charge is called a dipole The HF moleculeis a dipole.


To emphasize the dipole nature of the HF molecule, the formula canbe written as H + F −. The symbol is a lowercase Greek delta, which isused in science and math to mean partial. With polar molecules, such asHF, the symbol + is used to show a partial positive charge on one end ofthe molecule. Likewise, the symbol − is used to show a partial negativecharge on the other end.

Although + means a positive charge, and − means a negative charge,these symbols do not mean that the bond between hydrogen and fluorineis ionic. An electron is not transferred completely from hydrogen to fluorine,as in an ionic bond. Instead, the atoms share a pair of electrons,which makes the bond covalent. However, the shared pair of electrons ismore likely to be found nearer to the fluorine atom. This unequal distributionof charge makes the bond polar covalent.


H - F+ -


The diagram below shows the relationship between electronegativity differences and the type of bond that forms between two elements. Notice the general rulethat can be used to predict the type of bond that forms. If the difference inelectronegativity is between 0 and 0.5, the bond is probably nonpolar covalent.If the difference in electronegativity is between 0.5 and 2.1, the bondis considered polar covalent. If the difference is larger than 2.1, then thebond is usually ionic. Remember that this method of classifying bonds isjust one model. Another general rule states that covalent bonds tend to formbetween nonmetals, while a nonmetal and a metal will form an ionic bond.

Bonds Can Be Classified by Bond Character


Properties of Substances Depend on Bond TypeThe type of bond that forms determines the physical and chemical propertiesof the substance. For example, metals, such as potassium, are very goodelectric conductors in the solid state. This property is the result of metallicbonding. Metallic bonds are the result of the attraction between the electronsin the outermost energy level of each metal atom and all of the otheratoms in the solid metal. The metal atoms are held in the solid because allof the valence electrons are attracted to all of the atoms in the solid. Thesevalence electrons can move easily from one atom to another. They are freeto roam around in the solid and can conduct an electric current. These mobile electrons are sometime referred to as a “sea of mobile electrons”


In ionic substances, the overall attraction between all the cations andanions is very strong. Ionic compounds, such as potassium chloride, KCl,are made up of many K+ and Cl− ions. Each ion is held into place by manyoppositely charged neighbors, so the forces—the ionic bonds—that holdthem together are very strong and hard to break. In molecular substances, such as Cl2, the molecules are held togetherby sharing electrons. The shared electrons are attracted to the two bondingatoms, and they have little attraction for the atoms of other nearbymolecules. Therefore, the attractive forces between separate Cl2 moleculesare very small compared to the attractive forces between the ions in KCl.


Energy in Bonding

Energy is absorbed when a bond is broken.

Energy is released when a bond is formed.


Section Summary

Ionic Bonds form between metals and nonmetals with a transfer of electronsfrom the metal to the nonmetal forming ions. These ions highly attract ions of opposite charge around them making ionic bond strong.

Covalent bonds form between nonmetals with nonmetals when there is not enough electronegativity difference to allow a transfer of electrons. Becauseelectrons can not be transferred, they are shared. If the electrons are sharedEqually the bond is nonpolar, if the are shared unequally they are called polar.

Metallic bonds form between metals with other metals. The valence electrons in metals are loosely held and tend to be shared with metal atom that are nearby.This sea of mobile electrons is stronger than covalent bonds and is why metalsconduct heat and electricity well.


Two atoms with an electronegativity difference of 0.4 form a bond that is1. ionic, because electrons are shared 2. ionic, because electrons are transferred 3. covalent, because electrons are shared 4. covalent, because electrons are transferred

Which factor distinguishes a metallic bond from an ionic bond or a covalent bond?1. the mobility of electrons 2. the mobility of protons 3. the equal sharing of electrons 4. the unequal sharing of electrons

A white crystalline salt conducts electricity when it is melted and when it is dissolved in water. Which type of bond does this salt contain?1. ionic 2. metallic 3. covalent 4. network


In a nonpolar covalent bond, electrons are1. located in a mobile "sea" shared by many ions 2. transferred from one atom to another 3. shared equally by two atoms 4. shared unequally by two atoms

Which diagram best represents a polar molecule?


The ability to conduct electricity in the solid state is a characteristic of metallic bonding. This characteristic is best explained by the presence of1. high ionization energies 2. high electronegativities 3. mobile electrons 4. mobile protons

Which structural formula represents a nonpolar molecule?


Which formula represents a molecular substance?1. CaO 2. CO 3. Li2O 4. Al2O3

Which combination of atoms can form a polar covalent bond?1. H and H 2. H and Br 3. N and N 4. Na and Br

Which of the following elements has the highest electronegativity?1. H 2. K 3. Al 4. Ca


Which bond is most polar?1. H-F 2. H-Cl 3. H-Br 4. H-I

When a chemical bond is broken, energy is1. absorbed, only 2. released, only 3. both absorbed and released 4. neither absorbed nor released

The bonds in the compound MgSO4 can be described as1. ionic, only 2. covalent, only 3. both ionic and covalent 4. neither ionic nor covalent


As two chlorine atoms combine to form a molecule, energy is1. absorbed 2. released 3. created 4. destroyed

Covalent bonds are formed when electrons are1. transferred from one atom to another 2. captured by the nucleus 3. mobile within a metal 4. shared between two atoms

chapter 6 covalent compounds section 1 – covalent bonds sharing electrons you learned that...

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