State the number of atoms of each type in one molecule of methane, CH 4. A methane molecule is made up of one atom of carbon and four atoms of hydrogen. State the number and type of atoms in one molecule of chlorine, Cl 2. A chlorine molecule is made up of two chlorine atoms. An explanation of covalent bonding. Covalent bonds Forming a covalent bond A covalent bond is formed when two atoms share a pair of electrons.
Two hydrogen atoms. Two oxygen atoms. Two nitrogen atoms. Hydrogen chloride. However, the Lewis theory of covalent bonding does not account for some observations of compounds in nature. The theory predicts that with more shared electrons, the bond between the two atoms should be stronger.
According to the theory, triple bonds are stronger than double bonds, and double bonds are stronger than single bonds. This is true. However, the theory implies that the bond strength of double bonds is twice that of single bonds, which is not true. Therefore, while the covalent bonding model accounts for many physical observations, it does have its limitations. Privacy Policy. Skip to main content. Basic Concepts of Chemical Bonding. Search for:. Learning Objectives Identify element pairs which are likely to form ionic or covalent bonds.
Key Takeaways Key Points Ionic compounds are formed from strong electrostatic interactions between ions, which result in higher melting points and electrical conductivity compared to covalent compounds. Covalent compounds have bonds where electrons are shared between atoms. Due to the sharing of electrons, they exhibit characteristic physical properties that include lower melting points and electrical conductivity compared to ionic compounds. Key Terms valence electrons : Electrons in the outermost principal energy valence level of an atom that can participate in the formation of chemical bonds with other atoms.
Hydrogen and helium are exceptions because they can hold a maximum of two valence electrons. Single Covalent Bonds Single covalent bonds are sigma bonds, which occur when one pair of electrons is shared between atoms. Learning Objectives Identify the four orbital types used in covalent bond formation. Key Takeaways Key Points Covalent bonds occur when electrons are shared between two atoms.
A single covalent bond is when only one pair of electrons is shared between atoms. A sigma bond is the strongest type of covalent bond, in which the atomic orbitals directly overlap between the nuclei of two atoms. Sigma bonds can occur between any kind of atomic orbitals; the only requirement is that the atomic orbital overlap happens directly between the nuclei of atoms.
Key Terms sigma bond : A covalent bond whose electron density is concentrated in the region directly between the nuclei. Double and Triple Covalent Bonds Double and triple bonds, comprised of sigma and pi bonds, increase the stability and restrict the geometry of a compound. Learning Objectives Describe the types of orbital overlap that occur in single, double, and triple bonds. Key Takeaways Key Points Double and triple covalent bonds are stronger than single covalent bonds and they are characterized by the sharing of four or six electrons between atoms, respectively.
Double and triple bonds are comprised of sigma bonds between hybridized orbitals, and pi bonds between unhybridized p orbitals. Double and triple bonds offer added stability to compounds, and restrict any rotation around the bond axis.
Bond lengths between atoms with multiple bonds are shorter than in those with single bonds. Key Terms bond strength : Directly related to the amount of energy required to break the bond between two atoms.
The more energy required, the stronger the bond is said to be. It can be experimentally determined. Physical Properties of Covalent Molecules The covalent bonding model helps predict many of the physical properties of compounds.
Learning Objectives Discuss the qualitative predictions of covalent bond theory on the boiling and melting points, bond length and strength, and conductivity of molecules. Key Takeaways Key Points The Lewis theory of covalent bonding says that the bond strength of double bonds is twice that of single bonds, which is not true. General physical properties that can be explained by the covalent bonding model include boiling and melting points, electrical conductivity, bond strength, and bond length.
Key Terms bond length : The distance between the nuclei of two bonded atoms. It is not possible to measure lattice energies directly. However, the lattice energy can be calculated using the equation given in the previous section or by using a thermochemical cycle. Figure 9. We begin with the elements in their most common states, Cs s and F 2 g. In the next step, we account for the energy required to break the F—F bond to produce fluorine atoms. Converting one mole of fluorine atoms into fluoride ions is an exothermic process, so this step gives off energy the electron affinity and is shown as decreasing along the y -axis.
We now have one mole of Cs cations and one mole of F anions. These ions combine to produce solid cesium fluoride. The enthalpy change in this step is the negative of the lattice energy, so it is also an exothermic quantity. In this case, the overall change is exothermic. Table 9. Thus, the lattice energy can be calculated from other values. For cesium fluoride, using this data, the lattice energy is:.
The Born-Haber cycle may also be used to calculate any one of the other quantities in the equation for lattice energy, provided that the remainder is known. Lattice energies calculated for ionic compounds are typically much higher than bond dissociation energies measured for covalent bonds. Keep in mind, however, that these are not directly comparable values. For ionic compounds, lattice energies are associated with many interactions, as cations and anions pack together in an extended lattice.
For covalent bonds, the bond dissociation energy is associated with the interaction of just two atoms. As an Amazon Associate we earn from qualifying purchases.
Want to cite, share, or modify this book? This book is Creative Commons Attribution License 4. Skip to Content Go to accessibility page. Chemistry: Atoms First 2e 9. My highlights. Table of contents. Answer Key. By the end of this section, you will be able to: Describe the energetics of covalent and ionic bond formation and breakage Use the Born-Haber cycle to compute lattice energies for ionic compounds Use average covalent bond energies to estimate enthalpies of reaction.
The high-temperature reaction of steam and carbon produces a mixture of the gases carbon monoxide, CO, and hydrogen, H 2 , from which methanol can be produced.
The compound Al 2 Se 3 is used in the fabrication of some semiconductor devices. Which has the larger lattice energy, Al 2 O 3 or Al 2 Se 3?
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