Atoms gain stability when they share electrons and form covalent bonds. Section 1: The Covalent Bond K What I Know W What I Want to Find Out L What I Learned

7(C) Construct electron dot formulas to illustrate ionic and covalent bonds. 6(E) Express the arrangement of electrons in atoms through electron configurations and Lewis valence electron dot structures. 11(C) Use thermochemical equations to calculate energy changes that occur in chemical reactions and classify reactions as exothermic or endothermic. 2(H)Organize, analyze, evaluate, make inferences, and predict trends from data. The Covalent Bond Copyright © McGraw-Hill Education

2(I) Communicate valid conclusions supported by the data through methods such as lab reports, labeled drawings, graphs, journals, summaries, oral reports, and technology–based reports. 3(A)In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical reasoning, and experimental and observational testing, including examining all sides of scientific evidence of those scientific explanations, so as to encourage critical thinking by the student. The Covalent Bond Copyright © McGraw-Hill Education

Essential Questions Why do atoms form single, double, and triple covalent bonds? How are the strength of a covalent bond, its bond length, and its bond dissociation energy related? The Covalent Bond Copyright © McGraw-Hill Education

Review chemical bond New covalent bond molecule Lewis structure sigma bond pi bond endothermic reaction exothermic reaction The Covalent Bond Copyright © McGraw-Hill Education Vocabulary

Why do atoms bond? The stability of an atom, ion or compound is related to its energy: lower energy states are more stable. Metals and nonmetals gain stability by transferring electrons (gaining or losing) to form ions that have stable noble-gas electron configurations. Another way atoms can gain stability is by sharing valence electrons with other atoms, which also results in noble-gas electron configurations. The Covalent Bond Copyright © McGraw-Hill Education

What is a covalent bond? Atoms in non-ionic compounds share electrons. The chemical bond that results from sharing electrons is a covalent bond. A molecule is formed when two or more atoms bond covalently. The majority of covalent bonds form between atoms of nonmetallic elements. Diatomic molecules (H 2, N 2, F 2, O 2, I 2, Cl 2, Br 2 ) exist because the two-atom molecules are more stable than the individual atoms. The Covalent Bond Copyright © McGraw-Hill Education

What is a covalent bond? The most stable arrangement of atoms exists at the point of maximum net attraction, where the atoms bond covalently and form a molecule. The Covalent Bond Copyright © McGraw-Hill Education

Single Covalent Bonds When only one pair of electrons is shared, the result is a single covalent bond. The figure shows two hydrogen atoms forming a hydrogen molecule with a single covalent bond, resulting in an electron configuration like helium. In a Lewis structure dots or a line are used to symbolize a single covalent bond. The Covalent Bond Copyright © McGraw-Hill Education

Single Covalent Bonds The halogens—the group 17 elements—have 7 valence electrons and form single covalent bonds with atoms of other non-metals. Atoms in group 16 can share two electrons and form two covalent bonds. Water is formed from one oxygen with two hydrogen atoms covalently bonded to it. The Covalent Bond Copyright © McGraw-Hill Education

Single Covalent Bonds Atoms in group 15 form three single covalent bonds, such as in ammonia. Atoms of group 14 elements form four single covalent bonds, such as in methane. The Covalent Bond Copyright © McGraw-Hill Education

Single Covalent Bonds Sigma bonds are single covalent bonds. Sigma bonds occur when the pair of shared electrons is in an area centered between the two atoms. The Covalent Bond Copyright © McGraw-Hill Education

The Covalent Bond Copyright © McGraw-Hill Education Lewis Structure of a Molecule EVALUATE THE ANSWER Each atom in the new molecule now has a noble-gas configuration and is stable. Use with Example Problem 1. Problem Patterns on glass can be made by chemically etching its surface with hydrogen fluoride (HF). Draw the Lewis structure for a molecule of hydrogen fluoride. Response ANALYZE THE PROBLEM You are given the information that hydrogen and fluorine form the molecule hydrogen fluoride. An atom of hydrogen, a group 1 element, has only one valence electron. It can bond with any nonmetal atom when they share one pair of electrons. An atom of fluorine, a group 17 element, needs one electron to complete its octet. Therefore, a single covalent bond forms when atoms of hydrogen and fluorine bond. SOLVE FOR THE UNKNOWN To draw a Lewis structure, first draw the electron-dot diagram for each of the atoms. Then, rewrite the chemical symbols and draw a line between them to show the shared pair of electrons. Finally, add dots to show the unshared electron pairs.

Multiple Covalent Bonds Double bonds form when two pairs of electrons are shared between two atoms. Triple bonds form when three pairs of electrons are shared between two atoms. The Covalent Bond Copyright © McGraw-Hill Education

Multiple Covalent Bonds A multiple covalent bond consists of one sigma bond and at least one pi bond. The pi bond is formed when parallel orbitals overlap and share electrons. The pi bond occupies the space above and below the line that represents where the two atoms are joined together. The Covalent Bond Copyright © McGraw-Hill Education

The Strength of Covalent Bonds The strength depends on the distance between the two nuclei, or bond length. As length increases, strength decreases. The Covalent Bond Copyright © McGraw-Hill Education

The Strength of Covalent Bonds The amount of energy required to break a bond is called the bond dissociation energy. The shorter the bond length, the greater the energy required to break it. The Covalent Bond Copyright © McGraw-Hill Education

The Strength of Covalent Bonds An endothermic reaction is one where a greater amount of energy is required to break a bond in reactants than is released when the new bonds form in the products. An exothermic reaction is one where more energy is released than is required to break the bonds in the initial reactants. The Covalent Bond Copyright © McGraw-Hill Education

The Covalent Bond Copyright © McGraw-Hill Education Review Essential Questions Why do atoms form single, double, and triple covalent bonds? How are the strength of a covalent bond, its bond length, and its bond dissociation energy related? Vocabulary covalent bond molecule Lewis structure sigma bond pi bond endothermic reaction exothermic reaction