Introduction to Chemical Bonding

1. Introduction to Chemical Bonding

2. Chemical Bonding • Imagine getting onto a crowded elevator. As people squeeze into the confined space, they come in contact with each other. Many people will experience a sense of being too close together. • When atoms get close enough, their outer electrons repel each other. At the same time, however, each atom’s outer electrons are strongly attracted to the nuclei of the surrounding atoms. • The degree to which these outer electrons are attracted to other atoms determines the kind of chemical bonding that occurs between the atoms.

3. Chemical Bonding • A chemical bond is a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. • Most atoms are less stable existing by themselves than when they are combined. • By bonding with one another they become more stable. Single atom Less stable Molecule More stable

4. Types of Chemical Bonding • Chemical bonding that results from the electrical attraction between large numbers of cations and anions is called ionic bonding. • Covalent bonding results from the sharing of electron pairs between two atoms.

5. Bonding between atoms of different elements is rarely purely ionic or purely covalent. • The degree to which bonding of two elements is ionic or covalent can be estimated by calculating the difference in the elements’ electronegativities.

6. Bonding between atoms with an electronegativity difference of 1.7 or less has an ionic character of 50% or less and is classified as covalent.

7. Bonding between atoms of the same element is completely covalent. • A nonpolar-covalent bond is a covalent bond in which the bonding electrons are shared equally by the bonded atoms, resulting in a balanced distribution of electrical charge (difference of 0 to 0.3 in electronegativity).

8. A polar-covalent bond is a covalent bond in which the bonded atoms have an unequal attraction for the shared electrons.

9. Sample Problem: Use electronegativity values to classify bonding between sulfur, S, and the following elements: hydrogen, H; cesium, Cs; and chlorine, Cl. In each pair, which atom will be more negative? Electronegativity Difference: 0 to 0.3 nonpolar-covalent bond 0.3 to 1.7 polar-covalent bond Greater than 1.7 ionic

10. The electronegativity of sulfur is 2.5. The electronegativities of hydrogen, cesium, and chlorine are 2.1, 0.7, and 3.0, respectively. In each pair, the atom with the larger electronegativity will be the more-negative atom. Bonding between Electroneg. More-neg- sulfur and difference Bond type ative atom hydrogen 2.5 – 2.1 = 0.4 polar-covalent sulfur cesium 2.5 – 0.7 = 1.8 ionic sulfur chlorine 3.0 – 2.5 = 0.5 polar-covalent chlorine

11. What type of bonding would be expected between the following atoms? • Electronegativity Difference: • 0 to 0.3 nonpolar-covalent bond • 0.3 to 1.7 polar-covalent bond • Greater than 1.7 ionic • Li and F • Cu and S • I and Br • H and I • S and O • K and Br • Si and Cl • K and Cl • Se and S • C and H

12. Li and F • Cu and S • I and Br • H and I • S and O • K and Br • Si and Cl • K and Cl • Se and S • C and H