CHAPTER 7 Bonding 7.1 What is a Chemical Bond?

We also know that electrons are responsible for chemical bonding. Protons (+) There is an equilibrium in attractive and repulsive forces inside the atom Neutrons (0) Electrons (-) We also know that electrons are responsible for chemical bonding.

Is a chemical bond really a “stick” between two atoms?

Is a chemical bond really a “stick” between two atoms? No: The binding force between two atoms is an equilibrium of several forces.

That distortion is called polarization. The electron cloud responds to changes in the electromagnetic environment. That distortion is called polarization.

What happens when two hydrogen atoms approach each other?

What happens when two hydrogen atoms approach each other? Each nucleus attracts the electron cloud of the other atom. Each nucleus repels the other nucleus. The electron cloud repels the other electron cloud.

What happens when two hydrogen atoms approach each other? Each nucleus attracts the electron cloud of the other atom. Each nucleus repels the other nucleus. The electron cloud repels the other electron cloud. At a certain distance there is an equilibrium between attractive and repulsive forces.

If the distance is close enough, an electron can be transferred or shared. A chemical bond forms. At a certain distance there is an equilibrium between attractive and repulsive forces.

A covalent bond An ionic bond Electrons are shared between the two nuclei. One or more electrons are transferred to form ions. The positive and negative ions attract each other.

Molecular models are approximations of the real thing. Representation Water (H2O) Molecular models are approximations of the real thing.

Electrons are unevenly shared between oxygen and hydrogen. Some atoms are more greedy for electrons than others! Electrons are unevenly shared between oxygen and hydrogen.

Molecular surfaces colored by charge Hydrogen, H2 Water, H2O Electrons are equally shared between the hydrogen atoms There are more electrons on the oxygen side than on the hydrogen side

Electronegativity electronegativity: the relative affinity of an element for electrons from other atoms. Higher electronegativity means stronger attraction for electrons.

Oxygen is slightly more electronegative than hydrogen. Electronegativity (electron sharing) Oxygen is slightly more electronegative than hydrogen. This results in uneven sharing of electrons.

Ionization Energy ionization energy: the energy required to completely remove an electron.

Nonpolar covalent bond Types of bond Nonpolar covalent bond Atom 1 Atom 2 Difference in EN Electron sharing high EN very little equal or nearly equal sharing EN = electronegativity

Nonpolar covalent bond Types of bond Nonpolar covalent bond Polar covalent bond Atom 1 Atom 2 Difference in EN Electron sharing high EN very little equal or nearly equal sharing high EN medium EN moderate uneven sharing EN = electronegativity

Nonpolar covalent bond Types of bond Nonpolar covalent bond Polar covalent bond Ionic bond Atom 1 Atom 2 Difference in EN Electron sharing high EN very little equal or nearly equal sharing high EN medium EN moderate uneven sharing high EN low EN large transfer of electrons EN = electronegativity

Types of bond

Types of bond An ionic crystal Ionic bonds connect atoms to all neighbors, not just a single neighbor as in a molecule.

Types of bond A metallic bond Like a covalent bond Like an ionic bond Electrons are shared No two atoms are specifically bonded together metallic bond: an attraction between metal atoms that loosely involve many electrons.

Nonpolar covalent bond Ionic bond Difference in EN Electron sharing very little equal or nearly equal sharing moderate uneven sharing large transfer of electrons We can determine the bond type from the difference in electronegativity. EN = electronegativity

Nonpolar covalent bond Ionic bond Difference in EN Electron sharing very little equal or nearly equal sharing moderate uneven sharing large transfer of electrons EN = electronegativity

Electronegativity of atoms: Difference in electronegativity: I – I = 2.66 – 2.66 = 0

The I–I bond is nonpolar covalent. Electronegativity of atoms: I = 2.66 Difference in electronegativity: I – I = 2.66 – 2.66 = 0 The I–I bond is nonpolar covalent.

Electronegativity of atoms: C = 2.55 O = 3.44 Difference in electronegativity: O – C = 3.44 – 2.55 = 0.89

The C–O bond is polar covalent. Electronegativity of atoms: C = 2.55 O = 3.44 Difference in electronegativity: O – C = 3.44 – 2.55 = 0.89 The C–O bond is polar covalent. 0.89

A phospholipid molecule Most molecules contain more than two atoms and more than one bond. Some polar bonds All nonpolar bonds A phospholipid molecule (found in cell membranes)

Nonpolar bonds in a molecule make the molecule nonpolar.

Polar bonds in a molecule make the molecule polar.

Nonpolar covalent bond Types of bond Nonpolar covalent bond Polar covalent bond Ionic bond Atom 1 Atom 2 Difference in EN Electron sharing high EN very little equal or nearly equal sharing high EN medium EN moderate uneven sharing high EN low EN large transfer of electrons EN = electronegativity