Mark S. Cracolice Edward I. Peters Mark S. Cracolice The University of Montana Chapter 12 Chemical Bonding

Monatomic Ions Noble gas electron configurations are generally the most stable. Metal atoms can achieve a noble gas electron configuration by emptying their valence orbitals. Nonmetal atoms can achieve the electron configuration of the next noble gas by receiving more electrons on their emptied valence orbitals.

Monatomic Ions Lithium atom, which has electron configuration 1s 2 2s 1 can achieve the electron configuration of helium 1s 2 by losing one electron on orbital 2s, and thus becomes a cation Li +. Li - e → L i + 1s 2 2s 1 1s 2

Monatomic Ions Oxygen atom, whose electron configuration is 1s 2 2s 2 2p 4, can achieve the electron configuration 1s 2 2s 2 2p 6 of neon by receiving two more electrons on its 2p orbitals, and becomes ion O 2-. O + 2e → O 2- 1s 2 2s 2 2p 4 1s 2 2s 2 2p 6

Monatomic Ions Fluorine atom, whose electron configuration is 1s 2 2s 2 2p 5 can achieve the electron configuration 1s 2 2s 2 2p 6 of neon by accepting one electron on its 2p orbital, and becomes anion F - F + e → F - 1s 2 2s 2 2p 5 1s 2 2s 2 2p 6

Monatomic Ions Sodium atom, whose electron configuration is 1s 2 2s 2 2p 6 3s 1, can achieve the electron configuration 1s 2 2s 2 2p 6 of neon by giving away one electron on its 3s orbital, and becomes cation Na +. Na - e → Na + 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6

Monatomic Ions Magnesium atom whose electron configuration is 1s 2 2s 2 2p 6 3s 2, can achieve the electron configuration of neon by giving away two electrons on its 3s orbital, and becomes cation Mg 2+ Mg - 2 e → Mg 2+ 1s 2 2s 2 2p 6 3s 2 1s 2 2s 2 2p 6

Monatomic Ions Chlorine atom whose electron configuration is 1s 2 2s 2 2p 6 3s 2 3p 5, can achieve the electron configuration of argon by receiving one electron on its 3p orbital, and becomes ion Cl -. Cl + e → Cl - 1s 2 2s 2 2p 6 3s 2 3p 5 1s 2 2s 2 2p 6 3s 2 3p 6

Monatomic Ions Potassium atom (1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 ) can achieve the electron configuration 1s 2 2s 2 2p 6 3s 2 3p 6 of argon by losing one electron on its 4s orbital, and becomes ion K +. K - e → K + 1s 2 2s 2 2p 6 3s 2 3p 6 4s 1 1s 2 2s 2 2p 6 3s 2 3p 6

Monatomic Ions Calcium atom (1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 ) can achieve the electron configuration of argon by losing two electrons on its 4s orbital, and becomes ion Ca 2+. Ca - 2 e → Ca 2+ 1s 2 2s 2 2p 6 3s 2 3p 6 4s 2 1s 2 2s 2 2p 6 3s 2 3p 6

Monatomic Ions There are some exceptions to the rules discussed here. For example tin forms both Sn 2+ and Sn 4+ Sn - 2 e → Sn 2+ [Kr]5s 2 4d 10 5p 2 [Kr]5s 2 4d 10 Sn - 4 e → Sn 4+ [Kr]5s 2 4d 10 5p 2 [Kr]4d 10 Configuration with filled sublevel 4d is stable

Monatomic Ions Lead forms both Pb 2+ and Pb 4+ Pb - 2 e → Pb 2+ [Xe]6s 2 4f 14 5d 10 6p 2 [Xe]6s 2 4f 14 5d 10 Pb - 4e → Pb 4+ [Xe]6s 2 4f 14 5d 10 6p 2 [Xe]4f 14 5d 10 Configuration with filled sublevel 5d is stable

Monatomic Ions

Ionic Bonds Crystal: A solid with a definite geometric structure. Ionic compounds: compounds made up of ions. Ionic Bond : The electrostatic forces that hold the ions in fixed position in the crystal are called ionic bonds. Ionic bonds are very strong.

Ionic Bond in sodium chloride

Ionic Bonds The bonds in an ionic crystal are very strong, which is why nearly all ionic compounds are solids at room temperature. Solid ionic compounds are poor conductors of electricity because the ions are locked in place in the crystal. Only when ionic compounds are melted or dissolved that the ions are free to move and able to carry electric current.

Covalent Bonds: Hydrogen molecule Hydrogen molecule H 2 In the hydrogen molecule, the electrons reside primarily in the space between the two nuclei. The electron cloud or charge density is concentrated in the region between the nuclei..

Covalent Bond in Hydrogen Molecule

Covalent Bonds: Hydrogen molecule The simultaneous attraction of each electron by the two protons generates a force that pulls the protons toward each other and balances the repulsive force between protons and repulsive force between electrons..

Covalent Bonds The type of bonding in which electrons are shared by nuclei is called covalent bond. Using Lewis symbols, the formation of hydrogen molecule can be represented as: H + H ----> H : H or H-H The two dots or the straight line drawn between the two atoms represent the covalent bond.

Covalent Bonds By sharing electrons, each hydrogen atom in the molecule has two electrons. Each hydrogen atom has a filled valence shell. The pair of electrons with opposite spin shared by two atoms is called bonding pair.

Covalent Bond and ionic bond Covalent bond: Each atom has a noble gas electron configuration but shares electron pair(s) to do so. Ionic bond: Each ion has its own noble gas electron configuration

Covalent Bonds H + H or The two dots or the straight line drawn between the two atoms represent the covalent bond that holds the atoms together.

Covalent Bonds in F 2 Fluorine molecule F 2. Fluorine atom has the following electron configuration : 1s 2 2s 2 2p 5 When two fluorine atoms form a molecule, they share their unpaired electrons on orbitals 2p, so that each atom has eight electrons (octet rule).

Covalent Bonds A half-filled 2p orbital from one F atom overlaps a half-filled 2p orbital from the other F atom.

Covalent Bonds Lewis Diagram, Lewis Formula, Lewis Structure Electron-dot symbols used to show the bonding arrangement among atoms in a molecule. Lone pairs Unshared electron pairs in a Lewis diagram, not involved in bonding. Bonding pair The pair of electrons shared by two atoms in a Lewis diagram.

Covalent Bonds Octet Rule Covalent bonds tend to form between nonmetal atoms by filling the overlapping valence electron orbitals with the maximum number allowed, two in the s orbital and two in each of the three p orbitals, for a total of eight (octa-) valence electrons. Covalent bonds tend to form when half-filled orbitals overlap.

Polarity & Covalent Bonds Nonpolar Covalent Bond A bond in which bonding electrons are shared equally by the two nuclei. The charge density is centered in the region between the bonded atoms. A bond between identical atoms is always nonpolar.

Polarity & Covalent Bonds Polar Covalent Bond A bond in which the bonding electrons are shared unequally by the two nuclei. The charge density is shifted toward one atom and away from the other.

Polarity & Covalent Bonds A bond with an unsymmetrical distribution of bonding electron charge is a polar covalent bond. In the hydrogen fluoride molecule HF, the fluorine atom has a stronger attraction for the shared electrons than the hydrogen atom..

Polarity & Covalent Bonds The result is that the HF molecule has the following charge distribution:

Polarity & Covalent Bonds

Electronegativity Bond polarity in covalent bonds may be described in terms of the electronegativities of the bonded atoms. The electronegativity of an element is the ability of its atom in a molecule to attract shared electrons to itself The higher the electronegativity, the stronger is the attraction of the atom for bonding electrons.

Polarity & Covalent Bonds The electronegativity is highest at the upper right region of the periodic table and lowest at the lower left region

Polarity & Covalent Bonds The polarity of the bond increases as the difference in electronegativity increases. For example the following variation in bond polarity is expected H-H < S-H < Cl-H < O-H < F-H

Polarity & Covalent Bonds The polarity of a bond can be estimated by calculating the difference between the electronegativity values for the bonded elements. A C — F bond (4.0 – 2.4 = 1.6) is more polar than A C — H bond (2.4 – 2.1 = 0.3) The bonding electrons are displaced toward the element with the highest electronegativity value.

Multiple Bonds Single bond: one electron pair shared. Double bond: two electron pairs shared. Triple bond: three electron pairs shared. Double and triple bonds are multiple bonds. H H \ / H — H C = C : N N : / \ H H H 2 C 2 H 4 N 2

Atoms Bonded to More Than One Atom Formation of a Water Molecule From Its Atoms:

Atoms Bonded to More Than One Atom Additional Molecules with Atoms Bonded to Two or More Other Atoms: H H H | \ / H — C —H C = C H — C C — H | / \ H H H

Multiple Equivalent Structures: Resonance We can write three valid structures for nitrate ion The nitrate ion is represented by a blend of all structures. The blended structure is called resonance hybride of three Lewis structures. (a mule is a hybride of a horse and a donkey.) Resonance is a blending of structures with the same arrangement of atoms but different arrangement of electrons

Exceptions to the Octet Rule Odd-Electron Molecules The molecule with one unpaired electron is called a radical. One of the atoms must have an incomplete octet. nitrogen monoxide nitrogen dioxide = 11 valence electrons5 + 2(6) = 17 valence electrons

Exceptions to the Octet Rule Molecules with More Than Four Electron Pairs Around the Central Atom Atoms of elements in the third period and higher have empty d orbitals and big size, can have more than four electron pairs surrounding them: phosphorus pentafluoridesulfur hexafluoride

Exceptions to the Octet Rule Molecules with Fewer Than Four Electron Pairs Around the Central Atom Compounds of beryllium and boron are surrounded by two and three pairs of electrons, respectively: beryllium difluorideboron trifluoride

Paramagnetic property of oxygen Liquid oxygen becomes trapped in the field of a strong magnet because oxygen molecule has 2 unpaired electrons:

Limitation of Lewis Diagram Oxygen No Lewis diagram can be drawn for oxygen that matches experimental evidence about its paramagnetic property. Molecular orbital theory can better explain the paramagnetic property of oxygen molecule.

Metallic Bonds Metallic Bond Attractive force between positively-charged metal ions in a crystal and the negatively-charged electrons that move among them.

Metallic Bonds

Metals Electrons in a metal are said to be delocalized because they are not confined to a localized region near a single atom or a pair of atoms. Alloy A solid mixture of two or more elements that has macroscopic metallic properties.

Metallic Bonds

HOMEWORK 5, 7, 9, 13, 15, 19, 25, 45.