Section 8.1 Types of Chemical Bonds Chapter 9: Chemical Bonding: Basic Concepts

Section 8.1 Types of Chemical Bonds Copyright © Cengage Learning. All rights reserved ▪Forces that hold groups of atoms together and make them function as a unit. ▪A bond will form if the energy of the compound formed is lower than that of the separated atoms. Chemical Bonds

Section 8.1 Types of Chemical Bonds All chemical reactions involve making and breaking chemical bonds. ▪Bond formation always releases energy ▪Bond breaking always requires energy

Section 8.1 Types of Chemical Bonds Electronegativity: ▪The ability of an atom in a molecule to attract shared electrons to itself. ▪The most widely accepted method for determining values of electronegativity was derived by Linus Pauling. ▪The range of electronegativity values is from 4.0 for fluorine (the most electronegative) to 0.7 for cesium (the least electronegative). Copyright © Cengage Learning. All rights reserved I won the Nobel Prize in Chemistry and the Nobel Peace Prize

5 Electronegativity is the ability of an atom to attract toward itself the electrons in a chemical bond. Electron Affinity - measurable, Cl is highest Electronegativity - relative, F is highest X (g) + e - X - (g) electron poor region electron rich region H F

Section 8.1 Types of Chemical Bonds The electronegativity increases across a period: ▪Same energy level, but the number of protons increases which increases the effective nuclear charge. The electronegativity decreases going down a group ▪As more energy levels are added, the size of the atoms increases. The effective nuclear charge is not as great due to shielding. Copyright © Cengage Learning. All rights reserved

Section 8.1 Types of Chemical Bonds If lithium and fluorine react, which has more attraction for an electron? Why? ▪Fluorine has a greater nuclear pull. Both are in the same energy level, but F has more protons. More protons, greater nuclear attraction In a bond between fluorine and iodine, which has more attraction for an electron? Why? ▪Fluorine has a greater nuclear pull. Although iodine has a greater nuclear charge, the charge is being ‘shielded’ by the increase in energy levels. Copyright © Cengage Learning. All rights reserved CONCEPT CHECK!

Section 8.1 Types of Chemical Bonds As the different in electronegativity increases: -bond polarity increases -ionic character increases Covalent share e - Polar Covalent partial transfer of e - Ionic transfer e -

Section 8.1 Types of Chemical Bonds Three major type of intermolecular bonds can be described by the electronegativity difference 1.Covalent (non-polar covalent): Bond difference ▪ electrons are shared equally 2.Polar Covalent: Bond difference 0.4 → 1.9 ▪ Bond becomes increasingly polar with higher values; ▪ electrons shared unequally 3.Ionic: Bond difference greater than 1.9 ▪ Large difference; Bond becomes more ionic in nature ; electron transfer can occur.

Section 8.1 Types of Chemical Bonds Put the following bonds in order of increasing ionic character. Predict the type of bond each will incur. H-Cl H-F H-H H-O H-S NP Cov NP Cov P Cov P Cov Ionic

Section 8.1 Types of Chemical Bonds Arrange the following bonds from most to least polar: a) N–FO–FC–F b)C–FN–OSi–F c)Cl–ClB–ClS–Cl a) C–F, N–F, O–F b) Si–F, C–F, N–O c) B–Cl, S–Cl, Cl–Cl Copyright © Cengage Learning. All rights reserved EXERCISE!

Section 8.1 Types of Chemical Bonds Which of the following bonds would be the least polar yet still be considered polar covalent? Mg–O C–O O–O Si–O N–O Copyright © Cengage Learning. All rights reserved CONCEPT CHECK!

Section 8.1 Types of Chemical Bonds Which of the following bonds would be the most polar without being considered ionic? Mg–O C–O O–O Si–O N–O Copyright © Cengage Learning. All rights reserved CONCEPT CHECK!

Section 8.1 Types of Chemical Bonds 1. Ionic Bonding ▪Electrons are transferred ▪Metal and nonmetal react: ions form so that both ions achieve noble gas configurations (usually) resulting in an electrostatic attraction of oppositely charged ions ▪Any compound that conducts an electric current when melted will be classified as ionic. Types of Chemical Bonds

Section 8.1 Types of Chemical Bonds Metals lose electrons to achieve noble gas configurations. Non-metals gain electrons to achieve noble gas configurations. Types of Chemical Bonds

16 Li + F Li + F - The Ionic Bond 1s22s11s22s1 1s22s22p51s22s22p5 1s21s2 1s22s22p61s22s22p6 [He][Ne] Li Li + + e - e - + FF - F - Li + + Li + F - LiF Ionic bond: the electrostatic force that holds ions together in an ionic compound.

Section 8.1 Types of Chemical Bonds Ex: Explain how atoms of sodium and oxygen form an ionic compound using their electron configurations Na: 1s 2 2s 2 2p 6 3s 1 O: 1s 2 2s 2 2p 4 Oxygen has a higher electronegativity(the ability to attract an electron), so electrons are transferred from sodium to oxygen. Oxygen needs 2 electrons, so 2 sodium atoms are needed. Na 2 O is formed. 2Na → 2Na + + 2e - O + 2e - → O 2- Na + : 1s 2 2s 2 2p 6 O 2- : 1s 2 2s 2 2p 6

Section 8.1 Types of Chemical Bonds Lewis Structure (Electron Dot Diagrams) ▪A simplistic way of showing the reactive electrons (the valence electrons) of an atom. ▪Reflects central idea that stability of a compound relates to noble gas electron configuration. Copyright © Cengage Learning. All rights reserved

Section 8.1 Types of Chemical Bonds Draw the Lewis structure for each of the following: 1.O 2.Li 3.S 4.O 2- 5.Ca 2+ Electron dot structures

Section 8.1 Types of Chemical Bonds Use the electron dot structure to show how Na and O can become an ion Na Sodium atom → Na + sodium Ion + e-e- 1 electron O + 2e - → Oxygen atom O 2 electrons Oxide Ion 2-

Section 8.1 Types of Chemical Bonds Na 2 O [ [ ] ] Show the formation of Na 2 O using Lewis structures

Section 8.1 Types of Chemical Bonds ▪Show the formation of (A) calcium fluoride and (B) aluminum oxide using electron-dot structures

Section 8.1 Types of Chemical Bonds Lattice (Electrostatic) Energy ▪Lattice energy, is the energy release that occurs when separated gaseous ions are packed together to form an ionic solid (lattice crystal) X x+ (g) + Y y- (g) → X y Y x (s) + energy Ex: Na + (g) + Cl - (g) → NaCl(s) kJ H o = kJ/mol ▪Lattice energy indicates how strongly the ions attract each other in the solid state. Lattice energy

Section 8.1 Types of Chemical Bonds We can calculate the lattice energy of an ionic compound by using Coulomb’s Law: E = (2.31 x J·nm) x Q 1 Q 2 r k = proportionality constant =2.31 x J·nm Q 1 and Q 2 = charges on the ions r = distance between the ion centers in nm A negative sign indicates an attractive force! Coulomb’s Law Lattice energy increases as Q increases and/or as r decreases.

Section 8.1 Types of Chemical Bonds Lattice energy trend ▪Charge on ions: The greater the charge on the ions, the stronger the ionic bond ▪Radius or size of ion: If the charges are equal, the smaller ion will have the stronger ionic bond.

Section 8.1 Types of Chemical Bonds How does lattice energy effect melting point?

Section 8.1 Types of Chemical Bonds Example: Which would you predict has the most exothermic lattice energy: NaCl or KCl? Explain. Answer: NaCl ▪Both NaCl and KCl all have +1 or -1 charges. ▪Since Na+ is smaller than K+, the distance, r, is less, making the energy more. ▪As this energy increases, the strength and stability of the crystal lattice increases.

Section 8.1 Types of Chemical Bonds Example: In solid sodium chloride, the distance between the centers of the Na + and Cl - ions is 2.76Å. Determine the ionic energy per pair of ions. (1m = Å). E = (2.31 x J·nm) x Q 1 Q 2 r E = (2.31 x J·nm) x (+1)(-1) 0.276nm = x J The negative sign indicates an attractive force. The ion pair has LOWER energy than the separated ions.

Section 8.1 Types of Chemical Bonds ▪Coulomb’s law can also be used to calculate the repulsive energy when two like charged ions are brought together. This energy will have a positive sign. Example: The interaction of two hydrogen atoms ▪The hydrogen atoms will position themselves so that the system will achieve the lowest possible energy. ▪The distance where energy is minimal is called the bond length.

Section 8.1 Types of Chemical Bonds Copyright © Cengage Learning. All rights reserved The Interaction of Two Hydrogen Atoms: the molecule is more stable than two separated hydrogen atoms by a certain quantity of energy. PHET

Section 8.1 Types of Chemical Bonds End Lesson 1