Chapter 5 Chemical Bonding The Covalent Bond

Covalent or Ionic ??? Electronegativity – the attraction that an atom has for the electrons that it is sharing w/ another atom Scale devised by Nobel Prize winner Linus Pauling Based on scale with fluorine assigned 4.0, the highest value Material from karentimberlake.com and H. Stephen Stoker

Forming Chemical Bonds According to the Lewis model an atom may lose or gain enough electrons to acquire a filled valence shell and become an ion. An ionic bond is the result of the force of attraction between a cation and an anion. an atom may share electrons with one or more other atoms to acquire a filled valence shell. A covalent bond is the result of the force of attraction between two atoms that share one or more pairs of electrons. Material from karentimberlake.com and H. Stephen Stoker

Covalent Bonds A chemical bond in which 2 atoms share a single of electron to form one bond Examples F and H Material from karentimberlake.com and H. Stephen Stoker

Covalent Bonds H + H H : H = HH = H2 hydrogen molecule Two nonmetal atoms form a covalent bond because they have less energy after they bonded H + H H : H = HH = H2 hydrogen molecule Material from karentimberlake.com and H. Stephen Stoker

Double Covalent Bond 2 pairs of electrons are shared between 2 atoms Example O2          O  +  O   O::O double bond Material from karentimberlake.com and H. Stephen Stoker

Triple Covalent Bond 3 pairs of electrons are shared between 2 atoms Example N2          N  +  N   N:::N   triple bond Material from karentimberlake.com and H. Stephen Stoker

Diatomic Elements Elements that are naturally in molecules with 2 atoms each. HONClBrIF (pneumonic) Existing as diatomic molecule yields a stable octet Gases that exist as diatomic molecules are H2, F2, N2, O2, Cl2, Br2, I2 Examples Fluorine & Bromine Material from karentimberlake.com and H. Stephen Stoker

Learning Check Use the name of the element to name the following diatomic molecules. H2 hydrogen N2 nitrogen Cl2 _______________ O2 _______________ I2 _______________ Material from karentimberlake.com and H. Stephen Stoker

Solution Use the name of the element to name the following diatomic molecules. H2 hydrogen N2 nitrogen Cl2 chlorine O2 oxygen I2 iodine Material from karentimberlake.com and H. Stephen Stoker

Lewis Structures Other molecules having single covalent bonds H2O The hydrogens share their electrons w/ oxygen so that O has 8 e- and each H has 2 e- Material from karentimberlake.com and H. Stephen Stoker

Covalent Bonds in NH3 Bonding pairs H   H : N : H Lone pair of electrons (unshared pair) Material from karentimberlake.com and H. Stephen Stoker

Drawing Lewis Structures 1. Determine the number of valence electrons in the molecule 2. Decide on the arrangement of atoms in the molecule 3. Connect the atoms by single bonds 4. Show bonding electrons as a single line; show nonbonding electrons as a pair of Lewis dots 5. In a single bond, atoms share one pair of electrons; in a double bond, they share two pairs, and in a triple bond they share three pairs. Material from karentimberlake.com and H. Stephen Stoker

Coordinate Covalent Bond Bond in which only one atom donates electrons to form the bond Sometimes an arrow is used to designate the coordinate covalent bond Material from karentimberlake.com and H. Stephen Stoker

Chemical Bonding: The Covalent Bond Model cont’d Material from karentimberlake.com and H. Stephen Stoker

Chemical Bonding: The Covalent Bond Model cont’d Fig. 5.10 Linus Pauling received the Nobel Prize in chemistry in 1954 for his work on the nature of the chemical bond. © Bettman/CORBIS Material from karentimberlake.com and H. Stephen Stoker

Electronegativity The attraction of an atom for electrons is called its electronegativity. Fluorine has the greatest electronegativity. The metals have low electronegativities. Material from karentimberlake.com and H. Stephen Stoker

Chemical Bonding: The Covalent Bond Model cont’d Fig. 5.11 Abbreviated periodic table showing Pauling electronegativity values for selected representative elements. Material from karentimberlake.com and H. Stephen Stoker

Electronegativity Electronegativity: a measure an atom’s attraction for the electrons it shares in a chemical bond with another atom on the Pauling scale, fluorine, the most electronegative element is assigned a value of 4.0, and all other elements are assigned values relative to fluorine Material from karentimberlake.com and H. Stephen Stoker

Bond Polarity: Nonpolar Nonpolar covalent bond Electrons are shared between atoms with the same electronegativity values. Difference = 0 Examples: N2 Br2 Material from karentimberlake.com and H. Stephen Stoker

Bond Polarity: Polar Polar covalent bond Electrons are shared between different nonmetal atoms Examples: O-Cl O-S N-Cl Material from karentimberlake.com and H. Stephen Stoker

Chemical Bonding: The Covalent Bond Model Fig. 5.12 (a) In the nonpolar covalent bond present, there is a symmetrical distribution of electron density. (b) In the polar covalent bond present, electron density is displaced because of its electronegativity. Material from karentimberlake.com and H. Stephen Stoker

Chemical Bonding: The Covalent Bond Model Material from karentimberlake.com and H. Stephen Stoker

Learning Check Identify the type of bond between the following atoms A. K-N 1) nonpolar 2) polar 3) ionic B. N-O 1) nonpolar 2) polar 3) ionic C. Cl-Cl 1) nonpolar 2) polar 3) ionic Material from karentimberlake.com and H. Stephen Stoker

Solution A. K-N 3) ionic B. N-O 2) polar, covalent C. Cl-Cl 1) nonpolar, covalent Material from karentimberlake.com and H. Stephen Stoker

Covalent or Ionic ??? To decide whether a bond is covalent or ionic find the difference in electronegativities < 2.0 covalent > 2.0 ionic Try KF, MgS, Cl2 Material from karentimberlake.com and H. Stephen Stoker

Character of Bonds Chemist find it better to express chemical bonds as % ionic and % covalent Relates electronegativity to ionic and covalent percentages Table 7.2 (p 159) in text Try KF, MgS, Cl2 Material from karentimberlake.com and H. Stephen Stoker

Molecular Polarity Just like bonds molecules can have polarity Look at Molecule geometry atoms (how atoms are arranged in space) Bond polarity Material from karentimberlake.com and H. Stephen Stoker

Chemical Bonding: The Covalent Bond Model Fig. 5.13 (a) Methane is a nonpolar tetrahedral molecule. (b) Methyl chloride is a polar tetrahedral molecule. Material from karentimberlake.com and H. Stephen Stoker

Electronegativity Material from karentimberlake.com and H. Stephen Stoker

Writing Formulas Nonmetal/Nonmetal In covalent bonds, the element with the lowest electronegativity is written first Material from karentimberlake.com and H. Stephen Stoker

Chemical Bonding: The Covalent Bond Model Table 5.1 Material from karentimberlake.com and H. Stephen Stoker

Chemical Bonding: The Covalent Bond Model Table 5.2 Material from karentimberlake.com and H. Stephen Stoker

Naming of 2 Nonmetals Name each element End the last element in –ide Add prefixes to show more than 1 atom Prefixes mon 1 hexa 6 di 2 hepta 7 tri 3 octa 8 tetra 4 nona 9 pent 5 deca 10 Material from karentimberlake.com and H. Stephen Stoker

Learning Check Fill in the blanks to complete the following names of covalent compounds. CO carbon ______oxide CO2 carbon _______________ PCl3 phosphorus _______chloride CCl4 carbon ________chloride N2O _____nitrogen _____oxide Material from karentimberlake.com and H. Stephen Stoker © Karen Timberlake

Solution CO carbon monoxide CO2 carbon dioxide PCl3 phosphorus trichloride CCl4 carbon tetrachloride N2O dinitrogen monoxide Material from karentimberlake.com and H. Stephen Stoker © Karen Timberlake

Learning Check P2O5 Cl2O7 Cl2 Material from karentimberlake.com and H. Stephen Stoker

Solution A. P2O5 diphosphorus pentoxide B. Cl2O7 dichlorine heptoxide C. Cl2 chlorine Material from karentimberlake.com and H. Stephen Stoker © Karen Timberlake

Learning Check Examples draw a Lewis structure for hydrogen peroxide, H2O2 draw a Lewis structure for methanol, CH3OH draw a Lewis structure for acetic acid, CH3COOH Material from karentimberlake.com and H. Stephen Stoker

Lewis Structures Material from karentimberlake.com and H. Stephen Stoker

3-D Characteristics of Molecules Atoms and molecules have 3 dimensions Shapes of molecules lead to additional properties of covalent compounds Polar covalent Bonding When electrons are not shared equally between two atoms Bond that is certain % ionic Nonpolar covalent Bonding Electrons are shared equally Diatomic atoms Material from karentimberlake.com and H. Stephen Stoker

More Electron Pairs Electron Angle Bonded Name of Pairs Atoms Shape 4 109° 4 tetrahedral 4 109° 3 pyramidal 4 109° 2 bent, angular Material from karentimberlake.com and H. Stephen Stoker

Shapes of Molecules Number of electron pairs 2 (= negative charge clouds) Number of bonded atoms 2 Angle 180° Name of shape linear Material from karentimberlake.com and H. Stephen Stoker

Electron Shape with 3 Pairs Material from karentimberlake.com and H. Stephen Stoker

SO2 :O:: S:O: S S has 2 bonded atoms , 1 lone pair (electron cloud) 120°, angular .. .. .. :O:: S:O: S .. O O Material from karentimberlake.com and H. Stephen Stoker