Hydrogen and Chlorine: Covalent Bonding: Hydrogen and Chlorine: Covalent Bonding: H Cl or H-Cl H + Cl Sharing electrons 2) Hydrogen & hydrogen. (Single covalent bond) 3) Fluorine & fluorine. 4) Nitrogen & hydrogen. 5) Carbon & hydrogen.

Covalent Bonding: The Octet Rule in Covalent Bonding In covalent bonds, electron sharing usually occurs so that atoms attain the electron configurations of noble gases. The pair of shared electrons forming the covalent bond is also often represented as a dash, as in H—H for hydrogen (structural formula )

Covalent Bonding: Formation of chemical bonds (Lewis dot structure): 1)Oxygen and oxygen: O O or O=O O + O Two pairs of electrons shared (Double covalent bond) A double covalent bond is a bond that involves two shared pairs of electrons.

Three pairs of electrons shared 2) Nitrogen & nitrogen: N + N or N N N N Three pairs of electrons shared (Triple covalent bond) Similarly, a bond formed by sharing three pairs of electrons is a triple covalent bond.

Using electron-dots structure represent the following molecules: CO2 2) C2H4 3) C2H2

Bond Polarity: How do electronegativity values determine the charge distribution in a polar bond? Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Bond Polarity The nuclei of atoms pull on the shared electrons, much as the knot in the rope is pulled toward opposing sides in a tug-of-war. The bonding pairs of electrons in covalent bonds are pulled between the nuclei of the atoms sharing the electrons.

Bond Polarity A polar covalent bond, known also as a polar bond, is a covalent bond between atoms in which the electrons are shared unequally. The more electronegative atom attracts more strongly and gains a slightly negative charge. The less electronegative atom has a slightly positive charge. δ+ δ– H—Cl Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Bond Polarity H-H Br-Br O=O When the atoms in the bond pull equally (as occurs when identical atoms are bonded- same electronegativity), the bonding electrons are shared equally, and each bond formed is a nonpolar covalent bond. H-H Br-Br O=O Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Bond Polarity The electronegativity difference between two atoms tells you what kind of bond is likely to form. Electronegativity Differences and Bond Types Electronegativity difference range Most probable type of bond Example 0.0 – 0.49 Nonpolar covalent H—H (0.0) 0.5 – 0.99 Moderately polar covalent δ+ δ– H—Cl (0.9) 1.0 – 1.99 Very polar covalent H—F (1.9) ≥ 2.0 > 1.5 Ionic Ionic (if a metal is present) Na+Cl– (2.1) Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electronegativity Chart Sample Problem Identifying Bond Type Which type of bond (nonpolar covalent, moderately polar covalent, very polar covalent, or ionic) will form between each of the following pairs of atoms? a. N and H b. F and F c. Ca and Cl d. Al and Cl Electronegativity Chart Page 181

Calculate the electronegativity difference between the two atoms & determine the bond type. a. 3.0(N) - 2.1(H) = 0.9 Moderately polar covalent. Nonpolar covalent. b. 4.0(F) - 4.0(F) = 0.0 c. 3.0(Cl) - 1.0(Ca) = 2.0 Ionic. d. 3.0(Cl) - 1.5(Al) = 1.5 Very polar covalent. Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

Electronegativity:

Examples: Cl2(g), Br2(l), CCl4(l). Properties of Molecular Compounds: 1) Weak attraction forces between molecules. 2) Low melting and boiling points. 3) Gases, liquids or solids at room temperature. 4) The solids are very soft. 5) Poor conductors of electricity. 6) Polar covalent: Show solubility in water. Ex. HCl(g), NH3(g) No polar covalent: Show solubility in non polar solvents (CCl4, oil, gasoline, acetone, etc.) Examples: Cl2(g), Br2(l), CCl4(l).

Covalent Network Solids: A network solid or covalent network solid is a chemical compound in which the atoms are bonded by covalent bonds in a continuous network extending throughout the material Examples: Quartz or Silica (SiO2 silicon dioxide), diamond & graphite (made by carbon). diamond graphite

Covalent Network Solids: Properties: 1) Brittle & extremely hard solids. 2) Very high melting points. 3) Non conductors (heat or electricity), except graphite (good conductor)