Lesson 9.1 - Formation of Covalent Bonds

• Air contains oxygen; not in the form of ions (0²) nor of neutral oxygen atoms (O), but as diatomic molecules (O₂).
• Molecules are a group of atoms bound together by covalent bonds.
• Covalent bonds exist between nonmetal atoms, which have small electronegativity difference.
• Nonmetal atoms with relatively similar electronegativities tend to attract valence electrons equally and share them to achieve an octet or duet.
• Some elements exist as diatomic or polyatomic molecules such as hydrogen (H₂), oxygen (O₂), the halogens (e.g., I₂, Br₂, F₂), and sulfur (S₂).
• The atoms in polyatomic ions (e.g., NH,) are also bound by covalent bonds.
• Compounds that result from covalent bonding are called molecular compounds such as butane (C₂H₂) in liquefied petroleum gas (LPG).
• Two nonmetal atoms can form a maximum of three covalent bonds between each other depending on the number of electron pairs that they need to share to attain a noble gas configuration.
• Two hydrogen atoms-each with one valence electron-may share each other's electron to achieve the helium configuration.
• The orbitals that contain each valence electron overlap to form an orbital common to both atoms.
• The sharing of one electron pair forms a single covalent bond represented as (-).
• Two atoms, such as the diatomic oxygen, that share two pairs of electrons (i.e., four electrons in all) form a double covalent bond represented by (=).
• Double bonds are stronger than single bonds, and are thus depicted shorter than single covalent bonds.
• Two atoms sharing six valence electrons form a triple covalent bond.
• A neutral nitrogen atom (Group 5A) has five valence electrons.
• Two nitrogen atoms form three covalent bonds by sharing six electrons, three from each atom, for each to form an octet.
• Triple bonds are the strongest among the covalent bonds and are, thus, represented as the shortest among the three.
• Molecular compounds and their properties are different from aqueous ionic compounds in many aspects.
• Ionic bonding differs from covalent bonding in many aspects.
• Covalent compounds are electrically nonconducting because their constituent atoms are bound to the molecules and do not dissociate into electrically charged particles when dissolved in water.
• Aqueous ionic compounds are conducting in water.
• The forces of attraction between covalent molecules are relatively weaker than in ionic compounds; thus, they have low melting and boiling points and are soft.
• When compounds undergo phase changes, only the attraction between molecules is altered and not the covalent bonds between atoms.