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Chemistry 12: Chemical Bonding. Christopher Chui. Electronegativity. The relative tendency of an atom to attract electrons when it is bonded to another atom is electronegativity Electronegativity difference increases as bond strength increases
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Chemistry 12: Chemical Bonding Christopher Chui Chemical Bonding - C. Chui
Electronegativity • The relative tendency of an atom to attract electrons when it is bonded to another atom is electronegativity • Electronegativity difference increases as bond strength increases • The most active metals have the lowest electronegatives; the most active nonmetals have the highest electronegatives • The electronegativity difference between two atoms can be used to determine the character of the bond between the atoms • Nearly all bonds have both covalent and ionic characteristics Chemical Bonding - C. Chui
Ionic Bonds • Ionic bonds form because of an electrostatic attraction between ions • Elements are assigned oxidation numbers for ionic bonding based on the number of electrons that atoms must gain or lose in order to obtain a stable octet • Characteristics of compounds with ionic bonds: high melting points; soluble in water; well-defined crystals; conduct electricity in molten form • By adding the radii of two ions in a compound, the internuclear distance in a crystal can be found Chemical Bonding - C. Chui
Covalent Bonds and Radii • Atoms share electrons in covalent bonds • Characteristics of compounds with covalent bonds: low melting point; brittle; and do not conduct electricity • The line joining the nuclei of two bonded atoms in a molecule is called the bond axis • If one atom is bonded to each of two other atoms, the angle between the two bond axes is called the bond angle • The distance between nuclei along the bond axis is called the bond length • Approximate bond length can be determined by adding the covalent radii of 2 bonded atoms. The covalent radii are averages obtained from a number of different compounds Chemical Bonding - C. Chui
Polyatomic Ions & van der Waals Radii • Although the atoms in a polyatomic ion are bonded covalently, the combination still possesses a charge. Therefore, polyatomic ions form ionic bonds • The minimum distance maintained between nonbonded atoms because of electron cloud repulsion is the van der Waals radius • Radii are used to predict internuclear distances between atoms • The electrons in a metal bond move easily from atom to atom and are referred to as delocalized electrons • Metals bond through sharing delocalized electronsmetallic bond • The number of electrons available for metallic bonding determines the properties of metals Chemical Bonding - C. Chui