CHAPTER 12
CHEMICAL BONDING

12-1 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 most active metals have the lowest electronegativity; most active nonmetals have the highest

12-2 Bond character the electronegativity difference between 2 atoms can be used to determine the character of the bond between the atoms nearly all bonds have both covalent and ionic characteristics

12-3 Ionic bonds bond character ionic to covalentŠis on a continuum. the use of 1.67 as the breaking point is simply a convenience for working with compounds ionic bonds form because of an electrostatic attraction between ions/atoms lose or gain electrons oxidation numbers are assigned in ionic bonding based on the number of electrons that are lost or gained to achieve a stable octet characteristics of ionic bonds high melting point soluble in water well defined crystals conduct electricity in molten form

12-4 Ionic radii by adding the radii of 2 ions in a compound we get their internuclear distance in a crystal

12-5 Covalent bonds atoms share electrons in covalent bonds characteristics of covalent bonds low melting points brittle do not conduct electricity angle between two bond axes is called bond angle distance between nuclei along bond axis is called bond length molecular motions can be vibrational/rotational/translational Bond axis is a line joining the nuclei of two bonded atoms

12-6 Covalent radii 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 see tables 12-4 and 12-5 pg 236

12-7 Polyatomic ions called radicals in some books/they are groups of ions that act as if they are one-they are linked covalently but possess a charge. they form ionic bonds

12-8 Van Der Waals Radii the minimum distance maintained between nonbonded atoms because of electron cloud repulsion is the VDW radius

12-9 Summary of radii radii are used to predict internuclear distances between atoms

12-10 Special properties of Metals the electrons in a metal bond move easily from atom to atom and are referred to as delocalized(mobile) electrons. metals bond by sharing mobile electrons the number of electrons available for metallic bonding determines the properties of metals CHEMICAL BOND SUMMARY CHART(TABLE 12-7) PAGE 240 MEMORIZE The high number of delocalized electrons of such metals as iron, chromium, and nickel makes these metals very hard and strong in general the transition elements are the hardest and strongest elements