Chapter 8 AP CHEM Notes

● For a given arrangement of ions, the lattice energy increases as the charges on the ions increase and their radii decrease ● Lattice energy decreases as we go down a group ● Transition Metal Ions -1+-3+ charge ○ In forming ions, they lose valence shell s electrons first then d electrons to reach the charge of the ion 8.3 | Covalent Bonding ● Covalent Bond -chemical bond formed by sharing electrons ● The more bonds there are between 2 atoms, the shorter the distance between them ● They are molecules that are not ionic 8.4 | Bond Polarity and Electronegativity ● Bond Polarity -measure of how equally or unequally electrons in any covalent bond are shared ● Nonpolar Covalent Bond -one in which electrons are shared equally (electronegativities of bonded atoms are equal) ● Polar Covalent Bond -one of the atoms exerts a greater attraction for the bonding electrons than the other, if great enough difference, ionic bond forms ● Electronegativity -the ability of an atom in a molecule to attract electrons to itself ○ Greater = greater ability to attract electrons ○ Note

electron affinity and ionization energy are for single atoms ○ Exceptions on transition metals ● δ+ and δ-to symbolize partial positive and negative charges ○ In polar, they are less than the charges of the ions ● Electron density shifted towards more electronegative atom ● The greater the difference in electronegativity between two atoms, the more polar their bond ● Polar Molecule -a molecule in which the centers of positive and negative charge do not coincide ● +-> denotes shift in electron density towards > ● Dipole -when two electrical charges of equal magnitude but opposite sign are separated by a distance, a dipole is established ● Dipole Moment -quantitative measure of the magnitude of a dipole ○ [formula?]

● Covalent Bonding Properties ○ Exist as molecules ○ Low melting point ○ Low Boiling point ○ Nonelectrolyte behavior when dissolved in water ● Ionic Bonding Properties ○ Brittle ○ High melting solids ○ Extended lattice structures ○ Strong electrolyte behavior when dissolved in water 8.5 | Drawing Lewis Structures ● Complete outer atom octets first, but important to complete octet on center ● Formal charge = valence electrons [of atom] -½ (bonding electrons) -nonbonding electrons ● Dominant Lewis Structure ○ Atoms bear formal charges closest to zero ○ Lewis structure with negative charges residing on more electronegative atoms is more dominant ○ Note

formal charges do not represent real charges 8.6 | Resonance Structures ● Resonance structures -equally valid; atoms in same placement but placement of electrons is different ● Organic molecules ○ Aromatic molecules ○ Benzene 8.7 | Exceptions to the Octet Rule ● Exceptions ○ Molecules and polyatomic ions containing an odd number of electrons ○ Molecules and polyatomic ions in which an atom has fewer than an octet of valence electrons ○ Molecules and polyatomic ions in which an atom has more than an octet of valence electrons ■ Hypervalent ■ Only formed for central atoms from period 3 and below 8.8 | Strengths and Lengths of Covalent Bonds ● Bond Enthalpy -(∆H) enthalpy exchange for the breaking of a particular bond in one mole of gaseous substance ○ Is always a positive quantity bc energy is required to break chemical bonds ○ Often averaged values ○ [table 8.4] ● Breaking bonds -endothermic (absorb heat) ● Forming Bonds -exothermic (release heat) ● ∆𝐻 = Σ(𝑏𝑜𝑛𝑑 𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑖𝑒𝑠 𝑜𝑓 𝑏𝑜𝑛𝑑𝑠 𝑏𝑟𝑜𝑘𝑒𝑛) − Σ(𝑏𝑜𝑛𝑑 𝑒𝑛𝑡ℎ𝑎𝑙𝑝𝑖𝑒𝑠 𝑜𝑓 𝑏𝑜𝑛𝑑𝑠 𝑓𝑜𝑟𝑚𝑒𝑑)𝑟𝑥𝑛 ● The more bonds there are between atoms, the shorter bond lengths are and the greater the bond enthalpy is

Lattice Energy

the energy required to completely separate one mole of a solid ionic

Bond Polarity

measure of how equally or unequally electrons in any covalent bond are shared

Nonpolar Covalent Bond

one in which electrons are shared equally

Electronegativity

the ability of an atom in a molecule to attract electrons to itself

Polar Molecule

a molecule in which the centers of positive and negative charge do not coincide