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Flashcards in Chapter 9 Deck (23):

why do chemical bonds form

they lower potential energy between charged particles that compose atoms


ionic bond

metal + nonmetal bond and the metal transfer 1 or more electrons to nonmetal


covalent bond

nonmetal + nonmetal; electrons are shared, not transferred


metallic bonding

metal + metal; simplest form is electron sea model where atoms in metal lattice pool their valence electrons and are delocalized over the entire metal


lattice energy

energy associated with formation of crystalline lattice; always exothermic so lattice energy is always negative
ionic radii increase as we move down the column


ionic bond properties

ionic solids:
high melting points
solutions of ionic compounds conduct electricity


bond length and strength

double bond is shorter and stronger than single
triple bond is shorter and stronger than double


difference in direction and melting point for covalent vs ionic

covalent = shares a specific pair of electrons
ionic = non directional and share an array of ions
molecular compounds have lower melting and boiling points than ionic compounds



atom's ability to attract electrons in a chemical bond


periodic trends for electronegativity

increases across period
decreases down a column
flourine = most electronegative
Francium = lease electronegative


degree of polarity depends on..

difference between electronegativity of two bonding atoms
greater difference = more polar


dipole moment

measure of the separation of positive and negative charge


percent ionic character

increases with electronegativity difference
no bond is 100% ionic
ratio of bond's actual dipole moment to dipole moment it would have if electron was completely transferred


resonance structures

two or more Lewis structures for the same molecule
write out both structures with double headed arrow between
only resonance hybrid structures exist in nature


formal charge

charge the atom would have if all bonding electrons were shared equally


formal charge formula

formal charge = # of val electrons - (# of lone pair electrons + 1/2# of bonding electrons


how to determine most appropriate skeletal structure or resonance structure

1. sum of all formal charges in neutral molecule must be 0
2. sum of all formal charges in ion must equal charge of ion
3. small or zero formal charges on individual atoms are better than large ones
4. when formal charge can't be avoided, negative formal charge should be on most electronegative atom


odd electron species

molecules or electrons w/ odd # of electrons (called free radicals)
can't write a good Lewis structure for these, but generally don't exist in nature


incomplete octets

Boron = only has 6 electrons`


expanded octets

any element in third row and beyond usually have up to 12 (sometimes 14) electrons
typically octets are expanded to lower formal charge


bond energy

energy required to break 1 mole of the bond in the gas phase


exo vs endo bonds

break bonds = endothermic (positive)
form bonds = exothermic (negative)


Delta H of reaction formula

sum of bonds broken + sum of bonds formed