Lewis Structures Flashcards
What are types of chemical bonds? Explain each briefly.
ionic: electron transferred from metal to non-metal
covalent: electron shared between non-metals
metallic: valence electrons delocalized over many metal nuclei
What are the steps to drawing a lewis structure?
- calculate total number of valence electrons
- identify central atom
- draw a signle bond between each atom
- calculate remaining electrons
- distribute remaining electrons in pairs around the terminal atoms, then central atom
- if any atoms don’t have octets then make double or triple bonds
How can you identify the central atom?
atom with lowest group number
if in same group then atom with higher period is central
How many valence electrons are in each group?
group 1: 1 ve
group 2: 2 ve
group 13: 3 ve
group 14: 4 ve
group 15: 5 ve
group 16: 6 ve
group 17: 7 ve
When drawing lewis structures of polyatomic ions what is different?
add or subtract electrons to total ve count
draw square bracket to indicate charge
What is the born-haber cycle used for?
estimate lattice energy
What are the five reactions used in born haber cycle?
1.sublimation reaction of metal (solid to gas)
2. bond energy (breaking bond between diatomic molecule)
3. ionization of gaseous metal (removing electron)
4. electron affinity (adding electron to nonmetal)
5. formation of ionic compound from gaseous ions
How do you solve a born haber cycle?
find enthalpy of formation for the compound from solid metal and gas nonmetal
rearrange equation to find lattice energy
What is equation used to solve born haber cycle?
enthalpy of formation=(enthalpy of sublimation)+(enthalpy of IE)+(enthalpy of BE)+(enthalpy of EA)+(enthalpy of LE)
rearrange to find LE
What is trend for lattice energy?
magnitude decreases going down a column (less exothermic)
as magnitude of charges increases so does lattice energy
What is bond energy?
amount of energy required to homolytically break 1 mol of bonds between two atoms in the gas phase
homolytically means electrons in covalent bond are divided equally
Is bond energy positive or negative? Why?
positive
takes energy to break a bond
How can you use bond energy to caluclate enthalpy of a reaction?
break all bonds in the reactants and find all the values and add them together
break all bonds in products and find values and add them together and then make it negative
add these two values together
What happens when a bond get longer?
generally it gets weaker
What causes a polar covalent bond?
unequal sharing of electrons (one atom is more electronegative)
What is electronegativity?
measure of an atom’s ability to attract
electron towards itself in a chemical bond
What is the trend for electronegativity?
is decreases down a column and increases from left to right
What are the values for a difference in electronegativity for each bond?
0-0.4 is covalent
0.4-2.0 is polar covalent
above 2 is ionic
What are resonance structures? What are resonance hybrids? How are they drawn?
resonance structures are the different possibilities for the compound structure (drawn with arrow pointing between)
resonance hybrid have characteristics of all resonance structures (drawn with dashes to represent the possible bonds)
What is electron delocalization?
electrons go around the entire molecule
How can you calculate formal charge?
of ve-# of bonding electrons-1/2 bonded electrons
(take number of ve and count backwards for each electron/bond)
What can formal charges be used for?
comparing resonance structures to figure out the most dominant one
What is the optimal formal charge rules?
as many atoms as possible have full octets
magnitudes of formal charges as small as possible
negative formal chrages on most electronegative atom
What is a free radical? What does this usually mean?
an electron that is unpaired
more reactive
