Lewis Diagrams Flashcards
When electrons move between compounds/atoms they generally move from….?
Electron rich to electron deficient
What is resonance?
Movement/delocalization of electrons within a chemical structure
What do double-headed arrows show in resonance?
- Lone pair moving to form a bond
- Bond moving to form a lone pair
How do you calculate the number of valence electrons in an ion?
Subtract the charge on the ion from the valence electrons in the atom
What is the octet rule?
Atoms will gain or lose valence electrons in order to get 8 surrounding electrons. The goal is to achieve the configuration of noble gases because there is a special kind of stability achieved with full subshells
What is the duet rule?
Hydrogen will gain one electron to reach the electronic configuration of helium (1s^2)
How are ionic compounds formed again?
The electrostatic forces (attraction) between opposite charged ions
Are electrons localized or delocalized in lewis diagrams?
localized and are typically in pairs
In covalent lewis diagrams, how do you decide which atom goes in the center?
The atom with the most bonding sites goes in the middle to achieve high symmetry
How many electrons MUST surround each atom in a covalent lewis diagram?
8 electrons
How do you calculate the number of non-skeletal electrons?
Total number of valence electrons - number of electrons used for skeletal structure (bonds)
What is formal charge and how is it calculated?
It is the “apparent” charge on the atom; it is calculated for each atom on the lewis diagram.
FC = number of valence electrons in atom - number of non bonding electrons - (1/2) number of bonding electrons
What should the sum of formal charges on an atom be?
Zero.
What should the sum of formal charges on an ion be?
The charge on the ion.
What does a valid/correct lewis diagram have?
- correct elements
- atom with highest number of bonds in the center
- high symmetry
- Correct total number of valence é
- octet for elements in period n = 2
- Formal charges for each atom
- Minimized formal charge if possible
What is the “most significant contributor”?
The most stable valid lewis diagram of the species.
- small FC on individual atoms (0 best)
- few atoms with non-zero FC
- FC of 0 or negative on most electronegative atoms
- No adjacent positive (or negative) charges
Why do non-metals n = 3 and above have a capacity for more electrons?
Non-metals in n = 2 have only the 2s and 2p orbitals so they have a maximum capacity of 8 electrons. Non-metals in n = 3 and above have s,p, and d orbitals and so they can accomodate more.
When are octet rules not obeyed?
- Non-metals in N = 3 and above
- Beryllium sometimes has less than an octet (low electronegativity and electron deficient)
- Boron sometimes has less than an octet
- Nitrogen sometimes has less than an octet (undergoes dimerization it is a radical and super reactive)
What is a dimer?
A molecule consisting of two identical molecules linked together.
- For example, NO is radical and very reactive so it goes through dimerization to form a more stable compound
