Lewis VSEPR Flashcards
(25 cards)
What is a covalent bond?
A bond formed by the sharing of a pair of valence electrons between atoms.
How can you determine the number of valence electrons in an element?
From its group number in the periodic table (e.g., Group 16 elements have 6 valence electrons).
How do you calculate total valence electrons in a molecule?
Sum the valence electrons of all atoms present in the molecule.
What is the octet rule?
Atoms tend to form bonds to obtain 8 electrons in their valence shell (except H and He).
What is a Lewis structure?
A diagram showing the arrangement of valence electrons among atoms in a molecule.
What steps are used to draw a Lewis structure?
- Count valence electrons 2. Draw single bonds 3. Complete octets 4. Use multiple bonds if needed 5. Check formal charges.
When is the octet rule not followed?
By atoms in period 3 or above (can have expanded valence shells) and by sub-octet species like BF3.
What are lone pairs in Lewis structures?
Non-bonding pairs of electrons assigned to a specific atom.
When are multiple bonds used in Lewis structures?
When single bonds and lone pairs are insufficient to satisfy the octet rule.
How do you calculate formal charge?
FC = valence electrons - (non-bonding electrons + 0.5 × bonding electrons).
What is a resonance structure?
Alternate Lewis structures that differ only in electron arrangement, not atom placement.
What is the electron delocalisation model?
Describes electrons spread over multiple atoms or bonds, as in resonance structures (e.g., O3).
What is a radical in Lewis theory?
A molecule or atom with an unpaired electron; often highly reactive.
What is VSEPR theory used for?
Predicting the 3D molecular geometry based on electron pair repulsion.
What is electron pair geometry (epg)?
The spatial arrangement of all electron regions (bonding and lone pairs) around a central atom.
What is the molecular geometry of CH4?
Tetrahedral with 109.5° bond angles.
What shape and bond angle does NH3 have?
Trigonal pyramidal; approx. 107°.
What shape and bond angle does H2O have?
Bent or V-shaped; approx. 104.5°.
What are the bond angles for trigonal bipyramidal geometry?
90° and 120°.
What are the bond angles in octahedral geometry?
90°.
What is hybridisation?
The mixing of atomic orbitals to form new hybrid orbitals for bonding.
What hybridisation is typical for carbon in CH4?
sp3 hybridisation.
What hybridisation is seen in NH3 and H2O?
sp3 for both (with lone pairs affecting shape).
What is the valence bond model?
A bonding theory where orbitals overlap to form bonds; explains bond length and energy.
