Molecular shape and Bonding Flashcards
what is a non- polar covalent bond ?
_ Similar electronegativity
what is a polar covalent bond ?
- have dipoles
- difference in electronegativity less than 2
what are 3 properties of ionic compounds ?
- highly ordered crystal lattice
- conduct electricity when molten
- high bp
what are electropositive elements ?
- elements with low ionisation energy (outer e- easily removed)
what are electronegative elements ?
- elements that readily acquire electrons
what are the factors affecting lattice energy ?
- ionic radius
- ionic charge
- no of shells /sheilding
How does ionic radius affect LE ?
- smaller ionic radius = greater attraction so higher LE
How does ionic charge affect LE ?
- greater ionic charge = greater attraction so higher lE
what is electronegativity ?
- the ability of an atom to pull bonding electrons towards itself
what are degenerate orbitals ?
- have same energy level
- eg 2p orbitals
why do electrons in degenerate orbitlas occupy empty ones first ?
- to minimise repulsion
why is the 4s orbital filled before 3d ?
- it has a lower energy level
what is a radial node ?
- region where there is zero probability of finding an electron
what are 2 properties of 2p orbitals ?
- degenerate (same energy)
- each orbital is perpendicular to the other two
what is the rule for molecular orbital theory ?
- number of AO = number of MO
- always get a bonding and anti-bonding MO
what is a sigma bonding molecular orbital ?
- atomic orbitals of same phase sign overlap
what is anti-bonding molecular orbital ?
- atomic orbitals of opposite phase sign overlap
what is constructive combination ?
- wave function of e- are in the same phase
what is destructive combination ?
- wave function of e- are in opposite phases
what is the difference between anti bonding and bonding MO ?
- anti bonding has a node and no electrons
- anti - bonding is higher in energy
What does end on overlap of 2p orbitals lead to ?
- sigma bonds
what does side on overlap of p orbitals lead to ?
- pi bonds
explain the hybridization of carbon for CH4 ?
- one e- from a 2s orbital is promoted to a spare p orbital
- makes 4 degenerate sp3 orbitals
- helps from 4 equivalent bonds
How are C-H bonds formed in ethane ?
- overlap of sp3 and hydrogen s orbital
How are C-C bonds formed in ethane ?
- overlap of 2 carbon sp3 orbitals
what is the bond angle for sp3 hybrids ?
109.5
how is the c-c double bond formed in ethene?
- sigma bond formed by overall of 2 carbon sp2 orbitals
- Pi bond formed by side to side overlap of unhybridized p orbitals
what is the bond angle and shape of sp2 ?
120 - trigonal planar
what is the structure of ethyne ?
- triple bond between carbons
- each c attached to a H
What is bond angle and shape of sp orbital ?
- 180 - linear
how many sigma and pi bonds are in a triple bond ?
2 pi bonds
1 sigma bond
what is the shape + bonding in a methyl cation ?
- CH3 +
- sp2 hybridisation
- trigonal planar - 120
what is the bonding in a methyl radical ?
-CH3*
- sp2 hybridization
- trigonal planar - 120
what is the shape + bonding in a methyl anion ?
- three bonding pairs and 1 lone pair
- sp3 hybridization
- tetrahedral 109.5
what is hybridisation of NH3 ?
- 3 bonding pairs 1 lone pair
- sp3 orbitals
- bond angle is 107
How is the C-N bond formed ?
sp3 - sp3 overlap
hybridisation of H20 ?
- sp3 oribitals
- including lone pairs
- 104.5
What is the bonding in hydrogen halides ?
S-sp3
Why is H-F bond stronger than HCI bond?
HF = 1s and 2sp3 orbital
HCl = 1s and 3sp3 orbital
CL bigger than F so less electron density in s-sp3
As size of X increases h-x bond gets weaker
How does size of halide effect bond strength?
As size increases bond gets weaker + longer
What are Van Der Waal forces ?
- Weak interactions caused by momentary changes in e- density
What is an intermolecular bond?
- Between molecules
What is an intramolecular bond?
- Within a molecule
What is the order of bond strength?
electrostatic forces Ionic bonds > H bonds > permanent dipole - dipole >
London forces
What are the 2 conformations of alkanes?
- Staggered + eclipsed
- eclipsed the H are closer together
Is staggered or eclipsed conformation more stable ?
- staggered is more stable than eclipse , lower in energy
what is torsional strain ?
- repulsion of proximate bonding electrons
- only found in eclipse conformation
what is steric strain ?
- atoms / groups too close to eachother so e - clouds repel
- found in staggered or eclipsed
what is angle strain ?
- deviation from ideal tetrahedral bond angle
which conformation of cyclohexane is more stable ?
- chair conformation because no angular + torsional strain
