CHEMISTRY: TOPIC 14 BONDING
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CHEMISTRY: TOPIC 14 BONDING - Marcador
CHEMISTRY: TOPIC 14 BONDING - Detalles
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| 🇬🇧 | 🇬🇧 |
| What is the structure of XeF4 and ICl4-? | Square planar (90 degrees) because of 2 lone pairs on the central element 4 bonds square planar because of 3 lone pairs and one from the ion |
| What is the structure of ClF3? | T-shaped because of 2 lone pairs and 3 bonds |
| What is a sigma bond? (4) | Head on overlap of atomic orbitals so that the electron density is between the nuclei of the bonding atoms S-S P-P S-P |
| What is a pi bond? (7) | Sideways overlap of atomic orbitals so electron density is above and below the nuclei of the bonding atoms can only happen with p orbitals does not happen with single bonds only with double, triple there is always a sigma bond with a pi bond double bond = 1 pi bond triple bond = 2 pi bonds |
| What is formal charge? | Atomic charge of a molecule, if all the atoms had the same electronegativity used to determine which lewis structure is preferred by whichever is closest to 0 |
| What is the formula for formal charge? | Number of total valence electrons - Number of non-bonding electrons - number of bonding electrons / 2 |
| If both lewis structure's FC is 0? (2) | Whichever individual atoms are closest to 0 is preferred If the negative charge is on the more electronegative atom (F, O, N) |
| What are delocalized pi electrons? | Electrons that are shared between more than 2 nuclei = not fixed between a pair of atoms exist in all molecules or ions where there is more than one lewis structure possible (Resonance structures) represented by a dashed line |
| Why do electrons delocalize in resonance structures of a molecule? | Because the bond lengths and strengths are equal as there are equal contributions from both of the resonance structures makes a resonance hybrid (mixture of both the resonance forms) |
| What is delocalization? | Sharing of a pair of electrons bw 3 or more atoms |
| How do we know if something has delocalized pi electrons? | If more than one resonance structure is possible and the only difference is the position of a double bond |
| An example of a molecule with delocalised electrons? (7) Ben | Benzene C6H6 has 2 resonance structures where the double and single bonds are in different positions The bonds are intermediate = resonance hybrid structure Unhybridised P orbital == overlap to form a delocalised pi system shows with a dashed line 6 pi electrons - one form each unhybridised orbital circle shows delocalised pi electrons |
| What are resonance structures? | 2 or more lewis structures to represent a molecule or ion that can't be described with just one lewis structure difference in position of double bonds |
| Give another example of delocalised electrons in a molecule (ethan) | Ethanoate ion CH3COO- difference between the two resoncance structures is a different position for the double bond between O-C |
| What is VSEPR theory? | Valence shell electron pair repulsion theory is used to predict the geometry of molecules electron pairs repel each other and spread as far apart as possible |
| What is electron domain? | Bonds / lone pairs of electrons around an atom in a molecule single doube and triple bonds all count as one electron domain |
| Which atoms can have expanded octets? | Atoms in period 3 and onwards such as (Cl, Br, S and P) can use their d orbitals in bonding |
| What is hybridisation? | It is the mixing of atomic orbitals to produce hybrid orbitals in bonding 3 types are = sp3, sp2, and sp |
| Describe sp3 hybridisation | Eg: carbon atom 2s2 and 2p2 an electron from the 2s sub level is promoted to an empty orbital in the 2p sub level = excited state (1 e in 2s and 3 in 2p) The 2s and 2p orbitals mix to form sp3 hybrid orbitals = degenerate same energy explains why carbon can form 4 bonds |
| Describe sp2 hybridisation | An electron is promoted to the 2p sub level = excited state mix to form 3 sp2 orbitals with one unhybridised p orbital unhybridised p orbital forms a pi bond (double bond) |
| Describe sp hybridisation | Electron is promoted = excited 1 2s and 1 2p orbital mixes to form sp while 2 unhybridised p orbitals remain 2 unhybridised orbitals form 2 pi bonds |
| Molecular geometry of sp, sp2 and sp3 | Linear (2 domains) 180 degrees eg: co2 trigonal planar (3 domains)) 120 degrees BF3 Tetrahedral (4 domains) 109.5 H2O can be tetra, bent or trigonal pyramidal |
| What are free radicals? | Highly reactive atoms with unpaired electrons (an O2 atom with 2 unpaired electrons |