Structure and Bonding, Shapes and IM forces (5.2,5.3, Chapter 6 + 7.3) Flashcards
What is covalent bonding?
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
What is the name for a covalent compound with less than 8 electrons in the outer shell e.g. BF3 with 6 electrons?
Electron deficient compounds
What happens to the electronic configuration in BF3?
It stays the same, 1s2, 2s2, 2p1
What is actually happening in BF3?
The 2s and 2p orbitals become hybridised orbitals called “sp2” with one electron in each orbital
What is the name for a covalent compound with more than 8 electrons in its outer shell e.g. PCL5 or SF6?
Expanding the octet
Which elements can expand their octets and why?
Period 3,4 and 5 elements because they have low-lying d-orbitals (in the 3rd or more shell) which the extra electrons can be in, there can be up to 18 electrons in the outer shell
e.g. P, S and Cl
What is the difference between a lone pair and a bonding pair of electrons?
A lone pair is a pair of electrons not bonded to another atom (and often becomes a dative bond) e.g. ••
A bonding pair is pair of electrons bonded to two atoms in a covalent bond e.g. •x
What are double/triple covalent bonds?
- When the electrostatic attraction is between two/three shared pairs of electron and the nuclei of bonded atoms -
- Bonds that contain more than one shared pair of electrons between two atoms e.g. O2, N2 and CO2
What is a dative covalent bond/coordinate bond?
- A covalent bond in which the shared pair of electrons has been supplied by one of the bonding atoms only
- The shared electron pair was originally a lone pair of electrons from one of the bonded atoms
When does dative bonding occur?
When one atom or compound has at least one lone pair of electrons (or just a full outer shell) is covalently bonded to another atom or compound which needs electrons
What happens when NH3 becomes NH4+?
NH3 has a lone pair of electrons on the nitrogen
An H+ ion has no electrons in its outer shell
The H+ is datively bonded to the lone pair of electrons on the nitrogen to form NH4+
NH4+ has a positive charge because hydrogen has lost one electron
How do you draw a dative bond in a display formulae?
Instead of a line, an arrow is drawn starting at the atom which is donating the pair of electrons (at the lone pair) and goes towards the atom receiving the pair of electrons
What is the theory that describes the shapes of molecules?
VSEPR theory
Valence Shell Electron Pair Repulsion Theory
What is the shape and bond angle of a molecule with 2 electron pairs?
Linear, 180 e.g. CO2
What is the shape and bond angle of a molecule with 3 electron pairs?
Trigonal planar, 120 e.g. BF3
What is the shape and bond angle of a molecule with 4 electron pairs?
Tetrahedral, 109.5 e.g. CH4
What is the shape and bond angle of a molecule with 6 electron pairs?
Octahedral, 90 e.g. SF6
How do electron pairs interact?
Electron pairs repel each other as far apart as possible
What is the repulsion order for electron pairs?
L.p - L.p > L.p. - B.p > B.p - B.p
What happens when lone pairs are present?
The lone pair(s) repels the bonding pairs more so the bond angles are smaller as the bonding pairs are pushed closer together
What is the shape and and bond angle of a molecule when there is 1 lone pair and 3 bonding pairs?
Pyramidal, 107
What is the shape and bond angle of a molecule when there are 2 lone pairs and 2 bonding pairs?
Non-linear (bent), 104.5
What is the process for working out the shape and bond angle of a molecule?
1) dot and cross diagram
2) count the total number of electron pairs (bonding and lone)
3) based on the number of electron pairs, decide the overall base shape and starting bond angle
4) subtract 2.5 from the starting bond angle for each lone pair to get the bond angle of the molecule
What is electronegativity?
The ability of an atom to attract the bonding electrons in a covalent bond