3.1.3.5 Shapes of simple molecules and ions Flashcards
the bond angle found in an ammonia molecule
107°
why the bond angle in an amide ion is smaller than that in an ammonia molecule
More lone pairs on NH2 – , than on NH3
Lone pairs repel more than bonding pairs M
value for the H−O−O bond angle in hydrogen peroxide
94−105.5°
Definition: electronegativity
The power of an atom or nucleus to withdraw or attract electrons OR electron density OR a pair of electrons (towards itself) Ignore retain
In a covalent bond
why the electronegativity of the elements increases from lithium to fluorine
More protons / bigger nuclear charge
Same or similar shielding / electrons in the same shell or principal energy level / atoms get smaller
Name of the shape made by the three atoms in the NH2 – ion
Bent / v shape/ triangular
reason why neon does not form compounds with sodium
Ne has full sub-levels/ can’t get any more electrons in the sub-levels/ Ne has full shells
value for the F—N—F bond angle in NHF2
107°
the bond angle in the PH4 + ion
109.5° / 109½ / 109°
value for the bond angle in the H3O+ ion
107°
one molecule with the same number of atoms, the same number of electrons and the same shape as the H3O+ ion
NH3/ammonia
the number of lone pairs of electrons in the hydroxide ion
3
the bond angle in the BF4 – ion
109° to 109.5°
Predict the shape of the ion. Explain why it has this shape.
Tetrahedral
(Equal) repulsion
between four bonding pairs / bonds
why the bond angles in the NH4 + ion are all 109° 28’
4 bonding / electron pairs
repel equally
as far apart as possible
tetrahedron
Name of shape of NHF2
pyramidal / trigonal pyramid
Name of shape of BF3
trigonal planar
value for the F—N—F bond angle in NHF2
107°
the shape of CCl2
Bent / v shape
Explain how the electron pair repulsion theory can be used to deduce the shape of, and the bond angle in, PF3
Stage 1: Electrons round P
• P has 5 electrons in the outside shell
• With 3 electrons from 3 fluorine, there are a total of 8 electrons in outside shell
• so 3 bond pairs, 1 non-bond pair
Stage 2: Electron pair repulsion theory
• Electron pairs repel as far as possible
• Lone pair repels more than bonding pairs
Stage 3: Conclusions
• Therefore, tetrahedral / trigonal pyramidal shape
• With angle of 109(.5)° decreased to 107°
reason why electron pair repulsion theory cannot be used to predict the shape of the [CoCl4] 2− ion
Too many electrons in d sub-shell / orbitals
Predict the shape of, and the bond angle in, the complex rhodium ion [RhCl4] 2− .
Tetrahedral (shape)
109.5°
why the AsCl4 + ion has a bond angle of 109.5°.
There are 4 bonds or 4 pairs of electrons (around As)
(Electron pairs / bonds) repel equally
the bond angle found in an ammonia molecule
107°
