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°
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
Why is each bond angle exactly 120° in BCl3
3 (bonding) pairs of electrons
Predict the bond angle in CCl2 and explain why this angle is different from that in BCl3
Predicted bond angle: 118° (allow 117 - 119°)
Explanation: lone pair
repels more than bonding pair
bond angle in XeF4
90°
why the lone pairs of electrons are opposite each other in this molecule (XeF4)
lone pairs (or they) repel more than bonding pairs (or most) (1) (so are) as far apart as possible
Name the shape of this molecule, given that the shape describes the positions of the Xe and F atoms only (XeF4)
square planar
