Shapes of molecules Flashcards
State and account for the shape of a tetrachloromethane molecule. (L.C)
- Tetrahedral
- Four pairs electron and no lone pairs
Use electron pair repulsion theory to predict the shape of a molecule of boron trifluoride. (L.C)
Trigonal planar
Predict the shape of the arsine (AsH₃) molecule (L.C)
Pyramidal
Account for the difference in the shapes of the boron triflouide (BF₃) molecule and the ammonia (NH₃) molecule. (L.C)
Boron has three bond pairs of electrons
Nitrogen has three bond pairs and one lone pair of electrons
Ammonia (NH₃) and silane (SiH₄) are small molecules, each of which has four electron pairs in the valence shell of the central atom. Account for the difference in bond angle between the two molecules, 107.3 degrees in ammonia and 109.5 degrees in silane. (L.C)
- Lone pair of electrons has greater repelling power than a bond pair of electrons.
- Ammonia has three bond pairs (one lone pair) whereas silane has four bond pairs (no lone pair).
Give the shape and the corresponding bond angle for a molecule of formula QX₄ where Q is an element from group 4 of the periodic table. (L.C)
- Tetrahedral
- 109°28’
What are two possible shapes of molecules of general formula QX₂ ? (L.C)
- Linear
- V-shaped
Account for the difference in bond angle between water (104.5) and methane (109.5) (L.C)
- Lone pair(s) of electrons in water
- Have greater repelling power (repulsion)
Would you expect the hydrogen sulphide molecule to be linear or non-linear in shape? Justify your answer. (L.C)
- Non-linear
- There are non-bonding/lone pairs
What are the two possible shapes for molecule of general formula AB₂? (L.C)
- Linear
- V-shaped
Account for the difference in the shapes of the ammonia (NH₃) and boron trifluoride (BF₃) molecules. (L.C)
- NH₃ has three bond pairs and one lone pair
- BF₃ has three bond pairs (DRAWN ALSO)
Are the abbreviations b.p and l.p acceptable in exam?
NO!!
Define electronegativity (L.C)
The relative power of attraction an atom of an element has for the shared pair of electrons in a covalent bond.
Define covalent bond (L.C)
Covalent bonding occurs when electrons are shared between atoms. Atoms share to attain eight elements (usually). This type of bonding normally occurs between non-metal atoms.
State the valence shell electron pair repulsion theory (L.C).
Pairs of electrons in the outer shell of an atom arrange themselves to be as far away from each other as possible so as to minimise the repulsions between them.
