Shapes of Covalent Molecules Flashcards
What is the shape of a covalent molecule determined by?
The angles between bonds that join atoms together
What does Sidgewick and Powell’s theory - VSEPR (Valence Shell Electron Pair Repulsion) - conclude?
Electron pairs in the outer shell of atoms try to stay as far apart as possible to reduce electrostatic repulsion.
Molecules take up the shape that minimises the repulsion between electron pairs within the molecule.
What is the bond angle in a ‘linear’ molecule?
180 degrees
What is the bond angle in a ‘bent’ molecules?
109.5 degrees
What ‘bent’ molecule has a different bond angle?
Water, 104.5 degrees
What is the only possible bond angle in a ‘linear’ molecule?
180 degrees
What is the bond angle in a ‘tetrahedral’ molecule?
109.5 degrees
What is the bond angle in a ‘trigonal planar’ molecule?
120 degrees
What is the bond angle in a ‘trigonal pyramidal’ molecule?
107 degrees
What is the bond angle in an ‘octahedral’ molecule?
90 degrees
How many atoms can there be in a ‘linear’ molecule?
2 or 3
How many atoms are there in a ‘bent’ molecule?
3
How many atoms are there in a ‘tetrahedral’ molecule?
5
How many atoms are there in a ‘trigonal planar’ molecule?
4
How many atoms are there in a ‘trigonal pyramidal’ molecule?
4
Are there any unshared pair of electrons in ‘linear’ molecules?
In a ‘linear’ molecule with 3 atoms, there will be no unshared pairs of electrons; if there were, the molecule would be non linear or ‘bent.’
In a ‘linear’ molecule with 2 atoms, any unshared pairs of electrons will not affect the bond angle.
What group typically form ‘bent’ molecules and why?
Group 6 as there are 2 pairs of unshared electrons in elements such as oxygen and silicon (both group 6) which will repel any other atoms downwards.
What group typically form ‘tetrahedral’ molecules and are there any unshared pairs of electrons?
Group 4 elements, no unshared pairs of electrons
What group typically form ‘trigonal planar’ molecules and are there any unshared pairs of electrons?
Group 3 elements, no unshared electrons
What group typically form ‘trigonal pyramidal’ molecules and are there any unshared pairs of electrons?
Group 5 elements, 1 pair of unshared electrons will repel the bonded pairs down.
Give an example of 2 ‘linear’ molecules.
CO2, O2
Give an example of 2 ‘bent’ molecules.
H2O, SH2
Give an example of a ‘tetrahedral’ molecule.
CH4
Give an example of a ‘trigonal planar’ molecule.
BF3
