Shapes of Molecules Flashcards
How are molecules formed?
Atoms joined by covalent bond
What determines the shape of a molecule?
Arrangement in space of the atoms
What is the Electron Pair Repulsion Theory
It explains shapes of simple molecules with atoms bonded to a central atom. According to this theory,
- electron pairs in the valence shell of the central atoms repel eachother as far apart as geometrically possible
- lone pairs have a greater repelling effect than bonding pairs
If the central atom is in group 2, what shape will the molecule be and what will be the bond angle?
Linear, 180 degrees
If the central atom is in group 3, what shape will the molecule be and what will be the bond angle?
Trigonal planar, 120 degrees
If the central atom is in group 4, what shape will the molecule be and what will be the bond angle?
Tetrahedral, 109.5 degrees
If the central atom is in group 5, what shape will the molecule be and what will be the bond angle?
Pyramidal, 107 degrees
If the central atom is in group 6, what shape will the molecule be and what will be the bond angle?
V-shaped, 104.5 degrees
Which has the greatest repulsion between bonding pairs?
Lone pair : Lone Pair
Lone pair : Bond pair
Bond pair : Bond pair
Why when the central tom is in group 5, is the bond angle 107 degrees?
It has four bond pairs which gives it the tetrahedral arrangement, but due to the strong repulsion of the lone pairs, they bond pairs are pushed close together creating a bond angle of 107 degrees
How can a molecule have polar bonds but be a non-polar molecule?
Occurs when a molecule has a high degree of symmetry and geometric centre
If a molecule has a high degree of symmetry, what does this mean?
The molecule is non polar
What are the symmetrical molecules?
Linear, Trigonal, Tetrahedral
Which atom is partially negative?
Greater electronegativity
Which atom is partially positive?
Lesser electronegativity
How is a molecule symmetrical?
Example, Centre of negative charge in the central atom coincides with the geometric centre of positive charge, caused by the surrounding atoms.
How is a molecule not symmetrical?
Centres of positive and negative charge do not coincide. Negative charge of central atom is at the apex and the centre of positive charge is seperated
What is intramolecular bonding?
Bonding within the molecule that holds the atom together
What is intermolecular bonding?
Forces/bonding between molecules
What is hydrogen bonding?
a special type of dipole-dipole interaction, which occurs when hydrogen is bonded to small, highly electronegative atoms such as O, N or F
Hydrogen bonding in water
Highly polar due to electronegativity difference
Partial negative has strong attraction for partial positive
What do strong intermolecular forces mean?
It means high boiling point
Hydrogen sulfide has a electronegativity difference of 0.4, what does this mean
It means it is weakly polar. The partial negative charge is more diffuse and less effective on large sulphur atom than on oxygen atom
How does the boiling point usually increase?
It increases as the relative molecular mass increases
What occurs in hydrogen bonding?
Hydrogen bonds to a small, highly electronegative atom which means the share of electrons is going to be small. It readily attracts too another electronegative atom
Since the hydrogen atom is small, what does this mean?
Two atoms can bond to it, hydrogen bond and other by covalent bond
What is dipole-dipole interactions?
Negative end of one dipole is attracted to the positive end of another
Why are dipoles permanent?
Due to their polarity
