Unit 1: Bonding and Structure Flashcards
What repels more than bonded pairs of electrons?
Lone pairs
When may a permanent dipole arise?
When covalently bonded atoms have different electronegativities, resulting in a polar bond.
How are electron pairs arranged?
As far away from each other as possible to minimise repulsion.
If there are 2 electron pairs, what’s the shape of the molecule and bond angle?
Linear and 180 degrees.
If there are three electron pairs (areas of electron density) what is the shape of the molecule and the bond angle?
Trigonal planar and 120 degrees.
If there are four electron pairs (areas of electron density) what is the shape of the molecule and the bond angle?
Tetrahedral and 109.5 degrees.
If there are 4 electron pairs, 3 are bonded and 1 is a lone pair, then what is the shape of the molecule and the bond angle?
Pyramidal and 107 degrees.
If there are 4 electron pairs, 2 bonded and 2 lone, what is the shape of the molecule and bond angle?
V or bent shape and 104.5 degrees.
What are the four most electronegative elements?
F>O>N>Cl
What are Vaan Der Waals’ forces?
very weak attractive forces between induced dipoles in neighboring polar molecules
They are the only attractive intermolecular forces that act between non-polar molecules.
What do atoms of elements in the same group have in common?
Have similar outer shell electron configurations, resulting in similar properties.
What’s the trend of reactivity in group 2?
The reactivity increases down the group as the atomic size increases due to more electrons in electron shells and therefore more electron shielding (as well as a higher nuclear charge in the nucleus) the atoms are more willing to give away an electron down the group because the electrostatic attraction between the outer shell of electrons and the nucleus decreases down the group.
What’s the trend of reactivity in group 7?
The reactivity decreases down the group because as the atomic size increases and electron shielding increases, there’s less attraction between the outer shell and the nucleus and therefore more difficult to gain an electron.
How do van der Waals’ forces arise?
Electrons in molecules are constantly moving, and at any instant the distribution may not be symmetrical. This results in an instantaneous temporary dipole. This dipole induces dipoles in neighbouring molecules, leading to an attraction between the opposite charges in the dipoles (van der Waals’)
What affects the strength of Van der Waals’ forces?
Number of electrons - more electrons means greater fluctuations in electron cloud, so stronger van der Waals’ forces
Contact area between molecules - greater contact area between molecules, the stronger the van der Waals’
