6.4 Hydrogen bonding Flashcards
What are hydrogen bonds?
They are a special type of permanent dipole-dipole interaction found between molecules containing:
- An electronegative atom with a lone pair of electrons
- A hydrogen atom attached to an electronegative atom
What is the strongest type of intermolecular attraction?
Hydrogen bonds
What are the main anomalous properties of water?
The solid (ice) is less dense than liquid (water) Water has a relativiely high melting and bioling point Relatively high surface tension and viscosity
Why is the solid (ice) is less dense than liquid (water)?
- With 2 lone pairs on the oxygen and 2 hydrogen atoms, each water molecules can form 4 hydrogen bonds.
- The hydrogen bonds extend outwards, holding water molecules slightly apart and forming an open tetrahedral lattice full of holes. The holes in the open lattice structure decrease the density of water on freezing.
- The bond angle about the H atom involved in the hydrogen bond is close to 180o
- The hydrogen bonds hold water molecules apart in an open lattice structure
Due to the properties of ice what does it form?
It forms an insulating layer, preventing the water from freezing solid
Why does water have a relativiely high melting and bioling point?
It has London forces between the molecule
-H-bonds are extra forces, over and above the London forces
A lot of the energy is needed to break the H-bonds
Whn the ice lattice breakes, the rigid arrangements of the H-bonds in ice is broken (When H2O boils hydrogen bonds are completly brockem)
What would happen to water if it didn’t have hydrogen bonds (in terms of its boiling and melting point)?
Boiling point = -75oC
A gas at room temperature and pressure
No liquid water in most places on Earth =no life
What does water’s propertiy of a relatively high surface tension and viscosity allow?
It allows insects to walk on its surface
detergents are used to reduce this
