C6- shapes of molecules and intermolecular forces Flashcards

Question

What are intermolecular forces and covalent bonds each responsible for?

Answer 1

Intermolecular forces are responsible for physical properties such as melting and boiling points. Covalent bonds determine the identity and chemical reactions of molecules.

Answer 2

They exist between all molecules but are TEMPORARY. 1. Electron movement produces a changing dipole in a molecules. 2. At any instant, and instantaneous dipole will exist (very weak as it only lats for an instant) but its position is constantly shifting. 3. The instantaneous dipole induces a dipole on a neighbouring particle. 4. Further dipoles are induced which then attract to each other. They exist over short distances so molecules need to be close together to induce dipoles.

Answer 3

The more electrons in each molecules: - the larger the instantaneous and induced dipoles - the greater the induced dipole-dipole interactions. - the stronger the attractive forces between molecules. (This increases the boiling point as more energy is needed to overcome the IMF)

Answer 4

Act between the permanent dipoles in different polar molecules. If a molecule has London forces and permanent dipole- dipole interactions between molecules, extra energy is needed to break the additional permanent dipole- dipole interactions so therefore boiling point is often high.

Answer 5

A simple molecular substance is made up of simple molecules- small units containing a definite number of atoms with a definite molecular formula. In the solid state, they can form a simple molecular lattice: - the molecules are held in place by weak intermolecular forces. - the atoms within each molecule are bonded together strongly by covalent bonds.

Answer 6

They have a low melting and boiling point: All simple molecular substances can be solidified into simple molecular lattices by reducing the temperature. The weak intermolecular forces in the lattice can be broken even by the energy present at low temperatures. During melting the covalent bonds do not break.

Answer 7

Non-polar simple molecular substances tend to be soluble in non-polar solvents: > simple molecular compound+ non-polar solvent = intermolecular forces form, therefore, weaken the lattice and the compound dissolves. They tend to be insoluble in polar solvents: >little interaction between the lattice and solvent so intermolecular bonding within polar solvent is too strong to break.

Answer 8

- Polar covalent substances may dissolve in polar solvents as the solute molecules and solvent molecules attract each other. - solubility depends on the strength of the dipole (so it’s hard to predict) - compounds that contain both polar and non-polar parts can dissolve in either solvents. - some molecules = hydrophobic (non-polar) and hydrophilic (polar so interacts with water)

Answer 9

There are no mobile charges particles so therefore they are non-conductors of electricity.

Answer 10

A special type of permanent dipole- dipole interaction found between molecules containing: - an electronegative atom with a lone pair of electrons. (Eg. Oxygen, fluorine,nitrogen). - a hydrogen atom attached to an electronegative atom. Hydrogen bonds are the strongest type of intermolecular attraction. The shape around the hydrogen atom involved in the hydrogen bond is linear.

Answer 11

With 2 lone pairs on the oxygen atom and two hydrogen atoms, each water molecule can form 4 hydrogen bonds. The hydrogen bond extend outwards, holding water molecules slightly apart and forming an open tetrahedral lattice full of holes. (The bond angle about the hydrogen atom involved in the hydrogen bond is 180*) The holes in the open lattice structure decrease the density of water on freezing. When ice melts, the lattice collapses and the molecules move closer together making liquid more dense.

Answer 12

Water has a relatively high melting and boiling point: water has London forces between molecules. - hydrogen bonds are extra forces, above London forces so a large quantity of energy is needed to break the hydrogen bonds in water. - when the ice lattice breaks, the rigid arrangement of hydrogen bonds in ice is broken. When water boils, the hydrogen bonds break completely. Without hydrogen bonds water would have a boiling point of about -75*C and woukd exist as a gas at room temperature and pressure. > Water also has a relatively high surface tension and viscosity

Answer 13

Electrostatic attraction between positively charged ions

Answer 14

1. Draw dot and cross diagram. 2. Show loan pairs clearly. 3. State the number of bonded pairs and loan pairs. 4. Reduce 2.5* for each loan pair if necessary. 5. State the bond angle.