2.6 SHAPES OF MOLECULES AND INTERMOLECULAR FORCES Flashcards
What are molecules?
Molecules are two or more atoms bonded covalently
What is the electron pair repulsion theory?
Electron pair repulsion theory:
-e and e both negative
-e pairs repel as far away as possible
-lone pairs repel greater than bonded pairs
lone and lone = greatest repulsion
lone and bonded = less repulsion
bonded and bonded = least repulsion
What shape and angle is 2 bonded pairs?
2 bonded pairs = linear, 180
What shape and angle is 3 bonded pairs?
3 bonded = triaganol planar, 120
What shape and angle is 4 bonded pairs?
4 bonded = tetrahedral, 109.5
What shape and angle is 5 bonded pairs?
5 bonded = triagonal bi-pyramidal, 90
What shape and angle is 6 bonded pairs?
6 bonded = octahedral, 90
What shape and angle is 2 bonded pairs and 2 lone pairs?
2 bonded 2 lone = non-linear, 104.5
What shape and angle is 3 bonded pairs and 1 lone?
3 bonded 1 lone = pyramidal, 107
What is polarity?
Molecules that have a separation of charge are polar. As nuclear charge increases, molecules become more polar
What is electronegativity?
Electronegativity is the ability to attract electrons in a covalent bond.
Fluorine is the most electronegative, then oxygen, then nitrogen
What does electronegativity depend on?
Electronegativity depends on:
1. nuclear charge
2. distance between outer electrons and nucleus
3. level of shielding by other electron shells
What happens to electronegativity?
Electronegativity increases across a period as nuclear charge increases and decreases down a group as shielding increases.
Ionic bonding is the degree of separation (the degree of ability to attract electrons to itself)
What are intermolecular forces?
Intermolecular forces are weak interactions between the dipoles of different molecules
What are the types of intermolecular forces?
Types of intermolecular forces:
London forces = exist in all molecules, easily broken
permanent dipole-dipole interactions
hydrogen bonding
What are dipoles?
Dipoles:
-created when electrons move towards more electronegative atoms
-separation of opposite charges
-in symmetrical molecules, dipoles cancel out
-permanent dipoles = occur between permanent delta negative and positive ends of molecules
-induced dipoles (London forces) = exist between all molecules
How are London forces made?
London forces are made by:
1. random movement of electrons introduces and instantaneous dipole
2. this dipole will induce another dipole in a neighbouring molecule
3. induced dipole introduces more dipoles which attract one another
What is hydrogen bonding?
Hydrogen bonding occurs between the hydrogen atom that is bonded to either nitrogen, oxygen or fluorine and another electronegative atom
-electronegativity of O, N, F atom pulls electron away from H atom which gives it a small positive charge- forms a hydrogen bond with one pair of electrons on N, O or F atom
-strongest and hardest to overcome
