Chapter 6 - shapes of molecules and intermolecular forces Flashcards
Wedges
➜ a solid line = ━ represents a bond
➜ a solid wedge = ▲ comes out the plane of paper
➜ a dotted wedge = ┋ goes into the plane of paper
Bonded and Lone pair repulsions
➜ lone pair of electrons are slightly closer to central atom and occupies more space than bonded pair
➜ lone pairs repel more strongly than bonding pairs
2 bonded No lone pair
➜ Linear
➜ angle = 180
➜ e.g CO₂ & BeF₂
3 bonded No lone pair
➜ Trigonal Planar
➜ angle = 120
➜ e.g SO₂ & BF₃
4 bonded No lone pair
➜ Tetrahedral
➜ angle = 109.5
➜ e.g NH₃ & CH₄
5 bonded No lone pair
➜ Trigonal Bipyrmaidal
➜ angle = 120, 90
➜ e.g PF₅ & PCl₅
6 bonded No lone pair
➜ Octahedral
➜ angle = 90
➜ e.g SF₆ & SeF₆
2 bonded 2 lone pair
➜ Bent or non linear
➜ angle = 104.5
➜ e.g H₂O & SCl₂
3 bonded 1 lone pair
➜ Pyramidal
➜ angle = 107
➜ e.g NH₃
4 bonded 2 lone pair
➜ square planar
➜ angle = 90
Electronegativity
➜ the attraction of a bonded atom for the pair of electrons in a covalent bond
Electronegativity Increases across period
➜ effective nuclear charge increases across a period
➜ atomic radius decreases
➜ the shell distance stays same
Electronegativity decreases down a group
➜ more shielding of electrons = atomic radius increases = nuclear charge increases down a group, but the effective nuclear charge does not as it is negated
Polar bond
➜ a covalent bond between atoms with different electronegativities with positive and negative partial charges on the bonded atoms
➜ the shared pair of electrons is shared unequally between bonding atoms
Non Polar bond
➜ shared pair of electrons shared equally between bonded atoms
Dipole
➜ positive and negative partial charges separated by a short distance in a molecule
most electronegative element
➜ Fluorine is the most electronegative element
➜ The closer an element is to Fluorine the more electronegative the element
London Forces (induced dipole dipole)
➜ weakest
➜ exist between non polar and polar
➜ movement of electrons produces a changing dipole in a molecule
➜ instantaneous dipole induces a dipole on neighbouring molecule
➜ only temporary
➜ more electrons = stronger london forces
Permanent dipoe dipole interactions
➜ permanent between polar molecules
➜ can exist with london forces asw
Simple molecular substances
➜ molecules held by weak intermolecular forces
➜ ATOMS with in each molecule bonded together by STRONG covalent bonds
Properties of simple molecular
➜ low melting and boiling = weak intermolecular forces ez to break (covalent doesnt break)
➜ polar may dissolve in polar
➜ non conductors
Hydrogen Bonding
➜ special type of permanent dipole dipole interaction
➜ occur between to an electronegative atm (F, O, N)
Ice is less dense than water
➜ lattice structure of ice due to hydrogen bonds so it can float
➜ ice melts = lattice collapses = allowing molecules to move closer and increasing density
H₂O has high melting//boiling point
➜ strong H bonds and energy required
