year 12 physical Flashcards
requirements to form a dative covalent bond
lone pair of electrons
what happens to covalent bonds when melting a simple covalent molecule?
they break
define planar
all molecules electrons on same plane
what conducts electricity in metals
bonding electrons
what causes a change in shape around bonding atom?
difference in no. of electrons
metallic bonding
attraction between metallic ion (name) and delocalised electrons
why do ionic structures have high melting points
giant ionic lattice
electrostatic ATTRACTION between M+ ions and X- ions
why do metals have higher boiling points that simple covalent molecules
metallic bonding vs simple covalent bonding
weak van der waals in comparisons to strong electrostatic forces
more energy to overcome
forces between simple covalent molecules
intermolecular forces
what causes intermolecular forces to act stronger
larger molecule = more electrons = stronger
bonding in silicon dioxide
macromolecular
define macromolecular
giant covalent structure
why do metallic structures have high melting points?
strong electrostatic attraction
positive Mg+ ion and negative DELOCALISED electrons
reason for high malleability in metals
layers of ATOMS slide over one another
why does moulding metals not change strength
bond strength stays the same
why do salts not carry charge?
ions cant move so charge cannot be carried
define enthalpy change
heat change at a constant pressure
enthalpy of formation
1 mole
formed from elements
standard condition
enthalpy of combustion
1 mole
complete combustion
excess oxygen
from standard conditions
enthalpy of neutralisation
1 mole water formed
acid and alkali
standard conditions
enthalpy of reaction
stoichiometric equation
products under standard conditions
endothermic reaction
absorbs energy from surroundings
positive delta H
breaking bonds
exothermic reaction
releases energy to surroundings
negative delta H
forming bonds
combustion cycle
reactants to products
elements in standard states underneath
arrows pointing up
formation cycle
elements to products
combustion products underneath
arrows pointing down
why is a catalyst used if it doesn’t improve yield?
allows lower temperature to be used
q=mcT questions answers always?
negative
q=mcT reason for difference between experimental and theoretical
incomplete combustion
four types of crystal structures
ionic
metallic
macromolecular
molecular
sodium chloride lattice - structure, properties + uses
giant ionic, each ion surrounded by 6 ions of the opposite charge
high melting and boiling point
magnesium - structure + properties
tightly packed layers - slide over one another (malleable), attractive forces reform after slided (stays strong)
sea of delocalised BONDING electrons - carry a charge, travel freely
melting point - high, strong electrostatic forces
thermal conductors - layers vibrate when warmed, transfers kinetic energy to other side
electrical conductors - repel from negative terminal to positive terminal
graphite - structure + properties
each carbon bonded covert to 3x other carbons, hexagonal rings, 1 delocalised election per atom can move between layers, can carry a charge
layers can slide over each other
chemically inert
electron repulsion order
(greatest)
lone pair - lone pair
lone pair - bonding pair
bonding pair - bonding pair
(smallest)
shapes of molecules (two bonding pairs)
linear
180 degrees
shapes of molecules (two bonding pairs one lone pair)
bent
104.5 degrees
shapes of molecules (three bonding pairs)
trigonal planar
120 degrees
shapes of molecules (4 bonding pairs)
tetrahedral
109.5
shapes of molecules (three bonding pairs and one lone pair)
trigonal pyramidal
107 degrees
shapes of molecules (two bonding pairs and two lone pairs)
bent
104.5
shapes of molecules (two bonding pairs and three lone pairs)
linear
180 degrees
shapes of molecules (five bonding pairs)
trigonal bipyramidal
120/90 degrees
shapes of molecules (three bonding pairs and two lone pairs)
t shape
87.5
shapes of molecules (four bonding pairs and one lone pair)
seesaw
80.5/102 degrees
shapes of molecules (six bonding pairs)
octahedral
90 degrees
shapes of molecules (five bonding pairs and one lone pair)
square pyramidal
less than 90 degrees
shapes of molecules (four bonding pairs and two lone pairs)
square planar
90 degrees
reasons for shape of molecules
electrons have the same charges so they repel one another
the molecule needs to have particles of the same charge as far away as possible to maintain stability
only electrons in the outer shell determine bond shape
electronegativity
the power of an atom to attract a bonding pair of electrons in a covalent bond
induced dipole-dipole
electrons in an electron cloud are constantly moving
electrons may temporarily all be on one side of the molecule
makes one side partially negative so the other side is partially positive
effects surrounding molecules as all negatively charged electrons repulse
why are some molecules with polar bonds non polar
may cancel each other out
electrospray ionisation
dissolves in solvent
needle/nozzle
high voltage
gains a proton
