chemical bonding Flashcards
ionic bonding
transfer of electrons and subsequent electrostatic attraction (between oppositely charged ions)
metals lose
non-metals gain
ions pack into ionic crystal lattice
covalent bonding
sharing of at least 1 pair of electrons by 2 non metal atoms
forming molecule
mono
1
di
2
tri
3
tetra
4
penta
5
ionic naming
metal first
valancy method writing formula
swap+drop charges
simplify with highest common factor
naming transition metal
stock notation
covalent bond
a sharing of at least one pair of electrons by two non-metal atoms
electronegativity
a measure of the tendency of an atom to attract a bonding pair of electrons
0- non polar covalent bond
greater EN, more polar the bond is
<0,5 - very weak polar covalent bond
1- polar bond
1,4- highly polar covalent bond
2.0- polar covalent
metallic bonding
being between a positive kernel and a sea of delocalised electrons
intramolecular bond
a bond which occurs between atoms within molecules
intermolecular force
a weak force of attraction between molecules or atoms of noble gases
viscosity
a measure of how easily a liquid flows
london (dispersion) forces (3)
experienced by all molecular substances
only van der waals force that exists between non polar molecules
due to attraction of 1 molecule to the nucleus of another
origin of london forces (4)
-as a result of random movement of electrons, a temporary, instantaneous dipole is set up in one molecule
-this causes the electrons of the neighbouring molecule to disperse when molecules come close to one another
-this results in an induced dipole forming
-the 2 temporary dipoles are then able to electrostatically attract each other
forces w noble gases
do not participate in bonding as have full set of valance electrons (stable)
BUT noble gas atoms interact w london forces between their atoms
dipole dipole forces (3)
occurs between permanently polar molecules
slightly positive side of molecule attracts slightly negative of another
electron pair lives closer to the atom
origin of dipole dipole forces
-as a result of polar bonds (an unequal sharing of an electron pair as a result of END) and permanent asymmetrical distribution, these molecules are permanently polar
- and experience an attractive electrostatic force between the slightly positive side of one molecule and the slightly negative side of another molecule
hydrogen bond forces (2)
special case of dipole dipole forces
involves highly polar molecules
origin of hydrogen bond forces (3)
-within a molecule, a hydrogen atom must be covalently bonded to a small highly electronegative (N,O,F) atom (producing a greater END difference than in other polar bonds) with at least one pair of electrons
-within a molecule, a small highly electronegative atom attracts the bonded pair of electrons away from the covalently bonded hydrogen atom
-therefore, a naked proton is exposed and is attracted to a lone pair of electrons on another small highly electronegative atom of a neighbouring molecule , hence the forces exist between molecules
why are hydrogen bonds stronger than dipole dipole forces
-large END in bonds of molecule, making highly polar molecules with high charge density on exposed H atom
- the small atoms form molecules that can get close together and thus the forces act over shorter distances
substances that experience hydrogen bonding between their molecules
-water
-ammonia
-hydrogen fluoride
-alcohols
-carboxylic acids
hydrogen bonds in water
on average, each H20 molecule forms 4 hydrogen bonds with another H20 molecule at sites:
the 2 slightly hydrogen atoms
the 2 lone pairs on each atom oxygen atom
hydrogen bonds in ammonia
on average, each NH3 molecule forms 2 hydrogen bonds w other NH3 molecules at sites:
single lone pair on N atom
one of the slightly hydrogens (other 2 are wasted as there are insufficient lone pairs )
hydrogen bonds in hydrogen fluoride
on average, each HF molecule forms 2 hydrogen bonds w other HF molecules at sites:
-the single slightly positive hydrogen
-one of the lone pairs on the fluoride atom (other 2 lone pairs are wasted as there are insufficient slightly positive atoms on molecules)
properties of diamond
(C)-4
giant covalent structure
extremely strong, high MP+BP—many strong covalent bonds between atoms—more energy required to break bonds
poor electrical conductor-no charges in lattice to move + carry charge
properties of graphite
(C) -3 therefore unpaired e-
giant covalent structure
high MP+BP—many strong covalent bonds between atoms—more energy required to break bonds
sheets of carbon atoms held together by weak electrostatic forces (London)
good conductor of electricity- delocalised e-
why does diamond have higher MP+BP than graphite
more energy required to break larger no of covalently bonds in diamond (4>3)
silicon dioxide
SiO2
giant covalent structure
high MP+BP—many strong covalent bonds between atoms—more energy required to break bonds
poor electrical conductor-no charges in lattice to move + carry charge
atomic/covalent bonds
many strong covalent bonds between atoms
ionic structures properties
ionic bonding
structure made up by many,strong electrostatic forces of attraction between cations and anions -melting point determined by strength of these forces
brittle- shift in arrangement of ions brings like charges alongside each other which results in force of repulsion which causes solid to fracture
can’t conduct in solid state (cations +anions not free to move to carry charge)
- molten+ aqueous
metallics structures
metallic bonding
structure made up by many strong electrostatic forces of attraction between positive kernels + delocalised valence electrons
good electrical conductors - delocalised e-‘s can move over positive kernels
malleable-sheets of cations can slide past over each other but remains held together by electrostatic forces of attraction between delocalised electrons and cations
malleability
sheets of cations can slide over e-‘s but remiannheld tiegther by forces
interactions in non metal atoms (excl noble gases)
intramolecular bond, specifically covalent bonding
interactions in noble gas atoms
intermolecular forces , specifically london forces only
interactions in molecules
intermolecular forces, specifically london, dipole-dipole + hydrogen bond forces
interactions in metal atoms
electrostatic force of attraction in a metallic bond
interactions in ions
electrostatic forces of attraction in an ionic bond
what do MP+BP indicate
indicators of collective strength of forces holding substances together (increased strength - more energy to overcome forces - higher MP/BP)
intramolecular bond
bond between atoms w/in molecules
heating in molecular substances
as substance is heated-temp +average Ek of molecules increases- more energy provided to overcome come/break forces of attraction between molecules-changing physical properties of substances
( intramolecular/covalent bonds not broken by heating , only IMF forces broken or electrostatic forces of attraction overcome)
factors that influence strength of IMFs
-the type of IMF force (predom. and add. london force)
-no. of electrons in molecule (indicated by molar mass) which affects size of temporary dipoles formed which influences strength of london forces
-no of IMF forces which influences strength of hydrogen bond forces
-interacting surface area of molecules which affects london forces in organic substances
mp + bp questions
-identity types of IMFs present in both molecules
-compare relative strengths of IMF influenced by diff factors
-“more energy is required to overcome the collective stronger IMFs”
-conclude which substance has higher or lower BP/MP
what does phase of substance depend on
strength of IMF forces that hold it together
phases:liquids and SOLIDS
IMFs so strong- movement of molecules is limited
phases:gases
no or very weak IMFs between molecules
what happens when a PD is applied
charged particles move resulting in a current
what determines density
mass/volume (constant for substance at any temp) (molar mass indicator of density)
IMFs between molecules (greater attractive force= greater density, relative strength of IMFs in substance =greater density)
greater mass=greater density (at constant volumes)
solubility in ionic compounds
ions are attracted by polar water molecules of solvent
IMFs in each substance must be similar in nature and magnitude
solubility of covalent compounds
dependent on polarity of solute + solvent (like)
nature+ magnitude of forces between molecules of each substance ( like)
predominant IMF of solute important
how to collect non polar gases
downward displacement of water
gas bubbled through up turned cylinder filled w water
gas rises through H20 and is collected, H2O pushed down
collect polar gases
upward + downward displacement of air
(diff gases have diff densities relative to air which is mostly nitrogen)
higher density than air -air pushed up, gas sinks
lower density than air- air pushed down,gas rises
electronegativity
measure of tendency of atom to attract a bonding pair of e-‘s
END=0
equal sharing of bonding pair of electrons as both atoms have same tendency
therefore non polar (pure) covalent
non polar covalent molecule
an equal sharing of electrons
END>0
unequal sharing of bonding pair of electrons as both atoms have diff tendencies hence polar covalent bond
polar covalent bond
unequal sharing of electrons leading to a dipole forming (as a result of END)
molecule w END=0
non-polar covalent bond
non polar molecule
experiences london forces
molecule w END>0 and e- symmetry
polar covalent bond
non polar molecule
london forces only
END >0 w no e- symmetry
polar covalent bond
polar molecule (hydrogen bond force +LF OR dipole-dipole force + LF)
molecular substances mp+bp
affected by strength and relative no per molecule of IMF forces
polar covalent
unequal sharing of electrons leading to a dipole forming
the greater the END, the more polar the bond
shapes
Linear (HCl, CO2)
Trigonal planar (BF3)
Tetrahedral (CH4)
Pyramidal (NH3, sides under side)
bent/angular (H20, ^)
molecular polarity
if bonds non polar covalent - non polar molecule
if bonds are polar covalent :
- if symmetry in molecules electron cloud - non polar
else polar
non polar molecule
electron symmetry or END= 0
london forces only
polar molecule
polar covalent bonding (END> 0)
no electron symmetry
dipole dipole + london or
hydrogen bond + london
