Topic 4: Chemical Bonding and Structure Flashcards
Ion
an ion is a charged particle. Ions form from (groups of) atoms by the loss or gain of one or more electrons
Ionic bond
electrostatic attraction between oppositley charged ions
form when opositely charged ions attract (e.g nonmetal and a metal)
ionic compounds
have a lattice structure (3D chrystalline)
- fixed arrangement of ions based on repeating unit; have low volatility
- e.g. coordination number of NaCl lattice is 6 because each sodium ion surrounded by 6 chloride ions and vice versa
lattice energy
measure of the strength of attraction between ions in their lattice
volatility of ionic compounds
low volatility (tendency of a substance to vaporize)
solubility of ionic compounds
- determined by the degree to which separated particles of solute are able to form bonds/attractive forces with the solvent
= solubility depends on nature of solvent (‘like dissolves like’)
-ionic compounds are generally soluble in ionic/polar solvents but not in non-polar solvents
boiling/melting point of ionic compounds
high melting and boiling points
- strong electrostatic force attraction between ions
- solid at room temperature
- the higher the ion charge, the higher the mt and bp points
electrical and thermal conductivity of ionic compounds
don’t conduct electricity in solid state;
conduct in molten state or in an aqueous solution (due to free, delocalized electrons that can move)
physical properties of ionic compounds
BRITTLE; movement of ions of the same charge along each other causes repulsive forces to cause them to split
how do you make an ionic compound?
- reactive metal and non metal (cation and anion)
1. 8+ electronegativity difference between compounds (extent of ionic character)
covalent bond
electrostatic attraction between a pair of electrons and a postivley charged nuclei
- sharing of electrons
- nonmetal and nonmetal
molecule
a group of atoms held together by a covalent bond
- contains a fixed numbef of atoms
2 atoms=diatomic= Cl2 or O2
octet rule
when atoms react, they tend to achieve an outer shell with 8 electrons in order to form stability (full shell)
bond length…
measure of distance between two bonded nuclei
bond strength…
measure of enthalpy required to break bonds
strong bonds are short bonds
polar bonds
unsymetrical/unequal sharing of electrons
- dipole; two separated opposite electric charges of a bond
- can be determined by electronegativity difference ( over 0.4; polar)
pure covalent
when electronegativity is equal to 0; bonds between the same atoms
covalent structures
lewis diagrams show valence shell structures
coordinate bond
when both shared electrons from from one atom
exeptions to octet rule
BeCl2, H2 and BF3 (electron deficient atoms)
VSEPR theory
because electron pairs in the same valence shells carry the same charge, they repel each other so they spread themselves as far apart as possible
electron domain; all electron locations in the valence shell
repulsions
stronger repulsions on lone pairs
weaker repulsiosn on bonding pairs
linear
180
2 bonding electron pairs
0 non bonding electron pairs
2 electron domains
e.g. carbon dioxide
bent/v-shaped
less than 120 (117)
- 3 electron domains
- 2 bonding, 1 non ponding electron pair
e.g. silicon dioxide
trional planear
120
- 3 electron domains
- 3 bonding electrons, 0 non bonding electrons
e.g. boron fluoride
special bent/vshaped
105 (104.5)
4 electron domains
- 2 bonding, 2 non bonding electron pairs
e.g. water
tetrahedral
109.5
4 electron domains
4 bonding electrons, 0 non bonding
e.g. methane
trigonal pyramidal
107
4 electron domains
3 bonding, 1 non bonding
e.g. Nitrous acid
what is the polarity of a molecule determined by?
- polar bonds of the molecule
- shape and symmetry of the molecule
resonance
- delocalized bonds that can be in multiple positions
- results in more than one valid lewis structure (true structure is the average)
- bond enthalpy value often between a single and double bond
- e.g. triatomic oxygen where multiple representations are valid
benzene
hexagonal ring C6H6
kekules dream
trigonal planear arrangmenent of 120 bond angles
resonant structure
bond length and enthalpy between single and double bond
circle represents the delocalized electrons
giant moleculear crystalline
giant molecular/network covalent/macromolecular structure
-single molecule with repeating patterns of covalent bonds
silicon bonding
- each silicon atom bonded to 4 others in tetrahedral arrangement; forms silicon cyrstal structure
carbon allotropes
different forms of an element in a physical state; in this case carbon
graphite bonding
most stable allotrope;
each C is covalently bonded to 3 others
- hexagons in parallel layers with 120 bonds
- weak london dispersion forces; layers can slide over another
graphite electrical conductivity
good electrical conductivity; 1 non bonded delocalized electron per atom allows for electron mobility
graphite thermal conductivity
weak thermal conductor
- unless heat can be forced to conduct in parallel direction
graphite apperance and physical properties
- non lustrous
- grey crystalline solid
- soft and slippery sheets due to slippage of layers over each other
- brittle
graphite mt. and bp. points
high meting and boiling point
graphite uses
can be used as dry lubricant
pencils
electrode rods in electrolysis
diamond bonding + structure
each C atom is covalently bonded to 4 others in tetrahdral arrangement in regular repettitive pattern with 109.5 bond angles
diamond electrical conductivity
non conductor of electricity
- all electrons bonded; non mobile
diamond thermal conductivity
efficent thermal conductor
high melting and boiling points
diamond physical properties and apperance
highl transparent, lustrous crystals, hardest known substance
- brittle
- hard to scratch
diamond uses
jewllery
ornamants
tools
machines for cutting glass
fullerene bonding and structure
each C atom bonded in sphre to 60 carbon atoms
- 12 pentagons
- 20 hexagons
- closed spherical cage with each c atom bonded to 3 others
fullerene electrical conductivity
semi-conductor at normal temperature and pressure
- some electron mobility as it accepts electrons to form anions
fullerene thermal conductivity
low thermal conductivity
low melting point
fullerene physical properties and apperance
yellow crystaline solid
benzene soluble
light and strong; react with potassium to make superconducting crystalline moleucles
fullerene uses
lubrciant
medical and industrial uses for binding and reaction
nanotubules
catalyst
graphene bonding and structure
each c atom covalently bonded to 3 others to form hexagon with 1209 bond angles
- single layer (2D chicken wire construction)
graphene electrical conductivity
good conductivity; one delocalized electon per atom
graphene thermal conductivity
best thermal conductor
graphene physical properties and appearance
almost completly transparent one atom thick strong flexbile high melting point thinnest matieral
graphene uses
TEM grids photovolatic cells touch screen tech solar panels supercapacitators nanotechnoogy
london dispersion forces
(weakest form of attraction)
- instantaneous dipole-dipole induced forces that exist between any atoms
- electrons are mobile clouds of negative charge that are constnalty forming creating induced dipoles by their instantenous dipoles
- occurs between opposite ends; of these 2 temporary dipoles
- strengh increases with molecular size as more electrons avaialble
- only force that exists in non polar molecule
- correlation to boilding point
dipole to dipole forces
- in polar molecules
- permament seperation of charge within the bonds as a result of different electronegativities (permanent dipole)
- permanent dipoles of molecules attract other molecules by hydrogen bonding
- the more polar a substance, the higher the bp
hydrogen bonding
type of dipole to dipole
strongest form of attraction
hydogen directly bonds to F, N, O (highly electronegative element) between moleucles e.g. water
- make boiliding point of a substanec higher
intermolecular forces?
van der waal (london dispersion forces, dipole to dipole, hydrogen bonding)
trends in intermolecular forces (melting and boiling point)
stronger forces= harder to seperate molecules
increasing forces result in increasing Mt. an Bp. points
trends in intermolecular forces (solubility)
“like dissolves like’
non polar in non polar
polar in polar
trends in intermolecular forces (electrical conductivity)
covalent compounds have no ions
dont conduct electrons
polar covalent molecules can in water
metallic bond
electrostatic attraction between a lattice of positive ions and a sea of delocalized electrons
metal + metal
metal atoms withotu electrons from a lattic of positive ions in a pod of delocalized electrons
what is the strength of a metallic bond determined by?
- number of delocalized electrons
- charge on cation
- radius of cation
alloy
solutions of metals with enhanced properties
-metals are added together so different ions mix
alloy examples
steel (iron and carbon)
stailness steel (iron, nickle, chromium)
brass (copper and zinc)
bronze (copper and strontium(
metallic bond properties
- good electrical conductivity (circuits)
- good thermal conductivity; cooking
- malleable; moved into structures
- ductile; wires and cables
- high melting point; tools
- shiny and lustrous; ornaments
silicon dioxide
quartz; forms a giant covalent structure based on tetrahederal arrangement
- each Si atom boned covalently to 4 oxygen atoms
- each oxygen atom bonded to 2 silicon atoms
- strong
- insoluble in water
- high melting point
- nonconductor of electricity
