topic 2: structure and bonding Flashcards
ionic bonding
strong electrostatic attraction between oppositely charged ions
ions formation
- metals lose electrons from their valence shell, forming positive cations
- these electrons are transferred to non-metal atoms, which gain these to form negative anions
ions electron configuration
SAME AS NOBLE GAS
Ionic bonds high melting points
lots of energy is required to overcome the very strong electrostatic attraction between oppositely charged ions
ionic compound structure + charge
- lattice
- evenly distributed crystalline structure
- ions are in a regularly repeating pattern so positive cancels out negatice
- so the lattice is NEUTRAL
isoelectronic radius increases with…
INCREASING NEGATIVE CHARGE
ionic radius decreases with…
INCREASING POSITIVE CHARGE
Why do negative ions with more negative charge have a larger radius?
- outermost e- further away from the positive nucleus
- weak attraction
- more shielding
- larger radius
Why do positive ions with higher charge have a smaller radius?
- same nuclear charge
- less sheielding
- fewer electrons
- stronger electrostatic force of attraction to nucleus
isoelectronic ions
ions with the same electronic configuration
ionic radii of isoelectronic ions
- higher number of protons means electrons are pulled in closer to nucleus
- so largest negative charge is largest
why are ionic compounds solid at room temperature
- high melting point
- lots of energy required to over come strong electrostatic forces of attraction between oppositely charged ions in the lattice
charge of ions effect on melting point
- higher the charge the higher the melting point
- stronger efa between oppositely charged ions
- more energy required to overcome
ionic compounds electrical conductivity
- when solid, ions are in fixed positions in lattice and are unable to move
- can only conduct when molten or in solution has ions can move
ionic compounds dissolve in …
POLAR solvents eg water
how do ionic compounds dissolve
ions are hydrated
general rule of solubility of ionic compounds
the higher the ionic charge the less soluble
electrolysis (evidence of ionic)
- positive ions in solution attracted to negative electrode
- negative ions in solution attracted to positive electrode
cu2+ ions are
blue
CrO4 2- ions are
yellow
covalent bond is
strong electrostatic attraction between two nuclei and the shared pair of electrons between them
dative bonding
- lone pair of electrons can be donated to form a bond with an ELECTRON DEFICIENT ATOM
bond energy
is the energy required to break one mole of a particular covalent bond in the gaseous states
bond energy relationship to covalent bond
STRONGER bond = LARGER bond energy
bond length
INTERNUCLEAR DISTANCE of 2 covalently bonded atoms
triple bonds bond length and strength
- large electron density between 2 atoms
- increases attraction between nuclei and electrons between
- so atoms are pulled closer
- stronger covalent bond
how does VSEPR work (eg NH3)
- nitrogen (central atom) has 4 total e- pairs
- 3 bp, 1 lp
- lp-bp repulsion > bp-bp repulsion
- bond angle reduced from 109.5 to 107
- achieves max separation and minimum repulsion
- trigonal pyramidal
electronegativity
ability of an atom to attract the bonding electrons in a covalent bond
most electronegative element is
Fluorine
nuclear charge effect on electronegativity
- more protons = increased attraction for outer shell e-
- INCREASED electronegativity
atomic radius effect on electronegativity
- larger = electrons further, less strongly attracted to nucleus
- decreased electronegativity
shielding effect on electronegativity
- more = increased inner shells = less attractive force from nucleus = decreased electronegativity
electronegativity DOWN a group
DECREASES
- number of protons increase
- each element has an extra filled electron shell, so increased shielding
- increased atom radii
- decreased attraction between nucleus and bonding e-el
electronegativity across a period
INCREASES
- nuclear charge increases
- constant shielding as electrons added to same shells
- attraction increases between nucleus and bonding e-
- smaller atomic radii
non polar
both atoms have same electronegativity
electron density drawing map polar
delta + side is smaller, delta negative side is fatter
what is stronger between INTRAmolecular and INTERmolecular forces
INTRA - eg covalent > hydrogen
strength of imfs
hydrogen
permanent dipole- permanent dipole
London
how are London forces formed
- electron charge cloud constantly randomly moving
- INSTANTANEOUS, temporarily more on one side, causing a temporary INSTANTANEOUS DIPOLE
- induces a dipole on neighbouring molecules
- delta positive + delta negative attract
what affects strength of London forces
- number of electrons
- if its linear
permanent dipole-dipole forces cause
- between permanent dipoles on polar molecules
- delta + and negative attract
hydrogen bonding
TYPE of permanent dipole-dipole bonding
- needs O N F with H
- h is positive, forms a bond with LONE PAIR on ONF
Water high mp/bp
- hydrogen bonding
- strong imf
- lots of energy required to separate molecules
density of ice
- ice LESS dense than water
- water molecules in an open lattice
- more space between molecules
- HBs longer than covalent bonds
alkanes imfs
only london
boiling temp of alcohol vs alkane
- alkanes have only London
- alcohol have hydrogen
- more energy required to separate alcohol compared to alkane
hydrogen halides boiling point
- increases from HCl to HI
- but HF high due to hydrogen bonds
general solvent rule
‘like dissolves like’
- non polar dissolves non polar
- polar dissolves polar
water dissolving alcohols
GOOD SOLVENT
- hydrogen bonds
- larger the alcohol, the LESS soluble as the polar proportion is smaller
- h bonds between alcohol and water similar in strength to those within each
metallic bonding
- metal atoms in tight lattice
- delocalised electrons
- strong efa between positive metal atoms and delocalised electrons
giant lattices are present in …
ionic
giant covalent (diamond, graphite silicon IV dioxide)
giant metallic
giant covalent lattice mp
- very high
- lots of many strong covalent bonds require lots of energy to break
graphite is soft?
- metal cations arranged in layers
- weak imfs so can slide over each other
diamond and silicon IV dioxide hard
each carbon atom bonded to 4 other carbon atoms
- many strong covalent bonds difficult to break
covalent solubility
INSOLOUBLE
graphite electricity conduction
- each carbon atoms bonded to 3 others
- one free electron per carbon atom
- electrons can move therefore conducts electricity
diamond imfs
NO IMFS
GRAPHENE
- single layer of graphite
- 1 layer (atom) thick
metals solubility
NOT soluble in water
graphene ring shape
hexagonal
graphene structure
2 dimensional
dative bonding explanation (2)
- donation of lone pair from x
- to y which is electron deficient
bond angles in graphene
120
explain why x is polar but y isn’t
- x is linear so DIPOLES CANCEL
- y is v shaped so dipoles dont cancel
bonding in caco3
ionic AND covalent
non polar covalent
0-0.4
polar covalent
0.41-1.69
ionic
1.7
WHY does h2o have more hydrogen bonds than HF
- 2x the amount
- as 2 atoms of hydrogen for every molecule
why has a branched molecule isomer got a lower boiling point
- branching means fewer London forces
- due to less surface area/ points of contact
angle of the hydrogen bond
180
why is x more dense?
- larger atoms
- packed more closely together
why can x make that molecule but y cant
octet
- x can expand its octet
- y can only accommodate 8 outer shell e-
who can expand the octet
if they have 3p subshell, cos they can move into 3d
why is the hydrogen bond 180
- 2 pairs of bonding e-
- lp
- max separation
graph of ionic radius
linear decrease
group 5,6,7,1,2,3
ionic radius down group
INCREASES
- more shells of e-
- more shielding, further distance etc
why are ions 5,6,7 > radius than their atoms
- same no. protons
- more electrons
- attraction per electron is less
ionic bonding electron density map
- discrete (e- density is 0 between ions)
- negative ion is larger
CuCrO4 2- electrolysis
- Cu2+ ions (BLUE) migrate to cathode
- CrO4 2- ions (YELLOW) migrate to anode
- EVIDENCE FOR EXISTENCE OF IONS
COVALENT ELECTRON DENSITRY MAP
ellipse around both nuclei
pauling electronegativity range
0-4
how to know if a molecule is symmetrical
- identical bonds
- 0 lps
London forces aren’t present in
IONIC substances
how many HB’s can water form per molecule?
2
- oxygen has 2 lone pairs of e-
ionic dissolving in water
- lattice bonds broken
- negative ions attracted to delta +, positive attracted to delta -
- the higher the charge the less soluble as a stronger attraction
factors affecting strength of metallic bonding
- more protons, the stronger
- more delocalised electrons, the stronger
- smaller the ion the stronger
ionic compounds brittle (4)
- layers slide; REGULAR LATTICE DISRUPTED
- positive ions aligned with positive
- like charges repel
- structure breaks apart
description of solubility
IMFs the same strength in both
ionic bonding solubility terminology
HYDRATION of na+ and cl-
halogenoalkanes in water
INSOLUBLE
- hydrogen bonds between water stronger than permanent dipole-dipole
do giant covalent form liquid
SUBLIMES rather than melting
longer hydrocarbons alcohol solubility
LES SSOLUBLE
bond angle in graphite and graphene
120
in what shape are the carbon atoms arranged in graphite and graphene
hexagonal
importance of a molecule w polar bonds unsymmetrical
dipoles DONT CANCEL
MORE difference in eneg MEANS MORE OF WHICH CHARACTER?
ionic
