bonding Flashcards
what is ionic bonding
electrostatic force of attraction between oppositely charged ions formed by electron transfer
what do square brackets tell us
[Na]+
charge is spread over whole ion
what are electrostatic forces of attraction in an ionic lattice
ions in lattice are attracted to every other oppositely charged ion
physical properties of ionic compounds
- high melting and boiling point - due to large amount of energy to overcome strong electrostatic forces of attraction
- soluble in polar solvents - soluble substance e.g water, surrounds the ions and overcome electrostatic forces between the ions
(if charge of ions increase, solubility decreases as water cannot overcome the electrostatic forces of attraction)
3.do NOT conduct electricity when solid - ions locked in place by electrostatic forces of attraction and cant carry a charge
dissolved in water + conducts electricity as they’re free to move
ionic compounds examples
sodium chloride NaCl
what is covalent bonding
between two non-metals
electrons are shared between two outer shells to achieve a full outer shell (same electron configuration of a noble gas)
what are the pair of electrons attracted to in covalent bonding
the two nuclei of atoms forming the bond
what does the line represent in covalent bonds
H—–H
shared pair of electrons
what is dative covalent bonding/ coordinate bonding
when at atom uses a lone pair of electrons to form a covalent bond
(both electrons in shared pair are supplied from a single atom)
what is a lone pair
electrons that are not shared with another atom
for a dative bond to form, what must the acceptor atom be
electron deficient (available orbitals for electrons to occupy)
what is average bond enthalpy
tells us the strength of the bond
what do the solid lines tell us on shapes of molecule
that two bonds and atoms attached lie on the plane of the screen/page
what does a solid wedge tell us on shapes of molecule
bond is coming out of plane of page
what do the dotted wedge tell us on shape of molecules
bond is projected back behind plane of page
what is electron pair repulsion theory
shape of molecule is determined by the electron pairs surrounding the central atom (referring to outer shell)
electrons repel all of other electron pairs
electrons move as far apart as possible to minimise repulsion
what molecule has bond angle 180
linear
e.g beryllium chloride
Cl – Be – Cl
which molecule has bond angle 104.5
v - shaped or non linear
e.g H2O
which molecule has bond angle 120
trigonal planar
e.g BF3
which molecule has bond angle 107
triangular pyramid
e.g NH3
which molecule has bond angle 109.5
tetrahedral
e.g CH4 methane / NH3 ammonium
which molecule has bond angle 90 AND 120
trigonal bipyramid
e.g PCl5
which molecule has bond angle 90
octahedral
e.g SF6
for every lone pair present, what happens to the bond angle between covalent bonds
reduced by 2.5 degrees
how are dative bonds presented
indicated using an arrow from lone electron pair
H
|
H —- N ➜ H
|
H
why do lone pairs reduce bond angle by 2.5 degrees
repel more strongly than bonding pairs
define electronegativity
ability of an atom to attract a pair of electrons in a covalent bond
what happens to electronegativity ALONG a PERIOD
increases
what does the power of electronegativity depend on
- size of positive charge on nucleus
(more protons = increased positive charge ➜ increases attraction between nucleus and pair of electrons in covalent bond - atomic radius
(smaller atomic radius = closer bonding electrons to nucleus )
L➜R (periodic table) atomic radius decreases - shielding of nucleus of nucleus by electrons in inner shells
(more inner shells + lower electronegativity)
what happens to electronegativity DOWN a GROUP
decreases
what are some of most electronegative elements
fluorine
oxygen
nitrogen
chlorine
whats a dipole
a separation of charge
are elements on right or left of periodic table more electronegative
right
whats a pure covalent bond
has no dipole
how to show that a bond is polar
write delta positive (δ+) and delta negative (δ-)
to show charges
what does delta δ show
shows that the charge is small
as the electron pair has shifted towards the MORE electronegative atom
where does the delta negative δ- go
goes on more electronegative element
name the 3 intermolecular forces
- van de waals forces (induced dipole)
- permanent dipole
- hydrogen bonding
whats a polar bond
bonding of two atoms with different electronegativites
what are simple molecular substances
substances with small molecules
each molecule has fixed number of atoms
where do intermolecular forces take place
in-between molecules
intermolecular forces properties
weaker than covalent bonds
easily broken by high temp
what happens when intermolecular forces are heated
molecules move faster
intermolecular forces break at a certain temp
causes molecules to move away from each other
why do intermolecular forces have low boiling point
small amount of energy to break intermolecular forces
what are induced dipole-dipole interactions (van de waals)
- weakest type of intermolecular force
- caused by random electron movement
- acts as an induced dipole between molecules
what does strength of van de waals depend on
depends on number of electrons
(larger amount of electrons = higher boiling point - experience stronger van de waals)
what are permanent dipole-dipole interactions
when permanent dipoles leads to attraction
acts between polar molecules
δ+ and δ- attract each other
hold molecules together in lattice-like structure
what is the strongest type of intermolecular force
hydrogen bonding
what is the weakest type of intermolecular force
van de waals
where do hydrogen bonds only form between
between 3 most electronegative atoms:
nitrogen
oxygen
fluorine
(all have at least one lone pair of electrons)
what two conditions are needed for hydrogen bonding to take place
- hydrogen atom bonded to strong electronegative element
- electronegative atom must have at least one lone pair of electrons
what is hydrogen bonding
type of permanent dipole dipole bond
strongest intermolecular forces between neutral molecules
act between molecules containing permanent dipoles
where does hydrogen bonding take place
in compounds that have a hydrogen atom attached to one of the three most
electronegative atoms
why does water have a high melting and boiling point
it takes a great deal of energy to break the hydrogen bonds
properties of after due to hydrogen bonding
ice is less dense of liquid form therefore ice floats on water
liquid water = water molecules moving randomly freezing point = water molecules in ordered structure = ice - stabilised by hydrogen bonds
(in ice - water molecules are further apart than in liquid water making it less dense & floats)
what bond is between atoms of simple molecular substances
covalent
what do simple molecular substances have
small molecules with fixed number of atoms
2 examples of giant covalent structures
diamond and graphite
properties of simple molecular substances
low melting and boiling points due to weak intermolecular forces
what happens when you cool a simple molecular substance below its melting point
becomes a solid simple molecular lattice
molecule of iodine
consists of two iodine atoms joined by a single covalent bond with intermolecular forces between the molecules
what are non-polar molecules
atoms that have same electronegativity
means that only van de waals can act between the molecules
what the solubility of simple molecular substance depend on
depends on whether the substance is polar or none polar
iodine solubility
solid at room temp
iodine molecules held in simple molecular lattice by van de waals
what happens when non polar substances e.g iodine dissolve in non polar substances
solvent molecules form van de waals to iodine molecules
why are non polar substances insoluble in polar e.g water solvents
molecules with hydrogen bond remain hydrogen bonded rather than forming van de waals with non polar molecules
general rule of polar substances
polar substances dissolve in polar solvents
what dont simple molecular substances contain
mobile charged particles
(means that simple molecular substances cant conduct electricity)
