bonding Flashcards
Ionic bonding
Strong electrostatic forces of attraction between positive ions and negative ions
Ions are formed when one or more electrons are transferred from oNe atom to another
Why group four doesn’t forma charged ion
Form covalent bonds so no charge
Compound ions to remember
So4 2- SULFATE
OH- HYDROXIDE
NO3 -
NH4+
CO3 2-
Structure of ionic compounds
Each ion attracts oppositely charged ions in all directions
Giant ionic lattice
First electron needs the least energy
Being removed from a neutral stom
Second electron needs more energy
Because removed from +1ion
2nd ionisation equation
X=x2+ +2e-
covalent bonding
when non metals shared pair of electrons to get a full outer shell
the overlap of atomic orbitals each containing one electron to give a shared pair of electron
the shared pair of electrons are attracted to the nucleus of both the bonding atoms
graphite
each. carbon covalently binder to 3 other carbons
1 delocalised electron conducts electrons
high m+b
weak intermolecular forces
electronegativity
the power of an atom to attract the electron density of a covalent bind towards itself
some atoms attract bonding electrons more than others
shorter the distance the more electronegative
greater nucleus charge greater attraction
what does electronegativity depend one
1)the nuelcuer charge of the atom
2)the distance between the nucleus and the outer electrons
3)the shielding of nucleus charge by electrons in inner shells
across period electronegativity
increases
greater nucleus charge
down the group electronegativity
decreases
distance between nucleus and electrons increases
electronegatvitiy on the Pauli scale
measured on Pauli scale
4 is largest electronegatvity
nobles gases do not have a value as its unusual for them to form covalent bonds
most electronegative element
fluorine
polarity
the unequal sharing of electros I bind if the electron sharing is equal the bond is described as non polar
intermolecular forces
physical
strong
van der Waals forces
dipole dipole interaction
hydrogen bonds
intramoleculer forces
stronger than inter molecular forces
within a molecule
covalent bonds
eg.hydrogen bond is about 1/10TH of a covalent bond
strongest to weakens bonding
-metallic
-ionic
-covalent
-hydogen
-permanant dipole-dipole
-instantaneous dipole-dipole
permanent dipoles
weak electrostatic forces of attractions with neighbouring molecules
similar electromneagtivity
chlorine
hydrohen
permanent dipole-dipole forces
molecules with permanent dipole -dipole forces
opposite electronegativites
hydrogen chlorides
induced dipole-dipole interactions
-aka London forces /vanderwaals
-doesn’t need to have electronegative difference
1)electrons move this produces changing dipole in molecule
2)instantaneous dipole will exist but its position will constantly change
3)instantaneous dipole induces a dipole in a neighbouring molecule
4)induced dipole induces other dipoles in neighbouring molecules
5)electrons continually move so are created and destroyed all the time overall atoms are attracted to one another
between all molecules at all time
they are in addition to other intermolecular forces
the more electrons in each molecule the larger the induced dipole
boiling pint f noble gases increases as atomic number increases
the more electrons
more dipole induced
greater the billing point
boiling points of hydrocarbons increase as the chain length increases why
longer carbon chains form more Van der Waals interactions and have greater melting and boiling points
explain why the boiling point is higher in hcl and f2
hcl has a permanent dipole whereas fluorine doesn’t therefore more energy is needed to ver come the permanent dipole so it must have a high bp
fluorine as lower bp as it has a instantaneous dipole - dipole interaction therefore its able to form as quickly as it can break so its easy to overcome as its weak and doesn’t last long.
explain how induced dipole forms
fluctuation in electron density around molecule
creates instantaneous in molecule
instantaneous dipole induces a dipole in neighbouring molecules
hydrogen bonds
special type of permanent dipole-dipole interaction
found between molecules that contain an electronegative atom (O,N,F) and a hydrogen atom
the hydrogen bonds acts between a lone pair of electrons on the electronegative atom and a hydrogen on a different molecule
hydrogen bonding higher m+b
stronger in larger numbers as its between many molecules so more energy is needed to overcome
instantaneous- induced dipole /permanant dipole ,hyrdogen bonds
why is solid ice less dense than water
solid ice has intermolecular forces holding the molecules vibratining in fixed position and there’s less space between the molecules and therefore its less dense.
the position of hydrogen bonds causes molecules to push farther apart, which lowers the density.
The extra hydrogen bonds that occur when water freezes increase the space between molecules, causing a decrease in overall density. In fact, each water ice molecule forms hydrogen bonds with four other molecules, while water molecules only form hydrogen bonds with an average of 3.4 other molecules.
why does water have a relatively high melting and boiling point
water has a high boiling point because its molecules are bound together by hydrogen bonding, which is a very strong intermolecular force. It takes more kinetic energy, or a higher temperature, to break the hydrogen bonding between water molecules, thus allowing them to escape as steam.
describe the hydrogen bonding that happens in dna
Hydrogen bonds occur between the two strands and involve a base from one strand with a base from the second in complementary pairing. These hydrogen bonds are individually weak but collectively quite strong.
What is needed for hydrogen bonds
LOne pair
What forms hydrogen bonds
Oxygen
Nitrogen
Hydrogen
Electron pair repulsion theory
-each pair of electrons around an atom will repel all other electron pairs
-the pairs of electrons will therefore take up positions as far apart as possible to minimise repulsion
Linear molecule
2e pairs around central atom
Electrons go as far away as possible
180 degrees
Trigonal planar
3 electron pairs around central molecule
Electrons go far away as possible
120 degrees
Tetrahedral shape
4 bonding pairs of electrons as far apart as possible
109.5
Solid lime
Represents a bind in the plane of the paper
Wedge
Comes out of the plane Kf the pape
Dotted wedge
Into the plane of the paper
Trigonal bioyramidq
5 electron pairs
Octahedral
6 electrons
90 degrees
valence shell electron pair repulsion
a lone pair of electrons is slightly closer to the central atom
it occupies more space than a bonding pair
lone pairs repel more strongly so change the shape
keep your methane , then build NH3
polarity
the unequal sharing of electros I bind if the electron sharing is equal the bond is described as non polar
