Structure and Bonding Flashcards
when does ionic bonding occur
when a outer shell electrons from a metal atom transfer to fill the outer shell of a non-metal atom
how does an ionic compound form
The metal (magnesium) loses (2) electrons and become cations The nonmetal (chlorine) each gain one electron and become anions so they all have full outer shell The positive ions are attracted to the negative ions and have an electrostatic attraction between them
describe the bonding in an ionic compound
strong electrostatic attractions between the oppositely charged ions which extend across a giant lattice
coordination number
how many negative ions each positive ion is bonded to
factors affecting strength of ionic bonds
charge on the ions
size of ions (increase in radius decreases charge density so weaker attraction)
properties of ionic compounds
high melting point non conductive when solid conductive when aq/molten brittle soluble in water
describe the structure of ionic compounds
giant lattice which extends in all directions
why do ionic compounds have a high melting point
millions of strong electrostatic attractions between the oppositely charged ions in the giant lattice which require a lot of energy to break
why do ionic compounds not conduct when solid
ions are fixed in a giant lattice so the ions are not free to move to their oppositely charged electrode
why do ionic compounds conduct when aq/molten form
ions are free to move to their oppositely charged electrode and carry a charge
why are ionic compounds brittle
a sharp blow displaces ions so the ions with like charges come in contact with each other causing the structure to shatter
why are ionic compounds soluble in water
ions break apart from the giant lattice as water is a polar molecules so can overcome the electrostatic attractions between the oppositely charged ions
how does covalent bonding occur
non-metal ions share electrons
examples of molecules with covalent bonding
simple molecules
macromolecules
what is dative bonding
when the shared pair of electrons come from the same atom
one species must have a lone pair of electrons
other species must have a vacant orbital to accept the lone pair
properties of simple molecules
low melting point
non-conductive
weak
insoluble in water
why do simple molecules have a low melting point
weak intermolecular forces between the molecules require little energy to break
are there any exceptions to simple molecules having low melting points
water has a high melting point for its Mr
has hydrogen bonds between the molecules which are the strongest type of intermolecular force
why are simple molecules non-conductive
no free ions or delocalised electrons that could carry a charge
why are simple molecules weak
weak intermolecular forces between the molecules require little force to break them apart
why are simple molecules insoluble in water
non-polar molecule so no interactions with water
why is ice more dense than water
hydrogen bonds hold h2o molecules far apart when solid
broken hydrogen bonds means that the molecules can be closer together
properties of diamond
high melting point
hard
non-conductive
insoluble
shape of diamond and bond angle
tetrahedral 109.5
why does diamond have a high melting point and is hard
millions of strong covalent bonds between the millions of carbon atoms in the rigid macromolecular structure which requires a lot of energy to break
why is diamond non-conductive
each carbon atom is bonded to 4 carbon atoms by strong covalent bonds so there are no delocalised electrons that can flow throughout the structure
why is diamond insoluble
strong covalent bonds do not break apart as the macromolecular structure is non-polar so the atoms are not attracted to the polar molecule
what are the properties of graphite
high melting point
conductive
soft
insoluble
shape of graphite and bond angle
trigonal planar 120
why does graphite have a high melting point
millions of strong covalent bonds between the millions of carbon atoms in the macromolecular structure which requires a lot of energy to break
why is graphite conductive
each carbon atom is covalently bonded to 3 other carbon atoms so has delocalised electrons that can carry a charge throughout the structure
why is graphite soft
has a macromolecular structure consisting of layers with weak intermolecular forces between them so can easily slide over one another
why is graphite insoluble
attraction to the polar water molecules is weaker than the strong covalent bonds between the carbon atoms so they don’t break apart
can not form hydrogen bonds with water
how does metallic bonding occur
outer shell electrons are donated to the ‘sea’ of delocalised electrons
what is a metallic bond
strong electrostatic attractions between the positive ions and delocalised electrons to form a giant metallic lattice
factors affecting strength of metallic bond
charge on ion
number of delocalised electrons per positive ion
size of ion
properties of metallic structures
high melting point conductive strong malleable, ductile insoluble
why do metals have a high melting point
millions of strong electrostatic attractions between the positive ions and delocalised electrons require a lot of energy to break
why are metals conductive
there are delocalised electrons which are able to freely move throughout the structure and carry a charge
why are metals strong
strong electrostatic attractions extend across the structure
why are metals malleable and ductile
positive ions in metals can easily slide over one another as they are arranged in regular, closely packed parallel layers
how can metals become harder
add another metal element to form an alloy
different sized ions distort the layers
why are metals insoluble
requires a lot of energy to break the electrostatic forces between the positive ions and delocalised electrons
electronegativity definition
the power of an atom to attract a pair of electrons in a covalent bond
factors affecting electronegativity
nuclear charge
atomic radius
shielding
how does nuclear charge affect electronegativity
higher nuclear charge from more protons
stronger attraction between the nucleus and the bonding pair of electrons
how does the atomic radius affect electronegativity
shared pair of electrons are closer to the nucleus so stronger attraction
how does shielding affect electronegativity
less shells of electrons between the nucleus and the shared electrons decreases repulsion
stronger attraction
electronegativity trend down a group
decreases down a group
atomic radius increasing
more shielding
electronegativity trend across a period
increases across a period
atomic radius decreases
nuclear charge increases
same shielding
what is a polar covalent bond
between elements of different electronegativities
shared electrons are unevenly distributed towards the element with the higher electronegativity
elements have partial charges
what does charge separation create
permanent dipole-dipole attractions between the polar molecules
why do some molecules have polar bonds but is not a polar molecule
bond polarities cancel each other out if the molecule is symmetrical
types of intermolecular force
induced dipole-dipole (van der waals)
permanent dipole-dipole attraction
hydrogen bond
what are intermolecular forces between and what do they affect
simple molecules
melting points
what are van der waals forces between
between any molecule
why are there van der waals
caused by temporary uneven electron distribution from constant movement of electrons
δ+ of one molecule is attracted to δ- of another
how can van der waals forces be stronger
bigger molecules have stronger van der waals due to more electrons
why are molecules with van der waals forces insoluble
non-polar so no interactions
can not form hydrogen bonds with water molecules
what are permanent dipole-dipole attractions between
polar molecules
why are there permanent dipole-dipole attractions
δ+ of one molecule is attracted to δ- of another
high electron density at the atom with the greatest electronegativity
why are there hydrogen bonds
exposed nucleus of δ+H of one molecule is attacted to a lone pair of electrons of δ-F,O,N of another molecule
must have a large difference in electronegativity so the bond is very polar
what are hydrogen bonds between
δ+H of one molecule and δ-F,O,N of another
why are molecules with hydrogen bonds soluble
able to form hydrogen bonds with water molecules
order of boiling points of CH4, NH3 and H2O
warum
H2O > HF > NH3
H2O has equal numbers of lone pairs as δ+H so can all hydrogen bond
N is not as electronegative as F or O so hydrogen bonds are not as strong
strength of intermolecular forces
hydrogen bond > permanent dipole-dipole attraction > van der waals forces
ionic equation to become a cation
X –> X^n+ + ne-
ionic equation to become an anion
X + ne- –> X^n-
