Topic 2- bonding and structure Flashcards
What are ions
Charged particles that is formed when an atom loses or gains electrons
What are molecular ions
Covalently bonded atoms that lose or gain electrons
Which electrons are lost when an atom becomes a positive ion
Electrons in the highest energy levels
Do metals usually gain or lose electrons?
Do non metals usually gain or lose electrons?
Metals- lose electrons
Non metals- generally gain electrons
Which are the 4 elements that don’t tend to form ions and why?
The elements are beryllium, boron, carbon, and silicon
Requires a lot of energy to transfer outer shell electrons
What are the 3 main types of chemical bonds
Ionic
Covalent
Metallic
Define ionic bonding
The electrostatic attraction between positive and negative ions
Give an example of an ironically bonded substance
NaCl (sodium chloride- salt)
Typically a metal and non metal
What determines the strength of an ionic bond
the size of the charge
- the bigger the charge of an ion the stronger the electrostatic attraction between ions
- thus more energy is required to overcome these forces and so they have a high melting and boiling point
- eg KCL is made of K+ and Cl- has a melting point of 770c whereas CaO is made of Ca2+ and O2- has a melting point of 2572c
the size of the ion (ionic radii)
- the smaller the ion the stronger the forces of attraction between ions
- smaller ions can pack together more colsely and more energy is required to overcome the stronger forces. the melting and boiling points are higher.
- NaCl is made from Na+ and Cl- has a melting point of 801C
- KCL is made up of K+ and Cl- has a melting point of 770c (has bigger ionic radius)
smaller ion + big charge —> high charge density
Explain the trend in ionic radius down a group
Ionic radius increases going down the group. As the number of electron shells increases and so the ionic radius increases too.
what are isoelectric ions
Explain the trend in ionic radius of isoelectric ions
isolectric ions- these are different atoms that have the same number of electrons
as the number of protons increase in isolectric ions the ionic radius decreases. this pulls tin the outer electron shell more. (the number of shells are the same)
What are physical properties of ionic compounds
High melting points as there are many, strong electrostatic forces between oppositely charged ions. lots of energy neede to overcome these forces
Non conductor of electricity when solid- ions need to be free to move
Conductor of electricity when in solution or molten
Brittle-layers will slide past eachother.
positives will be next to positives and will repel- and so break apart really easily.
do ionic compounds dissolve in water?
Most ionic compounds dissolve in water as water molecules are polar they can attract positive and negative ions and break up the structure.
In a solution of CuCrO4 with connected electrodes which electrode will the 2 ions migrate to?
Cu2+- migrate to negative electrode
CrO4 2- migrated to positive electrode
Define covalent bonding
Electrostatic attraction between a shared pair of outer electrons and the positve nucleus.
what is dative covalent bonding
see notes for example
where one atom donates 2 electrons ro anotherion to form a bond.
represented by an arrow.
giant covalent structures include graphite and diamond
describe the structure of graphite?
-layers slide easily as there are weak forces between the layers
-delocalised electrons between the layers allow graphite to conduct electricity as they can carry charge
-layers are far apart in comparision to covalent bond length. this means it has a low density
-lots of strong covalent bonds mean graphite has a very high melting point.
-graphite is insoluble. the covalent bonds are too strong to break.
sulphur dioxide has similar structure to diamond describe the structure of diamond
- the tightly packed, rigid arrangement allows heat to conduct well in diamonds
- unlike graphite, diamond can be cut into gemstones
- ver high melting point due to many strong covalent bonds. it is also very hard
- diamond cannot conduct electricicty well as it doesnt have any delocalised electrons
- diamond is insoluble. the covalent bonds are too strong to break
graphene is another example of a giant covalent structure.
describe structure and use of graphene
-graphene is 1 layer of graphite. it is one atom thick and made up of hexagonal carbon rings.
-delocalised, free moving electrons make graphene an excellent conductor of electricty as they can carry charge.
- the same delocalised electrons strengthen the covalent bonds, this gives graphite a high strength property
- graphene is only one cell thick, it is transparent and lightweight
uses
aircraft shells
use in super computers and high speed computing
smart phone screens
Define metallic bonding
Electrostatic attraction between the positive metal ions and the sea of delocalised electrons
metals have a giant mettalic latice structure
explain properties of metallic bonding
see diagram (metallic bonding)
-metals are good thermal conductors as the delocalised electrons can transfer kinetic energy
- metals have high melting point due to the strong electrostatic attractions
- solid metals are insoluble as the metallic bond is too strong to break
- metals are good electrcial conductors as the delocalised electrons are mobile and can carry charge
- the more electrons an atom can donate to the delocalised system the higher the melting point eg magnesium has a higher melting point than sodium as magnesium can donate 2 electrons (group 2) where as sodium only donates 1 (group 1) per atom
- positive metal ions are formed as metals donate electrons to form a ‘sea’ of delocalised electrons.
- there is an electrostatic attraction between postive metal ions and the negative delocalised electrons.
Why does giant ionic lattices conduct electricity when liquid but not when solid
In solid state the ions are in fixed position and thus cannot move. When they are in liquid state the ions are mobile and thus can freely carry the charge
Giant ionic lattices have high or low melting and boiling point
They have high melting and boiling point becuase a large amount of energy is required to overcome the electrostatic bonds
In what type of solvents do ionic lattices dissolve
Polar solvents eg water
Explain why both water and carbon dioxide molecules have polar bonds but only
water is a polar molecule.
oxygen is more elctronegative than carbon or hydrogen
which results in a polar bond with oxygen so carbon and hydrogen +
carbn is a symmertrical molecule and so dipole vectors cancel out
lone pairs of electron in oxygen vectors do not cancel out (h20)
define periodicity
The study of trends within the periodic table. Often these trends are linked to elements’ electronic configurations.
what is Electrongegativity
electronegtivity is the ability for an atom to attract electrons towards itself in a covalent bond.
- the further right you go in the periodic table the more electronegatib=ve the elemnt is.
fluorine is the most electronegative
when can covalent bonds become polar?
covalent bonds can become polar if the atoms attached to it have a difference in electronegativity
the bigger the difference in electronegativity…
…the more polar the bond will be
when are bonds not polar
atoms bonded with same electronegativity or similar are non-polar. the shared electrons sit in the middle.
polar molecules is lead to
uneven distrubution to charge
what happens if bonds are arranged symmetrically
then the molecule is non-polar
what happens if bonds are arranged asymmetrically
then you have an overall polar molecule
name 3 types of intermolecular forces
London
dipole-dipole
hydrogen bonding
what are london forces
London forces are the weakest type of intermolecular forces
any electron can form a dipole when they move near to another atom or molecule
london forces are random
this occurs as electrons in a molecule or atom can move from one end to another - hence creating a temporary dipole
this temporary dipole only ecists when 2 molecules or atoms near by.
the slightly + on one atom or molecule will be attracted to the slightly negative on another and a force of attraction is created.
london forces can hold some molecule in crystal structures, iodine is an example
weak london forces - holds the I2 molecule together
strong covalentbonds holds the 2 iodine atoms together
force happens between molecules
bond happens between atoms
bond is much stronger than atom
the bigger the molecule or atom, the morelondon forces as you have a larger electron cloud
we must have enough enrgy to overcome these forces
london forces with hydrocarbons
longer straight chain hydrocarbons have more london forces and so more enrgy is needed to overcome these forces. this means the boiling point increases.
hydrocarbons with branches means they cant back together as close. this weakens the london forces between the chains and lowers the boiling points
what are dipole dipole forces
permant dipole eg HCL which are stronger than london forces
they also include having london forces
there are weak electrostatic forces that exist between molecules with polarity
if its non-polar only expereience london forces
what is hydrogen bonding
see example of ice
hydrogen bonding strongest type of bonding
hydrogen bonds with the lone pair of nitrogen, oxygen or fluorine (the most electronegative elements)
hydrogen bonding also have london forces and permant dipole dipole
Explain why hydrogen bonding causes ice to be less dense than liquid water (2 marks)
Ice has more space between molecules
Due to ring structure in ice
solubiliy
polar substances can dissolve in polar solvents
the delta positive in H is attracted to the negative ions and the delta negative oxygen is attracted to the positive ion and the structure starts to break down, the waters align them =selves surrounding the ions this is known as hydration
for this to happen the new bonds must be the same strength or greater than those broken. if not then the substance is very unlikely to dissolve.
eg AL2O2 doesnt dissolve as the ionic bonding is too strong even though its ionic
alcohols can dissolve too- they dissolve in polar solvents as they can hydrogen bond with water molecules but the hydrocarbon part is non-polar so cant dissolve in water. the bigger the hydrocarbon part the less soluble the alcohol is.
some polar molecules dont dissolve in water, haloalkanes dont dissolve as their dipoles arent very strong
solubility with non-polar solvents
non-polar solvents- these molecules thats dont have a polarity. an example would be alkanes lke butane. they only have london forces
non-polar molecules tend not dissolve in water as water is polar and water forms stronger hydrogen bonds; water interacts with its own molecules as appose to the non-polar one.
