Bonding - Part 1 Flashcards
Electronegativity
Ability of an atom to
attract a bonding pair of electrons in a covalent bond
towards itself
Elements that are highly electronegative?
Oxygen and Fluorine
Dipole
a pair of equal and oppositely charged poles
separated by a distance.
Explanation if electrons are shared equally in a compound?
Produces a NON-POLAR covalent bond.
Purely covalent character.
(electronegativity difference between the two atoms is minimal. Eg H—H
Explanation if electrons are unequally shared in a compound?
Produces a POLAR covalent bond.
Covalent bond with a little bit of ionic character Eg. H—F
(large electronegativity difference - between two atoms is between 0.4 to 2.0 then electrons are unequally shared as one atom pulls electrons more strongly, forming a dipole)
Explanation when an electron is transferred from one atom to another?
Occurs if large difference in electronegativity between two atoms (eg. Between 2 and 4)
Forms an ionic bond
Exist as separate ions, no distortion of electron cloud
Explain the bonding in carbon dioxide?
O=C=O
Symmetrical shape cancels out dipole with otherwise would form between C and O
Explain this bond H—F?
The difference in the electro negativity of the two atoms causes a dipole.
polar covalent bond
partial ionic character
Isoelectronic ions
Ions which have the same electron configuration. (Number of electrons)
Why does atomic radius decrease from N to Al (or down a group of isoelectronic ions)
Atomic number increases
Nuclear charge increases
Number of shells and electrons stays same
Greater electrostatic attraction between outer shell electron and nucleus
Smaller ionic radius
Two things that are evidence for the existence of ions?
1) The MPs of group 1 chlorides decrease down the group. This is because there are more shells and electrons so a larger atomic radius so a weaker attraction so less energy is required to break the ionic bonds.
2) Electrolysis provides evidence because The migration of coloured ions towards the respective electrodes and the coloured elements formed at each electrode proves the existence of separate ions.
What does a higher ionic charge mean?
Stronger ionic bond
Eg. Na5+ has lost 5 electrons
Larger positive charge
OR COULD U SAY: lost more shells which decreases the ionic radius so the distance between the two attracting ions is smaller so the bond is stronger. ???????¿¿¿
How does ionic radius relate to strength of ionic bond?
larger ionic radius
weaker ionic bond
because the more distance between the two attracting ions.
Typically it is the ionic radius of the cat ion (+) that has an effect on the strength of the bond. Why???????????
Non-polar definition
Electrons are evenly distributed so that no separate positive or negative poles form.
Polar definition
Electrons are unevenly distributed so separate negative and positive poles form.
Dative covalent bond definition
A covalent bond when the shared pair of electrons come from only one of the bonding atoms.
Eg. Ammonium ion, usually ammonia has a lone pair of electrons on its nitrogen
In the ammonium ion the nitrogen provides both of its lone electrons to hydrogen ion to form the dative covalent bond.
Why does the size of isoelectronic ions decrease
across a period of isoelectronic ions
number of electrons stays the same
number of protons in the nucleus increases (atomic number)
stronger attraction between the electrons and the protons in the nucleus
ionic radius decreases
ionic bond
electrostatic attraction between two oppositely charged ions
covalent bond
electrostatic attraction between positive nuclei of the atoms and their shared pair of electrons
What happens to the size of isoelectronic ions across a period?
they decrease
what happens to the size of ionic radius as you go down the group?
it increases because as you go down because you are adding more shells filled with electrons which all repel each other
(and maybe because all ions have the same charge so as shells increase there is a weaker attraction between the protons in the nucleus and their electrons)
Why is there a big jump up in ionic radius as you go from 3+ ions (group 3) to 3- ions (group 5)?
because a whole layer of electrons is added.
eg. these ions are in period 3:
Al 3+ = 10 electrons (2,8)
P 3- = 18 electrons (2,8,8)
Migration of ions example in U shaped drying tube
CuCrO4 (copper chromate)
blue colour of Cu2+ ions migrates to negative electrode
yellow colour of CrO4 2- ions migrates to the positive electrode
Migration of ions example on moist filter paper example
drop of purple potassium manganate solution on moist filter paper placed on microscopic slide.
Ends of the slide are connected to 24 V DC power supply.
After ten minutes the purple colour of the
MnO4 - ion migrates to positive electrode
4 physical properties of ionic compounds
1) high mps and bps - SEABOCI (strong electrostatic attraction between oppositely charged ions)
2) conduct electricity when molten - ions free to move
3) doesn’t conduct electricity when solid - ions not free to move
4) brittle/ easy to cleave apart
How is a bond formed?
the overlap of two orbitals
How to draw a dative covalent bond in an ammonium ion
NH4, for bonds, one bond replaced by an arrow pointing towards the H to represent the atom donating a lone pair
Explain the strength of multiple bonds
Nuclei joined by multiple double bonds have a greater electron density between them so there is a greater force of attraction between the nuclei and of the bonding atoms and their shared electrons.
There is therefore a shorter bond length and a greater bond strength.
How many electrons in Boron’s outer shell in BCl3?
6 electrons - not an octet
How many outer shell electrons does S in SF6 have?
12 electrons - not an octet
4 things dative covalent bonds are found in
1) NH4+
2) Between chlorine and electron deficient aluminium in Al2Cl6 (AlCl3 molecules join together to form this dimer)
3) Dative covalent bonds are the bonds between water ligands and the central metal ion in hexaaqua ions of metals such as [Mg(H2O)6]2+ and [Fe(H2O)6]2+
4) H3O+
How is the dot and cross diagram for dimer, Al2Cl6 drawn?
3 chlorines
2 alum
3 chlorines
where Cl = dot, Al = X
- each chlorine has one electron from aluminium
- each aluminium has three of its own electrons making up three pairs with three chlorine electrons (3 lots of X Dot) & one pair dative covalent pair of electrons from chlorine
Search this - Al2Cl6 displayed for another picture
most and least electronegative elements
fluorine - most
caesium - least
Pauling scale range?
0-4
Trend in electronegativity across a period
increases, proton and nuclear charge increases across a period whilst the number of shells and electrons remains the same so there is a stronger attraction between the electrons and the nucleus.
3 main factors affecting strength of metallic bonding
1) nuclear charge - more protons = stronger attraction with delocalised electrons
2) number of delocalised electrons per atom- more delocalised electrons = stronger bond
3) size of metal ion - smaller = stronger attraction
