Periodicity Flashcards
What is periodicity
pattern/trend in the change in the properties of a row of elements
Going across a period, what happens to the atomic radius and why?
it gets smaller
there are more protons
the atoms have the same number of shells
the atoms have the same amount of shielding
there’s a greater nuclear attraction between the nucleus and outer shell electrons
so there’s less distance between the nucleus and outer shell electrons because the outer shells are pulled closer to the nucleus
Going down a group, what happens to the atomic radius?
it increases
there are more shells
there’s a greater distance between the nucleus and outer electron
increased amount of shielding
so weaker attraction between nucleus and outer shell electrons
so outer shell electron further away
What is electronegativity
the power of an atom to attract a bonding pair of electrons in a covalent bond
Describe the electronegativity of group 0
there are not electronegative because they are inert gases
Describe what electronegativity is like across a period
it increases
there are more protons in the nucleus
atoms have a smaller atomic radius
so there’s a stronger force of attraction between the nucleus and 2 electrons in the covalent bond
Describe what electronegativity is like down a group of
it decreases
the number of shells in the atoms increases
the amount of shielding in the atoms increases
the atoms have a larger atomic radius
so weaker attraction between nucleus and 2 electrons in covalent bond
What is ionisation energy?
The energy needed to remove one mole of electrons from one mole of atoms in their gaseous state to form one mole of 1+ ions(also in their gaseous sate)
Describe what the ionisation energy is like going down a group
-it decreases
-the atoms have more shells
-the atoms have more shielding
-there’s a greater distance between the nucleus and outer shell electrons
-so weaker attraction between nucleus and outer shell electrons
-and less energy required to remove one electron from outer shell
describe what the general trend of 1st ionisation energy is across a period
-increases
-the atoms have more protons
-the atoms have the same number of shells and same amount of shielding
-the atoms get smaller
-therefore stronger attraction between nucleus and outer shell electron
What are the deviations in the general trend of 1st ionisation energy across a period(period 3)
Mg—>Al
P—>S
Explain the Mg—>Al deviation
HEL(Higher.Energy.Level)
The outer electron in Mg is in the s orbital whereas the outer electron in Al is in the p orbital.
This means that the outer electron in Al is on a higher energy level than Mg so it is further away from the nucleus and will require less energy to remove
Explain the P—>S deviation
EPR(Electron.Pair.Repulsion)
P has 3 electrons in the p orbital whereas S has 4 electrons in the p orbital
The extra electron-electron repulsion’s make it easier to lose an electron from p4 than p3(less energy required)
Describe the trend of mps and bps across a period(period 3)
Na—>Al increases
Al—>Sincreases a lot
S—>Ar decreases
Explain the increase in mps and bps from Na to Al
-all have metallic bonding
-they are all giant metallic lattices
-the charges increase
-the ions get smaller
-there are more delocalised electrons
-there’s a strong attraction between metal ions and delocalised electrons
Explain the big increase in mps and bps from Al to Si
Si is a giant covalent lattice and has many strong covalent bonds that need to be broken
Explain the decrease in mps and bps from Si to P, increase from P to S and decrease from S to Ar
-they are all simple molecular substances
-all have van der waal’s
P travels in 4s so P4(60 electrons)
S travels in 8s so S8(128 electrons)
Cl travels in 2s so Cl2(34 electrons)
Ar travels by itself so Ar1(18 electrons)
-the more electrons, the stronger the VDWs. S has the most electrons so has the strongest VDWs which require the most energy to overcome
-Ar has very weak van der waals’ forces between atoms
Is the second ionisation energy larger than the first?
Why/why not
Yes it’s larger. When an atom loses an electron and goes through the second ionisation, the shell gets tighter and the and the atom gets smaller so the 2nd ionisation energy energy is larger than the 1st because the electron will be harder to remove as the distance between the outer shell and
nucleus is smaller.
Which type of ionisation method is used for large compounds and which are used from small molecules
Electron gun- small molecules
Spray-large compounds
How does ionisation work with an electron gun in a ToF
high energy electrons from the gun knock off an electron from each particle in the sample(gas). The particles form a positive charge
How does ionisation work with an electron spray in a
ToF
The sample (a solution) is put through a hypodermic needle attached to a positive terminal of high voltage power supply.
The pericles gain a proton as they leave the needle spread out in a fine mist because the tively charged particles are all repelling each other
