Periodicity A level Chemistry Multiple Choice Question Walkthrough

welcome to this exam question walkthrough where we're going to be looking at multiple choice questions from the periodicity topic download the questions from the description link have go at them yourself then watch this video and see how you got on which element is classified as block element each region of the periodic table is called block there are four blocks and the blocks take their name from the outer occupied subshell that each element has that's in that region and so the elements of Group 1 and group 2 have their outer occupied subshell as an Sub shell and so that is known as the block then we've got the block and the block and the block so all that we're doing in this question is looking for the elements and finding out which one of them is in this middle region that is colored in Green for the block and so antimony is in group five so it's block molybdenum is right there in the middle in the Block so that's going to be the correct answer and you'll see that strontium is there in group two so block and last of all uranium is right down there in the block so is the correct answer which element in Period three has the highest melting point well here are the patterns for melt melting point and boiling points across period 3 with the melting point being the blue line here and you can see that the one with the highest melting point is silicon and we just need to check that silicon is one of the options and it is it's option so is the correct answer the reason that is the correct answer is that silicon has giant covalent structure that means there is huge number of silicon atoms connected by strong covalent bonds which require lot of energy to break and so that is higher than sodium magnesium and aluminum and they have metallic bonding which is strong electrostatic attractions but not as strong and not as many as the strong covalent bonds in Silicon and then phosphorus through to argon they're only connected by Van de vile's forces which are very weak and only require little bit of energy to break so far far weaker than the other two Which ion has the largest radius well the radius of an ion is determined by the balance between the nuclear charge and the electron shells that are occupied if there are more occupied electron shells it will be bigger ion smaller nuclear charge will be bigger ion and so if we look at each of these the atomic numbers of fluorine magnesium sodium and oxygen are 9 12 11 and 8. and so that's the number of protons and electrons the elements will have when they are negative ions they've gained electrons when they're positive ions they've lost electrons so the electrons and the protons of the ions are now shown here you can see that all of these ions have therefore got 10 electrons and so the same electron configuration so the size of the ion is all down to the nuclear charge the one with the largest radius will have the smallest nuclear charge which is oxide it's only got eight protons so is correct which element has first ionization energy lower than that of sulfur well first of all we need to remember that as we work our way across the period the ionization energy goes up and so chlorine is one space to the right of sulfur so it will have higher first ionization energy and we're looking for lower oxygen is above sulfur in its group and so the first ionization energy of oxygen will be much higher than sulfur because we're going in an energy level and then phosphorus is the previous one in the same period as sulfur and that's where we get that dip between the paired up orbitals in Sulfur and the single occupancy in phosphorus and so sulfur will have than phosphorus as well and so the correct answer must be selenium and that makes sense because selenium is one down in the group from sulfur so it will have an extra occupied shell and so it will be easier to remove the outer electron which of these is the correct order for the increasing radius of the ions each row has got the same four ions fluoride has got nine protons and ten electrons whereas oxide has got eight protons and ten electrons and so therefore the oxide ion will be bigger than the fluoride ion because it's got smaller nuclear charge pulling those electrons in and so and must be wrong because they've got oxide down as being smaller than fluoride and it would be bigger than fluoride and so then we need to consider out of and whether the fluoride and oxide ions would be bigger or the lithium and beryllium ions would be bigger now since the lithium and beryllium ions only have two electrons each they will be much smaller than the oxide and the fluoride ions and so that means that is wrong and must be correct which of these elements has the highest melting point while these are all period 3 elements and the pattern as we go across period three looks like this with the three metals on the left hand side then the giant covalent silicon and then the three simple molecular substances and last of all monoatomic argon and so you can see from the diagram that silicon has the highest melting points and the reason is that when we're melting silicon we're breaking vast number of very strong covalent bonds between these silicon atoms whereas the other three are either simple molecular for sulfur and chlorine or monoatomic for Argon and between those molecules or atoms we only have weak Van Der waals forces which are much easier to overcome than it's the energy required to break the covalent bonds in Silicon so silicon is the correct answer the diagram shows how property of period 3 elements varies across the period what is this property atomic radius no atomic radius goes down as we work our way across the period because of increased nuclear charge and the same shielding electronegativity no that is general increase across the period for the same reasons really stronger nuclear charge and the same shielding so atoms have bigger power to attract the covalently bonded electrons first ionization energy no that's quite complicated pattern it's general increase across the period but we get dip between the second and the third and between the fifth and the sixth so it's not that one either so it must be melting points and that makes sense because we've got our three metals on the left hand side with quite high melting points the giant covalent silicon with huge melting point and then the four elements on the right hand side that only have Van Der Val's forces so is correct which element has the highest first ionization energy so we're looking for the element where the outermost electron is most difficult to remove now how difficult it is depends on where the element is in the periodic table these are all period three elements so their outer MGR level electron will all be in Period three and so we need to look at actually what their electron configurations are you can see that aluminum's outermost electron is in 3p subshell and in fact all of these have their outermost electron in 3p subshell we also need to know that because of the increasing nuclear charge as we work our way across the period the ionization energy will increase which makes us think sulfur might be the highest but because there are three orbitals we need to look at the fact that in Sulfur we've got pair of electrons occupying the same orbital and because of that repulsion one of them will be easier to remove so in fact phosphorus as the next most one along that will have the highest first ionization energy and in fact the pattern looks like this and if you can remember it you can just count your way along to find out which element it's going to be and so is the correct answer it will be the highest because it has the highest nuclear charge without pairing electrons up in the orbitals which is the correct classification for the elements Atrium symbol to find out which block Atrium is we need to look for it in the periodic table the periodic table is split into blocks with Group 1 and 2 and helium being block because that's where you find the outermost electrons in these elements in the subshells then we've got groups three through to eight or zero as being block because they have their outer electrons in sub shell the Block is in the Middle where the outer electrons have occupied sub shells and last of all the block is the lanthanides and actinides and they have their outer electrons in an subshell so all we need to do here is find Atrium and it's in period five the first of the Block elements and so the answer is it is block element which of the following is correct statement about the trend in atomic radius across period 3 in the periodic table first of all our four options are mixed two of them are saying that the radius increases across the period and two that the radius decreases while the radius decreases across the period so we can rule out and without properly reading them because that part of these statements are not true then we need to look at and and decide if their justification is correct the nuclear charge increases that's what says and that is true and that is the reason why the electrons sit closer to the nucleus there is greater electrostatic attraction between the nucleus and the outermost electrons and so must be correct is false because the shielding does not decrease like it says the shielding is pretty much constant across the period which element is in the block of the periodic table well the periodic table is split into four blocks based on where you find the outer energy level electron and so the elements in group 1 and group 2 along with helium have their outer electron in an subshell and so this region is called the block and then we've got the Block in the middle which is the block and these have their outer electron in subshell the block has their outer electrons in the subshell and the block which is what we're looking for here have their outer energy electrons in an sub shell and so to answer this question we're just finding out which of these elements is in the block and you can see that platinum and Palladium they are in the Block so they are wrong phosphorus is in group five so block and so plutonium must be the correct answer because it's there in the f-block position which elements are shown in increasing order of the stated property so atomic radius well atomic radius decreases across the period so if this is correct we need to be working from right to left across these elements so phosphorus is in group five sulfur is in group six chlorine is group seven this is wrong the atomic radius would decrease first ionization energy for sodium magnesium and aluminum there's general increase in ionization energy across the period but between magnesium and aluminum there is dip so this is incorrect as well electronegativity sulfur phosphorus and then silicon well electronegativity increases across period and we are working our way from right to left so this is wrong as well we're going backwards across the period melting point therefore must be correct argon followed by chlorine followed by sulfur that's correct because these are just either simple molecular substances or in argon's case monoatomic so they only have Van Der Val's forces between them and argon as single atom with 18 electrons will have weaker Van Der waals forces than the diatomic cl2 with 34 electrons and sulfur is S8 and so that has got 128 electrons so that will have much higher Van Der waals forces and therefore much higher melting point than the other two which of these elements has the highest second ionization energy well the second ionization energy is where you take an electron from an ion that is now positively charged because it has lost its first electron and so the correct thing to do here to make our life easier is to work out what the electron configuration will be for the positive ion for each of these elements and so for sodium you can see once we've worked out the electron configuration we're now removing an electron from the second energy level from 2p energy level magnesium we're taking the electron from 3s energy level so that will be much easier than sodium so magnesium is definitely wrong neon we're taking it from 2p energy level as well so that's similar to sodium but Neons proton number is only 10 whereas sodiums is 11. so sodium has higher nuclear charge so it will be harder to remove that second electron on argon we're taking its electron away from three subshell so that will be much easier in fact than any of the others it will have the lowest second ionization energy because its electron will be further from the nucleus and that means that sodium must be the correct answer which element is in the block of the periodic table well the blocks of the periodic table take their letter initial from the outer occupied subshell that the elements have in that region and so the elements in group 1 and group 2 along with helium have their outer electron in an subshell so they are block then the right hand side is block and the middle of the periodic table is the Block because their outer electrons are in subshell and the bottom rows the lanthanides and the actinides are block so we're trying to find the elements that's in the Block in the middle so selenium is in group six so block antimony is in group five and so that is also block tantalum is here in the middle so that is the Block element and Lead is also in fact block so is the correct answer which one of the following statements is correct the first ionization energies of the elements in Period 3 show general decrease from sodium to chlorine no that's not true they show general increase across the period as I'm showing here the electronegativities of the group two elements decrease from magnesium to Barium that's definitely going to be the case because the nucleus is going to end up further from any covalently bonded electrons that it might have and its shielding is going to increase because there's intervening electron energy levels in the way and so the power of the nucleus to attract covalently bonded electrons is definitely going to decrease Down group two and in fact it would decrease down any group in fact so must be the correct answer checking for why it's wrong the strength of intermolecular forces increases from hydrogen fluoride to hydrogen chloride definitely not because hydrogen fluoride has hydrogen bonding which is much stronger than the permanent dipole-dipole forces in hydrogen chloride and the ability of the halide ion to act as reducing agent decreases from fluoride to iodide reducing ability is the ability to donate electrons and that is influenced by the ability of an ion to hold on to its electrons or in this case let them go and the bigger ions will have the weakest hold on the outer electrons and so therefore will be the best at giving them away and so iodide is much bigger than fluoride and so iodide will not control its electrons well it will let them go easily and will be better reducing agent so that is why is wrong