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AQA A2 Periodicity
| Question | Answer |
|---|---|
| Why does silicon, Si, have the largest melting point? | It is a giant covalent molecule so requires a lot of energy to break the covalent bonds between atoms. |
| Why does atomic radius decrease across a period? | The number of protons increases, and the shielding stays the same. Therefore the nuclear attraction BETWEEN LECTRONS AND NUCLEUS increases so the distance between the outer electrons and nucleus decreases. |
| What is the reaction of magnesium with steam? | Mg(s) + H20(g) --> MgO (s)+ H2(g) |
| How is aluminium oxide formed? | 4Al + 3O2 --> 2Al2O3 |
| What does amphoteric mean? | Reacts both as a base and an acid |
| Why is MgO less alkaline than Na2O? | As Mg(OH)2is the product of the reaction of MgO and H2O, we know due to HSBT that Mg(OH)2 is almost insoluble (milk of magnesia), thus very few OH- ions are formed, so the solution is less alkaline than the NaOHsolution formed when Na2O reacts with water |
| Why is there a large increase in melting point between Na and Al? | 1) TYPE BOND all show metallic bonding, 2) DESCRIPTION PARTICLES strong attraction between the cations and sea of delocalised e- 3) EXPLAIN DIFFERENCES increased number of delocalised electrons, where thus the increasing metallic bond strength |
| Which element has the highest melting point in period 3? | Silicon |
| How many bonds does Phosphorus form in PO4-3 phosphate ion? | 4 |
| Why is Al2O3 described as amphoteric? | As it reacts as a base and an acid, Al2O3+6HCl→2AlCl3+3H2O and as well it reacts with concentrated sodium hydroxide solution to produce a colourless solution of sodium tetrahydroxoaluminate: Al2O3+2NaOH+3H2O→2NaAl(OH)4 |
| Why does the ionisation energy increase across a period? | more protons in the nucleus from left to right, equal shielding, greater nuclear attraction between positive nucleus and negative OUTER electrons so the outer electron requires more energy to remove |
| Why is there a drop in the ionisation energy from Mg to Al? | the Mg atom will lose a 3s electron, and Al will lose a 3p electron. The p-electron is at a higher energy level thus requiring less energy to remove as it is easier to remove. |
| What is the order for the melting points of Phosphorus, Sulfur and Chlorine? Explain | S8> P4 > Cl2; 1)TYPE OF BOND: Simple covalent 2) DESCRIBE PARTICLES Strong sharing of pairs of electrons between atoms but weak VdW between molecules; 3) EXPLAIN DIFFERENCES more atoms in S8, the more electrons, the stronger the vdW |
| Why is the ionisation energy of Sulphur less than Phosphorus? | P has no paired electrons in any of its p orbitals, whereas S has 2 electrons in one p orbital, these will have opposite spin and repel each other which makes the electron more easily removed. |
| What is the general trend of acidity of solutions of oxides across the period? | solutions of oxides go from alkaline to acidic across the period |
| Why are Al2O3 and SiO2 insoluble in water? | SiO2 is a giant covalent structure without any polar groups so there will be no interactions with water. Despite containing oxide ions Al2O3 is unable to react with water because they are held to tightly in the lattice for H2O to break the atoms apart |
| Why is it important to know whether H2O is a liquid or a gas when reacted with Mg? | Mg + H2O(l) -> Mg(OH)2 + H2;but Mg + H2O(g) -> MgO + H2 |
| State whether the ionisation energy of He is higher of lower than that of lithium and explain why. | Higher, because there is no shielding around the He nucleus and there is therefore only a small distance between the electron and the nucleus. There is some shielding in lithium. |
| How does shielding along with other factors affect ionisation energy across a period? | Shielding remains the same but charge increases therefore e-are more attracted to the nucleus, distance between the nucleus and the electrons decreases, more energy is therefore needed to remove electrons and Ionisation energy across a period increases. |
| State and explain the trend in melting point across the period from Na to Ar | Melting point generally increases however, it decreases after Phosphorous, Sulfur, Chlorine and Argon as they are simple molecular substances containing van der Waals. |
| At which point along a period does IE decrease, state reasons why. | From period 2 to 3: Sub – shell structure and From period 5 to 6: Electron repulsion |
| What is the product when you react H2O with Na2O? | NaOH |
| Why does silicon have a high boiling point? | 1)TYPE BOND AND STRUCT: Silicon is a giant covalent structure 2) DESCRIBE PARTICLES: very strong sharing of pairs of electrons between ATOMS that requires a lot of energy to break |
| What is the formula for Phosphorus Oxide? | P4O10 |
| Why does Silicon Oxide not react with water? | There are no attractions which could occur between water molecules and the silicon or oxygen atoms which could overcome the strong covalent bonds in the giant structure. |
| Explain why the melting point of Al2O3 and MgO is higher than that of Na2O. | 1) TYPE BOND ionic 2)DESCR PARTICLES strong electrostatic attractions between ions 3) EXPLAIN DIFFERENCES charges on Mg2+&Al3+ are > Na+; Mg2+ &Al3+ are smaller in size than Na+ so attraction Mg2+ /O2-, and Al3+/O2- is greater than attraction Na+ /O2- |
| Why is it that SiO2 in water maintains a pH of 7 | SiO2 is insoluble in water |
| When sodium oxide reacts with water what is the resulting pH | 13-14 |
| Write an equation for the process occurring when the second ionisation energy of magnesium is measured. | Mg+(g) --> Mg2(g)+ + e- |
| Write the formula for phosphorus pentoxide | P4O10 |
| Write the chemical equation for P4O10 (i) with water (ii) with sodium hydroxide. | LEARN THE FORMULAE FOR THE PRODUCTS, then TRY TO BALANCE i) P4O10 (s) + 6H2O (l) 4H2PO4 (aq) (ii) P4O10 (s) + 12NaOH 4Na3PO4 (aq) + 6H2O(l) |
| Write an equation for aluminium oxide with dilute hydrochloric acid | Al2O3 (s) + 6HCl (aq) 2AlCl3 (aq) + 3H20 (l) |
| What is the trend in pH of period 3 oxides? | Na2O = 14; MgO = 9; Al2O3=7; SiO2 = 7 |
| State the 2 forms of the oxide of sulfur | SO2 and SO3 |
| CHALLENGE: Why does Al2O3 show covalent properties? | Al3+ ion has a large charge but a small ionic radius. This distorts the electron cloud of oxygen so that the electrons are closer to the middle of the bond. This gives Al2O3 covalent character. |
| Define First Ionisation Energy | Energy required to remove one mol of electrons from one mol of atoms in the gaseous state. |
| Why is there a drop in IE between Magnesium and Aluminium? | Mg has a completely full s orbital, whereas Al only has one electron in the p orbital, meaning the outer electron is further away, less attracted to the nucleus and need less energy to be removed. |
| How do you find what group and element is in, given the graph of its ionisation energies? | Spot the biggest jump between ionisation energies (e.g. Between IE 2 and 3). The group is therefore where the ionisation energy changes (e.g group 2) |
| Why does SiO2 not dissolve in water? | There are no possible attractions which could occur between solvent molecules and the silicon and oxygen atoms in SiO2 which could outweigh the attraction between the Si and O |
| What is the pH of the solution formed when SO3 reacts with water? | 0 |
| What is the pH of the solution formed when SO2 reacts with water? | 3 |
| What is the pH of the solution formed when P4O10 reacts with water? | 0 |
| What is the pH of the solution formed when SiO2 reacts with water? | 7 |
| What is the pH of the solution formed when Al2O3 reacts with water? | 7 |
| What is the pH of the solution formed when MgO reacts with water? | 9 |
| What is the pH of the solution formed when Na2O reacts with water? | 14 |
| What are the products of the reaction between Phosphorus oxide with water. Give the name and formulae. | Phosphoric acid H3PO4 |
| What are the products of the reaction between Sulfur dioxide with water. Give the name and formulae. | H2SO3 |
| What are the products of the reaction between Sulfur trioxide with water. Give the name and formulae. | Sulfuric acid H2SO4 |
| What are the products of the reaction between Sodium oxide with hydrochloric acid. Give the name and formulae. | Sodium Chloride (and water, a typical acid-base reaction) |
| What are the products of the reaction between Magnesium oxide with sulphuric acid. Give the name and formulae. | Magnesium Sulfate MgSO4 (and water, a typical acid-base reaction) |
| What are the products of the reaction between Aluminium oxide with sulphuric acid. Give the name and formulae. | Aluminium Sulfate (and water, a typical acid-base reaction) |
| What are the products of the reaction between Aluminium oxide with sodium hydroxide. Give the name and formulae. | Sodium Aluminate NaAl(OH)4 ONLY!, AND water is a reactant!!! |
| What are the products of the reaction between Silicon dioxide with sodium hydroxide. Give the name and formulae. | Sodium Silicate Na2SiO3 and water |
| What are the products of the reaction between Phosphorus oxide with sodium hydroxide. Give the name and formulae. | Sodium Phosphate Na3PO4 and water; it is as if the Phosphorus oxide became Phosphoric acid before reacting with NaOH |
| What are the products of the reaction between Sulphur dioxide with sodium carbonate. Give the name and formulae. | Sodium Sulfite Na2SO3 and Carbon Dioxide |
| Compare the melting point of Phosphorus to Silicon | 1)TYPE BOND/STRUCT:P=simple molecular, Si=giant covalent 2)DESCR PARTICLES: inP:vdW forces between molecules; 3) COMPARE vdW are weaker than covalent bonding. A lot of energy is required to break Si. |
| Explain the electrical conductivity trend from Sodium to Aluminium. | Increases, as number of delocalised electrons increases, so more electrons free to move. |
Created by:
UrsulineChem
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