h2 chem topical reminders

🧪 H2 chem last-minute reminders Disclaimer: These are general guidelines I got from my notes, teachers and friends. Reminders and styles of writing may differ from school to school, so please follow your own teachers’/school’s guidelines/facts in internal exams. For the actual As…it’s kinda up to you lol 🤩🫵 GENERAL REMINDERS - ‼ ‼ FOR SYNTHESIS QNS, NEVER USE FREE RADICAL SUB AS THE MAIN OPTION. ITS NOT GOOD - For steric hindrance etc, always say the bulky groups around a SMALL atom (small carbon, small whatever. Unless central atom is not small.) - ‼ ‼ ‼ FOR ALL STRUCTURAL ELUCIDATION. pls write every reaction (by its reaction name, see below.) even write the basic things like c:h ratio cause you WONT GET THE 1m unless u write it. - Eg: W + Na → explosive gas. So write: - Redox reaction occurred. Explosive gas is H2 (g) - W has -OH group. - 1 mole of W reacts with 1 mole of H2 (g) → W has 2 -OH groups - Anything about like why xxx and yyy react at same rate …what conclusion about the mechanism - answer wrt rate determining step - Eg this means that the bond breaking (or wtv, eg xxx has greater bond strength) is NOT PART OF RATE DETERMINING STEP - Why is KMnO4 the favoured oxidising agent in titration compared to K2Cr2O7? - KMnO4 colour change: dark purple to colour less /pale pink - Cr2O7: orange to green — ‼ ‼ end point colour change not distinct because both cr2o7 and cr3+ are coloured and end point cannot be detected sharply without use of a suitable indicator - **depends on what species you are oxidising though but if it’s like Fe2+ to Fe3+ which is yellow then the end result is yellow + whatever indicator colour was there - RMB TO WRITE COUNTER IONS!!! - State and explain type of reaction — unless it’s very obviously another type of reaction, it could also be redox so if it’s not clear just try calculating redox numbers - ‼ DONT FORGET YOUR CYCLIC ISOMERS!!!!!!! Salts/general ● BaO dissolves in water to form BaOH2 which is actually soluble in water…

Mole ● If they give some super weird reactants that don’t immediately balance nicely in an equation, try using redox equations to balance it. Or just try rlly hard to balance the normal eqn… Chem bonding ● Cations metal don’t act as charge carriers as they are not mobile ● Vsepr to MINIMISE REPULSION BETWEEN ELECTRON PAIRS ○ ALWAYS MENTION HOW MANY BOND PAIRS HOW MANY LONE PAIRS WHEN EXPLAINING MOLECULE SHAPE ● square pyramidal <90!! ● if stuff Mr suddenly increases (when dissolved, reacted etc) it has possibly dimerised (dimerisation of carboxylic acids in vapour and non polar stuff!!!) ○ Eg ethanoic acid dimerises with itself in benzene because benzene is non polar and doesn’t form bonds with ethanoic ● for all qns rmb to start by mentioning structure/bonding FIRST ● If number of electrons is different, id id is also different , must mention ○ Eg BrF is more polar than ClF hence more pdpd but ALSO BrF more electrons than ClF ● Dative arrow goes from DONOR TO ACCEPTOR ● Dative is sigma too ● MUST SHADE ORBITAL OVERLAP ● Pi bond is weaker than sigma!!! ● bond strength increases with more bonds BECAUSE NO OF SHARED ELECTRONS INCREASES ● state is binding BETWEEN WHAT AND WHAT ● For HX compounds bond energy trend, rmb to consider BOTH: orbital diffuse trend and electronegativity trend ● ‼ ‼ ‼ for AlCl wtv dimers. It is draw two diamonds. ● QUOTE LATTICE ENERGY FORMULA!!! exceptions examples Molecules with less than 8 electrons in the valence shell of an atom - Such molecules are electron deficient - More electrons can be accepted to achieve an octet configuration in the atom to form a dative bond AlCl3 and BeCl2 Molecules with unpaired electrons in the valence shell of an atom NO and NO2

- Such molecules are called radicals Chem bonding II ● NOTE graphite has HIGHER melting than diamond (still in the3000s) BECAUSE OF DIFF HYBRIDISATION HENCE GREATER OVERLAP HENCE LESS DIFFUSE THAT KINDA THING ● weak idid between layers is only related to lubricant stuffz ● Hybridisation number formula doesn’t really apply sometimes: ○ Benzene ring stuff are usually sp2 (eg phenoxide ion) ○ Amides N is sp2 despite getting sp3 from the steric number formula ○ It’s like that in stuff that want one normal (unhybridised) p orbital to overlap with electron cloud (like in a double bond, in amides etc) ● Intermediate bond length cannot explain equal bond length. Eg in graphite, must say electrons shared EQUALLY across the atoms hence equal bond length!!! Atomic Structure ‼ WRITE OUT FULL ELECTRONIC CONFIGURATIONS FIRST!!! ● “nucleus of xxx atom” -> POSITIVELY CHARGED so it will go towards negatively charged plate ○ in the nth electron shell ○ number of sub shells: n ○ number of orbitals n^2 ○ (Hence number of e- is 2n^2) ● trends: rmb to write increase decrease in size of electron cloud HENCE decrease radii or wtv ● spdf irregularity: Cr and Cu ● IE trend irregularity: grp 2&13 (s vs p electron, different energy levels) grp 15&16 (paired vs unpaired electrons) FOR FIRST IE ● orbital is a region of space where there is a high probability of finding an electron >95% ● Hund’s rule is occupied singly first, parallel spins ● Pauli exclusion is pairs must be opposite spins ● Sample explanation (example only. Not must-follow template) (and for a specific case?) (can’t find the question anymore) ○ Element C belongs to group 16 (name group) ○ The sharp decrease in the second ionisation energy from F to G implies that the second electron of F is removed from an electron shell of a lower principal quantum number, n, while the second electron of G is removed from an electron shell of a higher principal quantum number n+1 . Hence F has one valence electron and is from Group 1.

○ Since the elements differ by one proton number, elements E, D and C, should have 8, 7, 6 valence electrons respectively. Thus element C has 6 valence electrons and is from group 16 (how to work backwards to explain). Gaseous State ● main assumptions negligible volume and negligible attractive forces — then also that they are perfectly elastic and all particles at same temp have same KE ● negative deviation due to intermolecular attractive. Decreasing volume. Decreasing pV numerator ‼ AND IT DEPENDS ON THE IMF OF ATTRACTION ❗ ● positive deviation due to intermolecular repulsive. Electron cloud bigger = more repulsion ‼ AND IT DEPENDS ON ELECTRON CLOUD SIZE NOT IMF ‼ ‼ ● Boiling when saturated Vapor pressure is equal to external pressure on the liquid. ● When saying why something has discrepancy f