Chemistry Final Exam Notes PDF
Document Details
Uploaded by Deleted User
Tags
Summary
These notes cover various chemistry topics, including atomic radius, ionization energy, and mass spectrometry. The concepts of chemical bonding and periodic trends are also discussed.
Full Transcript
✓ Atomic radius decrease across each period This is because no. Of protons in the nucleus increases, so the nuclear charge increases and the additional electrons are in the same shell so experience similar shielding. So , there is an increase in the attraction forces between the outer electrons and...
✓ Atomic radius decrease across each period This is because no. Of protons in the nucleus increases, so the nuclear charge increases and the additional electrons are in the same shell so experience similar shielding. So , there is an increase in the attraction forces between the outer electrons and the nucleus. ✓ Atomic radius increase down each group, This is because number of electron shells increases, so the attraction forces between the outer electrons and nucleus decreases. In period 2 and 3 melting and bp points increase till gr 4 which is silicon and carbon the decreases State what is meant by the term orbital.: a region within an atom can hold (up to) two electrons (with opposing spins) s: contains 1 orbital - p: contains 3 orbitals - d: contains 5 orbitals first 3 quntum shells have 14 orbitals 29Cu : 1s2 , 2s2 , 2p6 ,3s2 , 3p6 ,4s1 , 3d10 24Cr: 1s2 , 2s2 , 2p6 ,3s2 , 3p6 ,4s1 , 3d is a measure of the energy required to remove one mole of electrons from one mole of gaseous atoms of an element to form one mole of gaseous ions. - Ionization energies are endothermic changes 1. Nuclear Charge The more protons there are in the nucleus, the more positive the nucleus is & the more strongly electrons will be attracted to it. 2. 2\. Distance of outer electrons from the nucleus The closer the electrons to the nucleus, the more strongly they are attracted to the nucleus and more difficult to be removed. 3. Shielding effect of inner electrons The more electron shells there are between the valence electron and the nucleus,The greater the shielding effect & the easier it is to remove the electron. 4. 4\. Spin-pair repulsion Two electrons in the same orbital will experience repulsion from each other, so the paired electrons are removed easily than single electrons. Ionization energies down a group Ionization energy decreases down a group As we go down the group: \- Nuclear charge increases as the no. Of protons increases. \- Atomic radius increases as more shells are added which makes the atoms bigger. \- Shielding by inner electrons increases as there are more electron shells. These factors outweigh the increased nuclear charge, meaning it becomes easier to remove the outer electron as we go down a group. ★ Ionization energies across period 2 and 3 Ionization energy generally increases across a period As we go across the period: \- Nuclear charge increases as the no. Of protons increases. \- Atomic radius decreases & the attraction between nucleus and outer shell electrons increases \- Shielding by inner electrons is almost constant as electrons are being added to the same shell. It becomes more difficult to remove the outer electron as we move across a period Mass Spec: Vaporization: ample injected into mass spec and heated and vaporized and must be gaseous. Ionization: bombarded with high speed electrons leading to loss of electrons Acceleration: negatively charged electric plates accelerate the ions Deflection: deflected by, a uniform magnetic field. The amount of deflection depends on the mass-to-charge (m/z) ratio of the ions. Ions with a small mass to charge ratio are deflected more than ions with a large mass to charge ratio, only ions with a certain m/z ratio pass through the slit and are detected In the mass spectrum, the Molecular Ion is the heaviest ion (the one with the greatest m/z value) When analysing organic compounds, there is always a small percentage of the carbon-13 isotope present in the compound, which can lead to appearance of a little peak next to the M+ peak, called M + 1 peak. The height of the M+1 peak depends on how many carbon atoms are there in the molecule. The larger the number of carbon atoms, the larger the M+ peak is CL RATIO 9 6 1 BR RATIO 1 2 1 Suggest why there might be a small peak at m/z = 36 in the mass spectrum of chlorine gas? Peak is due to molecular ion 35 Cl 37 Cl With a charge of 2+ Remember added for period 2 is its further from nucleus and experience more shielding for boron and Al examples ![A screenshot of a cell phone Description automatically generated](media/image2.png) All Nitrates are soluble All sulfates are soluble except Ca, Ba, Pb All halides are soluble except Ag, Pb Example of precipitation : AgNO3 (aq.) + NaCl (aq.) →AgCl (s) + NaNO3 Neutralization: KOH (aq) + HNO3 (aq) → KNO3 (aq) + H2O (l) H+ (aq) + OH- (aq) → H2O (l (Ar) Relative atomic mass: It's the weighed average mass of atoms of an element, compared to 1/12 of the mass of an atom of Carbon-12. Molecular formula = empirical formula x Mr of of the compound / Mr of the empirical formula Ionic Bond: Strong electrostatic attraction force between positive & negative ions which occurs in all direction. ‣ Cu2+ ions migrate towards the cathode → blue color is observed ‣ CrO4 2- migrate towards the anode → yellow color is observed Regular arrangement of alternating positive & negative ions in layers, held together by strong electrostatic attraction forces in all directions. ard & High melting & boiling points. Due to strong electrostatic attraction forces in all directions between oppositely charged ions in a giant lattice, which needs large amount of energy to overcome the forces. 2\. Bad conductor of electricity when solid, but good when (molten or aqueous) Bad when solid, as ions are fixed in place and can't move freely. Good when molten/ aqueous , as ions are free to move through the layers & carry charge. 3\. Brittle If a stress is applied to the crystal, layers may slide over each other. Ions of same charge repel each other & the crystal break apart Ionic charge The larger the charge on the ions, the stronger the ionic bond. Mg+2 O2- has stronger attraction force than Na+ Cl-. Thus requires larger amount of energy to over come the attraction forces Smaller sized ions (smaller ionic radius) and Higher ionic charge produce stronger bonds Polarisation is the distortion of electron density of a negative ion (anion). Polarising power: it's the ability of the positive ion (cation) to distort the electron density of the neighboring negative ion. Factors that increase Polarizing power of the Positive ion Smaller size of positive ion e.g.: Li+ has higher polarising power than Na+ Higher charge of positive ion e.g.: Mg2+ has higher polarising power than Na+ Polarisability: it's the ability of the negative ion (anion) to be distorted/ deformed by the positive ion. Factors that increase Polarisability of the Negative ion Larger size of negative ion e.g.: Br- is more polarised than Cl- Higher charge of negative ion e.g.: O2-- is more polarised than F It is the electrostatic attraction force between the two nuclei of the bonded atoms & the shared pair of electrons between them. ![A diagram of a diagram Description automatically generated](media/image4.png) Elements that have an expanded octet are elements that have a d-subshell available to accommodate the extra electrons. For example, phosphorus, sulfur and chlorine all have an empty 3d orbital to accommodate more electrons Simple molecule: They have low melting and boiling points. Due to weak intermolecular attraction forces which needs low amount of energy to be overcome. ② They are non conductors of electricity. As they have no free moving delocalized electrons. ③ They are usually insoluble in water A Dative covalent bond is formed when an empty orbital of one atom overlaps with an orbital containing a non-bonding pair (lone pair) of electrons of another atom. A screenshot of a paper with text Description automatically generated ![A screenshot of a computer Description automatically generated](media/image6.png) A diagram of a molecule Description automatically generated with medium confidence If all dipoles cancel each other, the molecule will have no overall dipole & is said to be 'non-polar'. If dipoles reinforce one another, the molecule will possess an overall dipole & is said to be 'polar'. None lone paired have non polar molecules ![A screenshot of a graphene diagram Description automatically generated](media/image8.png) A screenshot of a cell phone Description automatically generated Molecular Formula: A formula that shows the actual number of each atom in a molecule. Example: Choroethane has molecular formula C2H5Cl Empirical Formula: A formula that shows the numbers of each atom in the simplest whole number ratio. Example: Choroethane has empirical formula C2H5Cl Structural Formula: A formula that shows how the atoms are joined together. Example: Chloroethane has structural formula CH3 ---CH2--- Cl or CH3CH2Cl Displayed Formula: A formula that shows every atom and every bond. skeletal Formula: A formula that shows all the bonds between carbon atoms. Example: Chloroethane has skeletal formula The breaking of a covalent bond where each of the bonding electrons leaves with one species forming a free radical. Is homolytic the breaking of a covalent bond so that both bonding electrons are taken by one atom Forming negative ion and the other becomes a positive ion is hetrolytic Free radical is a species that contains an unpaired electron & is uncharged ![A diagram of different types of chemistry Description automatically generated](media/image10.png) ★Free radical substitution has a limited use in industry. The yield is low because of further substitution reactions, and because the products have to be separated. ![A diagram of a chemical reaction Description automatically generated](media/image12.png) Explain why: Geometric isomerism can exist in alkenes not in alkanes. Because the presence of C=C double bond leads to restricted rotation, so that there can't be any rotation around the double bond Polymers: Large molecules made from many smaller molecules called monomers joined together. Monomers: small molecules that combined together to form a polymers ![A screenshot of a computer Description automatically generated](media/image14.png) Alkenes have pi bond which is a region of high electron density around the C=C bond. This makes the alkene molecule attractive to Electrophiles (the species that are electron deficient, including polar bonds). ‣Electrophile: is the species that is attracted to a region of high electron density. ‣Electrophilic addition: It is a reaction in which two molecules form one molecule & the attacking molecule is an electrophile. It involves addition and attack by an electrophile MS important answers 1. (because) the formation of 2-chloropropane / the major product proceeds via a secondary carbocation (but) the reaction / the formation of 1-chloropropane / the formation of the minor product proceeds via a primary carbocation (and) secondary carbocations are more stable than primary carbocations 2)boron the electron (being removed) is from the 2p subshell (not the 2s as for Li and Be) which is further from the nucleus than the 2s electrons so is more shielded 3)Graphite / diamond / carbon are lattices / giant structure with covalent bonds (between the atoms) Held together by strong covalent bonds (which) require a lot of energy to break 4\) sulfur has 4 electrons in the 3p sub-shell and one 3p orbital is (doubly) filled / has a pair of electrons so there is a (slight) repulsion between the electrons in the same 3p orbital (resulting in a lower first ionisation energy) 5\) incineration advantages reduced volume of landfill or energy released for generating electricity incineration disadvantage produces toxins recycling advantage saves (precious) resources recycling disadvantage polymers need to be sorted (and this is expensive) or involves the use of energy (to make the new product) 6\) M1 bond angle of 107o (allow 106-108) M2 lone pairs repel more than bonding pairs (and adopt a position of minimum repulsion/maximum separation) 7\) (2nd ionisation is greater because) (second) electron removed is in a lower (main) energy level / from the inner (main) energy level (1) removal of an electron reduces electron-electron repulsion causing the ion to contract OR electron removed is closer to the nucleus 8\) (the student is correct that the alkene has polar bonds, as) the C-Cl bonds are polar (1) As Cl is more electronegative (than C) (1) but the molecule is not polar as it is symmetrical / has no net dipole (moment) / has an even distribution of charge 9\) barium ion has a greater charge than caesium ion / Ba has 2+ and Cs has 1+ charge barium ion is smaller than the caesium ion the (electrostatic) attraction/force(s) between the ions is greater in barium chloride so more energy is required to break the (ionic) bonding / higher (negative) lattice energy 10\) the difference in electronegativity between barium and chlorine is greater than that between beryllium and chlorine/ (electronegativity difference) in BaCl2 is 2.1 and in BeCl2 is 1.5 the Ba−Cl bond will have more ionic / less covalent character than the Be−Cl bond 11\) graphite has a giant covalent structure / many (strong) covalent bonds within the layers/ each carbon atom is covalently bonded to 3 other carbon atoms (which gives it) a high melting temperature /requires a lot of energy to break/melt it has delocalised electron(s) (between the layers) and which allows it to conduct electricity / carry charge/ can move when a potential difference is applied