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Summary AS level chemistry - CH1 - Unit 1 - WJEC (Wales) specification £3.99   Add to cart

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Summary AS level chemistry - CH1 - Unit 1 - WJEC (Wales) specification

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AS level chemistry - CH1 - Unit 1 - WJEC (Wales) specification: These notes are based on the WJEC curriculum but can be used for other specifications. Very in-depth in all topics (7 units) describing basic chemistry.

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  • May 17, 2024
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  • 2023/2024
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‭Chemistry‬
‭Formulae and equations: Unit 1.1‬
‭Useful definitions‬
‭Element‬ ‭A substance which cannot be split‬‭chemically‬‭into‬‭anything simpler‬

‭The atom‬ ‭The smallest part of an element that can take part in a chemical reactions‬

‭Molecule‬ T
‭ he smallest part of a compound‬
‭The smallest part of atoms that don't exist in the free state i.e H‬‭2‬

‭An ion‬ ‭An electrically charged atom or molecule, cations are +, anions are -‬

‭A symbol‬ ‭Represents an atom or mole of an element‬

‭Formula‬ ‭Represents one molecule of a compound or the simplest ratio of ions present‬

‭Valency‬ ‭ numerical measure of the combining power of an atom/ion‬
A
‭Historically the number of hydrogen atoms which will combine with one or a group of‬
‭atoms (because hydrogen has only 1 electron in its outer shell)‬
‭Also the number of positive or negative charges in an ion‬
‭Oxidation and reduction‬
‭●‬ ‭Oxidation‬ ‭●‬ ‭Reduction‬
− + ‭2‬+ − +
‭ ‬ ‭𝐿𝑖‬ − ‭1‭𝑒‬ ‬ → ‭𝐿‭𝑖‬ ‬
○ ‭○‬ ‭𝐶𝑢‬ + ‭1‭𝑒‬ ‬ → ‭𝐶‬‭𝑢‬
‭○‬ ‭Addition of oxygen‬ ‭○‬ ‭Removal of oxygen‬
‭○‬ ‭Loss of hydrogen‬ ‭○‬ ‭Gain of hydrogen‬
‭○‬ ‭Loss of electrons‬ ‭○‬ ‭Gain of electrons‬
‭Oxidation numbers and oxidation states‬
‭●‬ ‭The number of electrons needed to be gained or lost for an element to become‬
‭neutral‬
‭○‬ ‭Mg‬‭2+‬ ‭needs to gain 2 electrons, the O.N is +2‬
‭●‬ ‭O.N are given to various elements by applying the following rules‬
‭1.‬ ‭The O.N of an element is 0‬
‭2.‬ ‭The sum of oxidation number in a neutral compound is 0‬
‭3.‬ ‭In a compound containing hydrogen, hydrogen has an O.N of +1‬
‭○‬ ‭Except in metal hydrides such as NaH and KH, hydrogen has an O.N‬
‭of -1 and the metal becomes +1‬
‭4.‬ ‭In a compound containing oxygen, oxygen has an O.N of -2‬
‭○‬ ‭Except with fluoride or peroxides‬‭1‬‭, where the O.N is multiplied by the‬
‭number of oxygen atoms‬
‭5.‬ ‭In a compound containing a halogen, halogens have an O.N of -1‬
‭6.‬ ‭Group 1 metals have oxidation numbers of +1 in compounds‬
‭7.‬ ‭Group 2 metals have oxidation numbers of +2 in compounds‬
‭8.‬ ‭In species with atoms of different elements, the most electronegative element‬
‭is given the negative O.N‬


‭1‬
‭Compounds with more than one oxygen‬


‭1‬

, ‭Oxidation agent‬ ‭Causes oxidation by gaining electrons in a reaction‬

‭Reducing agent‬ ‭Causes reduction by losing electrons in a reaction‬




‭Ionic equations‬
‭●‬ ‭Provide a shorter equation which focuses on the changes taking place‬
‭●‬ ‭Spectator ions‬‭- have not taken part in any chemical‬‭change and can be removed‬
‭from the equation‬




‭2‬

,‭Basic ideas about atoms:Unit 1.2‬
‭Orbitals‬
‭●‬ ‭Region of space where there is a 95% chance of finding an electron‬‭𝑥‬ ∈ ‭𝑅‬
‭Orbit/shell/energy level‬ ‭The path of an electron around the nucleus‬

‭Charge cloud‬ ‭ he orbital is regarded as a spread of charge a the electron is likely to be‬
T
‭anywhere in the orbital‬
‭Greatest electron density at the centre‬
‭●‬ ‭Electrons can occupy 4 types orbitals within an orbit‬
‭○‬ ‭s,p,d and f orbitals‬
‭1.‬ ‭s-orbitals are spherical‬
‭2.‬ ‭p-orbitals are dum-bell shaped‬
‭Energy levels of sub-shells‬
‭●‬ ‭Shells are represented by n and are numbered‬
‭○‬ ‭n=1, n=2 etc‬
‭●‬ ‭Electrons exist in pairs‬
‭○‬ ‭Spin in opposite directions‬↑↓
‭●‬ ‭Orbitals can hold 2 electrons each‬
‭○‬ ‭s subshell - 1 s-orbital‬
‭○‬ ‭p subshell - 3 p-orbitals‬
‭○‬ ‭d subshell - 5 d-orbitals‬
‭●‬ ‭The 4s subshell is exceptional as it has a lower energy level than the 3d subshell‬
‭Electronic configuration‬
‭●‬ ‭Describes how electrons are arranged in their shells, subshells and orbitals‬
‭●‬ ‭Excited state configuration -‬‭Atoms with one or more‬‭excited electrons‬
‭●‬ ‭3 rules apply to atoms in the‬‭ground state‬
‭The Aufbau principle‬ ‭ lectrons in ground state occupy orbitals in order of orbital levels with‬
E
‭the lowest being filled first‬
‭-‬ ‭Intuitive except 4s has a lower energy level than 3d and is filled‬
‭first‬

‭The Pauli exclusion principle‬ ‭Each orbital can hold 2 electrons which must have opposite spins‬
‭-‬ ‭2 parallel spins is not allowed‬

‭Hund’s rule‬ ‭ ach orbital of the same energy level must be occupied singly with‬
E
‭parallel spin before pairing can take place‬
‭●‬ ‭Chromium and copper are exceptional‬
‭○‬ ‭More stable to have a ½ full or full 3d subshell than to have a full 4s subshell‬
‭and a 3d subshell with an empty orbital‬
‭■‬ ‭Only 1 electron is given to the 4s subshell‬




‭3‬

, ‭Noble gas cores‬
‭●‬ ‭Noble gases can be used to represent full shells when writing electronic configuration‬
‭●‬ ‭Only works using noble gases due to their full outer shells‬
‭●‬ ‭O‭2‬ -‬ ‭can be written as [Ne]‬
‭Ionisation energies‬
‭●‬ ‭Energy needed to remove electrons from an atom‬
‭●‬ ‭Molar first ionisation energy (1st I.E)‬
‭○‬ ‭Energy required to remove one mole of electrons from 1 mole of gaseous‬
‭atoms to form one mole of gaseous positively charged ions‬
‭●‬ ‭The electrons lost to form positive ions are always taken from the 4s subshell and‬
‭then the 3d subshell‬
‭Nuclear charge‬ ‭ otal positive charge of all the protons in a nucleus of an atom‬
T
‭Greater nuclear charge = greater attractive force‬

‭Effective nuclear charge‬ ‭The nuclear charge and outer electron experiences‬
‭●‬ ‭Energy required depends on:‬
‭Distance from nucleus‬ ‭Weaker attraction force therefore less effective nuclear charge‬

‭Shielding‬ ‭ illed inner shells weaken the attraction force, more shielding results in less‬
F
‭effective nuclear charge‬
‭-‬ ‭Filled subshells slightly increase shielding‬

‭Spin pair repulsion‬ ‭Paired e‬‭-‬ ‭is slightly easier to remove because its‬‭repelled by its pair‬
‭Nuclear charge‬
‭○‬ ‭Total positive charge of all the protons in a nucleus of an atom‬
‭■‬ ‭Greater nuclear charge = greater attractive force‬
‭●‬ ‭Effective nuclear charge‬
‭○‬ ‭The nuclear charge an outer shell electron experiences‬
‭●‬ ‭1st I.E generally increases across a row due to more protons for the same shielding,‬
‭therefore increase in nuclear charge‬
‭○‬ ‭Some decreases in 1st I.E needed due to shielding from subshells and spin‬
‭pair repulsion‬
‭●‬ ‭1st I.E generally decreases down a group due to less effective nuclear charge from‬
‭an increase in shielding‬
‭●‬ ‭Noble gases have the highest 1st I.E for their period‬
‭○‬ ‭Greatest number of protons in the nucleus and therefore greatest nuclear‬
‭charge for the same shielding‬
‭●‬ ‭Alkali metals have the lowest 1st I.E for their period‬
‭○‬ ‭Lowest number of protons in the nucleus therefore lowest nuclear charge for‬
‭the same shielding‬




‭4‬

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