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Topic 1 A Level Chemistry Edxcel Atomic Structure

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Published in: Chemistry
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Here we will discuss about the A level chemistry , atomic structure electrons , protons and neutrons

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  1. EARN CHEMISTRY WITH BABAR A LEV L CHEMISTRY TOPIC I EDXCEL ATOM C STRUCTURE
  2. ATOAAC STRUCTURE SUBATOÅVÅÅC Subatomic Particle Protons (P) Neutrons (n) Electrons (e-) Relative Charge +1 Relative Mass/ a.m.u 1 1 1/1840
  3. PROTONS, NEUTRONS ANO ELECTRONS Mass concentrated within the centre, nucleus An atom is electrically neutral; = e Atomic number or proton number (Z) = no. of protons Atomic mass or nucleon no. (A) = no. of P + N Nucleon number Il Proton number
  4. @ Isoelectronic Ions: ions having the same no. of e-s @ Isotopes are atoms of the same element with the same proton number but different numbers of neutrons • Isotopes have similar chemical properties since they have the same number of protons and electrons (so chemical interactions are similar) • Isotopes have different physical properties since they have different numbers of neutrons, causing them to have different masses and, therefore, different physical interactions.
  5. BEHAVPOUR OF A OF SUBATOMÅC Protons: positively charged . deflected to - ve pole Neutrons: no charge . not deflected Electrons: negatively charged . deflected to +ve pole e- lighter than .. deflected at greater angle
  6. ELECTRONUC CONFACURATAON Electrons are arranged in energy levels called shells Each shell is described by a principle quantum no. (P.Q) As the P.Q. increases, the energy of the shell increases @ Inside the shell, there are subshells: s, p, ds, p, d and ff Orbital: region in space where there is a maximum probability of finding an electron
  7. Each orbital can hold 2e-s in opposite directions When es are placed in a set of orbital of equal energy, they occupy them singly, and then pairing takes place e-s placed in the opposite direction: both -ve charge & if placed in the same direction, they'd repel. In the opposite direction, they create a spin to reduce repulsion Completely filled or half-filled (i.e. one e- in each orbital) are more stable (reduced repulsion) Examples of this Method are Shown Below: o In certain cases (e.g., period 3 elements), an electron would prefer the 4s orbital over 3d while filling up. For example, 2 electrons in Titanium would be filled into the 4s orbital before 2 electrons are filled in the 3d orbital. This is because the 4s orbital is a more stable (lower) energy level than the 3d orbital. However, while losing electrons, the electrons from the 4s orbital would be lost first, and then those from the 3d orbital would be lost. This is because the 4s orbital is outer than the 3d orbital.
  8. SIJBS#EUS Aufbau's Principle: method of showing how atomic orbitals are filled in a definite order to give the lowest energy arrangement possible Energy difference between 4s4s & 3d3d very small an e- from 4s4s can be promoted to half-fill or full-fill 3d3d orbital to make the atom more stable When filling, fill 4s before 3d and when removing, also remove first from 4s
  9. OGATA" @ s orbitals are spherical, with the nucleus at the centre p orbitals are dumbell-shaped A free radical is a species with one or more unpaired electrons. @ Note: ions and free radicals are different. s orbital Node Node The point where an electron cannot be located. More nodes, higher energy. p Orbitals pz
  10. PONASATAON 1st I.E: the energy needed to remove 1 mole of e-s from 1 mole of a gaseous atom to form 1 mole of unipositive ions Each Successive I.E is higher than the previous one because as e-s are removed, protons > e-s the attraction between protons and remaining electrons increases Successive I.Es have a large jump in their value when e-s removed from the lower energy shell Deduce group no. by checking when 1st big jump occurs
  11. FACTORS OONASATÅON Nuclear Charge • +ve charge due to protons in the nucleus Greater nuclear charge means greater ionization energy Shielding Effect • Inner shells of es repel outermost es, thus shielding them from the +ve nucleus. The more e- shells, the greater is the shielding effect Greater effect lower I.E because lesser attractive force between nucleus & outer es Atomic Radius Distance from the centre of the nucleus to the outermost orbit As the number of electron shells increases, the atomic radius increases As the number of electrons in the outermost shell increases, the atomic radius decreases as the electrostatic attraction between the nucleus and outer electrons increases Greater radius lower I.E; a distance of outermost e- to the nucleus is large less energy needed to remove e- Stable Configuration High I.E needed to remove e-s from completely or half-filled orbitals
  12. AONASATAON TRENDS Down a group (decreases): • New shells added • Attraction of nucleus to valence e-s decreases • Shielding effect increases Across a period (increases): • Shell number remains the same • Proton number increases • Effective nuclear charge increases • Atomic radius decreases
  13. ACROSS @ I.E of Al lower than Mg: e- removed in Al is from higher energy 3p orbital which is further away from nucleus than 3s e- being removed from Mg. Nuclear attraction is less for 3p than 3s I.E of Al is lower than Mg @ I.E of S lower than P: e- being removed in P is in a half filled, more stable 3p orbital whereas in S, the pairing of electrons in 3p results in increased repulsion less energy need to remove an e-
  14. Ionic Radius: describes the size of an ion Positive Ion: smaller radius than original neutral atom because shell no. decreases, the screening effect decreases, but the attraction of the nucleus increases. Negative Ion: larger ionic radius than neutral atom because e-s added while nuclear charge remains same Groupsl to 35 to 710nPositiveNegativeNo. of shells n Across the period: Proton no. and effective nuclear charge increases Ionic radius decreases Negative ions are always larger than positive ions in the same period as they have one more shell Ionic radius increases down the group since the number of electron shells increases. As the negative charge on anion increases, the ionic radius increases since the number of electrons gained increases such that the number of electrons exceeds the number of protons. As the positive charge on the cation increases, the number of electrons lost increases, so the electrostatic attraction between the nucleus and outer electrons increases.

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