chemistry note : atomic structure and periodic table

atomic number: number of protons in its nucleus

mass number : number of protons and neutrons in the nucleus

isotopes : atoms of the same elements with same atomic number but different mass number

relative atomic mass : weighted average mass of an atom of an element relative to 1/12 the mass of a C-12 atom

relative isotopic mass : mass of an atom of an isotope relative to 1/12 the mass of an C-12 atom

relative molecular mass : sum of the atomic masses of all the atoms in its molecular formula

the mass spectrometer
  1. the sample is injected into the mass spectrometer and first vaporised.
  2. the vapour is bombarded with high-energy electrons, which knock electron off atoms in the sample, forming positive ions.
  3. the ions are accelerated by an electric field.
  4. they pass through velocity selector, that make sure they are all travelling with same velocity.
  5. ions enter a uniform magnetic field. ion that is heavier, and with smaller positive charge will deflect less. ion that is lighter, and with bigger positive charge will deflect more.
ionization energy: energy needed to remove one electron from each atom in one mole of gaseous atoms to form one mole of singly positively charged gaseous ions.

factors affecting the i.e :
atomic radius (smaller, higher)
nuclear charge (higher, higher)
electron shielding (by inner electron)

second ionization energy: the energy required to remove 1 mole of electron from 1 mole of singly 1+ charged gaseous ions to form 1 mole of 2+ charged gaseous ions.

evidence of existence of the shell : difference in energy level ( in graph of i.e against number of electron removed) : big jump

*first ionization energy is the lowest because the electron is the furthest from the nucleus

*ionization energy generally increase across the period (but slightly decreased between Beryllium-Boron, Nitrogen-Oxygen, Magnesium-Aluminium, Phosphorus-Sulfur)

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