Atomic structure

• History of atom order + anagram

  Dalton, Thomson, Rutherford, Bohr, Modern

  do try reading both magazines
• History of the atom: Dalton

  Dalton proposed that all atom of one element are the

  same and that atoms of one element are different from the atoms of another element. Atoms in his model were tiny and indivisible.
• History of the atom: Thomson

  Thomson discovered the first sub-atomic particle

  — the electron. Thomson proposed the plum pudding model where negatively charged electrons move in a 'sea' of charge in a positively charged atom.
• History of the atom: Rutherford

  Rutherford carried out experiments to find that most of the mass of an atom is concentrated in the centre, where negatively charged electrons orbit the central positively charged nucleus. The positive and negative charges balance to make the atom neutral.
• History of the atom: Bohr

  Bohr suggested that electrons orbit the nucleus on paths. Bohr's planetary model provided an explanation for the difference in energy of electrons at different distances from the nucleus.
• History of the atom: modern

  The modern-day model of the atom states that it is composed of sub-atomic particles - protons, neutrons, and electrons. Protons and neutrons are found in the nucleus and are themselves made up of smaller particles, whereas electrons orbit the nucleus.
• relative mass of protons, neutrons and electrons

  1 , 1 , 1/1840
• Definition of isotope

  Atoms with the same number of protons and

  a different number of neutrons.
• Do isotopes react differently

  Isotopes of the same element have the same electronic configuration so react in the same way in chemical reactions.
• Why is apparatus kept under vacuum in time of flight mass spectrometry

  to prevent ions from colliding with molecules from the air.
• 5 stages of time of flight mass spectrometry

  ionisation

  acceleration

  ion drift

  detection

  data analysis
• Explain ionisation in time of flight

  the sample is dissolved in a volatilesolvent and ejected as tinydroplets through a hollowneedle. The needle is connected to a positive terminalof a high voltage supply. This produces tiny positively charged droplets as the atoms in the sample lose an electron, and the solvent evaporates
• Explain acceleration in time of flight

  positive ions are accelerated towards a negatively charged plate to give all ions constant kinetic energy.

  Therefore, the velocity of each ion will depend on its mass. Lighter and more highly charged ions will accelerate more
• Explain ion drift in time of flight

  ions pass through a hole in the negative plate, forming a beam which travels along the flight tube to a detector
• Explain detection in time of flight

  the positive ion picks up an electron which causes a current to flow. Flight times are recorded
• Explain data analysis in time of flight

  the signal from the detector passes to a computer which generates a mass spectrum
• relative atomic mass equation

  Sum of (isotope abundance x isotope mass number) / sum of abundances of all the isotopes
• How many electrons does each shell hold

  2n^2

  where n is the principal quantum number
• What are atomic orbitals?

  regions in space where electrons may be found. Each shell is composed of one or more orbitals and each orbital can hold one pair of electrons
• what are the four types of orbitals

  s-orbitals : spherical and can hold up to two electrons

  p-orbitals : three-dimensional dumbbell shape and can hold up to two electrons each, but they always come in groups of three of the same energy

  d-orbitals : more complex in shape. d-orbitals can hold up to two electrons each, but they always come in groups of five of the same energy.
• the spin of an electron is either

  up or down

  For two electrons in the same orbital, the spins must be opposite to minimise the repulsion
• energy levels

  The lowest energy levels correspond to s-orbitals as they are closest to the nucleus. The highest energy levels correspond to f-orbitals as they are the furthest from the nucleus.

  Note that 4s is lower in energy than 3d, so 4s will fill first.
• Electron configuration is represented by a specific

  notation

  nxy

  n principal quantum number

  x type of orbital, e.g. s, p, d, f

  y number of electrons in the orbitals of the subshell
• shorthand notation

  the noblegas that comes before the desired element is written in square brackets and then the electrons that come after are written using the general notation.

  For example, potassium has 19 electrons. The full electron configuration is written as: 1s22s22p63s23p64s1

  The electronic configuration of potassium can be simplified using the shorthand notation:[Ar]4s1
• S orbital holds ___ electrons

  2 electrons
• p orbitals holds ____ electrons

  6 electrons
• s block

  groups 1 and 2 on the periodic table
• p block

  groups 13-18
• d block

  Groups 3-12, transition metals
• explain how time of flight mass spectrometry works (5 marks)

  The sample is ionised.(ELECTROSPRAY IONISATION) By forming positive ions and electrons.

  The positive ions are then accelerated. towards a negatively charged plate.

  The ions accelerate by different magnitudes depending on their mass to charge ratio. Lighter or more highly charged ions accelerate more.

  The ions enter the flight tube, where they separate due to different speeds.

  The ions are detected at different times depending on their time of flight (current is produced and sent to computernto produce mass spectra).
• Define the term relative atomic mass

  The relative atomic mass of an element is the average mass of its atoms, compared to 1/12th the mass of a carbon-12 atom
• Define the term relative isotopic mass

  the mass of an atom of an isotope of an element measured on scale on which the mass of an atom of carbon-12 is exactly 12.
• relative molecular mass

  the average mass of a molecule when measured on scale on which the mass of an atom of carbon 12 is exactly 12.
• Define ionisation energy

  the minimum amount of energy required to remove 1 mole of electrons from 1 mole of atoms in a gaseous state
• shielding ionisation energy

  the more shells between the nucleus and the electron, the less energy needed to remove it.
• atomic size ionisation energy

  the bigger the atom the further the electrons are from the nucleus. Outer electrons from larger electrons are easier to remove.
• nuclear charge

  The more protons there are in the nucleus, the more positively charged the nucleus is and the stronger the attraction for the electrons
• Ionisation energy going down a group

  decreases

  atomic radius increases / distance from nucleus increases so less energy required to remove electron from outer shell.

  shielding increases as we go down a group - reduces energy required to remove outer electrons
• ionisation energy across a period

  increases

  increasing number of protons

  shielding is similar (marginal decrease)

  more energy required to remove electron
• Give three reasons why particles must be ionised before being analysed in a mass spectrometer.

  to allow ions to be accelerated (by an electric field), deflected and detected.