Atomic structure and isotopes

• proton relative charge and mass

  +1 1
• neutron relative charge and mass

  0. 1
• electron relative charge and mass

  -1. 1/1836
• what does the nucleus of an atom contain ?

  neutrons and protons
• what is the charge of the nucleus ?

  positive due to the protons
• where are electrons in an atom an dhow is an atom held together ?

  • Negatively charged electrons orbit the nucleus of the atom, contributing very little to its overall mass, but creating a ‘cloud’ of negative charge
  • The electrostatic attraction between the positive nucleus and negatively charged electrons orbiting around it is what holds an atom together
• what charge does an atom have ?

  an atom is neutral
• what are ions ?

  • Ions on the other hand are formed when atoms either gain or lose electrons, causing them to become charged
• what is the number of subatomic particles determined by ?

  The number of subatomic particles in atoms and ions can be determined given their atomic (proton) number, mass (nucleon) number and charge
• what determines what element and atom or ion is ?

  its atomic number
• number of protons =

  the atomic number
• the number of protons of an unknown element can be calculated by:

  Number of protons = mass number - number of neutrons
• atoms have the same number of ...

  protons and electrons
• describe the loss and gain of electrons to form ions

  Ions have a different number of electrons to their atomic number depending on their charge

  • A positively charged ion, or cation,  has lost electrons and therefore has fewer electrons than protons
  • A negatively charged ion, or anion, has gained electrons and therefore has more electrons than protons
• how can you find the number of neutrons from mass and atomic numbers

  Number of neutrons = mass number (A) - number of protons (Z)
• what are isotopes ?

  • Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons
• what is the symbol for an isotope ?

  • The symbol for an isotope is the chemical symbol (or word) followed by a dash and then the mass number
  • E.g. carbon-12 and carbon-14 are isotopes of carbon containing 6 and 8 neutrons respectively
• Isotopes have the same chemical properties but different physical properties
• why do isotopes have the same chemical properties ?

  • Isotopes of the same element display the same chemical characteristics
  • This is because they have the same number of electrons in their outer shells
  • Electrons take part in chemical reactions and therefore determine the chemistry of an atom
• why do isotopes have different physical properties ?

  • The only difference between isotopes is the number of neutrons
  • Since these are neutral subatomic particles, they only add mass to the atom
  • As a result of this, isotopes have different physical properties such as small differences in their mass and density
• what is the international standard used for relative mass and and the mass ?

  • The relative mass of an atom uses the carbon-12 isotope as the international standard 
  • One atom of carbon-12 has an accepted mass of 1.992646538 x 10-26 kg
• what is relative isotopic mass ?

  the mass of an isotope relative to  of a carbon-12 atom
• what is the relative atomic mass of?

  • The relative atomic mass is the weighted mean / average mass of an atom relative to  of the mass of a carbon-12 atom