2.1.1 & 2.1.2 - atomic structure and equations

• Daltons atomic theory says that

  atoms are tiny particles made of elements

  atoms cannot be divided

  all the atoms in an element are the same

  atoms of one element are different to those of other elements
• The plum pudding model explains that atoms are made up of negative electrons moving around in a sea of positive charge
• After the gold leaf experiment, Rutherford proposed:

  most of the mass and positive charge of the atom is in the nucleus

  electrons orbit the nucleus

  most of atoms volume is the space between nucleus and the electrons

  overall positive and negative charges must balance
• The current model of the atom explains:

  protons and neutrons are found in the nucleus

  electrons orbit in shells

  nucleus is tiny compared to total volume of atom

  most of atoms mass is in the nucleus

  most of the atom is empty space between nucleus and electrons
• Charge of a proton +1

  charge of a neutron 0

  charge of an electron -1
• Proton and neutron both have a mass of 1
• Mass of electron is 1/1800
• Atomic number of an element tells us how many protons are in an atom
• Mass number = number of protons + number of neutrons
• An isotope is an atom of the same element with the same number of protons but a different Number of neutrons
• Different isotpes still react in the same way as neutrons have no impact on chemical reactivity. reactions invoolve electrons and isotopes still have the same number of electrons in the same arrangement
• When electrons are gained the ion is negative

  when electrons are lost the ion is positive
• Relative atomic mass is the mean mass of an atom of an element compared to an atom of carbon-12 where on a scale carbon-12 is exactly 12.
• Relative isotopic mass is the mass of an atom of an isotope compared to the mass of carbon-12 where on a scale carbon-12 is exactly 12.
• The relative isotopic mass is the same as the mass number
• When calculating the mass number

  contribution of the electron is neglected

  mass of both proton and neutron is taken as 1.0
• Mass spectrometry is used to identify unknown compounds.

  Find relative abundance of each isotope of an element.

  Determine structural information.
• The group number in the periodic table relates to the number of electrons in the outer shell.
• Metals usually lose electrons.

  Non-metals usually gain electrons.
• Beryllium, boron, carbon and silicon don’t tend to form ions because it requires a lot of energy to transfer the outer shell electrons.
• Molecular ions are covalently bonded atoms that lose or gain electrons.

  eg) ammonium with a + charge
• Nitrates have a - charge ( NO3- )
• Hydroxides have a - charge ( OH- )
• Sulfate ions have a 2- charge ( SO4 2- )
• To calculate empirical formula:

  divide the amount of each element by its mr

  divide the answers by the smallest value obtained

  if there is a decimal, multiple by a suitable number to make it a whole number.
• What is relative atomic mass?

  weighted mean mass of an atom compared to 1/12th the mass of carbon-12