2 - Atoms & Isotopes

• the relative charge of a proton is 1+
• the relative charge of a neutron is 0
• the relative charge of an electron is 1-
• the relative mass of a proton is 1
• the relative mass of a neutron is 1
• the relative mass of an electron is 1/1836
• atomic number = number of protons in the nucleus of an atom
• relative atomic mass = protons + neutrons
• the nucleus contains all of the positive charge
• nearly all of the atom's mass is in the nucleus
• the majority of the atom is empty space
• the nucleus is small and dense
• element - a substance made up of only one type of atom
• the number of protons in an atom identifies the element
• the periodic table lists the elements in order of increasing atomic number
• isotopes - atoms of the same element (same number of protons) with different numbers of neutrons (different masses)
• complete the table

  A) 8

  B) 8

  C) 8

  D) 17

  E) 10

  
• can also be written as

  • 16O
  • oxygen-16

  
• why do different isotopes of an element react in the same way?

  • chemical reactions involve the electrons surrounding the nucleus
  • isotopes of the same element have the same number of electrons
  • and the number of neutrons has no effect on the reaction
• positive ions are called cations
• negative ions are called anions
• positive ions have fewer electrons than protons
• negative ions have more electrons than protons
• ions are formed when atoms lose or gain electrons
• complete the table

  A) 12

  B) 12

  C) 10

  D) 2+

  E) -

  F) 17

  G) 18

  H) 18

  I) 1-

  
• why can relative mass not be found by adding together the relative masses of p, n and e?

  there are strong forces holding protons and neutron together which cause a fractional loss of mass
• relative isotopic mass - mass of an atom of an isotope compared to 1/12th of the mass of an atom of carbon-12
• the mass of carbon-12 is defined as 12 atomic mass units (12u)
• 1/12th the mass of carbon 12 = 1u
• 1u is approximately the mass of a proton or a neutron
• complete the table

  A) 12

  B) 14

  C) 16

  D) 19

  E) 12

  F) isotopic

  
• relative isotopic mass is assumed to be the same as the mass number to 1 d.p
• there are no units for relative isotopic mass
• relative atomic mass (Ar) - the weighted mean mass of an atom of an element compared to 1/12th the mass of an atom of carbon-12
• relative atomic mass has no units and is not a whole number
• Ar takes into account the:

  • percentage abundance of each isotope
  • relative isotopic mass of each isotope
• percentage abundances of isotopes and their relative isotopic masses can be found experimentally using a mass spectrometer
• complete the diagram

  A) acceleration area

  B) drift region

  C) ion-detector

  D) time measurement

  E) ionisation area

  F) sample inlet

  G) accelerated

  H) kinetic

  I) Ke = 1/2mv2

  J) mass

  K) slowly

  L) longer

  M) detector

  N) positive

  O) vaporised

  P) ionised

  Q) e-

  R) X+

  S) e-

  
• complete the diagram

  A) 75.78

  B) mass to charge ratio

  C) isotopic

  D) percentage abundance

  
• complete the equation

  A) sum

  B) percentage abundance

  C) isotopic mass

  D) sum

  E) percentage abundance