Chemistry Paper 1

• Dalton's theory about the atom


  1. Atoms cannot be created, divided or destroyed.

  2. Atoms of the same element are exactly the same and atoms of different elements are different.

  3. Atoms join with other atoms to make new substances.
• The discovery of subatomic particles caused the original Dalton model of an atom to change
• How JJ Thomson discovered the electron

  Thomson experimented with a cathode ray tube.

  The beam moved towards the positively charged plate so he knew that the particles must have a negative charge.
• JJ Thomson's atomic model

  Plum pudding model.

  Negatively charged electrons scattered through a positively charged material.
• What Ernest Rutherford discovered from his gold foil experiment

  He shot a beam of positively charged particles at sheet of gold foil.

  • Most of the particles passed straight through suggesting that atoms were mostly empty space.
  • A few particles were deflected and a few bounced directly back showing that there must be a tiny, dense and positively-charged nucleus.
• Rutherford's new model of the atom

  • Mass is concentrated in the central nucleus.
  • Mostly empty space.
  • Electrons travel in random paths around the nucleus.
• Structure of an atom

  Small central nucleus made up of protons and neutrons.

  Electrons orbit (move around) the nucleus in shells.
• Radius of the nucleus

  The radius of the nucleus is 1x10-14 m.

  This is 1/10000 of the atomic radius.
• Relative masses of protons, neutrons and electrons

  Proton: 1

  Neutron: 1

  Electron: 1/1836
• Relative charges of protons, neutrons and electrons

  Proton: +1

  Neutron: 0

  Electron: -1
• Why atoms contain equal numbers of protons and electrons

  Atoms are stable with no overall charge.

  Protons are positively charged and electrons are negatively charged. For the charges to balance, the number of protons and electrons must be equal.
• The mass of an atom is concentrated in the nucleus
• Atomic number


  The number of protons.
• Mass number


  The number of protons and neutrons found in the nucleus of an atom.
• Atoms of the same element have the same number of protons in the nucleus and this is unique to that element
• Isotope


  Atoms with the same number of protons (so they are the same element) but a different number of neutrons.

  Isotopes of an element have the same atomic number but different mass numbers.
• Why relative atomic mass is not always a whole number

  Different isotopes of the same element have different mass numbers. The relative atomic mass is an average of the masses of all these isotopes.
• Values required to calculate relative atomic mass of chlorine

  Mass numbers and relative abundances of all the isotopes of chlorine.
• How Mendeleev arranged the elements in his periodic table

  Elements arranged with increasing atomic masses.

  Elements with similar properties put into groups (due to periodic trends in chemical properties).

  Switched the position of some elements.

  Gaps left for undiscovered elements.
• How Mendeleev was able to predict the properties of new elements

  Mendeleev left gaps in his periodic table. He used the properties of elements next to these gaps to predict the properties of undiscovered elements.
• Mendeleev's table lacked some amount of accuracy in the way he'd ordered his elements
• How elements are arranged in the modern periodic table

  In order of increasing atomic number.
• Elements in the same group (column) have similar

  Chemical properties
• Why elements in the same column have similar chemical properties

  Same number of outer shell electrons.

  Number of outer shell electrons determines how an atom reacts.
• Elements


  Arranged in the modern periodic table in order of increasing atomic number
• Elements in the same group (column)

  Have similar chemical properties
• Period (row) number


  Tells you that all the elements in that period have the same number of electron shells
• Group (column) number


  Tells you that all the elements in that group have the same number of outer electrons
• Metals are positioned on the left hand side of the periodic table
• What determines whether an element is a metal or non-metal

  Atomic structures of the elements
• Maximum number of electrons allowed in each of the first 3 shells

  • 1st shell: 2

  2nd shell: 8

  3rd shell: 8
• When atoms are most stable


  When they have full electron shells
• Electron configuration of Na (atomic number 11)


  2, 8, 1
• Electron configuration of an element

  Related to its position in the periodic table
• Ionic bond


  A bond between a metal and non-metal involving the transfer of electrons
• Ion


  An atom or group of atoms with a positive or negative charge
• Na+ has the atomic number 11 and the mass number 23. It has 11 protons, 10 electrons, and 12 neutrons.
• O2- has the atomic number 8 and the mass number 16. It has 8 protons, 10 electrons, and 8 neutrons.
• Ions formed by elements in group 1 and 2

  Cations (positive)

  Group 1 metals will form 1+ ions

  Group 2 metals will form 2+ ions
• Ions formed by elements in groups 6 and 7

  Anions (negative)

  Group 6 will form 2- ions

  Group 7 will form 1- ions