Chemistry P1 - C1

• All substances are made of atoms. An atom is the smallest part of an element that can exist.
• Elements are made of only one type of atom.
• Compounds are substances that are made up of two or more elements chemically bonded together.
• A mixture consists of two or more elements or compounds not chemically bonded together.
• Isotope is an atom with the same number of protons but different number of neutrons.
• Mixtures can be separated by physical processes including:

  • Filtration
  • Crystallisation
  • Simple distillation
  • Fractional distillation
  • Chromatography

  These physical processes do not involve chemical reactions and no new substances are made.
• The atomic number tells you the number of protons an atom has of an element.
• Atoms are very small, having a radius of about 0.1 nm (1 x 10-10 m).
• The mass number tells you the sum of the number of protons and neutrons.
• To calculate the number of neutrons = Mass Number – Atomic Number
• Relative masses of protons, neutrons and electrons:

  Protons - 1

  Neutrons - 1

  Electrons - 0
• An ion is a charged particle that has gained or lost electrons.
• The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element.
• Equation for the relative atomic mass:

  (% of isotope 1 × mass of isotope 1) + (% of isotope 2 × mass of isotope 2) ÷ 100
• In the periodic table, the elements are arranged in order of increasing atomic number.
• Elements with similar properties are in columns, known as groups. The group number tells you the number of electrons there are in the outer shell.
• The rows in the table are called periods. The periods tell you how many shells there are.
• It is called a periodic table because similar properties occur at regular intervals.
• The elements can be divided into metals and non-metals.

  Elements that react to form positive ions are metals.

  Elements that do not form positive ions are non-metals.
• Differences between metals and non-metals:

  Metals: dense, shiny, malleable, good conductors of heat and electricity

  Non-metals: low density, dull, brittle, poor conductors of heat and electricity
• Noble gases (Group 0):

  • unreactive because their atoms have stable arrangements of electrons – they have full outer shells.
  • boiling points increase as you go down the group with increasing relative atomic mass
• Alkali metals (Group 1):

  • low melting and boiling points
  • reactivity increases as you go down the group because the outer electron is further from the shells so there is less attraction between the nucleus and outer electron which makes the atom lose an electron more easily.
• Solid sphere model (tiny spheres that could not be divided) - John Dalton, 1803
• Plum pudding model (ball of positive charge with negative electrons embedded in it) - J.J Thomson discovered electrons, 1904
• Nuclear model - Ernest Rutherford discovered the nucleus, 1911

  • mass of an atom is concentrated at its centre, the nucleus
  • nucleus is positively charged
• Niels Bohr discovered protons, 1914

  • suggested that electrons orbit the nucleus in shells.
  • shells are at certain distances from the nucleus.
• James Chadwick discovered neutrons, 1932

  • found evidence for the existence of particles in the nucleus with mass but no charge.
• Alkalis reacting with water:

  Lithium + water = lithium hydroxide + hydrogen

  Sodium + water = sodium hydroxide + hydrogen

  Potassium + water = potassium hydroxide + hydrogen
• Lithium reaction with water, oxygen, chlorine:

  • Water -
  • Oxygen -
  • Chlorine -
• sodium reaction with water, oxygen, chlorine:

  • Water -
  • Oxygen -
  • Chlorine -
• potassium reaction with water, oxygen, chlorine:

  • Water -
  • Oxygen -
  • Chlorine -
• Development of the periodic table:

  John Dalton published a table of elements that were arranged in order of their atomic weights - 1808

  John Newlands published the law of octaves, table was incomplete and elements were placed in inappropriate groups. - 1864

  Dmitri Mendeleev overcame Dalton’s problem by leaving gaps for the elements that he thought had not been discovered and in some places changed the order based on atomic weight. - 1869
• Halogens (Group 7):

  • reactivity of the elements decreases going down the group
  • low melting and boiling points which increase down the group
  • diatomic (molecules made of pairs of atoms)
  • when non-metals react, form covalent bonds (shared electrons)
• Displacement reaction - A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.

  e.g chorine + potassium bromide = potassium chloride + bromine