Chemistry Paper 1

• In an element, all of the atoms are the same.
• Compounds contain two or more different elements chemically combined in fixed proportions.
• In a mixture, we have different elements or compounds, but they're not chemically combined.
• A molecule has any elements chemically combined.
• To separate a compound, a chemical reaction is needed. To separate a mixture, a physical separation technique is needed.
• Examples of physical separation techniques include filtration, crystallisation, distillation or chromatography.
• Filtration is used to separate an insoluble solid from a liquid.
• Insoluble means that the substance cannot be dissolved in water.
• In filtration use a filter funnel, filter paper and a conical flask. Pour the mixture into filter paper. The liquid passes through the tiny pores in the filter paper, scientists noe call this the filtrate. The solid remains in the filter paper and is separated from the liquid.
• Groups in the periodic table

  • 1
  • 2
  • 3
  • 4
  • 5
  • 6
  • 7
  • 0
• Periodic table


  • Metals are on the left of the stepped line
  • Non-metals are on the right of the stepped line
• Chemical formula


  Used to represent an element or compound in balanced chemical equations
• Molecular elements


  Non-metal elements that exist as molecules made up of two atoms joined together
• Compound names

  In compounds made up of non-metal elements only, the second word of the compound's name starts with mon-, di-, or tri- to show the number of atoms of this element for every one atom of the first element in the name
• There are over 100 different elements
• New experimental evidence may lead to a scientific model being changed or replaced
• Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided
• Plum pudding model of the atom

  The atom is a ball of positive charge with negative electrons embedded in it
• Alpha particle scattering experiment

  1. Concluded that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged

  2. This nuclear model replaced the plum pudding model
• Bohr model of the atom

  • Electrons orbit the nucleus at specific distances
  • Theoretical calculations agreed with experimental observations
• Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge
• The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus
• Relative electrical charges of particles in atoms

  • Proton: +1
  • Electron: -1
  • Neutron: 0
• In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge
• Atomic number


  The number of protons in an atom of an element
• All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of protons
• Atom size


  • Radius of about 0.1 nm (1 x 10-10 m)
  • Radius of nucleus is less than 1/10 000 of that of the atom (about 1 x 10-14 m)
• Almost all of the mass of an atom is in the nucleus
• Relative masses of particles

  • Proton: 1
  • Electron: very small
  • Neutron: 1
• Mass number


  The sum of the protons and neutrons in an atom
• Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element
• Relative atomic mass


  An average value that takes account of the abundance of the isotopes of the element
• Electronic structure of an atom


  • Electrons occupy the lowest available energy levels (innermost available shells)
  • Can be represented by numbers or by a diagram
• Periodic table


  • Elements are arranged in order of atomic (proton) number
  • Elements with similar properties are in columns, known as groups
  • Similar properties occur at regular intervals
• Group in periodic table

  • Elements have the same number of electrons in their outer shell (outer electrons)
  • This gives them similar chemical properties
• Before the discovery of protons, neutrons and electrons, scientists attempted to classify the elements by arranging them in order of their atomic weights
• The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed
• Mendeleev's periodic table


  • Left gaps for elements that had not been discovered
  • Changed the order based on atomic weights in some places
• Elements with properties predicted by Mendeleev were discovered and filled the gaps. Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct
• Metals


  Elements that react to form positive ions