Atomic Structure

• All substances are made of atoms. An atom is the smallest part of an element that can exist. Atoms of each element are represented by a chemical symbol for example the symbol for magnesium is Mg.
• The law of conservation of mass says that no atoms are lost or made during a chemical reaction. This means that the mass of the products equals the mass of the reactants, so symbol equations must be balanced.
• Compounds are formed from elements by chemical reactions. Compounds contain two or more elements chemically bonded together. They can be separated into elements by chemical reactions.
• A mixture consists of two or more elements or compounds not chemically joined together. This means that they still have the same chemical properties and they can be separated using different separation techniques. These techniques include filtration, crystallisation, distillation, fractional distillation and chromatography. These techniques do not involve chemical reactions.
• This is a separation technique to separate a soluble substance from a solvent. For example it can be used to separate salt from water or other substances that have dissolved. It involves adding the solution to an evaporating dish and heating it with a Bunsen Burner to get the water to evaporate. Heating is stopped when crystals form and the rest of the water is left to then evaporate at room temperature. To heat the salt more gently you can use a water bath which involves placing the evaporating dish on a beaker of water that is being heated with a Bunsen Burner.
• This is a separation technique to separate an insoluble substance from a solvent. For example it can be used to separate sand from water or other solids that have not dissolved. It involves a funnel and filter paper and pouring the solution through the filter paper. The insoluble substance collects on the filter paper and this can then be washed and dried.
• This is a separation technique to separate a mixture of miscible liquids such as ethanol and water that have different boiling points. It involves adding the mixture to round bottom flask connected fractionating column that usually contains glass beads. This is then fitted to a condenser. The mixture is then heated with a Bunsen Burner to get the liquids to evaporate. The substance with a higher boiling point will condense more readily and fall back into the solution, while the substance with the lower boiling point will rise up the column and into the condenser.
• Chromatography


  A separation technique to separate different soluble substances from each other
• Use of chromatography


  • Separate food colourings
• Chromatography process

  1. Get a piece of chromatography paper

  2. Draw an origin line in pencil

  3. Add a spot of the substance to be separated to the origin line

  4. Place the paper in a solvent with the origin line above the solvent

  5. Solvent moves up the chromatography paper

  6. Substance dissolves into the solvent

  7. More soluble substances move further up the paper

  8. Substances with different solubilities move up the paper different amounts, separating them
• The more soluble the substance, the further up the paper it moves
• Different substances have different solubilities, so they move up the paper different amounts and are separated
• Dalton suggested that atoms were tiny spheres that could not be divided. JJ Thompson then discovered the electron. He also suggested the Plum Pudding model. This was the idea that the atom was a ball of positive charge with negative electrons embedded in it.
• Due to results from the alpha scattering experiment, the nuclear model of the atom was suggested. Discovered the electron. Suggested the Plum Pudding Model. This was the idea that the atom was a ball of positive charge with negative electrons embedded in it. Niels Bohr then adapted this model by suggesting that electrons orbit the nucleus at specific distances. James Chadwick proved the existence of neutrons.
• Number of protons and neutrons an atom has. It is an average value that takes into account the abundance of the isotopes.
• Atomic number is the number of protons an atom has.
• An ion is when an atom has lost or gained electrons and so has a charge.
• Isotopes are atoms of the same element with the same number of protons but different number of neutrons.
• Reactants are what go into a chemical reaction while products are what are made. For example in the word equations hydrogen + oxygen = water, hydrogen and oxygen are the reactants and water is the product.
• The electrons in an atom occupy the lowest available energy levels. The electronic structure of an atom can be represented by numbers or by a diagram. 2 electrons fill the first shell and 8 fill shells after that.
• State Symbols:

  • solid (s)
  • liquid (l)
  • gas (g)
  • aqueous/solution (aq)
• Elements are made up of just one type of atom. In the periodic table there are about 100 different elements.
• All substances are made of atoms. An atom is the smallest part of an element that can exist.
• Atoms of each element are represented by a chemical symbol, eg O represents an atom of oxygen, Na represents an atom of sodium.
• There are about 100 different elements. Elements are shown in the periodic table.
• Compounds are formed from elements by chemical reactions
• Chemical reactions always involve the formation of one or more new substances, and often involve a detectable energy change.
• Compounds contain two or more elements chemically combined in fixed proportions and can be represented by formulae using the symbols of the atoms from which they were formed. Compounds can only be separated into elements by chemical reactions.
• Chemical reactions can be represented by word equations or equations using symbols and formulae.
• A mixture consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged.
• 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.
• The discovery of the electron led to the plum pudding model of the atom. The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it.
• The results from the alpha particle scattering experiment led to the conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged. This nuclear model replaced the plum pudding model.
• Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. The theoretical calculations of Bohr 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 name proton was given to these particles
• The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific idea.
• What are the relative charges of each subatomic particle?

  A) +1

  B) 0

  C) -1

  
• In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
• The number of protons in an atom of an element is its atomic number. All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of protons.