C1 Atomic Structure

• 4.1.1.1 - Atoms, Elements and Compounds


  • An atom is the smallest part of an element that can exist.
  • An element is a substance made up of atoms which all have the same number of protons in their nucleus
  • Compounds are formed when two or more elements in a chemical reaction chemically combine. They can only be separated by chemical reactions
  • Isotopes are different forms of the same element which have the same number of protons but a different number of neutrons (same atomic number, different mass number)
  • Mass is concentrated inside the nucleus of an atom
• Atoms

  • All substances are made up of atoms
  • Atoms of each element are represented by a chemical symbol e.g. Na represents an atom of sodium
  • The nucleus of an atom contains protons and neutrons and has a positive charge
  • Overall atoms are neutral and have no charge because they have the same number of protons as electrons
• You can say electrons have a relative mass of 0 (very small)

  
• Atomic number tells you the number of protons/electrons

  Mass number tells you the number of protons and neutrons

  
• Isotopes


  • Atoms of the same element can have a different number of neutrons.
  • These atoms are called isotopes of that element and they still have the same number of protons
• Ions


  • Ions are atoms that have lost or gained electrons to achieve a full outer shell
  • Atoms that lose electrons become positive ions (cation)
  • Atoms that gain electrons become negative ions (anion)
• 4.1.1.2 - Mixtures

  • A mixture consists of two or more elements or compounds not chemically combined together
  • No new substances are made and they can be easily separated
  • Mixtures can be separated by physical processes such as:
  • filtration, crystallisation, simple distillation, fractional distillation, chromatography
• 4.1.13 - Development of Atoms

  1. John Dalton describe atoms as tiny solid spheres that cannot be split and are identical
  2. 1897 JJ Thompson discovered atoms had negatively charged particles leading to the plum pudding model (positively charge atoms with negative electrons embedded in it)
  3. 1909 Rutherford did the Alpha Particle Scattering experiment and since some particles deflected backwards he discovered there was a positively charged nucleus in the middle of the atom which had negative electrons surrounding it so most of the atom was empty space
• Development of Atoms Part 2

  1. Niel Bohrs made the nuclear model of the atom which suggested electrons were contained in shells which orbit the nucleus
  2. 20 years later James Chadwick proved neutrons are within the nucleus and the mass of atoms were greater than previously accused for because of the mass of protons as well. Discovered most of the atoms mass is concentrated inside the nucleus
• Plum pudding vs Nuclear model

  
• 4.4.1.6 - Relative Atomic Mass


  • The relative atomic mass (RAM) is an average value that takes into account the abundance (amount) of isotopes of that element
  • Ar can be calculated by the total mass of atoms/total number of atoms or:

  
• • Atoms are very small and have a radius of about 0.1nm (1X10-10m)
  • The radius of a nucleus is less than 1/10000 of the atom
• 4.1.1.7 - Electronic Structure


  • Electrons occupy shells around the nucleus causing the chemistry and reactivity of the atom
  • The lowest energy shells are always filled first (the ones closes ti the nucleus)
  • 1st shell takes 2 electrons
  • 2nd shell takes 8 electrons
  • 3rd shell takes 8 electrons
  • Neon's has 10 protons so its electron configuration is 2,8

  
• 4.1.2.1 - Periodic Table


  • The elements in the periodic table are arranged in order of atomic (proton) number
  • Elements with similar properties are in columns, known as groups.
  • Elements in the same group have the same number of electrons in their outer shell giving them similar chemical properties
  • The table is called a periodic table because similar properties occur at regular intervals.
  • Periods are the horizontal tows which signify the highest energy level an electron in that element occupies/another full outer shell of electrons
• 4.1.2.2 - Development of periodic table

  • Initially elements were arranged by atomic weights and early periodic tables were incomplete with some elements being wrongly placed
  • Dobereiner arranged elements in triads and groups of 3 based on chemical properties
  • Newlands arranged the elements using law of octaves so every 8th element had similar properties however transition metals messed up the rule.
  • Mendeleev ordered the elements by atomic mass and left gaps for undiscovered elements allowing him to predict their properties
• 4.1.2.3 - Metals and non metals


  • Most elements are metals and found at the bottom left of the periodic table. Elements that react to form positive ions are metals
  • Non metals are found at the far top right side of the periodic table and don't form positive ions when they react
  • Properties of metals: strong, malleable, high melting and boiling points, good conductors of heat and electricity, sonorous, ductile
  • Properties of non metals: brittle, bad conductors of electricity, dull, low density
• 4.1.2.4 Group 0 or 8


  • group 0 elements are known as the noble gases and are unreactive
  • don't easily form molecules because of their full outer shell except helium with 2 electrons in it's outer shell
  • boiling points increase as you go down the group since the increase of electrons in each atom leads to more intermolecular forces which are stronger and need more energy to overcome also the atoms get larger
  • properties of noble gases: density and boiling point increases as you go down the group, non flammable and colourless, odourless and tasteless
• 4.1.2.5 - Group 1 elements


  • Group 1 elements are known as the alkali metals and only have 1 electron in their outer shell making them the most reactive elements
  • Form ionic compounds with non metals since they don't need much energy to lose their one outer electron
  • React with water vigorously to produce hydrogen gas and metal hydroxide: sizzle a lot and burn
  • React vigorously with chlorine to form white metal chloride salts
  • React with oxygen to form a metal oxide
  • Reactivity increases as you go down the group
  • Properties: soft with low densities and relatively low melting points
• 4.1.2.6 - Group 7 elements


  • known as the halogens and are non metals with coloured vapours
  • consist of molecules made up of pairs of atoms (diatomic elements)
  • They become less reactive as you go down the group because the more reactive halogens will displace the less reactive ones from an aqueous solution of its salt.
  • Going down group 7:the atoms become larger, the outer shell becomes further from the nucleus, the force of attraction between the nucleus and the outer shell decreases, an outer electron is gained less easily so the halogen becomes less reactive
• Properties of Group 7 elements


  • Fluorine is very reactive, poisonous and a yellow gas
  • Chlorine is fairly reactive, poisonous and a dense green gas
  • Bromine is a dense, poisonous red brown liquid
  • Iodine is a dark grey crystalline solid or a purple vapour
  • Properties of group 7 elements: high melting and boiling points as you go down the group, higher relative atomic mass as you go down group, forms salts when reacting with metal, electrons are easier gained down the group, reactivity decreases down group
• What happens when group 7 elements react with hydrogen

  
• 4.1.3.1 - Transition Metals 


  • Many transition elements have ions with different charges and form brightly coloured compounds
  • Placed in the central block of the periodic table between group 2 and 3
  • Do not show any trends unlike group 1 metals
  • Properties: ions of different charges, form coloured compounds, used as catalysts, ductile, sonorous, shiny
• Compare group 1 and transition metals


  • transition metals have high melting point but group 1 metals have low melting points
  • transition metals are hard while group 1 metals are soft
  • transition metals have a high density while group 1 metals have lower densities
  • transition metals are less reactive than alkali metals such as sodium
  • transition metals they coloured ions of different charges alkali metals don't
  • some transition metals are unreactive (silver and gold) but alkali metals are extremely reactive