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2 Atomic Structure
 

2 Atomic Structure

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    2 Atomic Structure 2 Atomic Structure Presentation Transcript

    • 2 Atomic Structure
    • Properties of subatomic particles Outside nucleus 0 -1 Electron nucleus 1 0 Neutron nucleus 1 +1 Proton Location Relative mass(amu) Relative charge Name
    • Terminology for the Atom
      • Atomic no (Z): no of protons
      • Mass No (A): no of protons + no of neutrons
      • Isoptopes: atoms of the same number of protons (the same element) but different numbers of neutrons
      • Atomic mass unit: 1/12 the mass of a carbon-12 atom. The mass of a carbon-12 atom is defined as exactly 12 atomic mass units
      • Atomic mass: the average of the masses of an elements naturally occurring isotopes weighted to their abundances
    • Isotope Calculations
      • Boron has 2 isotopes 10 B and 11 B. They are present in naturally occurring boron respectively at 18.7% and 81.3%. Calculate the relative atomic mass of boron.
      Ar = (18.7 x 10) + (81.3 x 11) 100 = 10.8
      • The element copper has relative atomic mass 63.55 and contains atoms with mass numbers 63 and 65. What is the percentage composition of a normal isotope of copper?
      65x + ((100-x) x 63) = 63.55 100 65x + 6300 – 63x = 6355 2x = 6355-6300 x = 27.5% 100 – x = 72.5% % composition = 27.5% 65Cu 72.5% 63Cu
    •  
    • Bonding Terminology
      • Ionic compounds: form when an atom of one element transfers electrons to an atom of another element
      • Covalent compounds: form when two atoms share electrons
      • Ion: a charged particle
      • Cation: a positively charged particle
      • Anion: a negatively charged particle
      • Monoatomic ion: an ion composed of a single aton
      • Polyatomic ion: two or more atoms bonded covalently and having net positive or negative charge e.g. NH 4 + , SO 4 2-
    • Electronic Configuration
      • Electrons are present in shells around the nucleus
      • The first shell can hold 2 electrons, the second 8 and the third 18
      • The no of outer shell electrons is the same as the group no
      • Find the electronic configuration of sodium
      Na atomic no = 11  there are 11 protons and 11 electrons Electronic Configuration is 2,8,1 Find the electronic configuration of chlorine Cl atomic no = 17  there are 17 protons and 17 electrons Electronic configuration is 2,8,7
    • Compounds
      • Ionic compounds are formed between a metal and a non metal e.g. magnesium chloride
      • Covalent compounds are formed between two or more non-metals e.g ammonia (NH 3 )
    • Formation of Covalent Bonds Drawing dot and cross diagrams
      • Only outer shell electrons are shown
      • Dots and crosses used to distinguish electrons from different atoms
    • x o o o o o o o x o o o o o o o H Cl HCl Formation of HCl
      • Draw dot and cross diagrams for methane (CH 4 ), ammonia (NH 3 ) and nitrogen N 2 and carbon dioxide (CO 2 )
      • Elements in Group 1 form unipositive cations e.g. Na +
      • Elements in Group 2 form dipositive cations e.g. Mg 2+
      • Elements in Group 3 form tripositive cations e.g. Al 3+
      • Elements in Group 7 form uninegative anions e.g. Cl -1
      • Elements in Group 6 form dinegative anions e.g. O 2-
      Formation of ionic bonds
      • Na Cl
      x o o o o o o o Na + + Cl - NaCl
      • Mg F
      x x o o F o o Mg 2+ + 2F - MgF 2 o o o o o o o o o o
      • Draw diagrams to represent the ionic bonding for aluminium iodide and sodium oxide
    • Properties of Ionic Compounds
      • High mp/bp
      • Conduct electricity when molten or in aqueous solution
      • Dissolve in polar solvents (eg water)
      • Hard and brittle
      • React readily with each other in solution
    • Covalent Compounds & Structures
      • Covalent compounds may be classed as simple e.g water, ammonia, chlorine, sulphur dioxide, carbon dioxide
      • or as giant e.g. silicon dioxide (sand) diamond, graphite
      • Simple covalent compounds are small molecules held together by Van der Waals forces only
      • Giant covalent structures are giant lattices where every atom is covalently bonded to many atoms
    • Diamond Structure
    • Properties of Simple Covalent Compounds
      • Low mp/bp
      • Non conducting
      • Soluble in non-polar solvents
      • Solids are soft
    • Properties of Giant Covalent Structures
      • High mp/bp
      • Non-conducting (except graphite and some semiconductors e.g. silicon dioxide)
      • Non-soluble
      • Hard (except graphite)