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C2 (1) (Investigating Atoms (Changed Ideas (All matter consists of…
C2 (1)
Investigating Atoms
Changed Ideas
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Atom
Greek suggested atoms, John Dalton revived it(19th century)
Electron(1897), Nucleus(1909), Electrons orbit the Nucleus(Rutherford in 1911), Protons(1919, Neutrons(1932)
Discovering the Nucleus
Rutherford's tam fired a-particles at gold foil. Most went straight through showing gold atoms are mostly empty space. some deflected showing that there was something bouncing the a-particles back(nucleus)
Mass number of Isotopes
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Dating with Isotopes
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From decaying isotopes, scientist can work out the age of remains such as mummies
Compounds and Mixtures
Relative Formula Mass
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Atoms and molecules are far too small to be counted(measured by the atomic or formula mass in grams a mole)
Complicated Formulae
A group of atoms sometimes has a set of brackets round it, and a subscript number outside the bracket,.You need to take this into account when working out the relative molecular mass
Electronic Structure
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Noble Gas Structures
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When atoms combine to make a compound, their outer electrons are shared(Noble gas electronic configuration)
Ionic Bonding
What is it?
When a metal reacts with a non-metal the metal atoms electrons and become positive ions, the non-metal atom gain electrons and become negative ions
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Conducting Electricity
Ionic compounds can conduct electricity, but only if the ions are free to carry the electric current. Solid sodium chloride does not conduct as the ions cannot move; dissolved water or molten, it can conduct electricity. This suggests the bonding is ionic
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Halogens
Halogens
fluorine(F, pale yellow poisonous gas)
chlorine(Cl, green poisonous gas)
bromine(Br, dark orange-red poisonous liquid that easily vaporises)
iodine(I, a dark grey solid which on heating becomes a purple gas)
Reactive elements, Unreactive compounds
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Ionic Lattices
Electronic Structures
Solid Sodium Chloride forms an ionic lattice that is very strong(the oppositely charged ions attracted equally causing each Chloride ion being attracted to six sodium ions)
Melting and boiling points are high, as it is hard to separate ions from each other(ionic lattices =500C boiling points)
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Multi-Atom ion
Many negative ions are not single atoms that have lost electrons to become ions, but several non-metal atoms that are covalently bonded together, and have gained electrons as well
One non-metal ion as a positive charge, ammonium ion(NH4+-)
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Covalent Molecules
Properties
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Whilst ionic compounds can dissolve in water, covalent compounds do not
Covalent bonds are very strong (only exist between atoms in molecules). Intermolecular forces (attractions between the molecules) are weak so are easily broken(colvalent molecules have low melting and boiling points)
Water is Odd
Water molecules have a high melting and boiling point but a very low molecular mass which means they should be a gas at room temperature
Covalent Lattices
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Graphite's Properties
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Each layer is only attracted to one above through weak intermolecular attractions(soft and slippery)