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ELEMENTS OF LIFE (Atomic Structure (The maximum number of electrons held…
ELEMENTS OF LIFE
Formulae, Equations and Amount of Substance
Definitions
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An isotope is an atom of the same element with a different mass number (due to a different number of neutrons)
Avogadro constant is 6.02x10(23). It is the number of atoms, molecules, ions or particles in 1 mole of any substance
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Relative atomic mass is the average of the various relative isotopic masses of an element to 1/12th of the mass of a carbon-12 atom, taking the abundance of the isotopes into account.
Relative formula/molecular mass are the sum of the relative atomic masses of the various elements in a compound
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Titration Calculations
- Find moles of known substance
- Find the concentration of the unknown substance
- Find moles of unknown substance (using balanced equation)
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Standard Solutions
Standard solutions are solutions containing a precisely known concentration of an element or a substance.
Standard solutions are used to determine the concentrations of other substances, such as solutions in titrations
Atomic Structure
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Fusion Reactions
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This is how certain elements are formed; ie. the fusion of certain isotopes of hydrogen produce helium
Models of the Atom
The Rutherford model suggested that atoms have a small, dense nucleus. This nucleus has a positive charge
In 1909, he conducted an experiment; he fired alpha particles at a thin sheet of gold foil. Most particles went straight through (as expected), whereas others were deflected
The experiment proved that the nucleus was very small as most particles went straight through (only some came into contact with the nucleus). It also proved that the nucleus has a positive charge because it repelled the positively charged alpha particles.
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Bonding and Structure
Types of Bonding
Ionic bonding is the overall attraction in a lattice and is made up of attraction between ions of different charge and repulsion between ions of the same charge
Covalent bonding is the sharing of pairs of electrons. In covalent bonding, there is a balance between the repulsive forces between nuclei and the attractive forces between the nuclei and the electrons.
Dative covalent bonding is covalent bonding in which one pair of bonding electrons come from the same atom
Metallic bonding arises from the electrostatic attraction between positively charged metal ions and the "sea'' of delocalised electrons
Types of Structures
Giant Metallic
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They have generally high melting points (except mercury), are hard but malleable, conduct electricity, and are insoluble in water and non-polar solvents
Giant Ionic
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They have high melting/boiling points, are hard but brittle, conduct when molten/dissolved in water, are often soluble in water and are insoluble in non-polar solvents
Giant Covalent Network
There are strong covalent bonds; the attraction of the nuclei of atoms and shared pairs of electrons
They have very high melting/boiling points, are very hard (if 3D), do not conduct electricity (apart from graphite), and are insoluble in water and non-polar solvents
Simple Molecular
There are weak intermolecular bonds between molecules, but intramolecular covalent bonds
They have typically low melting/boiling points, are soft, do not conduct electricity, are usually insoluble in water and are usually soluble in non-polar solvents
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VESPR Theory
2 electron pairs (bonded or lone) around a central atom gives a linear shape and a bond angle of 180°
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When 1/4 electron pairs is unbonded there is a trigonal pyramidal shape, with a bond angle of 107°
A bent shape arises when either 1/3 of the electron pairs are unbonded (118°) or 2/4 are unbonded (104.5°)
5 bonded pairs around a central atom, the shape is trigonal planar with bond angle of 90° and 120°
1/5 electron pairs are unbonded,it makes a seesaw shape with bond angles of 18-°, 90° and 120°
2/5 electron pairs are unbonded the molecule is T-shaped, with bond angles of slightly less than 90°
3/5 electron pairs are unbonded, the molecule is linear, with bond angles is 180°
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