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29 Cards in this Set
- Front
- Back
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What is a discrete molecule ? |
A discrete (simple) molecule is an electrically neutral group of two or more atoms held together by chemical bonds |
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What 2 types of bonding can be represented by dot and cross ? |
Polar covalent and covalent |
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How is a native covalent bond formed ? |
A native covalent bond forms when an empty orbital overlaps with an orbital containing a lone pair of electrons |
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What are dative bonds often represented by ? |
An arrow starting at the atom providing the electrons |
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What is the electron pair repulsion theory ? |
The shape of a molecule/ion depends on the repulsion caused by the bond pairs and lone pair. Electron pairs arrange themselves so repulsion is minimal. Lp-Lp > Lp-Bp > Bp-Bp |
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What is the name and angle for 2 bond pairs? |
Linear and 180° |
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What is the shape and angle for 3 bond pairs ? |
Trigonal planar and 120° |
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What is the name and angle for 4 bond pairs ? |
Tetrahedral and 109.5° |
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What is the name and angle for 5 bond pairs ? |
Trigonal bipyramidal and 90° and 120° |
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What is the name and angle for 6 bond pairs ? |
Hexagonal and 90° |
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What is the name and angle for 2 bong pairs and 2 lone pairs? |
V-shaped and 104.5° |
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What is the name and angle for 3 bond pairs and 1 lone pair ? |
Trigonal pyramidal and 107° |
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What is a dipole ? |
A dipole is the separation of charge due to the drift of bonded electrons towards the more electronegative element |
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What does the overall dipole of a molecule depend on ? |
The overall dipole depends on whether the individual dipole cancel each other out (non polar) or whether they reinforce each other (polar) |
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What are London forces ? |
London forces are the interactions that occur when an instantaneous dipole creates an induced dipole. |
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What happens as the number of electrons increase in an instantaneous dipole ? |
As the number of electrons increases the London forces become stronger as the dipole is more extreme so the attractions are stronger. This means boiling point is higher |
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How do permanent dipole behave ? |
Permanent dipole can either attract or repulse each other and therefore the interactions are less than those between instantaneous and induced dipoles |
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What are hydrogen bonds ? |
Hydrogen bonds are intermolecular interactions that occur between the hydrogen atom of a molecule and more electronegative than hydrogen and another atom in the same or a different molecule |
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Which elements can for a hydrogen bond with hydrogen ? |
Oxygen, fluorine and nitrogen |
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What are the only intermolecular interactions of significance in alkanes ? |
London forces |
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What is the difference between branched and unbranded aliases in terms of intermolecular attractions ? |
Branched alkanes have fewer points of contact as they do not fit together as well. Therefore there are less London forces so they have lower boiling points |
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What two intermolecular interactions exist in alcohols ? |
London forces and hydrogen bonding as alcohols contain an oh group. |
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When is hydrogen bonding not predominant in alcohols ? |
It is not predominant in longer chain lengths as there are so many more electrons |
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Why does water have high melting and boiling temperatures ? |
The relatively strong hydrogen bonding means the overall intermolecular forces are strong so a lot of energy is required to break them |
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Why does HF have the lowest Bp out of HF, NH3 and water ? And why is NH3 in the middle ? |
HF and NH3 have lower boiling points than water as each molecule only forms one hydrogen bond whereas water forms 2 per molecule. HF is the lowest as not all the hydrogen bonds are broken at vaporisation |
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Why is ice less dense than water ? |
Ice is less dense than water as the molecules are arranged in rings of 6 held together by hydrogen bonds therefore there are large areas of open space. When ice melts these rings break so the distance between molecules becomes less |
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What must happen for a substance to dissolve ? |
For a substance to dissolve the attraction between solvent and substance must be greater than substance-substance forces and solvent-solvent forces |
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What happens when ionic substances dissolve ? |
The -ve end of water is attracts the cation and forms an ion-dipole interaction. Surrounds the cation. The +ve end of water attracts the anion and forms a hydrogen bond. Surrounds the anion. |
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During hydration the energy released is called ? |
Hydration energy |
