2 - Bonding And Structure Flashcards
Giant covalent bonds?
Giant regular lattice Sharing of electrons Always solid at room temperature Hard Insoluble
Graphite?
Arranged in layers
each atom is bonded to 3 other atoms
Conductive
Small covalent molecules?
Low melting and boiling points because of weak intermolecular forces which break down easily.
Non conductive
Strong bonds between atoms, weak bonds between molecules
low melting and boiling points
Insulators
Metallic bonding?
Malleable because they’re in layers
Sea of delocalised electrons, free to move throughout.
sharing of many detatched electrons between positive ions.
This gives them structure and explains why many metals have high boiling points
Define metallic bonding?
Is the force of attraction, between valence electrons and metal atoms
Ionic bonding?
Between a metal and a non metal. Between atoms which give or receive electrons. DON'T conduct when solid Soluble High melting and boiling points
Structure of ionic bonding?
Lattice structure
Regular ion arrangement, results in crystals being produced.
Electrostatic forces of attraction between ions, means a lot of energy is required to separate negative and positive ions.
Proving existence of ions?
The migration of coloured ions during the electrolysis of copper (11) and chromate (v1) solution.
Potassium manganate and the DC current
Electron repulsion theory?
Greatest forces of repulsion:
Lone pair lone pair
lone pair bonded pair
Bonded pair bonded pair
Lone pairs?
Repel as much as possible.
Take off 2.5 degrees for every lone pair
Affect the bond angle.
Shapes of molecules?
Depends on the number of pairs of electrons in the outer shell.
All shapes depends on the number of pairs!
Linear?
2 pairs
180 degree bond anlge
Trigonal planar?
3 pairs
120 degrees
Tetrahedral?
4 pairs
104.5, 107, 109.5 degrees depending on lone pairs
Trigonal bipyramid?
5 pairs
90, 120, 180 degrees
Octahedral?
6 pairs
90, 180 degrees
What are the most electronegative elements?
N,O,F
nitrogen, oxygen, flourine
Define electronegativity?
Is the tendancy to attract the shared pair of electrons
Dative bonds?
Are formed when an ion attaches to the lone pair of an atom
Non polar molecules, eg O2?
Oxygen have the same electronegativity, therefore the electrons are equally shared between the atoms
Polar molecules eg, H2O?
Oxygen has a higher electronegativity than hydrogen, so the electrons will spend more time closer to the oxygen atom. This results in a partial negative charge around the oxygen atom.
What did Pauling do?
Assigned every element its electronegativity.
London Forces?
Occur between all molecules.
Fleeting repulsions and attraction between nuclei of the atoms and the electron cloud.
Temporary displacement cause temporary dipoles.
Neighbouring molecules are induced with temporary dipoles (opposite charge)
Dipole, dipole?
Attractive forces between the positive end of 1 polar molecule and the negative end of another.
Occurs between 2 polar substances
Creates a semi charge, or dipole in molecule
effected by: electronegativity of atoms and number of electronegative atoms
Hydrogen bonding?
Occurs between molecules where hydrogen is bonded to N,O,F
There must be a lone pair of electrons
Always a bond angle of 180.
Polarity?
If the shape is symmetrical and the electrons are the same, it’s non polar!
Solubiltiy?
Like dissolves like,,,
Polar dissolves polar
Non polar dissolves non polar
Why do polar solvents dissolve in polar substances?
because the partial charges in the polar solvent can hold onto the partial charges in the polar solute and dissolve.
Non polar and polar?
Won’t dissolve with eachother because the molecules would rather remain, and use their partial charges to stick together with hydrogen bonds than with the non polar molecules.
Bond length and strength?
x ray diffraction allows chemists to look at structures. Microwave spectroscopy can give us info on bond angles.
Testing polarity?
Charge a plastic rod, and hold next to a stream of the chemical you want to test, if its polar it will diffract!
Electronegativity patterns?
INCREASES across the periodic table
INCREASES up the groups
Why does electronegativity increase up a group?
There are more protons in the nucleus so it has a stronger pull
Why does electronegativity increase across the periodic table?
More shells, and therefore electrons are further away from the nucleus! they want to gain electrons
Polar bonds in a molecule?
polar bonds in a molecule does not mean the molecule has to be polar, if the moleules are symmetrical, then the dipoles cancel.
