Materials from molecules Flashcards
Molecule
A discrete group of atoms of known formula, bonded together
Lattice
Atoms bonded together in a continuous 3D structure
Intramolecular forces
bonds between non metal atoms which form molecules
Intermolecular forces
Bonds between molecules
Localised electrons
Shared electrons in a covalent bond which are found between the nuclei
VSEPR theory
Valence shell electron pair repulsion theory
Negatively charged electron pairs in the outer shell of an atom repel each other and are therefore placed as far away from each other as possible
Intermolecular forces strength
weaker than strong forms of bonding such as ionic, metallic and covalent bonds
when a substance is melted/vaporised
weak intermolecular forces are broken
Non polarised covalent bond
Equal distribution of valence electrons
no charge on either side of the bond (no net dipole)
Polarised covalent bond
Electrons will stay closer to the most electronegative atom which has a stronger pull on the electrons in the bond
created two oppositely charged poles- partial positive charge, partial negative charge
Level of polarity
Depends on the difference between the electronegativities
greater the difference, greater the polarity of the molecule
Non-polar molecules
Partial charges are evenly distributed around the molecule
Individual dipoles of the covalent bonds cancel each other out perfectly
no overall dipole
Polar molecules
Partial charges are unevenly distributed around the molecule
results in a net dipole
Strength order of intermolecular forces
H-bonding
Dipole-dipole
dispersion
Dipole-dipole
polar molecules
Attraction between the partial negative/positive ends of the polar molecules
more polar a molecule is, stronger the dipole-dipole forces
H-bonding
occurs in molecules where a hydrogen atom is covalently bonded to a FON atom
partial positive charge of hydrogen is attracted to lone pairs of electrons in FON atoms of neighbouring molecules
Dispersion forces
Caused by temporary dipoles
result of random movement of electrons surrounding molecules which cause instantaneous dipoles
always present between molecules
Strength increases as Mr of molecule increases. Larger molecules have a larger number of electrons.
In larger molecules, dispersion forces can dominate over dipole-dipole forces
Non metal properties
Soft
Low MP and BP
Don’t conduct electricity in molten or solid state
Non metals soft
Intermolecular forces are weak
Bonds can be readily broken and substance is easily crushed or moulded
Non metals low MP and BP
weak forces of attraction between particles
Non metals dont conduct electricity
no free moving charged particles in either state
