Bonding and Structure Flashcards
Ionic bonding
The electrostatic attraction between oppositely-charged ions
Formula for nitrate ion, carbonate ion, sulfate ion and ammonium ion
NO(3)^2- , CO(3)^2- , SO(4)^2- , NH(4)^+
Covalent bond
A shared pair of electron
What is the shape of a molecule determined by?
The repulsion between electron pairs surrounding the central atom
What type of electron pairs repel most?
Lone pairs repel more than bonded pairs
Trigonal planar molecules
3 bonded pairs, no lone pairs; bond angle of 120; e.g. BF(3)
Tetrahedral molecules
4 bonded pairs, no lone pairs; bond angle of 109.5; e.g. CH(4) or NH(4)^+
Octahedral molecules
6 bonded pairs, no lone pairs; bond angle of 90; e.g. SF(6)
Pyramidal molecules
3 bonded pairs, 1 lone pair; bond angle of 107; e.g. ammonia, NH(3)
Non-linear (V or bent shaped) molecules
2 bonded pairs, 2 lone pairs; bond angle of 104.5; e.g. water, H(2)O
Linear molecules
2 bonded pairs/bonding regions; bond angle of 180; e.g. CO(2)
Electronegativity
The ability of an atom to attract the bonding electrons towards itself in a covalent bond
When may a permanent dipole arise?
When covalently bonded atoms have different electronegativities, resulting in a polar bond
Permanent dipole-dipole interactions
The permanent dipole of one molecule attracts the permanent dipole in a different polar molecule towards itself, forming a weak permanent dipole-dipole force. delta + attracts delta -
Van der Waals’ forces
Exist between all molecules. Intermolecular attractions between small, temporary dipoles in neighbouring molecules. An instantaneous dipole may form due uneven distribution of electrons, inducing a dipole in the molecule next to it, creating weak intermolecular forces due to the attraction. The more electrons, the stronger the forces. The more points of contact, the stronger the forces
Hydrogen bonding
Strong dipole-dipole interaction between an electron-deficient hydrogen atom (delta +) on one molecule and a lone pair of electrons on a highly electronegative atom on a different molecule. In molecules with O-H and N-H groups. When drawing, draw Hd+, dashed line, lone pair on O/Nd- in line with another H.
Anomalous properties of water
- ice is less dense than water: open lattice of hydrogen bonds hold water molecules apart. These collapse when ice melts, allowing water molecules to move closer together
- water has relatively high freezing and boiling point: hydrogen bonds are an extra intermolecular force to be overcome when melting/boiling water.
- high surface tension and viscosity
Metallic bonding
The electrostatic attraction of positive ions to delocalised electrons
Giant metallic structures
Strong metallic bonds between positive metal ions and delocalised electrons results in high melting point and a good conductor of electricity and heat
Giant covalent structures
Strong covalent bonds between atoms results in a very high melting point. Don’t conduct as no mobile charges EXCEPT graphite, which has delocalised electrons between layers
Giant ionic structures
Strong ionic bonds between oppositely charged ions results in high melting point. Ions fixed in solid lattice, but conduct electricity when molten/in solution as ions can then move
Dative covalent bond
A shared pair of electrons (covalent bond) where both electrons are donated by one atom
