bonding Flashcards
What are the 3 types of chemical bonds? What atoms do they occur between?
Ionic: metals and non-metals, covalent: non-metals, metallic: metals
Define; covalent bond and dative/coordinate bond
Covalent bond = shared pair of electrons. Dative/coordinate bond = covalent bond where one atom donates both bonding electrons
What is valence shell electron pair repulsion? How does this create molecular shapes (hint – talk about electron pairs and repulsion)?
The idea that bonding pairs of electrons repel each other equally. Lone pairs of electrons exert more repulsion than bond pairs.
Which molecules/molecular ions should you remember that contain double bonds?
O2, N2, NO, NO2, NO3-, CO, CO2, CO32-, SO2, SO3, SO42- etc
What steps should you follow to work out molecular shapes?
Look at central atom. Group number = number of outer electrons, unless the molecule has a charge (add electrons for negative charge and subtract for positive charge). Look at the number of bonds and subtract from number of electrons. If any electrons are left over, divide by two to find number of lone pairs.
Define electronegativity
The ability of an atom to attract the bonding pair of electrons in a covalent bond
What happens to electronegativity as you go across a period (excluding group 0) and down a group
Electronegativity increases across a period (excluding group 0) because nuclear charge increases but shielding remains the same. Electronegativity decreases down a group because the electrons become further from the nucleus (shielding increases).
When are bond non-polar? When are they polar?
Non polar bonds occur when there is no/little difference in electronegativity between the atoms (two of the same atoms or C and H). Polar bonds occur when there is a difference in electronegativity between the atoms.
What is a permanent dipole?
A permanent dipole = polar molecule.
Why are some molecules, which contain polar bonds, non-polar?
If the polar bonds are arranged symmetrically, the dipoles cancel and this creates a non-polar molecule (no permanent dipole)
Name the molecular shapes that will be non-polar, despite containing polar bonds, if all the outside atoms are the same.
Linear (with 3 atoms and no lp OR 3 atoms and 3 lps), trigonal planar (no lp AND 2 lp), tetrahedral, trigonal bipyramidal, octahedral, square planar
What are the 3 types of intermolecular forces? Describe when they occur
Van der Waal forces = occur between all molecules and are the only intermolecular force to occur between non polar molecules. Van der Waal forces are caused when a temporary dipole in one molecule induces a dipole in a neighbouring molecule.
Permanent dipole-dipole = occur between polar molecules. The δ+ and δ- of neighbouring molecules are attracted.
Hydrogen bonds = occur between molecules that have a H directly bonded to N, O or F. The hydrogen bond occurs between the δ+ hydrogen of one molecule and a lone pair on a neighbouring N/O/F.
What are the two factors which increase the strength of Van der Waals forces?
1) Increased size/length of molecule as this means there will be more electrons and therefore stronger temporary and induced dipoles. 2) Straight chain compared to branched chain because these molecules can pack closer together and have more points of contact. This means that Van der Waals forces will be stronger.
What are the 4 crystal structures?
Ionic lattice, metallic lattice, simple molecular covalent and giant covalent/ macromolecular covalent
For ionic lattices, state and explain their melting point, electrical conductivity, brittleness, and solubility.
Melting point = high as it takes lots of energy to break the strong electrostatic attraction between the positive and negative ions. Electrical conductivity = doesn’t conduct as a solid because the ions can’t move (so no free charged particles). Does conduct when molten or dissolved because the ions can move and carry a current. Brittleness = when a force is applied it can push like charged ions together. These repel and this breaks the structure apart. Solubility = most ionic substances are soluble because both the positive and negative ions can attract water molecules.
