| what happens to the melting point of metals down a group | melting point decreases as there are more occupied energy levels, and so the nucleus is further away from delocalised electrons. The inner energy levels also screen the nucleus from delocalised electrons, decreasing the strength of the metallic bond |
| what is the name given to bonding inside molecules | intramolecular bonds |
| what is a metallic bond | the electrostatic force of attraction between positively charged ions and delocalised electrons |
| what is the metallic structure | a giant lattice of positively charged ions in a sea of delocalised electrons |
| name some properties of metals | electrical conductors due to delocalised electrons
high melting points due to having to break the strong metallic bonds
malleable and ductile as the metallic bond acts in all directions
good thermal conductors as the atoms are closely packed and can pass on heat through conduction |
| what happens to metal electrical conductivity across a period | it increases as there are more delocalised electrons |
| what happens to metal melting point across a period | melting point increases as the positive core is increasing in charge and the number of delocalised electrons increases, creating a stronger metallic bond |
| what happens to the melting point of metals down a group | melting point decreases as there are more occupied energy levels, and so the nucleus is further away from delocalised electrons. The inner energy levels also screen the nucleus from delocalised electrons, decreasing the strength of the metallic bond |
| what is the name given to bonding between molecules | intermolecular bonding |
| what are the three types of intramolecular bonds | non polar covalent bonds
polar covalent bonds
ionic bonds |
| when do non polar covalent bonds occur | non polar covalent bonds exist between two atoms with the same electronegativities. Electrons are shared equally.
Pure covalent bonds have no ionic character. |
| what is a polar covalent bond | polar covalent bonds are formed in compounds when atoms of different elements share electrons. Atoms with different electronegativity values will share the bonding electrons unequally, forming a permanent dipole. |
| what is a dipole | when an atom is slightly positive (?+) or slightly negative (?-) due to unequal sharing of electrons. |
| how are ionic bonds usually formed? | between a metal and non-metal with a large difference in electronegativity |
| describe why sodium chloride is an ionic compound | chlorine has far larger electronegativity chlorine pulls bonding electrons towards itself completely chlorine gains electron and forms negative ion sodium loses its bonding electron and forms a positive ion |
| how is ionic formula written | by giving the simplest ratio of each type of ion in the substance
eg. sodium chloride forms an ionic lattice and the ratio of sodium to chlorine is 1:1, which is why its formula is NaCl |
| what determines the type of bonding present in a compound | the differences in electronegativity between the elements involved |
| if two ions have a very large difference in electronegativity, what does that mean about the ionic character of the compound? | the compound is very ionic |
| name properties of ionic compounds | ionic compounds are high melting point solids due to the strong electrostatic attraction between oppositely charged ions that have to be overcome on melting
do not conduct electricity when solid as the ions are not free to move
conduct electricity when molten or in solution as the ions are free to move
many ionic compounds are soluble in water |
| what are the properties of covalent network substances | very high melting points as strong covalent bonds have to be broken on melting
form very hard substances are the atoms are held together in a giant network
do not conduct electricity as there are no free charged particles
are insoluble in water |
| what are the two types of van der waals forces | london dispersion forces of attraction
permanent dipole permanent dipole forces of attraction |
| what is the strength of london dispersion forces relative to other intermolecular bonds | they are the weakest intermolecular bonds, they exist between all atoms and molecules |
| how do we know that london dispersion forces exist between molecular elements and monatomic elements | they will condense, fomring solids if cooled to sufficiently low temperatures, which means there must be an attraction between the individual molecules that is being overcome |
| how are london dispersion forces caused | due to uneven distribution of electrons within an atom
slightly negative and slightly positive side of an atom; instantaneous dipole
instantaneous dipole induces instantaneous dipoles in neighbouring atoms |
| what is the strength of london dispersion forces dependent on | the size of the molecule or atom
larger atoms and molecules have more electrons, leading to larger dipoles being established |
| when do permanent dipole permanent dipole forces occur | they occur between polar molecules atoms in polar molecules have different electronegativity & electron pair is shared unequally one atom is slightly positive and the other slightly neagative oppositely charged ends of molecule are attracted to each other |
| what is hydrogen bonding | a specific type of permanent dipole permanent dipole attraction
occurs when hydrogen atom is covalently bonded to nitrogen oxygen or fluorine |
| why mightn't a substance that contains polar covalent bonds be overall polar? | the shape of the molecule
water is a polar molecule but due to the non symmetrical shape of the molecule (angular) the molecule itself is polar, due it it having a slightly positive and slightly negative side
carbon tetrachloride has four polar covalent bonds, it is a tetrahedral molecule so the charges are symmetrical. The molecule itself is non polar due to symmetry. |
| what are the properties of covalent molecular substances | they have low melting and boiling points
they do not conduct electricity
some covalent molecular compounds have higher melting points than expected, this is often due to hydrogen bonding |
| why does water have some unusual properties | due to the hydrogen bonding between its molecules |
| name some unusual properties of water | the density of ice is less than water, due to the water expanding as it is frozen, because of the hydrogen forming an open type lattice
high surface tension
relatively high viscosity |
| describe the solubility of all ionic lattices and polar covalent molecules (like dissolves like) | soluble in water and other polar solvents
insoluble in non-polar solutions |
| describe the solubility of all non-polar covalent substances (like dissolves like) | soluble in non-polar solvents
insoluble in water and other polar solvents |
