Chapter 3 Flashcards
catgeories of sunstances
giant structures ad molecular structures
differences between molecular and giant structures
molecules are made up of fixed numbers of atoms joined together by covalent bonds and the number of atoms per molecule is usually fairly small but can increase in cases involving big molecules such as plastics, DNA or proteins
giant structures however contain huge numbers of either atoms or ions arranged in some regular way however the number of particles is not fixed
physical properties of metals
-metals tend to be strong and have high b.p and m.p because of the strong forces of attractions involved
-metals are good conductors of electricity because of the mobility of the delocalised electrons. as electrons are pulled to the positive terminal and flow away along the wire more electrons flow along the wire from the negative terminal (the power source) to replace the ones moving away
-metals are good conductors of heat because of the mobility of the delocalised electrons. if one end of the metal is heated the heat energy is picked up by the electrons and as they move about, the energy is transferred throughout the structure.
-metals are easy to shape because their regular packing makes it easy for their atoms to slide over each other. they are ductile (can be pulled into wires) and malleable (can be beaten into shape)
-metals are elastic which means that if a small force is applied to them they will stretch and then return to their original shape after the force is removed. however, if a larger force is applied the particles of the metal can slide over each other and stay in their new positions.
what are metallic structures
metals consist of a regualr rray of positive ions in a sea of electrons. the metal is held together by the forces of attraction between the sea id delocalised elections and the positively charged metal ions
alloys/alloying/why do we alloy
alloys are metallic substances composed of 2 or more elements.
metals can be made harder by alloying them with other metals.
different metals have different sizes of atoms. mixng atoms of slightly different sizes dirsupts the regular packing of the metal, making it harder for the atoms to slide over one another, thus making the metal harder.
examples of alloy
brass- cu and zn
solder- sn and pb (melts at a lower temperature than both metals that make it up. this along with its conductivity makes it useful for joining components in electrical circuits)
bronze- cu and sn
stainless steel- fe cr and ni
cupronickle- cu and ni
physical properties giant ionic strcutures
-ionic compounds have high melting points this is because of the strong forces of attraction between the positive and negtaivbely charged ions hgolding the lattices together
-ionic compounds tend to be crystalline this reflects the regular arrangement of ions in the lattice. sometimes the crytsals are too small to be seen except under powerful microscopes
-ionic crystals tend to be brittle this is because any small distortion f the crystal will bring ions with the same charge alongside each other, and as like charges repel, the crystal splits
-ionic substances tend to be soluble in water this is because, although water is a covalent compound, it is polar, meaning that the lectrons in the bond are attracted towards the oxygen end of the ond making oxygen slightly negative and hydrogen slightly positive. the slightly positive hydrogens in the water molecules clkuster around the negativeions and the slighlty negative oxygens are attarcted to the posotive ions, the water molecules then pull the crystal apart
- ionic compounds tend to be insoluble in organic solvents. organic solvents contain nmolecules that have much smaller electronegtivity differences than in water, in other words, the molecules are less polar. there isnt enough atttraction between these molecules and the ions in the crystal to break the strong forces holding the lattice together
ion
atom or group of atoms that carries a charge
lattice
regular array of particles the lattice is held together by the strong forces of attraction between the positively and negatively charged ions
the electrical behaviour of ionic substances
ionic compounds do not conduct eletcrcity when they are solids because they do not contain any delocalised electrons , they do however, conduct eletcrcity in the molten state or if they are dissolved in water. this happens because the ions then vbnecome free to move around
diamond
diamond is a form of pure carbon
each carbon has four unpaired electrons in its outer energy level and it uses these four electrons to form four covalent bonds. in diamond, each carbon is strongly bopnded to four other carbon atoms
diamond physical properties
-diamond is very hard with a very hard bp and mop. this is because of the strong carbon carbon covalent bonds which ex5tend throughout the whole crystal in 3 dimensions
-diamon does not conduct electricity. all the electrons in the outer energy levels of the carbon atoms are tightly helf in covalent bonds between the atoms and thus none of the electrons are free to move around
-diamond does not dissolve in water or any otehr solvents becsuse of the pwoerful carbom carbon covalent bonds between the atoms which cannot be broken easily, making diamond insoluble as dissolution erquires bonds to be broken
graphite
graphitew is also a form of carbon, but the atoms are arranged differently. graphite has a layer strcuture whose layers are easily separated.
graphite physical properties
-graphite is a soft material with a slimy feel although the forces holding the atoms togetehr in each l;ayer are very strong, the attarctions between the layers are much weaker and so layers are easliy flaked off
-graphte has a high mp and bp and is insoluble in any solvents. to melt or dissolve graphite its not just the layers that have to be broken apart, but the entire structure as well including the strong carbon carbon covalent bonds. this would need a lot of energy
-graphite is less dense than diamond becaus ethe layers in graphite are relatively far apart. the distance between the graphite layers is more than twice the distance between the atoms in each layer. in a sense, graphite crystals contain a lot fo wasted space, which isnt there in a diamond crystal.
-graphite conducts electrity as each carbon atom, unlike in diamond, is bonded to only 3 otehrs, elavng 1 delocalised elctrons each to move aboput the structure, this mobility allows graphit eto conduct eletcricty
simple molecular compounds
-weak intermolecular forces of attraction so they tend to be gases kiquids or low mp solids
-insoluble in water unless they react with it in roder for a susbance to dissolve quite strong attractions between water molecules have to broken so that the dissolving moleucles can fit between them, any new attractions between wate rmolecules and the covalent molecules are not usually big enough to compenstae for this.
-often soluble in organic solvents as the inetrmolecular attractions betwene the two different types of moelcules are much the same qs in the pure substances
-do not ocnduct electrcity because the molecules do not have an overall charge or electrons mobile enought omove from molecule to molcule
