Chem (23.3.23) Flashcards
How is a Covalent Bond formed?
-Covalent bonding occurs in most non-metallic elements and in compounds of nonmetals
-When atoms share pairs of electrons, they form covalent bonds. These bonds between atoms are strong
How are the electrostatic attractions in c.b?
-Strong bonds between atoms that are covalently bonded are the result of electrostatic attraction between the + nuclei of atoms and the pairs of - electrons that are shared between them
Why do the melting/boiling points of substances increase with the realtive molecular mass?
-The intermolecular forces increase with the size of the molecules, so larger molescules (i.e molecules with greater r.m.m) have higher melting and boiling points
Why are giant covalent structures solids with high melting and boiling points?
-Substances that consist of g.c.s are solids with very high melting points
-All of the atoms in these structures are linked to other atoms by strong covalent bonds
-These bonds must be overcome to melt or boil these substances
What is the structure of a diamond?
-Each carbon is joined to 4 other carbons covalently
-It’s very hard, has a high melting point and does not conduct electricity
What is the structure of graphite?
-Each carbon is covalently bonded to 3 other carbons, forming layers of hexagonal rings,
-Between the layers there are weak forces of attraction
-The 4th unbound electron is delocalised and can move along layers
-Good conductor of electricity
-Layers can slide over eachother: good lubricant (soft + slippery)
What is the structure of Fullerences?
-C60 carbon atoms form a big ball of atoms where 3 c.b are established with other carbons, and the 4 unbound electron is delocalise
-Made up of large covalent molecules held together by intermolecular forces
-It is soft, can slide over each + poor conductors
What are the elements + rxns with water in Group 1 (Alkali metals)
-Lithium Li (s)+ H2O (l) = LiOH (aq) + H2 (g)
-Sodium Na ( s ) + H2O ( l ) → NaOH ( aq ) + H2 ( g )
-Potassium K (s) +H2O (l) →KOH (aq) + H2 (g)
What do the Alkali metals have in common?
-They all have properties due to the single electron in their outer shell
-React vigorously with water to create an alkaline solution and hydrogen
What are the differences between the rxns of the Alkali metals that show a trend in reactivity?
-They all react with oxygen to create an oxide
-More bubbles with reaction with water = more vigorous rxn = more reactive alkali metal
-Reactivity increases down the group -> therefore reactivity increases from Li to K
What are the elements in Group 7 (halogens)?
-Chlorine (Cl)
-Bromine (Br)
-Iodine (I)
What are the colours of these elements at room temp. + trends in physical properties?
-Chlorine is a green gas
-Bromine is a red-brown liquid
-Iodine is a purple solid
-There is a trend in state from gas to liquid to solid down the group
What are the properties of other halogens?
-There is a trend in state from gas to liquid to solid down the group
-this is because the melting and boiling points increase as you go down the group
-from this, you can predict that any halogens above chlorine will be gases (their boiling points will be even lower), and any below iodine will be solids (their melting points will be even greater)
How do displacement rxn involving hallogens and hallides affect the trend?
-a more reactive halogen can displace less in an aqueous solution of its salt
-e.g. Chlorine will displace bromine if you bubble the gas through a solution of pottasium bromide
Chlorine (green) + Potassium Bromide -> Potassium Chloride + Bromine (red)
-this happens because as you go down the group, the reactivity of halogens decreases
What happens when Li reacts with H20?
frizzes steadily
