Covalent bonding and Halogens - TN Flashcards
What is covalent bonding
- the electrostatic force of attraction between a shared pair of electrons and positively charged nuclei of bonding atoms
why does covalent bonding happen in non-metallic atoms
so that they can forms bonds to create a full outer shell
what is an inter-molecular bond
the bond between two molecules
- eg between two H2O molecules
what is an intra-molecular bond
the bond within a molecule
- eg the bond between on of the H and the O atom in H2O
what type of bonds does a simple molecule contain (simple molecular structure)
covalent bonds
can simple molecular substances conduct electricity
no - they have no overall charge or charged particles that can separate
- not even when liquid or dissolved in water
do simple molecular substances have high or low melt and boil points
low - the weak forces of attraction are broken by very little energy
what does RMM stand for
Relative Molecular Mass
what does IMF stand for
InterMolecular Forces
why do the melting and boiling points of simple molecular substances increase (in general) with RMM
This is because larger molecules have more forces of attraction between them which must be overcome
what is a simple covalent structure/ simple molecular substance
Give examples
contain only a few atoms held together by covalent bonds
eg - water, ammonia, methane, carbon dioxide, chlorine and hydrogen
are the different bonds within a covalent structure strong or weak?
the intramolecular bonds are strong but the intermolecular bonds are weak
what is a molecular solid and give an example
a substance that is solid at room temp
eg - iodine
(Iodine sublimes with very little energy)
all diatomic molecules have what type of bond
covalent bonds
what catalyst is best for breaking down Hydrogen Peroxide
Manganese Oxide
what is an allotrope
different arrangements of the same element
four allotropes of carbon
- diamond
- graphite
- silicon dioxide
- fullerenes (buckminsterfullerene)
what structure does a Buckminster fullerene have
60 carbon atoms each bonded to three others by two single bonds and a double
what are the two main types of covalently bonded substances
- simple molecules
- giant covalent structures
what is a giant covalent structure
a three-dimensional structure of atoms that are joined by covalent bonds
melting and boiling points of each allotrope of carbon
Diamond - very high
Graphite - high
Silicon dioxide - high
Buckminsterfullerene - low
why do graphite, diamond, and silicon dioxide have high melting and boiling points
because a lot of strong covalent bonds must be broken (high molecular mass)
does diamond conduct electricity (or heat)
no - (no free electrons)
does graphite conduct electricity
yes - it only uses 3 of its electrons to bond so each atom has one delocalised electron that is free to move throughout the structure
does silicon dioxide conduct electricity
no
can a Buckminster fullerene conduct electricity
no
structure of diamond
- GIANT COVALENT LATTICE
- tetrahedral
- made up of carbon atoms
- extremely strong covalent bonds
4 outer electrons all used to bond with four neighbouring atoms
structure of graphite
- EXISTS IN LAYERS
- covalent bonds between carbon atoms are strong but intermolecular bonds between layers are weak (so brittle)
- each carbon atom is bonded to only three others (rather than four)
layers able to slide over each other
structure of a Buckminster fullerene
round, cage like structure that consists of 60 carbon atoms
structure of silicon dioxide
- tetrahedral
- giant covalent lattice
- very similar to diamond except that is is made up of silicon and oxygen atoms
what are the group 7 elements called
halogens
what group in the periodic table are the Halogens
group 7
explain the reactivity of the halogens as you go down the group
as you go down, ATOMIC SIZE INCREASES so there is a LARGER DISTANCE between outer shell and nucleus, resulting in INCREASED SHIELDING. This means that ATTRACTION DECREASES so they are less able to attract another electron to complete its outer shell
why can the layers on graphite slide over each other
due to the weak intermolecular bonds
would you expect CHCl3 or CCl4 to have a higher boiling point
CCl4 - it has a greater molecular mass so the strength of the intermolecular forces are greater
what colours are the halogens: F, Cl, Br, I, At
F - Pale yellow
Cl - Green/yellow
Br - orange
I - grey(when solid) but purple(when vapour)
At - black (when solid) but dark purple (when vapour)
What states are the Halogens at room temperature
F - gas
Cl - gas
Br - liquid
I - solid
At - solid
explain the melting point trend of the halogens as you go down the group
The melting points increase as the Relative Molecular Mass increases. This means the inter-molecular forces get stronger so more energy is needed to break them down
test for chlorine
blue litmus being bleached white - this us because the chlorine acts as a bleaching agent so it removes the colour from the paper
what colour is blue litmus in acids
red
how do strong acids dissociate compared to weak acids
a strong acid dissociates fully into its ions
a weak acid will only partially break up
what is a halide
The resulting compound when halogens combine with other elements. they are formed when they gain an electron
eg NaCl
what are the halides of iodine, chlorine and bromine
Iodide
Chloride
Bromide
How to test for displacement in a reaction of halogens
If there is a displacement occurring there will be a colour change
you can then add cyclohexane and observe the colour of the top layer
how strong is the force of attraction between covalently bonded molecules and why
- very strong
- the shared pair of electrons effectively pull the nuclei of the atoms closer together
do simple molecular substances conduct electricity and why
no - because there are no charged particles as the molecules are neutral
describe and explain the physical features of a C60 fullerene
soft and slippery because the molecules can roll over each other easily
what is diamond used for practically
- cutting
how are all the halogens bonded and with what structure
- covaletnly
- simple molecular
how does Hydrogen Chloride (HCl [g]) become Hydrochloric acid (HCl[aq])
- HCl(g) is dissolved in water to form HCl(aq)
- this dissociates to form H+
- the H+ is acidic
