The Two Kinds Of Water
The two kinds of water
Credit: University of Basel
Pre-sorted ortho-water and para-water molecules with differently oriented nuclear spins (blue or red arrows) react with diazenylium ions (centre left) at different speeds.
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Researchers from the University of Basel’s Department of Chemistry, Switzerland, has investigated how the two forms of water differ in terms of their chemical reactivity – the ability to undergo a chemical reaction. Both forms have almost identical physical properties, which makes their separation particularly challenging.
It is less well-known that water exists in two different forms (isomers) at the molecular level. The difference is in the relative orientation of the nuclear spins of the two hydrogen atoms. Depending on whether the spins are aligned in the same or opposite direction, one refers to ortho- or para-water.
The was made possible by a method based on electric fields. Using this, researchers were able to initiate controlled reactions between the pre-sorted water isomers and ultracold diazenylium ions (protonated nitrogen) held in a trap. During this process, a diazenylium ion transfers its proton to a water molecule. This reaction is also observed in the chemistry of interstellar space.
It was discovered that para-water reacts about 25% faster than ortho-water. This can be explained in terms of the nuclear spin also influencing the rotation of the water molecules. As a result, different attractive forces act between the reaction partners. Para-water is able to attract its reaction partner more strongly than the ortho-form, which leads to an increased chemical reactivity.
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i just learned from animal crossing that pondskaters stay on top of the water by secreting an oil from their feet
that seems kinda obvious in hindsight. i always figured they were just, like, light enough to not break surface tension
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Alkanes: Saturated Hydrocarbons
So you want to be an organic chemist? Well, learning about hydrocarbons such as alkanes is a good place to start…
Alkanes are a homologous series of hydrocarbons, meaning that each of the series differs by -CH2 and that the compounds contain carbon and hydrogen atoms only. Carbon atoms in alkanes have four bonds which is the maximum a carbon atom can have - this is why the molecule is described to be saturated. Saturated hydrocarbons have only single bonds between the carbon atoms.
The general formula of an alkane is CnH2n+2 where n is the number of carbons. For example, if n = 3, the hydrocarbon formula would be C3H8 or propane. Naming alkanes comes from the number of carbons in the chain structure.
Here are the first three alkanes. Each one differs by -CH2.
Shorter chain alkanes are gases at room temperature, medium ones are liquids and the longer chain alkanes are waxy solids.
Alkanes have these physical properties:
1. They are non-polar due to the tiny difference in electronegativity between the carbon and hydrogen atoms.
2. Only Van der Waals intermolecular forces exist between alkane molecules. The strength of these increase as relative molecular mass increases therefore so does the melting/boiling point.
3. Branched chain alkanes have lower melting and boiling points than straight chain isomers with the same number of carbons. Since atoms are further apart due to a smaller surface area in contact with each other, the strength of the VDWs is decreased.
4. Alkanes are insoluble in water but can dissolve in non-polar liquids like hexane and cyclopentane. Mixtures are separated by fractional distillation or a separating funnel.
The fractional distillation of crude oil, cracking and the combustion equations of the alkanes will be in the next post.
SUMMARY
Alkanes are a homologous series of hydrocarbons. Carbon atoms in alkanes have four bonds which is the maximum a carbon atom can have - this is why the molecule is described to be saturated. Saturated hydrocarbons have only single bonds between the carbon atoms.
The general formula of an alkane is CnH2n+2 where n is the number of carbons.
Shorter chain alkanes are gases at room temperature, medium ones are liquids and the longer chain alkanes are waxy solids.
They are non-polar.
Only Van der Waals intermolecular forces exist between alkane molecules. The strength of these increase as relative molecular mass increases therefore so does the melting/boiling point.
Branched chain alkanes have lower melting and boiling points than straight chain isomers with the same number of carbons.
Alkanes are insoluble in water but can dissolve in non-polar liquids like hexane. Mixtures are separated by fractional distillation or a separating funnel.
#Thunderstorms are hitting the UK this week – here’s how thunder and lightning happen and some of the chemistry going on during a storm: https://ift.tt/2XUCKZc https://ift.tt/3gJ7ALD
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Metallic Bonding
A short one to finish off my first ever mini-series on bonding – ionic, covalent and finally metallic. There are metallic and metallic compounds and elements but for the A Level exam, we must look at the bonding within metals themselves. Don’t worry – I saved the easiest to last!
Metals are most usually solid so have particles packed close together. These are in layers which mean that the outer electrons can move between them rather than being bound to particular atoms. These are referred to as delocalised electrons because of this.
It’s pretty common knowledge that metals are good conductors of heat and electricity and it’s these delocalised electrons that give them this property.
Metals are therefore without their electrons so become positive ions. The metallic bond is actually the attraction between delocalised electrons and positive metal ions in the lattice. And that’s pretty much metallic bonding, you just need to know the properties of metals which are touched upon at lower levels of education.
These are the properties of metals:
1. High melting points
Metals have large regular structures with strong forces between the oppositely charged positive ions and negative electrons, meaning these must be overcome to melt the metal – this requires a large amount of heat energy. Transition metals tend to have higher melting points than the main group metals because they have large numbers of d-shell electrons which can become delocalised creating a stronger metallic bond. Melting points across a period increase because they can have progressively more delocalised electrons: Na+, Mg 2+ and Al 3+ for example.
2. Heat conductivity
Heat is conducted if particles can move and knock against each other to pass it on. Delocalised electrons allow this to happen. Silver is a particularly good conductor of heat.
3. Electrical conductivity
Delocalised electrons can carry charge and move, the two requirements of electrical conductivity. Current can flow because of these delocalised electrons.
4. Ductile and malleable
Metals can be stretched and hammered into shape, making them ideal for things such as wires. Layered lattices mean that layers can slide over each other without disrupting the bonding – it is all still held together by the delocalised electrons and their strong attraction to the positive metal ions.
5. High densities
Being a solid, metal ions are packed closely together so they have a high density, which makes them ideal for musical instrument strings. These can withstand the frequency of vibration whilst also being thinner.
SUMMARY
Metals are solid so have particles packed close together. These are in layers which mean that the outer electrons can move between them rather than being bound to particular atoms. These are referred to as delocalised electrons because of this.
Metals are therefore without their electrons so become positive ions. The metallic bond is actually the attraction between delocalised electrons and positive metal ions in the lattice.
Metals have high melting points.
Metals have large regular structures with strong forces between the oppositely charged positive ions and negative electrons, meaning these must be overcome to melt the metal – this requires a large amount of heat energy. Transition metals tend to have higher melting points than the main group metals because they have large numbers of d-shell electrons which can become delocalised creating a stronger metallic bond.
Metals conduct heat.
Heat is conducted if particles can move and knock against each other to pass it on. Delocalised electrons allow this to happen.
Metals have good electrical conductivity
Delocalised electrons can carry charge and move, the two requirements of electrical conductivity. Current can flow because of these delocalised electrons.
Metals are ductile and malleable.
Metals can be stretched and hammered into shape, making them ideal for things such as wires. Layered lattices mean that layers can slide over each other without disrupting the bonding – it is all still held together by the delocalised electrons and their strong attraction to the positive metal ions.
Being a solid, metal ions are packed closely together so they have a high density.
Happy studying!
