Rising Sea Levels – Expansion

sealevel2

TEMPERATURE RISE ºC

Making models of climate change is very difficult because there are many factors involved. When the Sun shines on the 70% of the Earth that is water , two factors will contribute to an accelerated rise in sea level. First, although the oceans have an enormous heat storage capacity, if global atmospheric temperatures rise, as they are, of course, doing, the oceans will absorb heat and expand, taking up more space. So,  average ocean density decreases and a greater volume of ocean water due to thermal expansion will lead to a rise in sea level. Second, rising temperatures will cause the ice and snowfields to melt, thereby increasing the amount of water in the oceans.

The world’s glaciers are both a clock and a thermometer.  These images are separated by only a few years and this Arctic1928_2000glacier2 snowfield has almost melted…

Only the melting of land-based ice and snow will increase sea level. The melting of floating ice doesn’t change sea level since the water is already present in the ocean body.

Avogadro – we do huge

A mole is an amount of stuff.
In 2g of hydrogen gas – or 1 mole – there are 600000000000000000000000 [six times ten to the twenty-three] molecules of hydrogen the same number as in 18g of water – can you see why?

Chemists don’t do big numbers – this is called the number of molecules in one mole, Avogadro’s Number.

Count Lorenzo Amadeo Avogadro

Count Lorenzo Amadeo Avogadro

Avogadro was an Italian Count, with a doctorate in ecclesiastical law and an interest in science. In 1811, he published an article that clearly showed the difference between molecules and atoms. Bear in mind that people didn’t really know what they were talking about in terms of how chemistry worked back then. He suggested that the great English chemist John Dalton had got himself muddled up and he pointed out that “atoms” of nitrogen and oxygen are in reality “molecules” containing two atoms each. Thus two molecules of hydrogen can combine with one molecule of oxygen to produce two molecules of water.

Avogadro’s big contribution was this…
‘Equal volumes of all gases at the same temperature and pressure contain the same number of molecules.’
which is now known as Avogadro’s Principle.

One mole of gas occupies 24 dm³ at standard temperature and pressure.

Atoms and molecules are very small but a moles-worth of anything bigger is huge. For example,
An Avogadro’s number of soft drink cans would cover the surface of the earth to a depth of over 300km.
If you had Avogadro’s number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of nearly ten miles.
If we were able to count atoms at the rate of a million per second, it would take about 20 billion years to count the atoms in one mole – older than the age of the Universe.
Put another way, only about 0.000000000000000014 moles worth of people watched Barack Obama’s swearing in as the 44th president of the USA, rather more than the 45th.

Mass Spectrometry: Finding isotopes

Over a hundred years ago, the study of gas discharges led to the discovery of anode and cathode rays, which turned out to be positive ions and electrons. We got better at separation of these positive ions which enabled the discovery of stable isotopes of the elements. The first such discovery was with neon, which was shown by mass spectrometry to have at least two stable isotopes: neon-20 with 10 protons and 10 neutrons and neon-22 with 10 protons and 12 neutrons. Mass spectrometers were used in the Manhattan Project for the separation of isotopes of uranium necessary to create the atomic bomb. Here’s how they work…

Atoms can be deflected by magnetic fields – provided the atom is first turned into an ion. Electrically charged particles are affected by a magnetic field although electrically neutral ones aren’t.

The sequence is :

Stage 1: Ionisation

The atom is ionised by knocking one or more electrons off to give a positive ion. This is true even for things which you would normally expect to form negative ions (chlorine, for example) or never form ions at all (argon, for example). Mass spectrometers always work with positive ions.

Stage 2: Acceleration and velocity selection

The ions are accelerated, then pass through crossed E and B fields which act as a velocity selector. Only ions having identical velocities can pass through a slit and into the magnetic field chamber.

Stage 3: Deflection

The ions are then deflected by a magnetic field according to their masses. The lighter they are, the more they are deflected.

The amount of deflection also depends on the number of positive charges on the ion – in other words, on how many electrons were knocked off in the first stage. The more the ion is charged, the more it gets deflected.

Stage 4: Detection

The beam of ions passing through the machine is detected electrically.bainbridge

Temperature & Thermometers

therm-digitalTemperature is the degree of hotness of a body. A thermometer tells us how hot by assigning a number to a temperature based on fixed points. Rather more formally and necessary to know if you’re doing IB is that temperature is a measure of the average kinetic energy of the molecules of a body.

A fixed point is a physical property that doesn’t change, such as the freezing point of pure water or its boiling point at standard atmospheric pressure. We then assign an equal scale between these two points, such as the Celsius scale (0 to 100)

There are lots of things that change with temperature – the length of a thin capillary tube filled with mercury, the resistance of a piece of wire, the pressure of an ideal gas – the list goes on and on. The nice thing about thermometers is that we can scratch the numbers on the glass like the numbers on a ruler – they are evenly spaced…

We don’t use mercury thermometers much these days because mercury is highly toxic and can’t be gotten rid of easily since it’s almost as unreactive as gold. Also, it might cause a little problem if you bit the end off accidentally while taking your temperature. Instead, we use digital thermometers which use resistors – called thermistors – whose resistance changes with temperature. A little processor measures the change in resistance and converts it to a digital display for us.

If temperatures change rapidly, we can’t use liquid-in-glass thermometers, they can’t respond quickly enough. [exam question alert…] Instead we can use a thermocouple. A thermocouple is made from two dissimilar metals ( not the same), twisted together at both ends with a meter in the loop.

Not a great picture - but you get the idea
Not a great picture – but you get the idea

If one end is hotter than the other a small voltage exists between the joined ends – this is called the Seebeck Effect. The bigger the temperature difference, the bigger the voltage measured by the voltmeter in the loop. We can calibrate the meter to read temperature.

These things are very versatile. Dependent on the choice of metals, they can measure rapid changes across very large ranges, also both high and low temperatures can be measured.

Evaporation

evapOn average, the molecules in a glass of water do not have enough heat energy to escape from the liquid, or else the liquid would turn into vapour quickly. When the molecules collide, they randomly bump into each other and transfer energy to each other in varying degrees, based on how they collide. Sometimes the transfer is so one-sided for a molecule near the surface that it ends up with enough energy to escape from the attractive pull of the liquid.
Volatile liquids (alcohol, petrol) need less energy for molecular escape
If the faster molecules escape, the slower, cooler ones are left behind. Evaporation  (sweating) causes cooling.
Evaporation happens at all temperatures, but faster in:
• Warm (average energy greater in the liquid, increasing probability of escape)
• Dry (allows molecules to escape into the air without competing for molecules already there)
• Windy conditions (evaporated molecules swept away, making room for more) This is why we blow on a drink to cool it
Boiling is forced evaporation and happens ONLY at one temperature.

Think about this applied to:

  • a puddle on a wet day (damp humid days puddles last longer)
  • washing drying (best if warm, dry and windy)
  • the shape of coffee cups (those with large surface area will cool more quickly than cofffe in little espresso cups)

This is a nice little interactive animation

Metallic bonding – a bit more

As we discussed in class, go to this site for an overview of bonding, including metallic bonding. We’re reminded that metals exist in a regular crystalline lattice, hence are shiny, densely packed with up to 12 nearest neighbours or touching atoms.

metal-tem1

The image is a transmission electron microscope picture of a metallic structure, at almost the molecular level. It shows how disjointed the structure is in real life. There are probably over a billion atoms in the picture

Fullerenes – carbon allotropes plus graphene (updated)

carbon 60
carbon 60

“Suppose we could find a material that is hundreds of times stronger than steel. Suppose that same material could also be used to make electronic circuits much smaller than today’s silicon-based computer chips? Well, such a material has been discovered and I was fortunate to be a member of one of the teams of scientists that discovered it – by accident.”

Bernd Eggen – SEED Foundation

Fullerenes are a range of newly found forms of carbon including carbon 60, a roundish molecule made of 60 carbon atoms If you imagine a flat sheet of graphite made round, that’s about it. It was named a fullerene or buckyball after Buckminster Fuller who  invented the geodesic dome which has a similar structure. This picture is of one in Antarctica – the structure can be made any size you like from a tent to a stadium.geodesic dome - living quarters in Antarctica


Back to fullerenes – how are the carbon atoms arranged?

The atoms of a C60 molecule are arranged in a shape that is exactly the same as a football.

The formal name for this shape is a truncated icosahedron. It has 32 faces, of which 20 are regular hexagons and 12 are regular pentagons. These faces come together at 60 points, or vertices. In a fullerene, there is a carbon atom at each of these vertices.

The truncated icosahedron is one of 13 Archimedean solids which you might have come across in Maths.

Have a go at making one, if you like.. Look here, download the pdf files and  try to make one.

What are fullerenes, or ‘buckyballs’ used for? The answer is more and more useful things like incorporation into armour plating, because they’re so strong, also they are making quite a stir in the medical world too.  Their ability to trap gases such as helium and store them, makes them suitable candidates for chemical and biological sponges.  For example, when the brain is injured it releases deadly nerve toxins,  which can have devastating effects on the brain.  Doctors could use them as sponges to soak up all the harmful chemicals surrounding the brain.  Then the chemicals would harmlessly pass through the body, without damaging any organs.

Researchers have found that buckyballs are a close fit on the site to block  HIV molecules.  Put another way way, they have found they can stop HIV activity by “plugging in” a buckyball..

Buckytubes
Buckytubes

The molecule also can be tubelike. Buckytubes have been found to be a possible replacement for any narrow “tube-like” part of the body – veins, neurons, muscle, which is very exciting for medical research.

NEW! The 2010 Nobel Prize for Physics has been won by Russian-born Geim and Novoselov, both now working at Manchester University in the UK for groundbreaking work on the monolayered allotrope of carbon called graphene. It’s like graphite but a single atom thick so it looks like a flat honeycomb with amazing possibilities for electronics since it’s a  fabulously good conductor and might one day be used instead of silicon chips in computers which generate a lot of heat.