In the spirit of the wonderful photobook The Elements by Theodore Gray (which I have previously blogged about), starting a collection of elements is a great way of introducing yourself (or your children) to basic chemistry. Here are some suggestions, and a list of 24 elements to start with….
2: Helium (He)
Helium is lighter than air, so balloons are often filled with helium.
6: Carbon (C)
Carbon is most easily added to your collection in the form of charcoal. Zinc–carbon batteries have a carbon rod at the centre.
7: Nitrogen (N)
Air is about 78% nitrogen. To add nitrogen to your collection, just fill a small bottle with air.
8: Oxygen (O)
Air is about 21% oxygen. To add oxygen to your collection, just fill a small bottle with air.
9: Fluorine (F)
Fluorine is a toxic gas. But octahedral fluorite crystals (calcium fluoride, CaF2) make a great addition to a collection.
11: Sodium (Na)
Sodium is a reactive metal which will spontaneously catch fire when in contact with water. But sodium chloride (ordinary table salt, NaCl) is perfectly safe.
12: Magnesium (Mg)
Magnesium is a flammable metal, but you can substitute crystals of Epsom salts (magnesium sulfate, MgSO4), which can be obtained from a pharmacy.
13: Aluminium (Al)
Aluminium (aluminum in the USA) is most easily available as aluminium foil.
14: Silicon (Si)
Silicon is widely used in transistors and integrated circuits (chips).
15: Phosphorus (P)
The side of a box of matches is largely composed of phosphorus.
16: Sulfur (S)
Sulfur powder, also called “flowers of sulfur,” is available from pharmacies.
17: Chlorine (Cl)
Chlorine is a toxic yellowish-green gas. But sodium chloride (ordinary table salt, NaCl) is perfectly safe.
20: Calcium (Ca)
Calcium is a reactive metal, but you can substitute crystals of calcite (calcium carbonate, CaCO3) or gypsum (calcium sulfate, CaSO4).
24: Chromium (Cr)
Chromium is used for plating (“chrome plating”) to prevent rusting. Also, “stainless steel” is between about 16% and 25% chromium.
26: Iron (Fe)
Iron is one of the most widely used metals. Iron nails are easy to add to your collection. Like nickel and cobalt, iron is attracted by a magnet.
28: Nickel (Ni)
The United States “nickel” coin is actually only 25% nickel (and 75% copper), but objects made of pure nickel can be found. Indeed, Canadian “nickel” coins from 1955–1981 are almost pure nickel.
29: Copper (Cu)
Copper pipes are widely used in plumbing. You can buy copper plumbing fittings, or get offcuts of pipe from a plumber. Copper electrical wire is also easy to find.
30: Zinc (Zn)
Galvanised iron is coated with zinc to prevent rusting. Also, filing off the copper coating on a US penny reveals a coin made mostly of zinc.
47: Silver (Ag)
A silver coin, or a piece of silver jewellery, would make a fine addition to your collection.
53: Iodine (I)
Iodine is a dark solid, but is sold in pharmacies as a brown solution in alcohol, called “tincture of iodine.”
60: Neodymium (Nd)
Neodymium is one of the “rare earth” elements. Neodymium magnets are the most common form of strong magnet. They are made of an alloy of neodymium, iron and boron (Nd2Fe14B).
74: Tungsten (W )
The filament in an incandescent light bulb is made from tungsten (but because of the danger of broken glass, only an adult should attempt to remove the filament, and then only with very great care).
79: Gold (Au)
A gold coin, or a piece of gold jewellery, would make a truly wonderful addition to your collection. Alternatively, for under $10, science museums will sell impressive-looking bottles of gold leaf floating in liquid.
82: Lead (Pb)
A fishing sinker is probably the easiest lead object to find.
So there you are. Those could be the first 24 elements in your collection!
- Helium (He, element 2) – used in balloons, because it is lighter than air
- Carbon (C, element 6) – one of the key elements in living things
- Nitrogen (N, element 7) – makes up 78% of the atmosphere
- Oxygen (O, element 8) – makes up 21% of the atmosphere
- Aluminium (Al, element 13) – a light metal used to make saucepans and aeroplanes
- Silicon (Si, element 14) – used to make electronics
- Phosphorus (P, element 15) – used in elemental form on the side of matchboxes
- Sulfur (S, element 16) – a widely used element which occurs naturally in elemental form
- Titanium (Ti, element 22) – a light, strong metal
- Iron (Fe, element 26) – the most widely used metal (mixed with other elements it becomes steel)
- Copper (Cu, element 29) – a metal that has been used for about 10,000 years, named after the island of Cyprus
- Zinc (Zn, element 30) – used in batteries and to prevent corrosion
- Silver (Ag, element 47) – widely used in jewellery since ancient times (the symbol is from the Latin argentum)
- Tin (Sn, element 50) – about 5,000 years ago, tin (Latin stannum) was mixed with copper to produce bronze
- Iodine (I, element 53) – dissolved in alcohol, it is used as a disinfectant
- Gold (Au, element 79) – widely used in jewellery since ancient times (the symbol is from the Latin aurum)
Our previous kitchen chemistry post discussed soap. Soap consists of sodium salts (or potassium salts) of fatty acids. For example, sodium stearate soap consists of sodium (Na+) and stearate C17H35COO−) ions:
These ions do their soapy job because the charged oxygen end of the molecule is attracted to water (since the hydrogen side of a water molecule has a slight positive charge). The long hydrocarbon tail, on the other hand, is attracted to oil and grease. Mixing soap and water with oil or grease therefore produces little grease droplets surrounded by many, many stearate (or other fatty acid) ions, with their tails embedded in the grease droplet, and their oxygen heads poking out into the water. I’ve only had the patience to draw eight for this droplet:
Because these little droplets are surrounded by negative charges (on the oxygen atoms), the droplets repel each other. This means the droplets stay separate from each other, and cannot combine into larger oily blobs. Because the negatively charged oxygen atoms are attracted to water molecules, the droplets also remain dispersed within the water (so that they can later be rinsed away). In fact, what we have here is an emulsion (or sol) of oil or grease in water, stabilised by the soap. Recall the image with which we began this post series:
Other kinds of emulsion will likewise need some kind of molecule that keeps the droplets separate – usually also a molecule with a distinct head and tail. In mayonnaise, for example, the emulsion of oil in water is stabilised by phospholipid molecules from egg yolks. These molecules also have a “head” attracted to water and a “tail” attracted to oil.
This post brings our kitchen chemistry series to a close, at least for now.
Our previous kitchen chemistry post discussed fats and oils, which are “triple esters” of glycerol:
Apart from their role in diet, fats are also used to produce soap:
The soap-making process involves reacting fats with strongly alkaline substances, such as lye (sodium hydroxide, NaOH). This can be done at home, but since lye is dangerous, soap-making is not appropriate for children (see these precautions: 1, 2, 3).
In solution, the lye exists as sodium (Na+) and hydroxide (OH−) ions (indeed, the presence of hydroxide ions is what “alkaline” means). The hydroxide ions react with the fat to free the glycerol:
Fatty acid ions (such as stearate ions, C17H35COO−) are also produced:
Since the sodium ions from the lye still exist, soap is basically sodium stearate, sodium palmitate, or something similar. Because it is the result of reacting a very strongly alkaline substance (sodium hydroxide) with very weak acids (fatty acids), soap itself is also alkaline. This alkaline nature can be harsh on the skin, and especially on the hair. Shampoos are therefore usually made from synthetic detergents, and formulated to be mildly acidic (with a pH between 5 and 7).
Another problem with soap is that it reacts with dissolved calcium, iron, or magnesium ions in hard water, giving an insoluble soap scum of compounds such as magnesium stearate. This can be demonstrated at home by mixing soap solution with a solution of epsom salts (see here or here).
Our previous kitchen chemistry post discussed esters. Fats and oils (triglycerides) are an important special case of esters. The alcohol in triglycerides is glycerol, a “triple alcohol” with three OH groups:
The glycerol combines with “fatty acids” (like the one on the right) which resemble acetic acid (left), but with a much longer hydrocarbon chain hanging off the COOH group:
The resulting triglyceride esters have three COO groups:
Fatty acids have important dietary implications, and they can be classified in dietary terms, but the most common classifications are chemical. The three main chemical classifications all refer to the presence of carbon-carbon double bonds:
One important classification is in terms of the number of carbon-carbon double bonds:
- Saturated fatty acids have no carbon-carbon double bonds (they are “saturated” in the sense of containing as much hydrogen as possible). Fats made from saturated fatty acids (“saturated fats”) tend to be solid at room temperature, because the straight-line molecules stick to each other. Saturated fats are usually of animal origin (although coconut oil and palm oil are also mostly saturated).
- Monounsaturated fatty acids have exactly one carbon-carbon double bond per molecule. Oleic acid (in e.g. olive oil) is an example.
- Polyunsaturated fatty acids have two or more carbon-carbon double bonds per molecule. Linoleic acid (in e.g. sunflower oil) is an example.
The position of carbon-carbon double bonds is also significant. A common classification counts the position of the first double bond, starting from the “omega” end of the molecule (the end furthest from the oxygen atoms). For example, there are omega-3, omega-6, and omega-9 fatty acids:
Finally, the orientation of double bonds is very important. In cis fatty acids, there are two hydrogen atoms on the same side of the double bond, giving a molecule with a “kink.” In trans fatty acids, the two hydrogen atoms are on the opposite sides of the double bond, giving a straight-line molecule (trans fats are usually synthetic, resulting from the partial hydrogenation of vegetable oils). Since the straight-line molecules tend to stick together, “trans fats” (made from trans fatty acids) tend to be solid at room temperature, while “cis fats” (made from cis fatty acids) tend to be liquid – that is, oils (such as olive oil) rather than fats:
Fatty acids can also be classified in dietary terms. The body needs fatty acids, but can manufacture most of them itself. Essential fatty acids are fatty acids that must be included in the diet. Both ALA and linoleic acid (found in vegetable oils) are essential. Adult men need about 13 grams of linoleic acid and 1.3 grams of ALA per day. Some omega-3 fatty acids from oily fish should also be included in the diet.
In contrast, trans fats are particularly unhealthy, and should be eliminated from the diet completely. This can be difficult in the USA, since pre-packaged foods there often contain trans fats (because of their long shelf life). Monounsaturated and polyunsaturated oils are also preferable to solid saturated fats.
Our previous kitchen chemistry post discussed acids, particularly the acetic acid in vinegar (and its reaction with sodium bicarbonate):
Acids like acetic acid, with a structure that looks like X–COOH, are also important because they react with alcohols (with a structure Y–OH) to form compounds called esters. The reaction is X–COOH + Y–OH → X–COO–Y + H2O. For example:
Industrially, strong acids are often used to make this reaction happen, but biologically, enzymes do the job. The combination of acetic acid and ethanol is ethyl acetate (used in some nail polish removers), and the image below also shows isoamyl acetate and geranyl acetate. Each ester has the same X–COO–Y structure:
Esters have a “fruity” smell, and indeed the odour of fruit is largely a result of a mix of various esters (go on, sniff some fruit, and celebrate the complex odours that you smell!). Synthetic fruit flavours likewise use esters, but typically in a simpler mix that never smells quite like the real thing.
James Kennedy has produced this wonderful infographic of esters and their smells (click on the thumbnail to zoom):