Ionize or Ionise?

 In chemistry we have a verb to describe the process of producing ions, but how do you spell it?

Is it ionize? (rhymes with prize)

Or is it ionise? (rhymes with surprise)

The root of the word is Greek, so according to my school grammar teacher, the suffix should be "ize". The preferred IUPAC spelling appears to be ionize, and hence ionizing and ionization.

Similarly, we also have a verb to describe the process of producing atoms, also from a Greek root, so the preferred spelling should be atomize, not atomise. Hence we form the words atomizing and atomization.

I'm sure we'll continue to see the alternative spellings with an "s" rather than a "z" but they won't get you a Nobel Prise. Surprize!

Astatine's Ionization Energy

Astatine is the product of the radioactive decay of some heavier elements and is the rarest naturally occurring element on Earth, only a few grams of astatine is estimated be present in the whole of the Earth's crust at any one time. All of astatine's isotopes are short-lived, with astatine-210 having the longest half-life of all its isotopes, 8.1 hours. As a result, astatine was unknown until 1940, when scientists bombarded bismuth-209 with alpha particles and produced astatine.
Even today we don't know very much about astatine, but estimates about its properties have been made based on its position in the Periodic Table, right under iodine in Group 17 (halogens). The first ionization energy of astatine has been estimated to be between 849.11 and 926.29 kJ/mol (8.8 and 9.6 eV).

The ionization energy, the energy required to remove an electron from the valence shell of an atom, is one of the most important properties that influences the chemical behaviour of an element.

In May 2013 an international team of researchers announced that they had measured the first ionization energy of astatine using laser ionization spectroscopy and found it be be 9.31751 eV (899.02 kJ/mol)

Reference:
Rothe, S. et al. Measurement of the first ionization potential of astatine by laser ionization spectroscopy. Nat. Commun. 4:1835 doi: 10.1038/ncomms2819 (2013).

Further Reading:
http://www.ausetute.com.au/pertable.html

http://www.ausetute.com.au/trendgp7.html 
http://www.ausetute.com.au/trendie.html 
http://www.ausetute.com.au/isotopes.html
http://www.ausetute.com.au/nucledec.html
http://www.ausetute.com.au/halflife.html

Suggested Study Questions:

1. Use the Periodic Table to find the following:
   • astatine's chemical symbol
   • astatine's atomic number
2.  Use the Periodic Table to find the
   • The group astatine belongs to
   • the period astatine belongs to
3. How many valence electrons does an atom of astatine have? Explain your answer.
4. Describe the trend in melting points as you go down astatine's group in the periodic table, then estimate the melting point of astatine.
5. Describe what you think astatine would look like at room temperature and justify your answer on the basis of trends in the periodic table. 
6. How does astatine-207 differ from astatine-210? 
7. Astatine-211 and 2 neutrons are produced when bismuth-209 is bombarded with alpha particles.  Write a nuclear equation for this reaction.
8. Imagine working in a laboratory. You have been given 100 μg of astatine-210 at 9 am for your experiment. Assuming the half-life of astatine is 8 hours, how much astatine-210 would you have left when you leave the lab at 5 pm?
9. The half-life of astatine-219 is about 1 minute. If you had 100 μg of astatine-219 at 9 am, how much astatine-219 would you have 5 minutes later at 9:05 am ?
10. Use the information in the article above to estimate the conversion factor between electronvolts (eV) and kJ/mol. 
11. Why do we not have an accurate measure of how much astatine is found in the Earth's crust?
12. Suggest a way that scientists can estimate the amount of astatine in existence in the Earth's crust.  

Neutral pH?

We hear this term a lot, often in advertising. But what does it mean?

From a Chemist's point of view, there are two different concepts involved in this seemingly harmless "neutral pH" expression. These two different concepts are:

• neutral
• pH

Let's take a look at the Chemist's definition of neutral first.
A solution is neutral if the concentration of hydrogen ions, [H⁺], is equal to the concentration of hydroxide ions, [OH^-].
Chemists often use square brackets to denote concentration, the concentration of  hydrogen ions can be written as [H⁺] and the concentration of hydroxide ions can be written as [OH^-].
So, for a neutral solution:

[H⁺] = [OH^-] = neutral solution 

Pure water is an excellent example of a neutral substance.

Some of the water molecules, actually very few of them, dissociate to form hydrogen ions and hydroxide ions:

H2O

H+ + OH-

Every time a water molecule dissociates, it produces one hydrogen ion, H⁺, and one hydroxide ion, OH^-, so that the concentration of hydrogen ions is always the same as the concentration of hydroxide ions.
Therefore, pure water is always neutral!

The pH of a solution is a measure of the hydrogen ion concentration in the solution. pH can be defined as:

pH = -log₁₀[H⁺]

This equation can be used to calculate the pH of our neutral water, but only if we know the concentration of  hydrogen ions in the water.

The concentration of hydrogen ions in water is not constant!

The concentration of hydrogen ions in water depends on the temperature of the water!
The dissociation of water molecules requires energy:

H2O + energy

H+ + OH-

If you put more energy into the system by heating it, then more water molecules dissociate, the concentration of hydrogen ions increases and the concentration of hydroxide ions also increases.
If you take energy away from the system by cooling it, then fewer water molecules dissociate, the concentration of hydrogen ions decreases and the concentration of hydroxide ions also decreases.
If we were to measure the concentration of hydrogen ions in pure water at various temperatures, we would find the following values:

Water temperature	[H+] x 10−7 M	pH
0°C	0.32	7.50
10°C	0.55	7.26
18°C	0.84	7.08
25°C	1.10	6.96
30°C	1.34	6.87
50°C	2.82	6.55
60°C	3.55	6.46
70°C	4.60	6.34
80°C	5.92	6.23
90°C	7.28	6.14
100°C	8.54	6.07

So what is the pH of water?
The pH of water is dependent on the temperature of the water.
Water is neutral for every value of pH because the concentration of hydrogen ions is always equal to the concentration of the hydroxide ions.
We can ONLY talk about the pH of water IF we state the temperature of the water.
For example, we can talk about water having a pH of approximately 7 at 25^oC, or we could say that the pH of water is approximately 6 at 100^oC.
Pure water is always neutral.
Pure water is neutral at 25^oC.
Pure water is neutral at 100^oC.

As Chemistry students, what we can't say is that water has a pH of 7, or that a neutral aqueous solution has a particular pH, unless we state the temperature of the system.

Further Reading:
Definitions of Acids and Bases
pH
Dissociation Constant for Water

Suggested Study Questions:

1. Plot a graph of temperature versus concentration of hydrogen ions in water. Describe the shape of the line, and write a generalization that links hydrogen ion concentration and temperature.
2. Plot a graph of temperature versus pH of water. Describe the shape of the line and write a generalization linking the  temperature of water and its pH.
3. Use your graph to find the pH of water at:
   • 12^oC
   • 22^oC
   • 32^oC
4. Construct a table giving the concentration of hydroxide ions in water at each of the temperatures shown above.
5. Plot a graph of temperature versus concentration of hydroxide ions in water. Describe the shape of the line, and write a generalization linking hydroxide ion concentration in water and temperature.
6. Use your graph to find the concentration of hydroxide ions in water at:
   • 12^oC
   • 22^oC
   • 32^oC
7. Explain why water is neutral at all temperatures.
8. Explain why the pH of water varies with temperature.