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.  

AUS-e-TUTE Update

The following resources have been added to AUS-e-TUTE:

• Neutralisation Reactions (tutorial, game, test)
• Acidic, Basic, Neutral Solutions (tutorial, game, test)
• Properties of Alkanes (tutorial, game, test, exam)
• Properties of Alkanols (alcohols) (tutorial, game, test, exam)
• Properties of Alkanoic (carboxylic) acids (tutorial, game, test, exam)
• Properties of Amines (tutorial, game, test, exam)

Syllabus Study Guides have also been updated.

Ancient Elements

Only about a dozen elements were known to the people living in ancient civilizations.

• Copper beads dating from about 6000 B.C. have been found in Turkey.

• A lead statuette found in an Egyptian temple dates from around 3800 B.C. and golden artefacts have also been found in ancient Egyptian tombs.

• Silver was used by the ancient Greeks and Romans to prevent infection, and was used as an early form of currency.

• There is evidence of the systematic production of iron in Turkey around 2000 B.C. for use in tools and weapons.

• Carbon, in the form of diamonds, was also known in the Ancient world, but, carbon in the form of charcoal was far more important to these early people because it could be used in the production of copper, tin, and therefore bronze (an alloy of copper and tin).

• Sulfur was also known to the Ancient Egyptians and Greeks, who used it as a medicine.

• The ancient Chinese, Indians and Egyptians also knew about mercury, using it in ointments and cosmetics.

• Before 1000 B.C., Indians were extracting zinc from its ores. Ornaments containing 80% or more of zinc have been found.

• During the Bronze Age (an earlier period than the Iron Age), arsenic was included in bronze to make the alloy harder. Ancient people understood that they could produce arsenic by heating certain substances (which we would now call arsenic sulfides and oxides).

• Antimony was used in cosmetics in the Ancient world, notably by the Egyptians who used it around their eyes (known as kohl).

• Chromium has been found in ancient Chinese artifacts. The weapons the Chinese Terracotta Army carry are coated in chromium oxide and date from around the 3rd century B.C.

In fact, these were really the only elements known  until the 17th century A.D.
Today we know of over a 100 elements.
Chemistry has come a long way in the last few hundred years!

Further Reading:
History of the Elements
Metal Extraction Concepts
Periodic Table
Metals and Non-metals
Pure Substances and Mixtures

Suggested Study Questions:

1.  Find each of the elements mentioned above on the Periodic Table.
2. Draw up a table of the name and chemical symbol for each of the elements mentioned above.
3. Draw up a table classifying each of these elements as metals, non-metals or semi-metals (metalloids).
4. Name a mixture mentioned in the article above.
5. Name a compound mentioned in the article above.
6. There are only 3 metallic elements that are not a "silvery" colour. One of these is cesium (or caesium), but if the sample of cesium is very pure it loses its golden colour. Name the other two non-silvery metallic elements.
7. Explain why you often find weapons like swords made of iron, but you never find functional weapons made of gold.
8. Explain why you find ornamental weapons made out of gold, but rarely out of zinc.
9. Ancient people could have produced mercury by heating cinnabar (mercury(II) sulfide). The cinnabar decomposes, producing liquid mercury and sulfur. Write a word equation for the decomposition of cinnabar.

Phlogiston Theory

Before the modern chemical ideas of atoms and elements, phlogiston theory was a widely held belief.
According to phlogiston theory, matter consisted of three essential essences:

• sulfur (terra pinguis - the essence of inflammability, which was to become known as phlogiston)
• mercury (terra mercurialis - the essence of fluidity)
• salt (terra lapida - the essence of fixity and inertness)

 Phlogiston theory was an early attempt to to try to explain what happened when things were burnt or combusted. In phlogiston theory, substances were made up of a "calx" (or residue) combined with phlogiston (the essence of inflammability). When a substance was burnt (combusted), phlogiston was released, and the residue (calx) was left behind. Even the rusting of iron could be explained using phlogiston theory, because the "iron" would lose its phlogiston during the rusting process and leave behind the "calx" or residue. One of the problems with the phlogiston theory is that metals should lose mass when they burn, owing to the loss of phlogiston.

In the 18th century, Antoine-Laurent de Lavoisier, the man who is considered to be the father of modern of modern chemistry, conducted a series of combustion experiments. In these experiments he carefully weighed the substances to be combusted as well as the products of combustion, and found that the weight of the products of combustion was greater than the weight of the substance before combustion. He also demonstrated that when a substance corrodes in a sealed container, the gain in weight of the substance is equal to the loss in weight of the air in the container.
This was the beginning of the downfall of the phlogiston theory, but it was the beginning of the modern chemistry when Lavoisier generalized that if the weights of all substances involved in a chemical reaction are considered then there is no overall loss or gain in weight.

Further Reading:
http://www.ausetute.com.au/elemhist.html
http://www.ausetute.com.au/elements.html
http://www.ausetute.com.au/atomichist.html
http://www.ausetute.com.au/wriiform.html
http://www.ausetute.com.au/namiform.html
http://www.ausetute.com.au/namcform.html
http://www.ausetute.com.au/balcheme.html

Suggested Study Questions

1. Lavoisier burnt sulfur. When sulfur burns in air, it reacts with oxygen to form sulfur dioxide. Write a word equation for this reaction.
2. Write the chemical formula for each of the following:
   • sulfur
   • oxygen gas
   • sulfur dioxide gas
3. Write a balanced chemical equation for the combustion of sulfur to produce sulfur dioxide gas.
4. If Lavoisier had weighed out 32 grams of sulfur and then burnt it in air, the sulfur dioxide he collected would have a mass of 64 grams. What mass of oxygen would have been reacted with the sulfur? 
5. Explain why a substance such as sulfur appears to gain mass when it is combusted.
6. When wood is burnt, the mass of the ashes left behind is actually less than the mass of wood you started with. How do you explain this loss of mass?
7. Magnesium is a metal that combusts readily in oxygen gas to form magnesium oxide.
   • Write a word equation for the combustion of magnesium to form magnesium oxide,
   • Write a balanced chemical equation for this reaction.
8. If 20.16 grams of magnesium oxide is produced as a result of the combustion of 12.16 grams of magnesium, how much oxygen gas was consumed during the reaction?
9. Imagine you are living in the 18th century and that you are a firm believer in the phlogiston theory. How would you explain to Lavoisier how metals gain mass when they burn?

Calculations for Strong Bases

AUS-e-TUTE has just added new resources!
As part of the update of our "Acids and Bases" topic, tutorials, games, tests, and exams have been added for the following:

• pOH Concepts
• Strength of Bases
• Calculating the pOH of Strong Bases (aqueous solutions)
• Calculating the Hydroxide Ion Concentration of Strong Bases (aqueous solutions)
• Calculating the pH of Strong Bases (aqueous solutions)
• Calculating the Hydrogen Ion Concentration of Strong Bases (aqueous solutions)

AUS-e-NEWS March 2013

Since the 1960's, superacids have become an essential tool in industry.

Without the powerful ability of superacids to react with, and break down, raw petroleum we would not have a supply of cheap, high-strength plastics.

But what is a superacid?

Read this super issue of AUS-e-NEWS to find out !

Links to the following new resources can be found in the Test Centre (http://www.ausetute.com.au/members/testcent.html)

                - Properties of Acids and Bases (tutorial, game, test)

                - Definitions of Acids and Bases (tutorial, game, tests, exams)

                - pH Scale (Tutorial, game, test, exam)

                - pH Calculations, introductory (tutorial, game, test, drill)

                - pOH Calculations, introductory (tutorial, game, test, drill)

                - Hydrogen Ion Concentration calcuations, introductory (tutorial, game, test, drill)

                - Hydroxide Ion Concentration Calculations, introductory (tutorial, game, test, drill)

                - Strength of Acids (Tutorial, game, test,exams)

                - Strong Acid pH Calculations (Tutorial, game, test, exam)

                - Strong Acid Hydrogen Ion Concentration Calculations (Tutorial, game, test, exam)

                - Strong Acid Hydroxide Ion Calculations Calculations (Tutorial, game, test)

                - Strong Acid pOH Calculations (Tutorial, game, test)

                - Oxidation of Alkenes (tutorial, game, test, exam)

If you have haven't received your issue of AUS-e-NEWS, please contact us.

pH of the Manning River

"A POISONOUS plume of acid 'comparable to car batteries' is forming in the Manning River, near Taree in northern NSW, researchers from the University of NSW say." reports Ben Cubby in his article "Acid plume poisons river after floods"  in the Sydney Morning Herald, Thursday 28^th February 2013.
Let's take a look at the chemistry behind the story.
Firstly, Taree, a town located about 3 hours north of Sydney, is surrounded by farm land, land reclaimed from the wetlands. The sulfate ion, SO₄^2-, is commonly found in fertilizers used in commercial farming. Recent rain, and flooding, has concentrated these acidic sulfates in the river.

A little later in the story we find that "Tests carried out by the university's water research laboratory show alarming amounts of acid, with a pH level of two - compared with a normal level of seven - meaning the Manning River water is roughly as acidic as lemon juice."
Chemistry students would realize that there are many factors that can effect the pH of river water, for example, if the river runs through limestone rocks the pH of the water will increase, but if the river runs through areas of peat the pH of the water will decrease.
The pH of river water typically lies within the range of about 6.5 to 8.5.  Water with a low pH is said to be acidic, water with a high pH is said to be basic or alkaline. Most organisms, with the exception of some bacteria, can not live in water with a pH less than 6.5. Similarly, a pH greater than 8.5 also presents problems for the survival of most organisms in rivers.
The juice of a lemon often has a pH of about 2, and the vinegar you buy from the shop will also have a pH around 2. Both lemon juice and vinegar are acidic substances.
On the other hand, oven cleaner has a pH of about 13 and soapy water has a pH of about 12. Both oven cleaner and soapy water are basic solutions (or alkaline solutions).

Is river water with a pH of 2 "comparable to car batteries" as claimed in the story?
Lead-acid batteries, such as those found in cars, contain sulfuric acid, H₂SO₄. Sulfuric acid is a strong acid that undergoes dissociation in water so that an aqueous solution of sulfuric acid contains both hydrogen ions, H⁺, and sulfate ions, SO₄^2-. The acidic river water will contain both hydrogen ions, H⁺, and sulfate ions, SO₄^2-, if sulfate fertilizers have been used on the land where the river runs, so the acid in the car's lead-acid battery and the river water are comparable in that they contain the same ions.
The concentration of sulfuric acid in the lead-battery will usually be between 4 and 5 mol L^-1 (let's just assume its 4.5 mol L^-1 ).
If we assume the complete dissociation of sulfuric acid:
H₂SO₄ → 2H⁺ + SO₄^2-
Then the concentration of hydrogen ions, H⁺, in solution is 2 times the concentration of the sulfuric acid:
[H⁺] = 2[H₂SO₄ ] = 2 x 4.5 = 9.0 mol L^-1
We can calculate the pH of the battery acid, since pH = -log₁₀[H⁺] = -log₁₀[9.0] = -0.95
Battery acid is very, very acidic!
While you might be very happy to put vinegar on your chips (pH~2) and eat them, you  should most definitely NEVER put battery acid on your chips and eat them!

Reference:

 http://www.smh.com.au/environment/conservation/acid-plume-poisons-river-after-floods-20130227-2f6bh.html#ixzz2MA2XQ5AJ

Further Reading:
Calculating pH

Suggested Study Questions:

1. Draw up a table with two headings; acid and base. Place each of the following substances in  the correct column in the table : orange juice (pH =3), baking soda (pH = 9), milk (pH =6), tomato juice (pH =4),  drain cleaner (pH =14), black coffee (pH=5).
2. Calculate the concentration of hydrogen ions in each of the substances in the table, in mol/L
3. Assume a drinking glass has a total value of 250 mL, and that a "full glass" of a drink is actually only 225 mL. Calculate the moles of hydrogen ions found in a "full glass" of
   • orange juice
   • milk
   • black coffee
4. Consider 225 mL of the river water with a pH =2. Calculate the moles of hydrogen ions present.
5. Imagine you took 25 mL of orange juice (pH=3) and diluted it with water to a volume of 500 mL. 
   • Calculate the concentration of hydrogen ions in the diluted solution.
   • Calculate the pH of the diluted solution.
6.  Sometimes cooks heat ingredients to "release their flavour". Acids, like vinegar, tend to have a sour taste. A cook has 200 mL of vinegar (pH=2.2)  in a pan.
   • Calculate the concentration of hydrogen ions present in the solution.
   • On very gentle heating, the volume of the vinegar solution is reduced until it is only 50 mL. Calculate the pH of this concentrated solution.
7. We could prepare a solution of sulfuric acid with a pH of 2 using the acid out of the car's lead-acid battery.
   • Calculate the concentration of hydrogen ions present in 4.5 mol L^-1 sulfuric acid.
   • Calculate the concentration of hydrogen ions present in sulfuric acid with a pH of 2.
   • If you had 10 mL of battery acid, what volume of water would you have to add in order to prepare a sulfuric acid solution with a pH of 2?
8. Imagine the a dam with a volume of 250,000ML and a pH=2. How much water would have to be added to the dam in order for the dam to have a pH=7 ?