Why is the heat of formation for gaseous oxygen equal to 0?

Question: Why is the heat of formation for gaseous oxygen equal to 0?

Answer:
1. The standard heat of formation of any compound is defined as the enthalpy change for the compound when it is formed from its elements in their standard states.

2. Gaseous oxygen (O_2(g)) is a molecule (not a compound). The standard state for oxygen is as a gas, O_2(g).

3. There is no need to change gaseous oxygen, O_2(g) into its standard state because that is how it exists under standard conditions, therefore its heat of formation is 0.

Find out more at, and see worked examples, at https://www.ausetute.com.au/heatform.html

Periodic Table Challenge

 2019 is the International Year of the Periodic Table and IUPAC has a game you can play online!
Here is the link https://iupac.org/100/pt-challenge/

Before you can play, you need to choose an avatar (an element ofcourse!).
Now I don't want to influence your decision in anyway, but ..... the ONLY element named after a woman is Meitnerium, Mt, after Lise Meitner (Curium is named after the wife and husband team of Marie and Pierre Curie).

There are 15 multiple choice questions to answer.
Complete the quiz and generate your certificate.
Get 9 or more correct answers and you get the chance to enter the Nobelium Contest with a chance to win a limited edition Periodic Table autographed by a Nobel Laureate in Chemistry.

The questions are really interesting. Here is a sample..

•  In the 1920s, many companies promoted their products by adding radium. One of the top-selling radium-containing products was 'Radithor'. What was it?

• In the 1880s, Lord Rayleigh found that the density of nitrogen from air was 0.5% greater than the density of nitrogen obtained from other sources. What discovery resulted from this small discrepancy? 

• The 1944 American film ‘Arsenic and Old Lace’, starring Cary Grant, features what use of this chemical element? 

• Despite having few uses, erbium has one very important use that makes it beneficial to the modern world. Which one? 

• Whereas in humans oxygen is bound to iron-containing haemoglobin, spiders and other animals transport oxygen via a different protein in their blood, hemocyanin, which contains copper. What is the color of their blood?

• What happens when a teaspoon made of gallium is used to stir a cup of warm tea?

• The atomic weight of argon varies depending on its source. What is the reason for this phenomenon?

•  Vincent van Gogh’s painting Sunflowers is getting darker due to the presence of chromium in the paint. What is the chemistry behind this change in appearance?

•  When tellurium is absorbed through the skin, it is excreted through sweat as hydrogen telluride making you unfit for social interactions. Why?

• Indium is mostly used to make indium tin oxide which is an important part of touchscreens. How did indium get its name?

•  What name was proposed for bromine by its discoverer, the French scientist Antoine Balard?

 

Gold Nuggets in 2019

Between 1850 and 1900, the city of Bendigo in Victoria, Australia, was the centre of a Gold Rush. Central Deborah Gold Mine, the last commercial gold mine to operate in Bendigo, re-opened as a tourist attraction in 1986.
Gold can still be found in the Bendigo area.
On Mothers' Day 2019, a family out walking Lucky their dog on the outskirts of Bendigo walked onto a gold nugget. They took it along to the local IGA supermarket to weigh it. The gold nugget weighed 624 grams (about 20 ounces).
Today, the price of gold in Australia is listed as $65.76 per gram. So, if pure, the gold in this nugget would be worth 624 × $65.76 ≈ $41,000.
How big would this gold nugget be?
We know the mass of the nugget is 624 grams.
We can look up the density of gold in tables, ρ = 19.3 g cm^-3
Since density = mass (g) ÷ volume (cm³)
19.3 = 624 ÷ volume (cm³)
volume (cm³) = 624 g ÷ 19.3 g cm^-3 = 32.3 cm³
Which could be represented by a cube approximately 3.2 cm × 3.2 cm × 3.2 cm
Not very big at all is it!

Ballarat, another Victorian Gold Rush town and site of the historic "Eureka Stockade", was also the place where another spectacular gold nugget was found in June 2019 (and reported nationally in July 2019). This gold nugget weighed about 2 kilograms, or 2,000 grams.
At today's prices, it would have a value of about 2,000 × $65.76 ≈ $130,000
And how big would this nugget be?
density = mass (g) ÷ volume (cm³) volume (cm³)
density = mass (g) ÷ density (g cm^-3) = 2,000 g ÷ 19.3 g cm^-3 = 103.6 cm³
The dimensions of a cube with this volume would be about 4.7 cm × 4.7 cm × 4.7 cm
Which would fit nicely into the palm of your hand as shown in the photograph below

Further Reading:
Density Calculations

Suggested Study Questions:

1.  The density of gold is 19.3 g cm^-3. Calculate the mass of
   • 1 cm³ of gold 
   • 10 cm³ of gold 
   • 1 m³ of gold
2.  The density of gold is 19.3 g cm^-3. Calculate the volume of
   • 1 g of gold
   • 10 g of gold
   • 1 kg of gold 
3.  The density of gold is 19.3 g cm^-3. Calculate the dimensions of a cube of gold which has a mass of
   • 5 g
   • 500 g
   • 5 kg
4. The density of gold is 19.3 g cm^-3. Calculate the diameter of a sphere of gold which has a mass of
   • 2 g
   • 200 g
   • 2 kg
5. A credit card has the approximate dimensions 65 mm × 55 mm × 1 mm. Calculate:
   • volume of the credit card in cm³
   • mass of a gold credit card
   • value of a gold credit card if the cost of gold is $65 per gram
   • Why aren't "gold" credit cards really made out of gold?
6. Gold is one of the few metals that is found in nature as the "native" element (that is, it is found as the element and not in compounds). Explain why gold can be found in nuggets.
7. Name some other metals that can also be found in their native state (that is, found as the element and not as compounds). Explain why these metals can be found in their native state. 
8. Name a metal that is not found on Earth in its native state, and explain why it is not found in nature as the uncombined element.

Formula for Hydrogen?

I admit it. I love TV game shows. Last Friday I watched one of my favourite shows while eating my (late) lunch. I was even moderately successful at answering some of the questions, until the Host asked The Chaser what the chemical formula for hydrogen was. This led to the following exchange:
Chaser: H
Host: Incorrect
Contestants: H one (we will assume they meant H₁)
Host: Incorrect. The correct answer is H two (we will assume he meant H₂)

So, who was right?

Let's take the Host's "correct" answer first.
The Earth's atmosphere contains small amounts of diatomic molecules of hydrogen gas. "Di" means two and "atomic" refers to atoms so hydrogen gas in the atmosphere is made up of molecules in which 2 atoms of hydrogen are bonded together. When we make hydrogen gas in the laboratory we are making these H₂ molecules. So it seems that the Host got it right ..... except ..... the question didn't ask for the formula of hydrogen gas found in the atmosphere!

So let's turn our attention to the Contestants' response.
Is H₁ a plausible chemical formula for hydrogen?
Not really. If there is only 1 atom of an element in the chemical formula, the "1" is trivial and not included in the formula, so H₁ is the same as H which was the Chaser's response!

So, was the Chaser right?
Is H a valid chemical formula for hydrogen?
Hydrogen is a strange atom. It has 1 proton in its nucleus, and 1 electron "orbiting" that nucleus. In fact, this 1 so-called "valence electron" is a feature common to all Group 1 metals (alkali metals), but other properties of hydrogen suggest it is more like a non-metal than a metal. This similarity to the Group 1 metals led to the prediction that it should be possible to create metallic hydrogen. This would be a solid in which the hydrogen atoms (protons in effect) would be held in a 3-dimensional array with delocalised electrons acting as the metallic bonds holding the array together. This metallic hydrogen would, in theory, be an excellent conductor, indeed it would be a "superconductor", which is why the race has been on to create it!

A chemical formula of a covalent molecule tells us how many atoms of each element are covalently bonded together, H₂ has 2 atoms of hydrogen with a covalent bond between them.
But the chemical formula for a 3-dimensional metallic array refers to the ratio of atoms of each element, if only 1 element is present in a metallic array, like that of sodium metal, then the chemical formula is just the symbol for the element, Na, in this case, or H if you are referring to metallic hydrogen.
So, H is a valid chemical formula for metallic hydrogen, if it exists.
But does metallic hydrogen exist?

In January 2017, researchers at Harvard University announced that they had produced metallic hydrogen in the laboratory using immense pressure. So metallic hydrogen, H, can exist.

Back to the game show.
The Host was right, H₂ is the chemical formula for gaseous hydrogen in the atmosphere.
The Chaser was right, H is the chemical formula for metallic hydrogen.
The Contestants were almost right: Chemists don't write H₁ they just write H.

There is a moral to this story.
Be careful when writing questions. The question should not be ambiguous unless you are prepared to accept multiple different answers that are correct.
Be even more careful when answering test and exam questions. If you need to make assumptions to answer the question you MUST state what those assumptions are when you write your answer.

Reference:

1. Ranga P. Dias, Isaac F. Silvera. Observation of the Wigner-Huntington Transition to Metallic Hydrogen. Science, 2017 DOI: 10.1126/science.aal1579

Tutorials Relevant to this Post

Periodic Table of the Elements
Elements and Compounds
Metals and Nonmetals
Molecular Formula

Naming Covalent Compounds
Empirical Formula and Molecular Formula
Trends in Group 1 Elements
Metallic Bonding

Suggested Study Questions

1. Use the Periodic Table of the Elements to find the chemical symbol for each of the following atoms:
• hydrogen
• helium
• carbon
• nitrogen
• oxygen
• chlorine
2. Write a molecular formula for each of the following diatomic gas molecules:
• hydrogen
• nitrogen
• oxygen
• chlorine
3. Give the number of atoms of each element present in the molecular formulae below:
• H₂O
• H₂O₂
• CO
• CO₂
• NH₃
• NO
• NO₂
• N₂O₂
4. Let M represent an atom of an element. Circle the elements below for which the molecular formula of the element at room temperature and pressure could be represented by M
• helium
• sodium
• oxygen
• iron
• gold
• neon
• chlorine
• nitrogen
• hydrogen
5. For the description of each molecule below, write the molecular formula
• one carbon atom and four hydrogen atoms
• one nitrogen atom and three chlorine atoms
• two nitrogen atoms and one oxygen atom
• one nitrogen atom and five oxygen atoms
• two chlorine atoms and two oxygen atoms
• one carbon atom, one hydrogen atom and three chlorine atoms
6. Given the name of each molecule below, write the molecular formula:
• hydrogen chloride
• carbon monoxide
• carbon dioxide
• sulfur dioxide
• sulfur trioxide
• sulfur dichloride
7. Consider the list of compounds with a possible molecular formulae below. Circle the incorrect formulae and justify your answer:
• water, 2HO
• carbon monoxide, C₁O₁
• hydrogen peroxide, H2O₂
• sulfur trioxide: SO₂
• ammonia, NH3
• hydrogen sulfide, H₂S
• carbon dioxide, C₂O
• sulfur dichloride, S₁Cl₂
8. From the list below, circle the elements that belong to Group 1 of the Periodic Table of the Elements:
• sodium
• helium
• oxygen
• lithium
• chlorine
• nitrogen
• carbon
• potassium
• calcium
9. Draw a table with the headings "metal" and "nonmetal". Place each of the following elements in the correct column:
• hydrogen
• helium
• calcium
• carbon
• nitrogen 
• potassium
• oxygen
• chlorine
• sodium
10. From the list below, circle the elements that would exist at room temperature and pressure as an array of "atoms" help together by delocalised electrons:
• hydrogen
• carbon
• sodium
• lithium
• nitrogen
• chlorine
• iron
• gold
• oxygen

Oxygen Gas From Comets

Rosetta was a European Space Agency (ESA) Mission, launched in 2004 with the goal of capturing comet 67P/Churyumov-Gerasimenko in 2014 and to accompany it into the interior solar system. Onboard was an instrument known as ROSINA (Rosetta Orbiter Sensor for Ion and Neutral Analysis) which combined two mass mass spectrometers to study the composition of  the comet's corona.
In 2015, researchers from the Center for Space and Habitability (CSH) at the University of Bern analysed the comet's gases and made an unexpected discovery, traces of molecular oxygen (O_2(g)) were detected! It turned out that molecular oxygen was the fourth most abundant gas in the comet's atmosphere after water, carbon monoxide and carbon dioxide!
Where did this molecular oxygen come from? Surely if it was formed very early, at about the same time as the Solar System, it would have reacted with other substances by now because molecular oxygen is very reactive. We could expect compounds containing oxygen like carbon dioxide and water, but not molecular oxygen.
This puzzle was only solved in 2017.

Caltech Professor Konstantinos P. Giapis studies chemical reactions involving high-speed ions colliding with semiconductor surfaces as a means to create faster computer chips and larger digital memories for computers and phones. He thought the same thing was happening in the comet.

First, as the comet is heated by the sun, water vapor is released from the icy comet..
Next, ultraviolet light from the sun causes the water molecules to become ionised.
Then the ionized water molecules are pushed back towards the surface of the comet by the sun's wind.
After that the ionized water molecules hit oxygen containing compounds on the surface of the comet like rust and sand.
Finally the molecules pick up another oxygen atom from these surfaces to form molecular oxygen.

This gives us a possible mechanism by which molecular oxygen could be produced in space without the need for living things, and, could change the way we search for signs of life on planets beyond our solar system.


Reference
California Institute of Technology. "Chemical engineer explains oxygen mystery on comets." ScienceDaily. ScienceDaily, 8 May 2017. .

Further Reading:
Pure Substances and Mixtures

Elements and Compounds

Molecular Formula

Molecular Formula for Covalent Compounds

Physical and Chemical Changes

Mass and Moles in a Chemical Reaction

Mass Spectroscopy for Isotopes

Mass Spectroscopy for Structural Determination


Suggested study Questions:

1.  Which of the following are pure substances?
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
   • rust
2.  Which of the following substances are mixtures?
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
   • rust
3. Which of the following substances are elements?
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
   • rust
4. Which of the following substances are compounds?
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
   • rust
5.  Write the molecular formula for each of the following:
   • molecular oxygen
   • water
   • carbon monoxide
   • carbon dioxide
6.  Write chemical equation for the first reaction that occurs on the comet's surface.
7.  Explain how a water molecule could be ionized.
8.  Explain why molecular oxygen is considered to be a reactive molecule. 
9.  Assume that a comet has a mass of 10¹⁴ kg and that it is composed only of water. Calculate the maximum mass of molecular oxygen that could be formed if the entire comet was vaporized.
10.  Explain how a mass spectrometer can be used to identify elements and compounds in space.

  

Titanium Gold Alloy

Titanium is the metal used to replace hip and knee joints because it is strong, resistant to wear, and, is nontoxic.

Before titanium was used to replace hips and knees, stainless steel was used.
The density of stainless steel used to make replacement hips and knees is about 7.8 g cm³. The density of titanium metal is 4.506 g cm³, about half the density of stainless steel. This means that a replacement joint made out of titanium will weigh less than the same replacement joint made out of stainless steel.
Titanium is also strong. The strength of the material used to replace hip and knee joints is important because you do not want your new joint to bend or break or under strain.

Titanium has a melting point of 1670°C and a boiling point of 3287°C, which means it remains solid over the range of temperatures humans are exposed to. This is important because you want your new hip or knee replacement to remain a solid!
Naturally occurring titanium is made up of a number of isotopes, all of which are stable so they do not undergo nuclear decay. This is important because it means that there is no loss of titanium mass due to radioactive decay, and there is no fear of damage to cells from the emission of radiation.

isotope	atomic mass	abundance
46Ti	45.953	8.25
47Ti	46.952	7.44
48Ti	47.948	73.72
49Ti	48.948	5.41
50Ti	49.945	5.18

Titanium metal will react with water, halogens and dilute hydrochloric acid, but only if the temperature is elevated well above body temperature. Similarly, titanium metal will react with oxygen in a combustion reaction at elevated temperatures. Titanium metal does not appear to react with bases at all. Therefore, titanium is unlikely to react with substances found in the human body.

Researchers at Rice University have found that alloying titanium with gold can produce an even better material to use for replacement hips and knees. Mixing titanium and gold in the ratio of 3:1 at high temperature produces an alloy that is 3 times harder than steel and 4 times harder than the pure titanium commonly in use for hip and knee replacements. The atoms of titanium and gold in this alloy are packed in a cubic arrangement, an arrangement that is usually associated hardness. The structure of this alloy is shown below:

This titanium gold alloy has been found to be even more biocompatible that pure titanium.
The researchers intend to undertake further studies to investigate whether using chemical dopants might improve the alloy's hardness even further.

Reference:
Rice University. "Titanium and gold equals new gold standard for artificial joints: Titanium-gold alloy that is 4 times harder than most steels." ScienceDaily. ScienceDaily, 20 July 2016. 

Further Reading
Metals and Non-metals 
Density
Isotopes
Relative Atomic Mass
Alloys

Suggested Study Questions

1. Titanium and gold are both metallic metallic elements.
   • What are the physical properties common to most metallic elements?
   • What are the chemical properties common to most metallic elements?
2. Draw up a table of the physical properties of titanium.
3. A typical knee replacement made out of titanium has a mass of 560 g.
   • Calculate the volume of the titanium knee replacement.
   • Calculate the mass of the same knee replacement if it were made out of stainless steel
4. Define the term isotope.
5. Determine the number of protons in the nucleus of an atom of each of the isotopes of titanium listed in the article above.
6. Determine the number of neutrons in the nucleus of an atom of each of the isotopes of titanium lists in the article above.
7. Which is the most abundant isotope of titanium? Explain your answer.
8. Use the data in the article above to calculate the relative atomic mass of naturally occurring titanium.
9. Given the atomic radius of titanium is  176 pm (1.76 x 10^-10 m) and the atomic radius of gold is 174 pm (1.74 x 10^-10 m), do you think the alloy of titanium and gold discussed in the article above is an interstitial alloy or a substitutional alloy? Explain your answer.
10. Consider the structure of the titanium gold alloy shown in the diagram in the article above.
    • The blue balls represent which atoms of which element?
    • The red balls represent which atoms of which element?

Mine the Moon!

After The Jade Rabbit lander touched down on the Moon in December 2013, the Chinese space agency publicly suggested establishing mining bases on the Moon.

What could be so valuable that it would warrant the cost of going to the Moon to mine it then bringing it back to Earth to be used?

Gold? No.

Diamonds? No again.

Rare earth elements!

Why have rare earth elements (REE) become so important?

Find out in this edition of AUS-e-NEWS.

If you haven't received your December 2016 issue of AUS-e-NEWS in your inbox, please email us at  

 

Elemental Fun

For this activity you will need a modern Periodic Table
(here's one I prepared earlier at http://www.ausetute.com.au/pertable.html )

This activity is designed to let students have some fun while they use a Periodic Table to extract information about elements (names, symbols, atomic number and atomic weight).

Ask the students a question.
Students use a Periodic Table find the answers.
After doing a few of these, the students will usually start making up their own questions and answers.
They can try out their questions/answers on their fellow students (and you!).

Names from Symbols

1. Question: What is candy made of?
    Answer: calcium, nitrogen and dysprosium (Ca N Dy )

2. Question: What ingredients do you need to make chocolate?
    Answer: carbon, holmium, cobalt, lanthanum, tellurium (C Ho Co La Te)

3. Question: What elements make up a body?
    Answer: boron, oxygen, dysprosium (B O Dy)

4. Question: What makes up the atmosphere?
     Answer: astatine, molybdenum, sulfur, phosphorus, helium, rhenium (At Mo S P He Re)

5. Question: Prove that these elements are compounds!

• xenon (It's made up of xenon, nobelium nitrogen, Xe No N)
• neon (It's made up of neon, oxygen, nitrogen, Ne O N)
• iron (It's made up of iridium, oxygen, nitrogen, Ir O N)
• copper (It's made up of cobalt, phosphorus (twice), erbium, Co P P Er)
• silver (It's made up of sulfur, iodine, livermorium, erbium, S I Lv Er)
• arsenic (It's made up of argon, selenium, nitrogen, iodine, carbon, Ar Se N I C)

6. Question: What is the most negative element?

    Answer: nobelium, it always spells No

Symbols from Names

1. Question: What fruit is made up of 1 part barium and two parts sodium?

    Answer: Ba Na Na

2. Question: Can you use potassium, nickel and iron to cut an apple?

    Answer: Yes because they make a K Ni Fe

3. Question: If you add some fluorine, uranium and nitrogen to a game, what will happen?

    Answer: It will be more F U N !

4. Question:  What natural fiber is made up of lithium, neon and nitrogen?

    Answer: Li Ne N 

5. Question: What sort of jokes do chemists make out of cobalt, radon, and yttrium?

   Answer: Co Rn Y jokes.

Symbols from Atomic Numbers (crack the code)

1. Code: 1,18,15 

    Clue: A heavenly musical instrument?

    Answer: harp, H (Z=1), Ar ( Z=18), P (Z=15)

2. Code:  66, 7, 95, 53, 52

    Clue: Explosive stuff!

    Answer: dynamite, Dy(Z=66), N(Z=7), Am(Z=95), I(Z=53), Te(Z=52)

3. Code: 20, 28, 10

    Clue: What a cat is afraid of?

    Answer: canine, Ca(Z=20), Ni(Z=28), Ne(Z=10)

4. Code: 1, 85

    Clue: Head covering?

    Answer: hat, H(Z=1), At(Z=85)

5. Code: 67, 8, 19

    Clue: Somewhere to hang your coat?

    Answer: hook, Ho(Z=67), O(Z=8), K(Z=19)

Molecular Weight from Symbols

1. Question: What is a Chemist's favourite number?

    Answer: 315.02 because it is Lu C K Y (175 + 12.01 + 39.1 + 88.91 = 315.02)

2. Question: What is the molecular weight of a gene?

    Answer: 92.82 because it's made up of Ge and Ne (72.64 + 20.18 = 92.82)

3. Question: What is the value of life?

    Answer: 62.791 Li Fe (6.941 + 55.85 = 62.791)

4. Question: What does a boy weigh?

    Answer: 115.72 B O Y (10.81 + 16.00 + 88.91 = 115.72)

5. Question: How heavy is a phone?

    Answer: 68.158 P H O Ne (30.97 + 1.008 + 16.00 + 20.18 = 68.158)

Words You Can Make Using the First Twenty Elements Only

• Al O Ne
• Ar C
• Ar K
• B Ar
• B Ar K
• B Ar N
• Be Ar
• B Li N K
• B Li S S
• B O Ar
• B O Ne
• B O O K
• B O S S
• Ca B
• C Al F
• Ca N
• Ca N Al
• Ca Ne
• Ca N O N
• Ca P
• C Ar
• C Ar B O N
• Ca S H
• C H O O K
• C H O P
• C Li C K
• C Li F F
• C Li N K
• Cl O C K
• Cl O Ne
• C O B
• C O Ne
• C O O K
• C O S H
• F Ar
• F Li C K
• F Li P
• F O Al
• H Al F
• H Al O
• H Ar K
• H Ar P
• He Al
• He Ar
• H O C K
• H O N K
• H O P
• K Na C K
• K N O B
• K N O C K
• Li Ar
• Li C K
• Li Ne
• Li N K
• Li P S
• Li S P
• Na B
• Na P
• Ne O N
• Ne P Al
• N O O K
• O Ne
• O P Al
• P Al
• P Ar
• P Ar K
• P H O Ne
• P O P
• S Ca N
• S C O Ne
• S He
• S He Ar
• Si C K
• Si N
• Si N K
• S Li C K
• S Li P
• S Na C K
• S Na P
• S O B
• S O C K
• S O N Ar
• S P O O K

Number of elements in period 2

Question: Give the number of elements in period 2 of the periodic table
Answer: 8

The rows going from left to right across the Periodic Table are called Periods.
The periods are numbered from 1 at the top to 7 on the bottom.
The first period contains only 2 elements: hydrogen and helium.
The second period contains 8 elements: lithium, beryllium, boron, carbon, nitrogen, oxygen,  fluorine and neon.

Find out more about how the periodic table is arranged at http://www.ausetute.com.au/pertable.html

Find more about the elements making up Period 2 at http://www.ausetute.com.au/trendpd2.html

Essential Elements

Most of the mass of the human body is made up of just 6 elements:

• 65% oxygen
• 18.5% carbon
• 9.5% hydrogen
• 3.2% nitrogen
• 1.5% calcium
• 1% phosphorus

Carbon and hydrogen are the building blocks making up organic (carbon) molecules, and so, since the human body is just an incredibly complicated organic chemical factory, it is no surprise that carbon and hydrogen make up such a huge amount of the mass of a human body. Oxygen is present in most of the biochemicals making up your body, while nitrogen is an essential component of proteins. Why is there so much phosphorus? Phosphorus and oxygen combine to make up the glue that holds your DNA together, no phosphorus, no DNA, no you! And calcium is ofcourse present in bones and teeth.
Then there are minor amounts of other elements such as potassium, sulfur, sodium, chlorine and magnesium which make up less than 1% of the remaining mass of the human body.

Some elements, like iron, are absolutely essential in order for the human body to survive, but are present in extremely minute amounts, for iron this is about 0.006%

H																		He
Li	Be												B	C	N	O	F	Ne
Na	Mg												Al	Si	P	S	Cl	Ar
K	Ca		Sc	Ti	V	Cr	Mn	Fe	Co	Ni	Cu	Zn	Ga	Ge	As	Se	Br	Kr
Rb	Sr		Y	Zr	Nb	Mo	Tc	Ru	Rh	Pd	Ag	Cd	In	Sn	Sb	Te	I	Xe
Cs	Ba	*	Lu	Hf	Ta	W	Re	Os	Ir	Pt	Au	Hg	Tl	Pb	Bi	Po	At	Rn
Fr	Ra	**	Lr	Rf	Db	Sg	Bh	Hs	Mt	Ds	Rg	Cn	Uut	Fl	Uup	Lv	Uus	Uuo
		*	La	Ce	Pr	Nd	Pm	Sm	Eu	Gd	Tb	Dy	Ho	Er	Tm	Yb
		**	Ac	Th	Pa	U	Np	Pu	Am	Cm	Bk	Cf	Es	Fm	Md	No

Vanderbilt University Scientists have just found out that bromine is also essential.It appears that bromine is important to an enzyme that is used to make a particular type of sulfur-nitrogen bond within the collagen IV structure used to make the scaffold for cells.

Reference:
A. Scott McCall, Christopher F. Cummings, Gautam Bhave, Roberto Vanacore, Andrea Page-McCaw, Billy G. Hudson. Bromine Is an Essential Trace Element for Assembly of Collagen IV Scaffolds in Tissue Development and Architecture. Cell, 2014; 157 (6): 1380 DOI: 10.1016/j.cell.2014.05.009

Further Reading
Periodic Table
Metals and Non-metals

Percentage Composition
Mass-Mole Calculations 

Suggested Study Questions:

1.  Give the chemical symbol for each of the following elements:
   • oxygen
   • carbon
   • hydrogen
   • nitrogen
2. Give the name for each of the following elements:
   • Fe
   • Ca
   • P
   • K
   • Mg
3. Give the atomic number for each of the following elements
   • sulfur
   • sodium
   • iodine
   • Cl
   • F
   • Br
4. Make a table of the metals and non-metals named in the article above
5. Chris the Chemist has a mass of 90 kg. Calculate the mass, in kilograms, of each of the following elements in Chris' body
   • carbon
   • hydrogen
   • oxygen
   • nitrogen
6. Calculate the mass of iron in Chris' body in
   • kilograms
   • grams
   • milligrams
   • micrograms
7. Calculate the moles of each of the following elements found in Chris' body
   • carbon
   • hydrogen
   • oxygen
   • nitrogen
8. Do you think Scientists will one day claim that lead is an element essential for human life? Explain your answer.

Graphene Capillary

Graphene is made up of carbon atoms, it is an allotrope of carbon.
 Each carbon atoms bonds to 3 other carbon atoms forming hexagons. Each hexagon shares each side with another hexagon. So this lattice of hexagons extends indefinitely, but it is only 1 carbon atom high! For this reason graphene is referred to as a two-dimensioal lattice or array.

Graphene is strong, light, nearly transparent and an excellent conductor of heat and electricity. Graphene is also hydrophobic, it repels water. However, narrow capillaries made out of graphene actually suck in water, if the water layer is only one atom thick.

Two years ago, researchers at the University of Manchester found that graphene capillaries could be made by stacking layers of graphene oxide on top of each to form a laminate. One-atom wide graphene capillaries are produced between these layers. These laminates are impermeable to all gases and vapours, except for water. This means that no gas or vapour, except for water, can pass through the laminate. Even helium, the smallest of the Nobel Gases cannot pass through the laminate.

These results suggest that graphene capillaries could be used to filter water. Researchers at the University of Manchester having been studying the use of graphene for water filtration and have found that ions less than 9 angstroms can quickly flow through with the water, but larger ions are blocked. With further research it is hoped to control the graphene mesh size to reduce it below 9 angstroms so that even the smallest ions like those found in seawater could be filtered out of water.

Reference:
R. K. Joshi, P. Carbone, F. C. Wang, V. G. Kravets, Y. Su, I. V. Grigorieva, H. A. Wu, A. K. Geim, R. R. Nair. Precise and Ultrafast Molecular Sieving Through Graphene Oxide Membranes. Science, February 14, 2014 DOI: 10.1126/science.1245711

Further Reading
Allotropes
Metric Conversions

Suggested Study Questions:

1. What is meant by the term "graphene is an allotrope of carbon?"
2. Name, and describe the structure of, two other allotropes of carbon.
3. Explain how the structure of graphene is different to the structure of graphite.
4. Why is graphene considered to be a good electrical conductor? 
5. Which other allotrope of carbon is considered to be good electrical conductor? Explain how this allotrope conducts electricity.
6. 1 angstrom = 1 Å = 10^-10 metres. Convert 9 Å to:
   • metres
   • millimetres
   • microns (micrometres)
   • nanometres
7. 1 picometre = 1 pm = 10^-12 metres. Convert 900 pm to :
   • metres
   • millimetres
   • microns (micrometres)
   • nanometres
   • angstroms
8. Consider the crystal ionic radius for each of the following ions commonly found in seawater:
   • Na⁺ : 116 pm
   • Mg²⁺: 86 pm
   • Cl^- : 167 pm
   • F^- : 119 pm
   • What is the diameter of each of these ions in angstroms?
   • Which, if any, of these ions would pass through a graphene capillary? Explain your answer.
9. A nitrate ion has a diameter of about 0.33nm and a sulfate ion has a diameter of about 0.49 nm. Which of these ions, if any, could pass through a graphene capillary? Explain your answer.

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.  

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.