What is green chemistry?

Green chemistry is both the chemistry of the future and the chemistry of today. It is based on a number of principles that ensure that both processes and end products are clean and safe. These principles are :

1. Prevention is better than cure – it is better to design processes that produce no waste than to produce waste and clean it up.
2. Processes should be designed to incorporate the maximum amount of the raw materials into the final product, thus reducing waste products.
3. Raw materials should come from renewable sources.
4. Energy requirements of processes should be minimised.
5. Catalysts are better than reagents that are used up in a process.
6. Chemical products should be designed so that they break down at the end of their useful life to form harmless products.
7. Methods of making chemicals should be designed to make products that cause no harm to human health or to the environment and that do not cause accidents such as explosions and fires.
8. Methods of making chemicals should be monitored to prevent the formation of hazardous substances.

Green chemistry aims to conserve both energy and raw materials. In practice, this means that ‘green’ processes are often cheaper than conventional methods. Some current processes are already ‘green’, and the use of green chemistry is growing because it is environmentally friendly, and also because of legislation and international agreements that aim to reduce pollution. One of the basic ideas of green chemistry is to prevent production of hazardous and polluting materials rather than producing them and then cleaning up.

Green chemistry:

• is safe;
• conserves raw materials and energy; and
• is more cost-effective than conventional methods.

Approaches to making chemical processes ‘greener’ include:

• redesigning production methods to use different starting materials;
• using different reaction conditions, catalysts, solvents etc; and
• using production methods with fewer steps.

Article source : http://www.rsc.org/education/teachers/learnnet/green/whatis/index.htm

Aluminum

Properties: Aluminum has a melting point of 660.37°C, boiling point of 2467°C, specific gravity of 2.6989 (20°C), and valence of 3. Pure aluminum is a silvery-white metal. It is soft, light, relatively nontoxic, with a high thermal conductivity, and high corrosion resistance. It can be easily formed, machined, or cast. Aluminum is nonmagnetic and nonsparking. It is second among metals in terms of malleability and sixth in ductility. Aluminum coatings are highly reflective of both visible and radiant heat. The coatings form a thin layer of protective oxide and do not deteriorate like silver coatings.

Uses: Ancient Greeks and Romans used alum as an astringent, for medicinal purposes, and as a mordant in dyeing. It is used in kitchen utensils, exterior decorations, and thousands of industrial applications. Although the electrical conductivity of aluminum is only about 60% that of copper per area of cross section, aluminum is used in electrical transmission lines because of its light weight. The alloys of aluminum are used in the construction of aircraft and rockets. Reflective aluminum coatings are used for telescope mirrors, making decorative paper, packaging, and many other uses. Alumina is used in glassmaking and refractories. Synthetic ruby and sapphire have applications in producing coherent light for lasers.

Sources: Aluminum is the most abundant metal in the Earth's crust (8.1%), although it is not found free in nature. In 1886, Hall in the United States and Heroult in France discovered how to obtain aluminum metal from electrolysis of alumina dissolved in cryolite. Cryolite is an aluminum ore, although it is has been replaced for commercial aluminum purification by an artificial mixture of sodium, aluminum, and calcium fluorides. The Bayer process is commonly used to refine the impure hydrated oxide ore, bauxite, for use in the Hall-Heroult refining process. Aluminum also can be produced from clay, although this is not the most economically feasible method at present. In addition to cryolite and bauxite, aluminum is found in feldspars, granite, and many other common minerals. The oxide, alumina, occurs naturally as ruby, sapphire, emery, and corundum.

Element Classification: Metal

Density (g/cc): 2.6989

Appearance: soft, lightweight, silvery-white metal

Atomic Radius (pm): 143

Atomic Volume (cc/mol): 10.0

Covalent Radius (pm): 118

Ionic Radius: 51 (+3e)

Specific Heat (@20°C J/g mol): 0.900

Fusion Heat (kJ/mol): 10.75

Evaporation Heat (kJ/mol): 284.1

Debye Temperature (K): 394.00

Pauling Negativity Number: 1.61

First Ionizing Energy (kJ/mol): 577.2

Oxidation States: 3

Lattice Structure: Face-Centered Cubic

Lattice Constant (Å): 4.050

Article source:http://chemistry.about.com/od/elementfacts/a/aluminum.htm

What Is the Most Abundant Element?

The most abundant element in the universe is hydrogen, which makes up about 3/4 of all matter! Helium makes up most of the remaining 25%. Oxygen is the third most abundant element in the universe. All of the other elements are relatively rare.

The chemical composition of the earth is quite a bit different from that of the universe. The most abundant element in the earth's crust is oxygen, making up 46.6% of the earth's mass. Silicon is the second most abundant element (27.7%), followed by aluminum (8.1%), iron (5.0%), calcium (3.6%), sodium (2.8%), potassium (2.6%). and magnesium (2.1%). These eight elements account for approximately 98.5% of the total mass of the earth's crust. Of course, the earth's crust is only the outer portion of the earth. Future research will tell us about the composition of the mantle and core.

Article source: http://chemistry.about.com/cs/howthingswork/f/blabundant.htm

Gases

The States of Matter

The term state can be defined as a set of conditions that describe a person or thing at a given time. It is in this sense of the word that scientists divide matter into the three states shown in the figure below.

The three states of matter have characteristic properties. Solids have a distinct shape. When they melt, the resulting liquid conforms to the shape of its container. Gases expand to fill their containers.

There are two reasons for studying gases before liquids or solids. First, the behavior of gases is easier to describe because most of the properties of gases do not depend on the identity of the gas. We can therefore develop a model for a gas without worrying about whether the gas is O₂, N₂, H₂, or a mixture of these gases. Second, a relatively simple, yet powerful, model known as the kinetic molecular theory is available, which explains most of the behavior of gases.

---

Elements or compounds that are Gases at Room Temperature

Before examining the chemical and physical properties of gases, it might be useful to ask: What kinds of elements or compounds are gases at room temperature? To help answer this question, a list of some common compounds that are gases at room temperature is given in the table below.

Common Gases at Room Temperature

Element or Compound		Atomic or Molecular Weight
H2 (hydrogen)		2.02
He (helium)		4.00
CH4 (methane)		16.04
NH3 (ammonia)		17.03
Ne (neon)		20.18
HCN (hydrogen cyanide)		27.03
CO (carbon monoxide)		28.01
N2 (nitrogen)		28.01
NO (nitrogen oxide)		30.01
C2H6 (ethane)		30.07
O2 (oxygen)		32.00
PH3 (phosphine)		34.00
H2S (hydrogen sulfide)		34.08
HCl (hydrogen chloride)		36.46
F2 (fluorine)		38.00
Ar (argon)		39.95
CO2 (carbon dioxide)		44.01
N2O (dinitrogen oxide)		44.01
C3H8 (propane)		44.10
NO2 (nitrogen dioxide)		46.01
O3 (ozone)		48.00
C4H10 (butane)		58.12
SO2 (sulfur dioxide)		64.06
BF3 (boron trifluoride)		67.80
Cl2 (chlorine)		70.91
Kr (krypton)		83.80
CF2Cl2 (dichlorodifluoromethane)		120.91
SF6 (sulfur hexafluoride)		146.05
Xe (xenon)		131.30

There are several patterns in the table above.

• Common gases at room temperature include both elements (such as H₂ and O₂) and compounds (such as CO₂ and NH₃).
• Elements that are gases at room temperature are all nonmetals (such as He, Ar, N₂, O₂, and so on).
• Compounds that are gases at room temperature are all covalent compounds (such as CO₂, SO₂, and NH₃) that contain two or more nonmetals.
• With only rare exception, these gases have relatively small molecular weights.

As a general rule, compounds that consist of relatively light, covalent molecules are most likely to be gases at room temperature.

Article source : http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch4/index.php

Elements, Compounds, and Mixtures

Elements

Any substance that contains only one kind of an atom is known as an element. Because atoms cannot be created or destroyed in a chemical reaction, elements such as phosphorus (P₄) or sulfur (S₈) cannot be broken down into simpler substances by these reactions.

Example: Water decomposes into a mixture of hydrogen and oxygen when an electric current is passed through the liquid. Hydrogen and oxygen, on the other hand, cannot be decomposed into simpler substances. They are therefore the elementary, or simplest, chemical substances - elements.

Each element is represented by a unique symbol. The notation for each element can be found on the periodic table of elements.

The elements can be divided into three categories that have characteristic properties: metals, nonmetals, and semimetals. Most elements are metals, which are found on the left and toward the bottom of the periodic table. A handful of nonmetals are clustered in the upper right corner of the periodic table. The semimetals can be found along the dividing line between the metals and the nonmetals.

Atoms

Elements are made up of atoms, the smallest particle that has any of the properties of the element.John Dalton, in 1803, proposed a modern theory of the atom based on the following assumptions.

1. Matter is made up of atoms that are indivisible and indestructible.

2. All atoms of an element are identical.

3. Atoms of different elements have different weights and different chemical properties.

4. Atoms of different elements combine in simple whole numbers to form compounds.

5. Atoms cannot be created or destroyed. When a compound decomposes, the atoms are recovered unchanged.

Compounds

Elements combine to form chemical compounds that are often divided into two categories.

Metals often react with nonmetals to form ionic compounds. These compounds are composed of positive and negative ions formed by adding or subtracting electrons from neutral atoms and molecules.

Nonmetals combine with each other to form covalent compounds, which exist as neutral molecules.

The shorthand notation for a compound describes the number of atoms of each element, which is indicated by a subscript written after the symbol for the element. By convention, no subscript is written when a molecule contains only one atom of an element. Thus, water is H₂O and carbon dioxide is CO₂.

Characteristics of Ionic and Covalent Compounds

Ionic Compounds		Covalent Compounds
Contain positive and negative ions (Na+Cl-)		Exist as neutral molecules (C6H12O2)
Solids suchs as table salt (NaCl(s))		Solids, liquids,or gases (C6H12O6(s), H2O(l), CO2(g))
High melting and boiling points		Lower melting and boiling points (i.e., often exist as a liquid or gas at room temperature)
Strong force of attraction between particles		Relatively weak force of attraction between molecules
Separate into charged particles in water to give a solution that conducts electricity		Remain as same molecule in water and will not conduct electricity

Determining if a Compound is Ionic or Covalent

Calculate the difference between the electronegativities of two elements in a compound and the average of their electronegativites, and find the intersection of these values on the figure shown below to help determine if the compound is ionic or covalent, or metallic.

Article source : http://chemed.chem.purdue.edu/genchem/topicreview/bp/ch2/index.php

The periodic table

The periodic table of the chemical elements is a display of known chemical elements, arranged by electron structure so that many chemical properties vary regularly across the table.

The original table was created without a knowledge of the inner structure of atoms: if one orders the elements by atomic mass, and then plots certain other properties against atomic mass, one sees an undulation or periodicity to these properties as a function of atomic mass. The first to recognize these regularities was the German chemist Johann Wolfgang D�berreiner who noticed a number of triads of similar elements:

Some Triads
Element	Atomic Mass	Density
Cl	35.5	1.56/td>	79.9	3.12/td>	126.9	4.95/td>
Ca	40.1	1.55 g/cm3
Sr	87.6	2.6 g/cm3
Ba	137	3.5 g/cm3

This was followed by the English chemist John Alexander Reina Newlands, who noticed that the elements of similar type recurred at intervals of eight, which he likened to the octaves of music, though his law of octaves was ridiculed by his contemporaries. Finally the German Lothar Meyer and the Russian chemist Dmitry Ivanovich Mendeleev almost simultaneously developed the first periodic table, arranging the elements by mass (though Mendeleev plotted a few elements out of strict mass sequence in order to make a better match to the properties of their neighbours in the table - this was later vindicated by the discovery of the electronic structure of the elements in the late 19th and early 20th century.)

Lists of the elements by name, by symbol, and by atomic number are available. The following figure shows the currently known periodic table of the elements. Each element is listed by its atomic number and chemical symbol. Elements in the same column ("group") are chemically similar.

Group

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

Period

1

1 H

2 He

2

3 Li

4 Be

5 B

6 C

7 N

8 O

9 F

10 Ne

3

11 Na

12 Mg

13 Al

14 Si

15 P

16 S

17 Cl

18 Ar

4

19 K

20 Ca

21 Sc

22 Ti

23 V

24 Cr

25 Mn

26 Fe

27 Co

28 Ni

29 Cu

30 Zn

31 Ga

32 Ge

33 As

34 Se

35 Br

36 Kr

5

37 Rb

38 Sr

39 Y

40 Zr

41 Nb

42 Mo

43 Tc

44 Ru

45 Rh

46 Pd

47 Ag

48 Cd

49 In

50 Sn

51 Sb

52 Te

53 I

54 Xe

6

55 Cs

56 Ba

*

71 Lu

72 Hf

73 Ta

74 W

75 Re

76 Os

77 Ir

78 Pt

79 Au

80 Hg

81 Tl

82 Pb

83 Bi

84 Po

85 At

86 Rn

7

87 Fr

88 Ra

* *

103 Lr

104 Rf

105 Db

106 Sg

107 Bh

108 Hs

109 Mt

110 Ds

111 Uuu

112 Uub

113 Uut

114 Uuq

115 Uup

116 Uuh

117 Uus

118 Uuo

* Lanthanides

57 La

58 Ce

59 Pr

60 Nd

61 Pm

62 Sm

63 Eu

64 Gd

65 Tb

66 Dy

67 Ho

68 Er

69 Tm

70 Yb

** Actinides

89 Ac

90 Th

91 Pa

92 U

93 Np

94 Pu

95 Am

96 Cm

97 Bk

98 Cf

99 Es

100 Fm

101 Md

102 No

Chemical Series of the Periodic Table

Alkali metals	Alkaline earths	Lanthanide	Actinides	Transition metals
Poor metals	Metalloids	Nonmetals	Halogens	Noble gases

Colour coding for atomic numbers:

• Elements numbered in blue are liquids at room temperature;
• those in green are gases at room temperature;
• those in black are solid at room temperature;
• those in red are synthetic and do not occur naturally (all are solid at room temperature).
• those in gray have not yet been discovered (they also have muted fill colors indicating the likely chemical series they would fall under).

And here is the periodic table for magnetic resonance

The number of electron shells an atom has determines what period it belongs to. Each shell is divided into different subshells, which as atomic number increases are filled in roughly this order:

1s
2s           2p
3s           3p
4s        3d 4p
5s        4d 5p
6s     4f 5d 6p
7s     5f 6d 7p
8s  5g 6f 7d 8p
...

Hence the structure of the table. Since the outermost electrons determine chemical properties, those tend to be similar within groups. Elements adjacent to one another within a group have similar physical properties, despite their significant differences in mass. Elements adjacent to one another within a period have similar mass but different properties.

For example, very near to nitrogen (N) in the second period of the chart are carbon (C) and oxygen (O). Despite their similarities in mass (they differ by only a few atomic mass units), they have extremely different properties, as can be seen by looking at their allotropes : diatomic oxygen is a gas that supports burning, diatomic nitrogen is a gas that does not support burning, and carbon is a solid which can be burnt (yes, diamonds can be burnt!).

In contrast, very near to chlorine (Cl) in the next-to-last group in the chart (the halogens) are fluorine (F) and bromine (Br). Despite their dramatic differences in mass within the group, their allotropes have very similar properties: They are all highly corrosive (meaning they combine readily with metals to form metal halide salts); chlorine and fluorine are gases, while bromine is a very low-boiling liquid; chlorine and bromine at least are highly colored.

Article source :http://www.encyclopedia4u.com/p/periodic-table-1.html