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CHAPTER 2 THE ELEMENTS: BASIC BUILDING BLOCKS OF GREEN CHEMICALS. From Green Chemistry and the Ten Commandments of Sustainability , Stanley E. Manahan, ChemChar Research, Inc., 2006 manahans@missouri.edu. 2.1. Elements, Atoms, and Atomic Theory. Atoms are composed of subatomic particles

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CHAPTER 2

THE ELEMENTS: BASIC BUILDING BLOCKS OF GREEN CHEMICALS

From Green Chemistry and the Ten Commandments of Sustainability, Stanley E. Manahan, ChemChar Research, Inc., 2006

manahans@missouri.edu

2 1 elements atoms and atomic theory
2.1. Elements, Atoms, and Atomic Theory
  • Atoms are composed of subatomic particles
  • Positively charged proton (+)
  • Negatively charged electron (-)
  • Electrically neutral neutron (n)
  • Properties of atoms determine matter’s chemical behavior
  • Arrangement and energy levels of electrons in atoms
elemental behavior varies periodically with increasing atomic number
Elemental behavior varies periodically with increasing atomic number
  • Enables placing elements in the periodic table
  • As atomic number increases, electrons are added incrementally to atoms
  • Electrons occupy shells in atoms, which are filled with a specific number of electrons
  • As each shell is filled, a new shell is started, thus beginning a new period (row) of the periodic table
  • The construction of a simplified 20-element periodic table is shown in this chapter
green aspects of elements
Green Aspects of Elements
  • Nitrogen, oxygen, and carbon (contained in carbon dioxide gas) from the “green” atmosphere
  • Hydrogen and oxygen in water, the “greenest” compound
  • Sodium and chlorine in common table salt
  • Silicon, calcium, and oxygen in soil that grows plants supplying food to most organisms
  • Hydrogen, oxygen, carbon, nitrogen, and sulfur in all living material
dalton s atomic theory
Dalton’s Atomic Theory

Very different

Two atoms in Cl2 molecule

Very similar, but not identical

1. Each element is composed of extremely small particles with the same chemical properties called atoms.

Very different

2. Atoms of different elements do not have identical chemical properties.

2H2 + O2 2H2O

3. Chemical compounds are formed by the combination of atoms of different elements in definite, constant ratios that usually can be expressed as integers or simple fractions.

dalton s atomic theory 2
Dalton’s Atomic Theory (2)

CH4 + 2O2 CO2 + 2H2O

4. Chemical reactions involve the separation and combination of atoms as in the example above where bonds are broken between C and H in CH4 and between O and O in O2, and bonds are formed between C and O in CO2 and between H and O in H2O.

5. Atoms are not created, destroyed, or changed to atoms of other elements in ordinary chemical reactions.

three laws explained by the atomic theory
Three Laws Explained by the Atomic Theory

Conservation of Mass: There is no detectable change of mass in ordinary chemical reactions.

Constant Composition: A specific chemical compounds always contains the same elements in the same proportions by mass.

Multiple Proportions: When two elements combine to form two or more compounds, the masses of one combining with a fixed mass of the other are in ratios of small whole numbers.

the nature of atoms
The Nature of Atoms
  • Atoms are extremely small and light
  • Individual masses are expressed in atomic mass units, u
  • Size in picometers, picometer = 0.000 000 1 millimeters
  • Atoms may be regarded as spheres 100-300 picometers in diameter

Atoms are composed of three kinds of subatomic particles

  • • Positively charged proton (+), mass essentially 1 u
  • Neutral neutron (n), mass essentially 1 u
  • Negatively charged electron (-), mass essentially 0
atoms

Each atom of a specific element has the same number of protons in its nucleus

• Atomic number

Isotopes are atoms of the same element that have different numbers of neutrons and, therefore, different masses

• Isotopes are represented by special symbols:

Atoms

Mass number

Element symbol

Atomic number

• The mass number is the sum of protons and neutrons in the nucleus

The average mass of all atoms of an element is the atomic mass

• Normally not integers

electrons in atoms
Electrons in Atoms

Behavior of electrons in atoms determines chemical properties

Electrons are strongly attracted to the atom’s nucleus, but do not come to rest on it

• Energy levels

• Orientations in space

• Electron configuration

2 2 hydrogen the simplest atom
2.2. Hydrogen, The Simplest Atom

Lewis symbols show electrons (outer shell electrons) in atoms

Lewis symbol of the hydrogen atom

Lewis formulas can be used to show electrons in molecules, such as H2

Elemental hydrogen does not exist as individual H atoms

Instead, it exists as molecules, each composed of 2 H atoms with the chemical formula H2

The covalent bond holding the two H atoms together consists of 2 shared electrons shown in the Lewis formula of H2 above.

properties and uses of elemental h 2
Properties and Uses of Elemental H2

Elemental H2 is a colorless, odorless gas

• Lowest density of any pure substance

• Liquid hydrogen boils at -253C

Hydrogen gas is widely used in the chemical industry to react chemically with a large number of substances

Burns readily with a large release of energy; mixtures of hydrogen with oxygen or air are extremely explosive

2H2 + O2 2H2O + energy

Hydrogen is a very green element because when it is used to generate energy, the reaction product is simply water, H2O

properties and uses of h 2 2
Properties and Uses of H2 (2)

Hydrogen can be produced by

2H2O (Electrical current)  2H2 + O2

or by steam reforming of methane or other hydrocarbons at high temperatures and pressures:

CH4 + H2O (800C T, 30 atm P)  CO + 3H2

Hydrogen is used to manufacture a number of chemicals, for example methyl alcohol, CH3OH):

CO + 2H2 CH3OH

Methanol can be used as a fuel or blended with gasoline to run internal combustion engines

Now methane is broken down to elemental hydrogen and carbon dioxide to produce hydrogen used in fuel cells

2 3 helium the first noble gas
2.3. Helium, The First Noble Gas

Helium, He, atomic number 2

• Predominantly

• Some

Helium is a noble gas meaning that it exists only as atoms of the elements that are never bonded to other atoms

The Lewis symbol of helium is simply He with 2 dots:

helium 2
Helium (2)

Electrons added at various levels known as electron shells

• The one electron in hydrogen, H, goes into the first electron shell, the one with the lowest possible energy

The lowest electron shell can contain a maximum of only 2 electrons

• So helium has a filled electron shell making it a noble gas

Helium is a nontoxic, odorless, tasteless, colorless gas with a very low density of only 0.164 g/L at 25C and 1 atm pressure

Helium comes from some sources of natural gas containing up to 10% helium by volume

• Helium was first observed in the light spectrum of the sun by the specific wavelengths of light emitted by hot helium atoms

uses of helium
Uses of Helium

Helium gas used for

• Inert atmosphere

• Weather balloons

• Breathing by divers

Super-cold liquid helium at 4.2 K (-269°C)

• Cryogenics (very low temperatures)

• Superconductor

hydrogen wants to be like helium
Hydrogen Wants to be Like Helium

Elemental hydrogen exists as diatomic molecules, formula H2

Hydrogen comes just before helium in the periodic table

Hydrogen acquires a noble gas electron configuration by two H atoms sharing electrons as shown below:

2 4 lithium the first metal
2.4. Lithium, The First Metal

Lithium, Li, atomic number 3, atomic mass 6.941

• Most abundant lithium isotope is having 4 neutrons in its nucleus

• A few percent of lithium atoms are the isotope, which has 3 neutrons

Lithium’s lowest electron shell is filled with 2 electrons

The third electron in lithium goes into a second shell, an outer shell

The lithium atom showing both inner shell and outer shell electrons

inner shell and outer shell electrons
Inner Shell and Outer Shell Electrons

Two of lithium’s 3 electrons are inner electrons contained in an inner shell

• As in the immediately preceding noble gas helium

Inner electrons

• Stay on average relatively close to the nucleus

• Very tightly held

• Not exchanged or shared in chemical bonds

The third electron in lithium is an outer electron in the atom’s outer shell farther from, and less strongly attracted to, the nucleus

loss of outer shell electrons to produce cations
Loss of Outer-Shell Electrons to Produce Cations

Lewis symbols normally show outer-shell electrons

Lithium loses its outer shell electron to become like helium:

• No longer a neutral atom, but has become a positively charged Li+cation

• In losing an electron, the lithium atom is said to be oxidized

• Li+ cations are attracted to negatively charged anions in ionic compounds

lithium is the first metal
Lithium is the First Metal

Metals

• 1-3 outer-shell electrons

• Form +1, +2, or +3 cations

• Luster (shine)

• Malleable

• Conduct electricity

uses of lithium
Uses of Lithium

Lithium has several important uses

• Li2CO3 to treat manic-depressive and schizoaffective mental disorder, starting material for the preparation of other lithium compounds, ingredient of specialty glasses and enamels

• Lithium hydroxide, LiOH, is used to formulate some kinds of lubricant greases and in some long-life alkaline storage batteries

• In combination with iodine to power cardiac pacemakers lasting up to 10 years

2 5 the second period of the periodic table
2.5. The Second Period of the Periodic Table

First period consists of only hydrogen and helium

Second period consists of elements 3-10

All atoms in the second period have 2 inner-shell electrons like helium and 3-8 outer-shell electrons

beryllium
Beryllium

Beryllium, atomic number 4, atomic mass 9.012

4 protons and 5 neutrons in Be nuclei

Formation of Be2+ cation

Be:  Be2+ + 2e-

Beryllium is used in alloys mixed with other metals

Beryllium alloys

• Hard and corrosion-resistant

• Good electrical conductors, nonsparking when struck

• Specialty springs, switches, small electrical contacts

• Aircraft brake components

Beryllium is not a very green element

• Cause of berylliosis, a diseased marked by lung deterioration

boron a metalloid
Boron, a Metalloid

Boron, B, atomic number of 5, atomic mass 10.81

• Most boron atoms have 6 neutrons in addition to 5 protons in their nuclei

• A less common isotope has 5 electrons

• Two of boron’s 5 electrons are in a helium core and 3 are outer electrons as shown by the Lewis symbol

Boron is a metalloid

• Among the first 20 elements, silicon is also a metalloid

• Metalloids are semiconductors

boron 2
Boron(2)

Boron is a high-melting substance (2190C)

• Alloyed with copper, aluminum, and steel metals to improve their properties

• Absorbs neutrons in nuclear reactors

• Boron nitride, BN, is extraordinarily hard

• Boron oxide, B2O3, in heat-insulating fiberglass

• Boric acid, H3BO3, is used as a flame retardant in cellulose insulation

carbon the element of life
Carbon, The Element of Life

Carbon, C, atomic number 6

Detectable amounts of radioactive carbon-14, designated

are produced by nuclear processes high in the atmosphere

• Radioactivity of carbon-14 used to date carbon-containing artifacts

Carbon is the “element of life”

Carbon is involved in organic compounds, thus forming the basis of organic chemistry

elemental carbon
Elemental Carbon

Elemental carbon has some important uses

• Very finely divided carbon black used in tires, inks, and printer toner

• Graphite atoms bonded in large, flat molecules used as a dry lubricant

• Activated carbon produced by reacting carbon with steam or carbon dioxide used to purify foods, remove organic pollutants from water, and remove pollutant vapors from air

• Composites consisting of carbon fibers bonded together with epoxy resins

• Carbon in very hard and rigid structure of diamond

green carbon from the air
Green Carbon From The Air

Air is about 0.038% CO2 by volume, serving as a carbon source for photosynthesis:

6CO2 + 6H2O (Sunlight energy)  C6H12O6 + 6O2

Organic carbon generated by photosynthesis produced petroleum, coal, and other fossil fuels

There is much current interest in photosynthesis to provide carbon raw material and fuel

nitrogen from the atmosphere
Nitrogen From The Atmosphere

Nitrogen, N, atomic number 7, atomic mass 14.01

Diatomic N2 comprises 78% by volume of air

• Isolated from air by distillation of cold liquid air and by adsorption processes

The molecules of elemental nitrogen are extremely stable NN

Elemental nitrogen is chemically rather unreactive

Liquid nitrogen boils at -190C

• Used in cryogenics to quick-freeze foods, for drying materials in freeze-drying processes, preserve biological materials, such as semen used in artificical breeding of animals or embryos used in in vitro fertilization

nitrogen a green raw material from the atmosphere
Nitrogen, A Green Raw Material From The Atmosphere

Inexhaustible nitrogen in the atmosphere, but hard to convert to nitrogen compounds

N2 + 3H2 2NH3

Bacteria such as Rhizobium bacteria fix atmospheric nitrogen

Nitrogen is an essential life element

• Proteins, hemoglobin, chlorophyll, enzymes, and other life molecules

• Nitrogen cycle

oxygen the breath of life
Oxygen, The Breath Of Life

Oxygen, atomic number 8, atomic mass 16.00

O2 molecules make up 21% of the volume of air

Oxygen may be regarded as a green element

• O2 is in the atmosphere for the taking

• From distillation of liquid air

Pure oxygen used for breathing, in chemical synthesis, oxyacetylene torches

oxygen 2
Oxygen (2)

Oxygen in the stratosphere (from Chapter 1)

• O2 (Ultraviolet radiation)  O + O

• O2 + O  O3

• Protective ozone layer in the stratosphere

Ozone is detrimental and toxic in the atmosphere at sea level

Oxygen reacts with other substances to produce energy:

• Combustion of hydrocarbons at high temperatures to provide heat or mechanical energy in an engine

2C8H18 + 25O2 16CO2 + 18H2O + energy

• Oxidation of glucose in an organism to provide energy

C6H12O6 (Glucose) + 6O2 6CO2 + 6H2O + energy (at 37C)

fluorine the most nonmetallic element
Fluorine, The Most Nonmetallic Element

Fluorine, F, atomic number 9, atomic mass 19.00 has 7 outer electrons as shown by its Lewis symbol:

Elemental fluorine exists as diatomic F2

Fluorine is the most nonmetallic of all elements

Fluorine reacts violently with metals, organic matter, even glass!

Fluorine is a very corrosive poison that attacks flesh and produces wounds that heal very poorly

Practice of green chemistry seeks to minimize the generation or use of F2 and of highly corrosive HF

Fluorine is widely used in chemical synthesis, for example, to make teflon and Freon substitutes, such as HFC-134a, CH2FCF3

2 6 the magic octet of 8 outer shell electrons
2.6. The Magic Octet of 8 Outer-Shell Electrons

Neon, atomic number 10, atomic mass 20.18

Most neon atoms have 10 neutrons, some have 12, and very few 11

Exists as individual Ne atoms, never combined with other atoms

About 2 parts per thousand by volume in air

• Neon is obtained from distillation of liquid air

• Most common use in glowing neon signs

Neon has a filled outer electron shell of 8 electrons

This filled shell makes neon a noble gas

special significance of the octet
Special Significance of the Octet

Noble gas elements other than neon are argon (atomic number 18), krypton (atomic number 36), xenon (atomic number 54), and radon (atomic number 86)

• Other than helium, which has a filled outer shell of 2 electrons, the noble gases share a common characteristic of 8 outer-shell electrons

The filled outer-shell electron configuration can by shown by the following general Lewis symbol

• Represents an octet of electrons

the octet rule
The Octet Rule

The octet rule is the tendency of atoms to acquire stable octets through chemical bonding as shown for elemental N2 below:

• In N2 there are only 10 electrons potentially available for bonding

• The 2 inner-shell electrons are not available for bonding

• Therefore, 6 electrons have to be shared in a triple bond

• The triple bond is extraordinarily strong accounting for the extreme stability of the elemental N2 species

2 7 completing the 20 element periodic table
2.7. Completing the 20-Element Periodic Table

Ten more elements to complete the periodic table

Sodium, Na, atomic number 11, atomic mass 22.99

Soft, chemically very reactive metal

Below is a representation of the electrons in 2 inner shells and 1 outer shell of sodium and the Lewis symbol of sodium showing the single outer-shell electron as a dot:

magnesium and aluminum
Magnesium and Aluminum

Magnesium, Mg, atomic number 12, atomic mass 24.31 exists in the elemental form as a strong lightweight metal

• Extension ladders • Portable tools • Aircraft

Aluminum, Al, atomic number 13, atomic mass 26.98 is a strong, lightweight metal

• Aircraft • Automobiles • Electrical lines • Building construction

Aluminum metal forms a self-protecting oxide coating

Aluminum can be regarded as a green metal

• Strong, lightweight component in aircraft and automobiles

• Efficient transmission of electricity

• Abundant element

• May be extracted from fly ash left over from coal combustion

• Highly recyclable

• Recycling aluminum saves enormous amounts of energy required to prepare aluminum metal from aluminum (bauxite) ore

silicon
Silicon

Silicon, Si, atomic number 14, atomic mass 28.09

• A metalloid and semiconductor

• Key element in semiconductor industry

• Second most abundant element in Earth’s crust

Silicon is a green element in electronics and signal transmission

• Vastly reduced bulk of electronic components, saving materials in computers, radios, televisions, communications equipment

• Solid-state electronics consume only a fraction of the electricity once used by vacuum tube based devices

• Silicon fiber optics: No bulky, expensive copper, less energy

phosphorus
Phosphorus

Phosphorus, P, atomic number 15, atomic mass 30.95

Most common elemental form is white phosphorus

• Chemically very reactive nonmetal that may catch fire spontaneously in the atmosphere

• Toxic and causes deterioration of the bone and a condition called “phossy jaw”

Phosphorus is an essential life element that is one of the components of DNA, the macromolecule that directs life processes

Essential plant fertilizer

Ingredient of many industrial chemicals including some pesticides

Chemically related arsenic contaminates phosphorus

• Arsenic is toxic and must be removed from phosphorus put in food, such as phosphoric acid added to soft drinks

slide44

Sulfur

Sulfur, S, atomic number 16, atomic mass 32.06

Essential nutrient for plants and animals, occurring in the amino acids that compose proteins

Common air pollutant emitted as sulfur dioxide, SO2, in the combustion of fossil fuels that contain sulfur

Much of the sulfur that is used is obtained from hydrogen sulfide, H2S, that contaminates much of natural gas

2H2S + 3O2 2SO2 + 2H2O

2H2S + SO2 3S + 2H2O

chlorine

Chlorine, Cl, atomic number 17, atomic mass 35.453

Has 7 outer-shell electrons, just 1 electron short of a full octet

Chlorine

Formation of ionic NaCl. The Cl atom accepts an electron to gain a stable octet as the Cl- anion and the Na atom loses an electron leaving it as the Na+ cation with a stable octet.

greenish yellow cl 2 gas
Greenish-yellow Cl2 gas

• Chlorine is an important industrial chemical used to make plastics and solvents

Green aspects of chlorine

• Abundant

• Important for public health because of its use in water disinfection

• Polyvinyl chloride (PVC) used in water pipe and drain pipe replace relatively scarce and expensive copper metal and toxic lead

non green aspects of chlorine
Non-green Aspects of Chlorine

• Toxic substance (first military poison used)

• Organochlorine solvents pollute air and water and are somewhat toxic

• Waste products of organochlorine compound manufacture are pollutants

• Chlorine-containing vinyl chloride used to make PVC products is a known human carcinogen

The practice of green chemistry minimizes the production and use of elemental chlorine and generally attempts to minimize production of organochlorine compounds and their dispersion to the environment

argon
Argon

Argon, Ar, atomic number 18, atomic mass 39.95

Complete octet of outer-shell electrons makes argon a noble gas

Argon composes about 1% by volume of atmospheric air and is recovered from distillation of liquid air

Uses of argon depend upon its chemically inert nature

• Argon is used to fill incandescent light bulbs to prevent evaporation of white-hot tungsten atoms from the glowing lamp filament, thus significantly extending bulb life

• Argon is used as a plasma medium in instruments employed for inductively coupled plasma atomic emission analysis of elements in environmental, biological, and other samples

completing the periodic table
Completing the Periodic Table

Potassium, K, atomic number 19, atomic mass 39.10

Like sodium, potassium is a very reactive alkali metal

An essential element for life and a common crop fertilizer

Produces K+ ion

calcium
Calcium

Calcium, Ca, atomic number 20, atomic mass 40.08

Readily loses its 2 outer-shell electrons to produce Ca2+ cation

Alkaline earth metal

Elemental calcium metal is chemically reactive

Chemical properties very similar to those of magnesium

Essential for life, plant growth

Essential animal nutrient to form hydroxyapatite, Ca5OH(PO4)3 in teeth and bones

Deficiency can cause disabling osteoporosis

elements above atomic number 20
Elements Above Atomic Number 20

Placement of electrons in elements with atomic number 21 and higher becomes complicated

Important elements above atomic number 20 include:

• Transition metals including chromium, manganese, iron, cobalt, nickel, and copper

• Lanthanides and actinides including thorium, uranium, and plutonium, which are important in nuclear energy and nuclear weaponry

aspects of the periodic table
Aspects of the Periodic Table

Hydrogen is unique

Elements in vertical columns belong to groups with similar chemical properties

First group on the left of the table — lithium, sodium, and potassium — are alkali metals

• Very low density and so soft that they can be cut with a knife

• Exposed metal corrodes very rapidly

• Violent reaction with water to produce strong base metal hydroxides

2M + 2H2O  2MOH + H2

• React with elemental chlorine to produce ionic LiCl, NaCl, and KCl

The second group consists of alkaline earth metals: beryllium, magnesium, calcium

• Highly reactive metals that produce Be2+, Mg2+, Ca2+ ions

aspects of the periodic table cont
Aspects of the Periodic Table (Cont.)

Halogens compose the second group from the right

• Diatomic gases in which the two atoms of F2 or Cl2 are held together by a single covalent bond consisting of two shared electrons

• Most nonmetallic elements

• Readily gain electrons to complete their outer shell octets producing F- and Cl- anions

The far right group consists of noble gases composed of single atoms: helium, neon, and argon

He has a complete outer shell of 2e-, Ne and Ar have 8