A Short Revision in Inorganic Chemistry for Undergraduates

 

Among the undergraduate Bachelor's degree courses I studied was chemistry, zoology, physiology, mathematics and medicine 

I still have some of these textbooks on: 

1. inorganic chemistry. 

2. organic chemistry. 

3. physical chemistry. 

4. zoology. 

No less than than 40 books on medicine 

I have been reading some on chemistry over the last two weeks for revision as an academic exercise to jolt back my memory. 

I just like to share with younger students today what we learnt in chemistry way back over 60  years ago in this revision journey. Come along with me in this short revision journey. 

Let me structure this revision in the following way:

1. Inorganic Chemistry – A review of periodic trends, chemical bonding, coordination compounds, acids and bases, redox reactions, and main group & transition metal chemistry.

2. Organic Chemistry – A refresher on fundamental concepts like hybridization, isomerism, reaction mechanisms (substitution, addition, elimination, rearrangement), functional groups, and important reactions.

3. Physical Chemistry – Revisiting thermodynamics, kinetics, quantum chemistry, spectroscopy, electrochemistry, and surface chemistry.

We shall discuss botany and zoology as separate subjects  with a review on zoology with animal classification, physiology, evolutionary biology, and selected topics in genetics, anatomy, and ecological adaptations.

Let me start with Inorganic Chemistry and move sequentially.

 

Inorganic Chemistry: Revision Part 1

Let’s begin with Periodic Trends—a fundamental concept in inorganic chemistry that helps in understanding element properties.

1. The Periodic Table & Periodic Trends

The periodic table is arranged in increasing atomic number, with elements grouped by similar chemical properties. The key periodic trends include:

• Atomic Radius: Decreases across a period (left to right) due to increased nuclear charge but increases down a group due to additional electron shells.
• Ionization Energy: Increases across a period as electrons are held more tightly and decreases down a group as electrons are farther from the nucleus.
• Electron Affinity: Becomes more negative across a period as atoms gain electrons more easily; however, noble gases have near-zero electron affinity.
• Electronegativity: Increases across a period and decreases down a group; fluorine (F) has the highest electronegativity.

2. Chemical Bonding

• Ionic Bonding: Transfer of electrons (e.g., NaCl)

• Covalent Bonding: Sharing of electrons (e.g., H₂, CH₄)

• Metallic Bonding: Delocalized electrons in a lattice of positive ions (e.g., Cu, Fe)

• Coordinate Covalent Bonding: A single atom donates both electrons in a bond (e.g., NH₃ → BF₃ complex)

3. Acid-Base Theories

• Arrhenius Theory: Acids produce H⁺ in water, bases produce OH⁻.

• Bronsted-Lowry Theory: Acids donate protons, bases accept protons.

• Lewis Theory: Acids accept electron pairs, bases donate electron pairs.

Let us now continue with Inorganic Chemistry, covering Coordination Chemistry and Redox Reactions, both of which are crucial topics in this field.

4. Coordination Chemistry

Coordination compounds consist of a central metal ion surrounded by ligands (molecules or ions that donate electron pairs). These compounds are fundamental in bioinorganic chemistry, catalysis, and industrial applications.

Key Terms in Coordination Chemistry are: 

• Coordination Number: The number of ligand donor atoms attached to the central metal (e.g., in [Cu(NH₃)₄]²⁺, Cu²⁺ has a coordination number of 4).

• Ligands: Can be classified based on the number of donor atoms:

1. Monodentate: Bind through a single donor atom (e.g., NH₃, Cl⁻, H₂O).
2. Bidentate: Bind through two donor atoms (e.g., ethylenediamine, C₂O₄²⁻).
3. Polydentate (Chelating Ligands): Bind through multiple donor atoms (e.g., EDTA⁴⁻).   

Common Geometries of Coordination Complexes

• Linear (CN = 2) → Example: [Ag(NH₃)₂]⁺
• Tetrahedral (CN = 4) → Example: [ZnCl₄]²⁻
• Square Planar (CN = 4) → Example: [Pt(NH₃)₂Cl₂] (cisplatin)
• Octahedral (CN = 6) → Example: [Fe(CN)₆]³⁻

Crystal Field Theory (CFT)

This theory explains the color and magnetic properties of coordination compounds by describing how d-orbitals split in an electric field created by ligands.

• Octahedral Splitting: d-orbitals split into two sets:

  1. Higher energy: ${\mathrm{<br>}}_{}$ ($d_{x^2-y^2},d_{z^2}$)

  2. Lower energy: $t_{2g}$ (${}_{}$dxy,dxz,dyzd_{xy}, d_{xz}, d_{yz})

• Tetrahedral Splitting: The energy levels are reversed; $e_g$ orbitals are lower than $t_{2g}$
  

• High-spin vs. Low-spin Complexes:

1. Weak field ligands (e.g., Cl⁻, H₂O) → high-spin (more unpaired electrons, paramagnetic).
2. Strong field ligands (e.g., CN⁻, CO) → low-spin (fewer unpaired electrons, often diamagnetic).  

This explains why [Fe(H₂O)₆]³⁺ is pale violet (high-spin) while [Fe(CN)₆]³⁻ is yellow (low-spin) due to different energy gaps in d-orbital splitting.

Applications of Coordination Chemistry

• Biological systems: Hemoglobin (Fe), Vitamin B₁₂ (Co), and chlorophyll (Mg).
• Medicinal chemistry: Cisplatin for cancer therapy.
• Catalysis: Zeigler-Natta catalysts in polymer production.

5. Redox Reactions & Electrochemistry

Redox (reduction-oxidation) reactions involve the transfer of electrons.

Oxidation & Reduction

• Oxidation: Loss of electrons (increase in oxidation number).
• Reduction: Gain of electrons (decrease in oxidation number).

• Redox Example:

$$Zn+C{u}^{2+}\to Z{n}^{2+}+Cu\mathrm{<br>}\mathrm{<br>}\mathrm{<br>}$$

Zn is oxidized (loses electrons, reducing agent).
Cu²⁺ is reduced (gains electrons, oxidizing agent).

Balancing Redox Equations (Ion-Electron Method)

1. Split into half-reactions (oxidation & reduction).
2. Balance atoms (except H & O).
3. Balance O with H₂O, then balance H with H⁺.
4. Balance charge with electrons (e⁻).
5. Equalize electron transfer and combine half-reactions.

Example: Balancing the acidic reaction

$$MnO_4^- + Fe^{2+} → Mn^{2+} + Fe^{3+}$$

Half-reactions:

$$MnO_4^- + 8H^+ + 5e^- → Mn^{2+} + 4H_2O$$
$$Fe^{2+} → Fe^{3+} + e^-$$

Multiply Fe half-reaction by 5 and add them.

Final balanced equation:

$$MnO_4^- + 5Fe^{2+} + 8H^+ → Mn^{2+} + 5Fe^{3+} + 4H_2O$$

Electrochemical Cells

Redox reactions drive electrochemical cells, categorized into:

1. Galvanic (Voltaic) Cells – Spontaneous reaction producing electrical energy (e.g., Daniell cell).
2. Electrolytic Cells – Non-spontaneous reaction driven by an external voltage (e.g., electrolysis of water).

Standard Electrode Potential ($E^\circ$)

• Measures a species' tendency to gain/lose electrons.

• Standard Hydrogen Electrode (SHE) is set at 0.00V.

• A positive $E^\circ$ means a species is a strong oxidizing agent (e.g., $E^\circ_{Cu^{2+}/Cu} = +0.34V$).

• A negative ${\mathrm{E0 means\; a\; species\; is\; a\; strong reducing\; agent<br>}}^{}$$E^\circ_{Zn^{2+}/Zn} = -0.76V$), e.g.

Nernst Equation (for non-standard conditions):

$$E = E^\circ - \frac{0.0591}{n} \log Q$$

where $Q$ is the reaction quotient, and $n$ is the number of electrons transferred.

Next Steps in Inorganic Chemistry

Now that we have covered Periodic Trends, Bonding, Coordination Chemistry, and Redox Reactions, the next topics could be:

1. Main Group & Transition Metal Chemistry (properties & trends of Groups 1-18, d-block elements).

2. Industrial & Environmental Applications (e.g., Haber process, metallurgy).

Inorganic chemistry overlaps with physical chemistry in areas like electrochemistry, bonding theories, thermodynamics, and reaction kinetics. As we continue, I will highlight these connections so you can see the interplay between these disciplines.

Let’s move forward with Main Group & Transition Metal Chemistry, followed by Metallurgy and Industrial Applications.

6. Main Group & Transition Metal Chemistry

The periodic table is divided into main group elements (s- and p-block) and transition metals (d- and f-block). Their chemistry is crucial in industry, medicine, and materials science.

6.1 Main Group Elements (s- and p-block)

Group 1: Alkali Metals (Li, Na, K, Rb, Cs, Fr)

• Highly reactive metals, react vigorously with water:

  $$2Na+2H_{2}O\to 2NaOH+H_2$$
  

• Form strong bases (e.g., NaOH, KOH).

• Exist as ionic compounds (e.g., NaCl, K₂CO₃).

• Low ionization energy → easily lose electrons to form +1 oxidation state.

Group 2: Alkaline Earth Metals (Be, Mg, Ca, Sr, Ba, Ra)

• Less reactive than alkali metals, but still react with water (except Be).

• Important in biological systems (e.g., Ca²⁺ in bones, Mg²⁺ in chlorophyll).

• Form oxides and hydroxides:

  $$CaO+H_{2}O\to Ca(OH{)}_{\mathrm{2<span\; style="font-weight:\; bold;"></span>}}$$

• Common compounds: Mg(OH)₂ (milk of magnesia), CaCO₃ (limestone), BaSO₄ (used in X-rays).

Group 13: Boron Group (B, Al, Ga, In, Tl)

• Boron (B) is a metalloid, others are metals.

• Aluminum is amphoteric:

  $$Al(OH{)}_3+NaOH\to Na[Al(OH{)}_4](\text{acts as an acid})$$

$$Al(OH{)}_3+HCl\to AlC{l}_3+H_{2}O(\text{acts as a base)}$$

Group 14: Carbon Group (C, Si, Ge, Sn, Pb)

• Carbon: Basis of organic chemistry; forms strong covalent bonds.

• Silicon (Si): Found in sand (SiO₂), semiconductors.

• Tin & Lead: Show +2 and +4 oxidation states due to the inert pair effect.

Group 15: Nitrogen Group (N, P, As, Sb, Bi)

• Nitrogen (N₂) is an inert gas due to its strong triple bond.

• Phosphorus (P) forms allotropes:

  • White P (reactive, stored in water).

  • Red P (stable, used in matches).

• Ammonia (NH₃) is a key base:

  $$N{H}_3+H^{+}\to N{H}_4^{}$$

Group 16: Oxygen Group (O, S, Se, Te, Po)

• Oxygen (O₂): Strong oxidizing agent.

• Sulfur (S): Forms oxides like SO₂ (acid rain precursor).

• Sulfuric Acid (H₂SO₄): Industrially significant; acts as an oxidizer and dehydrating agent.

Group 17: Halogens (F, Cl, Br, I, At)

• Highly reactive nonmetals, exist as diatomic molecules (F₂, Cl₂).

• Fluorine (F₂): Most electronegative element, strong oxidizer.

• Chlorine (Cl₂): Used in water purification.

• Form halide salts:

  $$Na+C{\mathrm{l }}_{}\to NaCl$$
  

Group 18: Noble Gases (He, Ne, Ar, Kr, Xe, Rn)

• Chemically inert, but Xe can form compounds (e.g., XeF₄).

• Argon (Ar) used in welding to provide an inert atmosphere.

6.2 Transition Metals (d-block)

Transition metals show variable oxidation states, complex formation, and catalytic properties.

General Properties

• Partially filled d-orbitals lead to colorful compounds.

• Multiple oxidation states:

  • Fe → Fe²⁺, Fe³⁺

  • Cu → Cu⁺, Cu²⁺

• Good catalysts: Fe in Haber process, Pt in catalytic converters.

Notable Transition Metals

• Iron (Fe): Found in hemoglobin, steel.

• Copper (Cu): Electrical wiring, corrosion-resistant.

• Silver (Ag): Photography, antimicrobial properties.

• Platinum (Pt): Catalysts, jewelry.

• Chromium (Cr): Stainless steel, pigments

Aluminum oxide (Al2O3) and aluminium hydroxide (Al (OH) are amphoteric salts, meaning they can react with both acids and bases. 

Here's how: Aluminum Oxide (Al₂O₃):

• Reaction with acids (acting as a base):

  • Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l) 
  • Al₂O₃(s) + 3H₂SO₄(aq) → Al₂(SO₄)₃(aq) + 3H₂O(l) 
• Reaction with bases (acting as an acid):

  • Al₂O₃(s) + 2NaOH(aq) + 3H₂O(l) → 2NaAl(OH)₄ 
  • Al₂O₃(s) + 2NaOH(aq) → 2NaAlO₂(aq) + H₂O(l) 

Aluminum Hydroxide (Al(OH)₃):

• Reaction with acids (acting as a base):
  • Al(OH)₃(s) + 3H⁺(aq) → Al³⁺(aq) + 3H₂O(l)
• Reaction with bases (acting as an acid):
  • Al(OH)₃(s) + OH⁻(aq) → [Al(OH)₄]⁻(aq) 

7. Metallurgy & Industrial Applications

Metallurgy is the process of extracting metals from ores and refining them.

Metallurgical Processes

1. Ore Concentration (removing impurities).

2. Froth flotation for sulfide ores.

3. Magnetic separation for iron ores.

4. Extraction (reducing metal ions to metals).

   1. Reduction of oxides:

      $$F{e}_2{O}_3+3CO\to 2Fe+3C{O}_2$$

   2. Electrolysis for reactive metals (Al, Na, Mg).

5. Refining (purifying the metal).

• Electrolytic refining for Cu, Ag.

• Zone refining for semiconductors (Si, Ge).

Connections to Physical Chemistry

Many inorganic concepts involve physical chemistry principles:

• Crystal Field Theory (CFT) (Quantum Mechanics).

• Electrochemistry (Redox & Nernst Equation).

• Metallurgy (Thermodynamics & Gibbs Free Energy).

• Transition Metal Spectroscopy (Absorption of light in d-orbitals).

This sums up an undergraduate  course in inorganic chemistry in a nutshell  

Articles Awaiting

Thank you Professor Dr Ling Siew Ching for your interest. Give me time to think and write.

The following articles shall be written in stages within these two months - April and May  

1. The Mystery on the Chemistry of Life
2. Does Soul Exist (Part 1)
3. Does Souls Exist (Part 2)  
4. The Vast Knowledge of the Human Brain 
5. A Short Introduction on Microbiology of Medical Importance
6. Visibility of the Great Wall of China from the Moon (Part 2) 
7. How Modern Medicine was Hijacked for Profit (Part 1)
8. How Modern Medicine was Hijacked for Profit (Part 2) 
9. Summary on the Physics and Physiology of Falling from 10,000 Metres 

Thank you for your enquiry 

Meantime take care!

jb lim 

The Water of Life

 Scientists always believe that in order for life to exist, water is probably the most important ingredient needed.

 

We know that in order for us, animals, plants, and microorganisms to survive and flourish on this planet water is the key ingredient for life and for them to first evolve from the primordial oceans.

 

Astronomers and astrobiologists have been searching for life in our galaxy for evidence of life on other planets. They have been looking for water first, and other life-giving chemicals such as carbon and amino-acids among the planets as prerequisites for life to be possible in their space probes. But are these the chemical criteria for life to be possible or rather for physical forms of life to be possible?

 

According to Dr Anne Jungblut, a specialist in life living in extreme conditions, and Dr Paul Kenrick, a specialist on the early evolution of life, explain what they were looking for.

 

According to them as well as to all scientists, the processes to make life possible, there must be life-giving chemicals and water for chemical reactions to take place in a living body, and for water to break down those substances so these reactions can move and interact freely.

 

Liquid water is probably the only essential requirement for life on Earth because it functions as a solvent. It is efficient in dissolving substances to enable these biochemical reactions to take place in animals, plants and in the microbial cells.

 

The chemical and physical properties of water is to allow it to dissolve more substances than other liquids, as water is a universal solvent for most chemicals.  Other physical characteristics of water essential for life are its heat conducting ability, high boiling and melting points, and its capability to allow life-giving light to penetrate.

 

According to another scientist, he says 'As water plays such an essential role in life on Earth, the presence of water has been vital in the search of other habitable planets and moons'.

 

Many thousands of biomolecules are involved in the reactions with water for complex life to be made possible. Carbon-based life is only possible in the presence of water for the synthesis of proteins, carbohydrates and fats that make up life. Hence, we conclude that physical life as we know it here on Earth is only possible in the presence of water.

 

The molecular structure of carbon allows its atoms to form long chains, with each other with two potential free bonds to join up with other atoms especially with oxygen, hydrogen and nitrogen to make life organic compounds very complex.

 

Many of these free bonds in carbon can even join up with other carbon atoms to form complex rings and 3D molecular structures. These carbon bonds are strong and stable for building life-giving structures since carbon along with water are the most abundant substance on Earth on which all life is made possible. Hence, we assume that this hypothesis holds true for the entire Universe where life exists, or does it?

 

Although carbon is possibly the main component of organic compounds on which all life is based, other elements such as nitrogen on which complex proteins are based are also required for smaller units called amino acids. The synthesis of DNA and RNA, the carriers of the genetic code for life on Earth also requires nitrogen, not just water or carbon.

 

Microorganisms like bacteria convert nitrogen from the atmosphere into nitrogen compounds such as nitrates that is also essential for plants as nitrates are needed for their protein synthesis

 

Besides water and nitrogen, phosphorus is also essential for life as the element is needed for the synthesis of adenosine triphosphate (ATP), the compound that drives the biochemical power and machinery of life.

Energy-rich phosphate bond in ATP is converted into ADP (adenosine diphosphate) in anaerobic respiration to yield energy to be converted back into ATP in the presence of oxygen.

ATP is a nucleoside triphosphate, containing a nitrogenous base (adenine), a ribose sugar, and three serially bonded phosphate groups. ATP is often referred to as an "energy currency" of the cell that provides readily releasable energy in the bond between the second and third phosphate groups.

 

In addition to its source of cellular energy, the breakdown of ATP through hydrolysis provides a broad spectrum of cellular functions such as in cellular signalling and in DNA /  RNA synthesis. ATP synthesis utilizes energy from multiple catabolic mechanisms, including cellular respiration, beta-oxidation, and ketosis.

 

This may be true in cellular chemistry where water is needed to drive the chemical reactions, but water is not needed in the life forces themselves existing in a living body that drive these biochemical reactions. In short, it is the life forces that are the master command to these chemistries of life, and life itself. 

 

Phosphorus is also another vibrant element in cell membranes that regulates the flow of substances in and out of cells besides being part of the DNA and RNA.

 

Besides water, carbon, nitrogen, sulphur that makes up the enzyme, hormones and vitamins is also essential for life. However, in the absence of oxygen and light, it is also possible to use sulphur as an energy source. Some bacteria called extremophiles can live without light and oxygen under severe environmental conditions such as in hydrothermal vents on ocean floors, frozen lakes, areas with high salinity and even in areas with high radio activities.

 

The question we need to ask is, if some of these life forms found here on Earth living under extreme conditions, would it be possible for other physical life forms found living under extreme conditions in other planets and other extra-terrestrial worlds?

  

Life on Earth took at least 4 billion years to evolve from single-celled organisms to complex life as we now know them. The age of the universe is 13.8 billion years, and the age of Earth is 4.543 billion years. The accretion of Earth took place 4,500 to 4,400 million years ago, after the atmosphere and oceans were formed 4,200 million years ago. It was only when the oceans where there was water, life became possible in the form of the first prebiotic chemistry.  That was 4,000 million years ago. Life was not possible in its earliest stages of Earth’s formation as it was too hot then.

 

The entire scenario of from the creation of the Universe till the early agriculture 12,000 years ago till the use of iron tools by humans is given here:

 

Creation of Heavens and the Universe:

 

https://scientificlogic.blogspot.com/search?q=age+of+universe

 

It is possible that life exists on other planets, but such life would have a lot of evolutionary process to catch up. It took complex life so long to form due to its complex genetic and biochemical systems.  Microorganisms with simple cells have to evolve first. According to one scientist, he says:

 

'To make tissues and organs, cells need to multiply, specialise in function, and co-operate. The evolution of these basic building blocks and their integration took time. Larger organisms require even more specialised and integrated cellular systems. The fossil record tells us that this took billions of years.' 

 

Having explained all that, especially the presence of water as the first requirement, scientists always assume that life elsewhere in the Universe is also the same as we know them here on Earth. So, they came up with the hypothesis that life in other worlds is only possible within the Goldilocks Zone, meaning a planet has to be like Earth to be just right from its Sun or their star from a distance that is not too hot, or not too cold for liquid water to exist on its surface?

 

Astronomers have been searching for planets within this hypothesis in the Goldilocks’s Zone for ages without success for the existence of (physical) life there. Not just light at the right distance, but also light and radiation of certain wavelengths that does not damage the DNA of life there. Here on Earth damaging ultraviolet light for instance from the Sun is screened off by the ozone. So, astronomers need to look for those other life-damaging conditions too, not just water, light and the right temperature.

 

Now the question that is troubling me as a scientist myself who is trained and familiar in astronomy, astrobiology, evolution of life on Earth, biology and zoology, medicine and other fields of life sciences, I have always asked myself, is it necessary that life has to be in the physical form to meet all these criteria for its existence throughout the Universe or at least in other nearby worlds that other scientists have been vainly trying in their Search for Extra-terrestrial Intelligence (SETI) with their radio telescopes.

 

Frank Drake and his colleagues in 1961 even came out with unreliable guesses to look for life in other worlds using his equation that looks like this:

 

• R_∗ = 1 yr⁻¹ (1 star formed per year, on the average over the life of the galaxy; this was regarded as conservative)
• f_p = 0.2 to 0.5 (one fifth to one half of all stars formed will have planets)
• n_e = 1 to 5 (stars with planets will have between 1 and 5 planets capable of developing life)
• f_l = 1 (100% of these planets will develop life)
• f_i = 1 (100% of which will develop intelligent life)
• f_c = 0.1 to 0.2 (10–20% of which will be able to communicate)
• L = 1000 to 100,000,000 communicative civilizations (which will last somewhere between 1000 and 100,000,000 years)

Inserting the above minimum numbers into the equation gives a minimum N of 20 Inserting the maximum numbers gives a maximum of 50,000,000. Drake states that given the uncertainties, the original meeting concluded that N ≈ L, and there were probably between 1000 and 100,000,000 planets with civilizations in the Milky Way Galaxy.

 

They assume all life elsewhere must satisfy all the same criteria for life as we know them here in this physical world, or is it?

 

The question that troubles me for a long time is, what about life that has no physical body but just pure life such as spiritual life existing and residing inside a physical body that does not require water such as a soul that leaves the physical body on death? If they exist, I don’t think such pure life tagged or trapped inside a physical body requires any water to exist. But that’s life to me, not a physical living body

 

See my arguments among others on this here:  

 

Read also the “The Mystery of Life”:

 

https://scientificlogic.blogspot.com/search?q=mystery+of+life

 

The Spark of Life:

 

https://scientificlogic.blogspot.com/search?q=spark+of+life

 

Jesus First Miracle:

 

https://scientificlogic.blogspot.com/search?q=jesus+first+miracle

 

 

https://scientificlogic.blogspot.com/search?q=does+soul+exist

 

We often read accounts of UFOs, presuming beings from other worlds visiting Earth. If they exist with strong possibilities they do -  from numerous reports of their sightings all over the world seen by people with different belief systems, religion, cultures, ethnicities, ages and genders. How did these “living beings” from other worlds travel vast chasms of interstellar spaces, distances of tens, hundreds or thousands of light years between stars to undertake those horrendously long journeys without food and water as we know them to arrive here on Earth? What about them?

 

If they are living creatures from other worlds, don’t they also require food and water during their unspeakably long journey between the stars? Yet they managed to arrive here without water or food in deep interstellar space. Give this a thought as I do.   

 

Furthermore, when all life on Earth is destroyed, and a new heaven and a new Earth is created with non-physical life existing there. It says there is “no more sea”, meaning there is no more water needed for spiritual life there as in Revelation 21:1?

 

But our life and all life on Earth is physical and all  require water as already explained above. Give this also another thought. It troubles me greatly unlike other scientists and the common man-in-the-street who only believes what scientists tell them. 

 

In summary, I don't think it is safe to assume that everything that happens or exists we know here in this world, applies to other worlds too, even in the nearest ones in the Milky Way Galaxy, let alone in the entire Universe spanning 93 billion light years across. 

 

For instance, we can easily calculate and measure the amount of energy output of the Sun, measure the distances to the stars using various methods such as measuring its parallax, using Cepheids variables, by observing the length  of their period and intrinsic luminosity, and use simple physics to calculate their distances. 

 

Astronomers can even tell the evolution and ages of the main sequence stars by looking at their luminosity in the Hertzsprung–Russell diagram.  As they grow older, their luminosity increases, and by knowing their mass, and their increase in luminosity we can tell  the ages of younger and older stars. 

 

We can tell a lot about the Universe, their origin and ultimate fate, how they work, their age, size, numbers of galaxies, make estimates of the number of stars in each galaxy...a 1000 and one thing we know, but we have not a clue if life even in their simplest form exist elsewhere other than our own. 

 

We don't even have an acceptable definition for life despite over 100 definitions being offered, let alone measure it. If we are so blind in knowing exactly what makes some organic molecules almost suddenly come alive, or tell ourselves exactly how life originated, how they were created, designed, or spontaneously evolved, then how are we going to know if other life elsewhere requires water in such horrendously vast cosmic oceans containing an estimated 100 trillion, trillion (1 followed by 26 zeros) other worlds - Earth we live in, is just one of them? 

 

We can only give ourselves a very deep thought on the mysteries of life!

 

jb lim 

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