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Lassen Astrobiology Student Intern Program. Assignment 1:. Basic Properties of Water and Their Importance to Astrobiology. Click on underlined items and m agnified graphics to navigate the assignment. If you see neither, simply click the mouse.
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Lassen Astrobiology Student Intern Program Assignment 1: Basic Properties of Water and Their Importance to Astrobiology
Click on underlineditems and magnified graphics to navigate the assignment. If you see neither, simply click the mouse. (HINT: There are navigable items on this slide.)
Hydrogen and Oxygen are the 1st and 3rd most abundant elements in the Universe, respectively. Hydrogen alone accounts for nearly 75% of the Universe’s normal atomic mass. Oxygen, by comparison, constitutes only 1%.
Hydrogen first formed only moments after the birth of the Universe – an event known as the Big Bang – which occurred nearly 14.6 billion years ago.
As the first stars powered on, they began fusing hydrogen into helium in their cores. This process is known as nuclear fusion and occurs in all stars to this day. This is when elemental oxygen is formed. A star nears the end of its life as it begins running out of hydrogen fuel. At this time, it starts fusing heavier elements in its core (up to iron in the largest stars).
All stars eventually burn out (some more violently than others), shedding layers of gas and dust into the interstellar medium. The story of water begins here.
This is a planetary nebula. Within it exists all the gas and dust necessary to build new stars, planets, and even you. It is within this matrix you will find hydrogen and oxygen, the two constituents of water.
H This is a planetary nebula. A water molecule just doesn’t “come into being”. Within it exists all the gas and dust necessary to build new stars, planets, and even you. In fact, oxygen and hydrogen each possess unique atomic characteristics which complement each other to bond. O It is within this matrix you will find hydrogen and oxygen, the two constituents of water. Consequently, water molecules in themselves possess unique physical properties. H Let’s take a look:
H This is a planetary nebula. Within it exists all the gas and dust necessary to build new stars, planets, and even you. Electron Affinity Electronegativity O Bond Character and Polarity It is within this matrix you will find hydrogen and oxygen, the two constituents of water. Molecular Shape Hydrogen Bonding H Phase Diagram of Water The Universal Solvent Next
Electron affinity is a measure of the tendency of an atom to accept an electron. As a general rule, electron affinity increases as you go across a period and decreases as you go down a group. This notion is correlated with the concept of the octet rule – that is, atoms tend to combine with each other in such a way that they each possess eight electrons in their valence shell. H O In this sense, hydrogen, with its low electron affinity and 1 valence electron, is likely to pair up with another hydrogen atom to satisfy the octet rule with oxygen, an atom with high electron affinity and 6 valence electrons. H Back
Electronegativity is a measure of the tendency of an atom to attract bonding electron pairs. An atom’s electronegativity is affected by both its atomic number and the distance that its valence electrons reside from the nucleus. As a general rule, it increases as you go across a period and decreases as you go down a group. INCREASING DECREASING
Oxygen has a higher electronegativity than hydrogen. The resulting difference in electronegativity owes to the fact that, when a water molecule forms, the hydrogen pair’s shared electrons are more attracted to the oxygen’s nucleus than their own. INCREASING O H H DECREASING Back
The electronegativity difference between two bonded atoms can determine the character of their bond. The electronegativity difference of oxygen and hydrogen is 1.24. Consequently, we define their bond as covalent – meaning that they share electrons – and polar, meaning that the distribution of charge focuses on one atom (in this case, oxygen). 1.24 This uneven electron distribution results in the oxygen atom being slightly more negative, while the two hydrogen atoms are comparatively more positive. These opposite but equal charges are separated by a distance. This is called a dipole moment. The polar nature of water is important to life for a variety of reasons. It also provides rigidity to DNA, RNA, and proteins, tightly binding around their structures. H O It enhances the stability of the cell membrane, regulating the transfer of nonpolar organics in and out of the cell. H Back
Bonded electrons in a molecule are most stable when they maximize distance between each other. H In the case of a water molecule, the central oxygen atom possesses two lone pairs of electrons. H O O These two lone pairs results in extra repulsion on the two bonding hydrogen atoms, causing the bonding shape to “bend”. H 104.5˚ H Consequently, the bond angle between the two hydrogen atoms is slightly compressed to 104.5˚. The resulting molecular shape is bent. Back
A hydrogen bond is an attractive interaction between a hydrogen atom and another electronegative atom. H O H O It is in this way water molecules adhere to each other, as end hydrogens attract to the more electronegative central oxygen atoms of other molecules. H H A hydrogen bond is not nearly as strong as either a covalent or ionic bond, but it does play an important role in shaping many physical properties in water. O H O H H H Example: Hydrogen bonds make liquid water more structured and stable. This stability permits an increased boiling point, allowing for water to remain a liquid over a wide range of temperature and pressure. Back
The following is a phase diagram to help you understand the influence of temperature and pressure on water’s physical state: One of water’s greatest properties is its ability to exist in three stages -- solid, liquid, and gas – on Earth. More importantly, water exists as a liquid over a remarkably broad range of temperatures. This is a crucial feature which supports all life in one way or another. Notice the steep slope of the melting/freezing line Melting It tells us that solid ice is less dense than liquid water, and can consequently float on top of it. Freezing As far as we know, there is no other body in our solar system or beyond which possesses these three regimes in such a habitable equilibrium. Vaporization This is a rare molecular property; however, it has had a huge impact on our planet’s hydrology. Condensation If ice did not float, but instead sank to the bottom of the world’s oceans, it would create a positive feedback loop in which the liquid water above it would be forced to the surface, where it would freeze, sink, and eventually result in a completely frozen planet highly unsuitable for life. 1 atm refers to 1 atmosphere, the pressure of outside air at sea level on Earth. Sublimation Deposition
It is a unique feature in our solar system. Even Mars, our most similar planetary relative, does not at present have a dense enough atmosphere to allow for liquid water to exist on its surface. Instead, with average temperatures hovering around -50˚C and atmospheric pressure being 1/1000 that of Earth, water ice on Mars’ surface sublimates directly into vapor when temperatures are high enough. This may have been a different story in the distant past. Mars’ surface may indeed have been very similar to Earth’s. However, since liquid water is necessary for cellular stability, the surface of Mars seems comparatively inhospitable today. The triple point is the temperature and pressure at which water exists in all phases in equilibrium Sublimation Back
Water’s polarity makes it a good solvent. Pure, deionized water, however, cannot conduct electricity on its own. Dissolved solutes, such as salts, are necessary to facilitate conduction. It is called the universal solvent because of its ability to dissolve salts and nutrients, which are key facilitators of several biological processes, including ingestion, excretion, and chemical transport within and between cells. The higher the ion concentration, the higher the water’s electrical conductivity. We can measure these changes using a conductivity meter. As the universal solvent, water dissolves cations (positively charged particles) and anions (negatively charged particles) to conduct electric currents. Similarly, the H+ concentration of an aqueous solution can give us insight into that solution’s pH. We can also measure it using a meter. When ionized, it is the perfect medium by which cells can facilitate biochemical reactions necessary for energy exchange, metabolism, and growth. Back
pH is a numerical figure expressing the acidity or alkalinity on a logarithmic scale, on which 7 is neutral, lower values are more acidic, and higher values are more alkaline. Back
Lassen Astrobiology Student Internship Assignment 1 complete
