Excitation and Ionization Energy and Potential

The minimum energy required to excite an electron in the ground state of an atom to any excited state is called excitation energy. This note provides us an information on excitation and ionization energy and potential.

Summary

Things to Remember

The minimum energy required to excite an electron from the ground state of an atom to any excited state is called excitation energy.

Exciting an electron in an atom from its ground state (i.e. n = 1 state) to the infinite state (i.e. n \(\alpha \) state) is called ionization.

The potential difference through which the extra electron is to be acceleration in order for it to cause the ionization of an atom is called the ionization potential of the atom.

Emission spectra are classified into continuous, line and a band spectrum visible from hot solid is an example of continuous spectrum.

Absorption spectra are obtained when electrons are taken from lower energy states to the higher energy states.

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Subjective Questions

Q1:

Write a short note on Classification of enzymes.

Type: Short Difficulty: Easy

Show/Hide Answer

Answer: <h3>Enzymes</h3>
<h4>Introduction</h4>
<p>Enzyme- a substance that acts as a catalyst in living organisms, regulating the rate at which chemical reactions proceed without itself being altered in the process. The biological processes that occur within all living organisms are chemical reactions, and most are regulated by enzymes. Without enzymes, many of these reactions would not take place at a perceptible rate. Enzymes catalyze all aspects of cell metabolism. This includes the digestion of food, in which large nutrient molecules (such as proteins, carbohydrates, and fats) are broken down into smaller molecules; the conservation and transformation of chemical energy; and the construction of cellular macromolecules from smaller precursors.</p>
<h4>Definition</h4>
<p>Enzymes are defined as biocatalysts synthesized by living cells, they are protein in nature, colloidal and thermolabile in character and specific in their action.</p>
<p>They are produced by living cells but are capable of acting independently of the cells.</p>
<p>Most of the enzymes are protein in nature and exhibit all the properties of protein.</p>
<p>They are water soluble, precipitated by the usual protein precipitate like alcohol, ammonium sulfate, and alkaloidal reagents.</p>
<p>Extreme alteration of pH and high temperatures denature the enzymes and make them inactive.</p>
<h3>Classification of Enzymes</h3>
<p>According to the International Union of Biochemistry (IUB) system, enzymes are classified into six major classes:</p>
<ol>
<li>Oxidoreductases</li>
<li>Transferases</li>
<li>Hydrolases</li>
<li>Isomerases</li>
<li>Lyases</li>
<li>Ligases</li>
</ol>
<h4><strong>1.</strong> Oxidoreductase</h4>
<p>These catalyze oxidation – reduction reactions or involved in oxidation – reduction reactions.</p>
<p>Oxidation-Reduction</p>
<p>AH<sub>2</sub> + B A + BH<sub>2</sub></p>
<p>FOR EXAMPLES:</p>
<ul>
<li>Alcohol dehydrogenases</li>
<li>Cytochrome oxidase</li>
<li>L and D amino acid oxidase</li>
</ul>
<p>These enzymes can be grouped in following ways:</p>
<ul>
<li><strong>Oxidase </strong>– these enzymes use oxygen as a hydrogen acceptor. For e.g. Tyrosinase, cytochrome oxidase, uricase.</li>
<li><strong>Anaerobic dehydrogenase</strong> – these enzymes used some other substances as a hydrogen acceptor. For e.g. Malate dehydrogenase, Succinate dehydrogenase, Lactate dehydrogenase.</li>
<li><strong>Aerobic dehydrogenase</strong> – these enzymes are used either oxygen or other substances as a hydrogen acceptor. For e.g. L-and –D-amino acid oxidases</li>
</ul>
<p>1. Xanthine oxidases</p>
<p>2. Aldehyde oxidase</p>
<ul>
<li><strong>Hydroperoxidase</strong> - these enzymes are used hydrogen peroxide as a substrate. For e.g. peroxidase, catalase.</li>
<li><strong>Oxygenase </strong>– these enzymes which act on single hydrogen donors with incorporation of oxygen. For e.g. Tryptophan oxygenase.</li>
<li><strong>Hydroxylases</strong> – these enzymes act on paired donors with incorporation of oxygen into one donor. For e.g. steroid hydroxylases.</li>
</ul>
<h4><strong>2.</strong> Transferases</h4>
<p>These enzymes catalyze the transfer of a functional group from one substrate to another.</p>
<p>A-X+B → A+B-X</p>
<p>For example- Hexokinase</p>
<p>Glucokinase</p>
<p>Transmethylases</p>
<p>Transaminases</p>
<p>Pyruvate kinase.</p>
<ol start="3">
<li>
<h4>Hydrolases</h4>
These enzymes bring out hydrolysis of various compounds</li>
</ol>
<p>A-B+H<sub>2</sub>O →AH+BOH</p>
<p>For example –Lipase</p>
<p>Pepsin</p>
<p>Urease</p>
<p>Alkaline phosphate</p>
<p>Choline esterase</p>
<p>Acid phosphate</p>
<ol start="4">
<li>
<h4>Isomerases</h4>
</li>
</ol>
<p>These enzymes catalyze the interconversion of optical, geometric or positional isomers.</p>
<p>A → A<sup>1</sup></p>
<p>For example – Retinol isomerase</p>
<p>Phosphohexose isomerase</p>
<p>Triose phosphate isomerase</p>
<ol start="5">
<li>
<h4>Lyases</h4>
</li>
</ol>
<p>These enzymes catalyze removal of group of mechanism other than hydrolysis</p>
<p>A-B+X-Y → AX-BY</p>
<p>For example – Histidase</p>
<p>Fumarase</p>
<p>Aldolase</p>
<ol start="6">
<li>
<h4>Ligases</h4>
</li>
</ol>
<p>These enzymes catalyze the synthetic reaction where two molecules are joined together and ATP is used.</p>
<p>For example – Glutamine synthetase</p>
<p>Acetyl-CoA carboxylase</p>
<p>Succinate thiokinase.</p>

Q2:

Write a short note on Factors affecting the enzyme activity.

Type: Short Difficulty: Easy

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Answer: <h3>Factors affecting the enzyme activity</h3>
<ol>
<li>
<h4>Effects of enzyme concentration</h4>
</li>
</ol>
<p>As the concentration of enzyme is increased there is a gradual increase in reaction velocity.</p>
<p><strong>Explanation</strong></p>
<ul>
<li>The formation of an enzyme-substrate complex is necessary for the formation of product from the reactant.</li>
<li>As the number of an enzyme, molecule increased there is a gradual increase in a number of enzyme-substrate complexes. Increased in the number of enzyme-substrate complexes leads to increased in the number of product formation.</li>
</ul>
<p> </p>
<p><img src="/uploads/enzyme_concentration.PNG" alt="c" width="414" height="172" /></p>
<figure class="" style="width: 459px;"></figure>
<ol start="2">
<li>
<h4>Effect of substrate concentration</h4>
</li>
</ol>
<p>As the concentration of substrate increased there is a gradual increase in reaction velocity up to a particular point beyond which the velocity does not increase.</p>
<p><strong>Explanation</strong></p>
<ul>
<li>At low concentration of substrate-free enzyme are available. So, an addition of more substrate can increase the reaction velocity till saturation.</li>
<li>After saturation of the enzyme even if the substrate is added there are no more free enzyme molecules to convert the substrate into product. So, the reaction velocity does not increase after this point.</li>
</ul>
<p> </p>
<p> </p>
<p><img src="/uploads/effect_of_substrate_concentration.PNG" alt="n" width="505" height="163" /></p>
<figure class="" style="width: 522px;"><br /><figcaption><br /></figcaption></figure>
<p> </p>
<ol start="3">
<li>
<h4>Effect on Temperature</h4>
</li>
</ol>
<p>The velocity of enzyme reaction increases with the increase in temperature up to a particular point and the declines.</p>
<p><strong>Explanation</strong></p>
<ul>
<li>An increase in temperature increases the kinetic energy of the reactants, increasing the chances of formation of an enzyme-substrate complex. So, up to the optimum temperature of 37<sup>o</sup>c the enzyme velocity increases.</li>
<li>Beyond this optimum temperature undergo denaturation making in inactive for its action.</li>
</ul>
<p><img src="http://alevelnotes.com/content_images/i71_gcsechem_18part2.gif" alt="Image result for Effect on Temperature affecting enzyme" /></p>
<p> </p>
<p> </p>
<ol start="4">
<li>
<h4>Effect of PH</h4>
</li>
</ol>
<p>Each enzyme has an optimum activity at particular PH. This PH at which the enzyme have optimum activity is known as optimum PH. Below and above the optimum PH, the enzyme activity is gradually low.</p>
<p><strong>Explanation</strong></p>
<ul>
<li>Above and below optimum PH the enzyme which is all proteinaceous in nature undergoes a structural change or chemical changes making the enzyme totally ineffective.</li>
</ul>
<p> </p>
<p><img src="http://www.bbc.co.uk/staticarchive/db7ba3135d8cf5ce20b58387bf6b7784436ce279.gif" alt="Image result for Effect of PH affecting enzyme" /></p>
<p> </p>
<ol start="5">
<li>
<h4>Effect of Activator and Inhibitors</h4>
</li>
</ol>
<p>Some of the enzymes are activated by certain metallic ions such metallic ions which activate the enzymes are known as activators. For e.g. chlorine activates the enzyme amylase so, chlorine is an activator for amylase. Similarly, Magnesium is an activator for the enzyme enclose so magnesium is called activator of enolase.</p>
<ul>
<li>Certain metals can inhibit the enzyme. Such metals are called Inhibitors. For e.g. sodium fluoride inhibits the enzyme enolase. So, sodium fluoride is an inhibitor of enolase.</li>
</ul>

Q3:

Write a short on coenzymes.

Type: Short Difficulty: Easy

Show/Hide Answer

Answer: <h3>Coenzymes</h3>
<p>A non-proteinaceous organic substance that usually contains a vitamin or mineral and combines with a specific protein, the apoenzyme, to form an active enzyme system.</p>
<p><img src="http://www.memrise.com/s3_proxy/?f=uploads/mems/983423000160426194647.jpg" alt="Image result for coenzyme model" /></p>
<h4>Characteristics</h4>
<ol>
<li>They are thermostable</li>
<li>Generally derived from vitamins</li>
<li>Functions as co-substrate</li>
<li>Participate in :</li>
</ol>
<ul>
<li><strong>Electron transfer</strong> reaction e.g. NAD<sup>+</sup>, NADP, FMN, FAD( flavin adenine dinucleotide)</li>
<li><strong>Group transfer</strong> reaction e.g. CoA, TPP( thiamine pyrophosphate), pyridoxal phosphate</li>
</ul>
<h4>Functions of coenzyme</h4>
<ol>
<li>NAD and NADP co-enzymes function as hydrogen acceptors in dehydrogenation reaction.</li>
<li>They accept atoms or group from a substrate and transfer them to other molecules.</li>
<li>CoA carries acyl groups which are used in the oxidative decarboxylation of pyruvic acid and synthesis of fatty acids and acetylation.</li>
<li>TPP carries active aldehyde group.</li>
<li>B<sub>6</sub> – PO<sub>4 </sub>(pyridoxal phosphate) is involved in transamination reaction.</li>
</ol>
<h3>Isoenzyme</h3>
<p>Isoenzymes are multiple forms of the enzyme that catalyze the same biochemical reaction but differ in physical properties like electrophoretic mobility and k<sub>m.</sub></p>
<h4>Characteristics</h4>
<ol>
<li>The difference between some isoenzyme is due to different in the quarternary structures of the enzymes.</li>
<li>They catalyze the same reaction but they can be distinguished by physical methods such as electrophoresis, or by immunological methods.</li>
<li>Isoenzymes synthesized from different genes e.g. malate dehydrogenase of cytosol is different from that found in mitochondria.</li>
<li>Oligomeric enzymes consisting of more than one type of subunits e.g. lactate dehydrogenase and creatine phosphokinase.</li>
<li>Similarly, other enzymes having isoenzymes are as mentioned below</li>
</ol>
<ul>
<li>Alkaline phosphate – 6 isoenzymes</li>
<li>Acid phosphatase – 2 isoenzymes</li>
<li>Creatinine phosphokinase (CPK) – 3 isoenzymes</li>
</ul>
<h3>Significance of Enzymes</h3>
<p>Enzymes are the sparks that start the essential chemical reactions our bodies need to live. They are necessary for digesting food, for stimulating the brain, for providing cellular energy, and for repairing all tissues, organs, and cells. Humbart Santillo, in his book, Food Enzymes, quotes a Scottish medical journal that says it well: "Each of us, as with all living organisms, could be regarded as an orderly, integrated succession of enzyme reactions."</p>
<p>There are three types of enzymes: metabolic enzymes, digestive enzymes, and food enzymes.</p>
<p>Metabolic enzymes catalyze, or spark, the reactions within the cells. The body's organs, tissues, and cells are run by metabolic enzymes. Without them, our bodies would not work. Among their chores are helping to turn phosphorus into bone, attaching iron to our red blood cells, healing wounds, thinking, and making a heartbeat.</p>
<p>Digestive enzymes break down foods, allowing their nutrients to be absorbed into the bloodstream and used in body functions. Digestive enzymes ensure that we get the greatest possible nutritional value from foods.</p>
<p>Food enzymes are enzymes supplied to us through the foods we eat. Nature has placed them there to aid in our digestion of foods. This way, we do not use as many of the body's "in-house" enzymes in the digestive process.</p>
<p> </p>

Videos

Introduction to Enzymes & It's Classification

Excitation and Ionization Energy and Potential

Excitation and Ionization Energy

The minimum energy required to excite an electron from the ground state of an atom to any excited state is called excitation energy. Thus, the energy required to excite an electron in the ground state to the first excited state is called the first excitation energy and so on. The excitation energy of an energy state is the difference between the energy of the excited state and that of the ground state. For example, for the hydrogen atom, the ground state energy(energy of the first orbit) is E₁ = -13.6 eV and energy of the second orbit is E₂ = -3.4 eV. This means to excite hydrogen atom, the energy required to be given to it is E₂ – E₁ = -3.4 + 13.6 = 10.2 eV. Hence, 10.2 eV is the first excitation energy of the hydrogen atom. Similarly, the II, the III excitation energy of hydrogen atom are E₃ – E₁, E₄ – E₁ etc.

Ionization Energy

Exciting an electron in an atom from its ground state (i.e. n = 1 state) to the infinite state (i.e. n \(\alpha \) state) is called ionization. Thus, the energy required to excite an atom from its ground state to the infinite state is called ionization energy. The ionization energy of an atom, in fact, is the difference of energy when it is in infinite state and in the ground state. If E₁ and E_{\(\infty \)} represent the energy of the atom when it is in the ground state and in the infinite state respectively, than the ionization energy of the atom is given by E_{\(\infty \)} – E₁ = 0 + 13.6 = 13.6 eV.

Excitation and Ionization Potential

Excitation Potential

By definition, if an electron is accelerated by 1 volt of potential difference, it acquires 1 eV of energy. So if the electron is accelerated through a p.d. of 10.2 volts, it acquires 10.2 eV energy. If such an extra electron collides with a ground state hydrogen atom, the hydrogen atom may be excited to the first excited energy state. Hence, the 10,2 volt of potential difference is the first excitation potential for a hydrogen atom. Second excitation potential for the hydrogen atom is given by (E₃ in eV – E₁ in eV) volt and so on.

Thus, the excitation potential of an energy of an atom is the potential, which is required for an electron to jump from the ground state to any one of its excited states.

Ionization Potential

The potential difference through which the extra electron is to be in acceleration in order for it to cause the ionization of an atom is called the ionization potential of the atom. For example, for the hydrogen atom, the ionization energy is 13.6 eV. By definition of 1 eV, an electron acquires 13.6 eV energy when it is accelerated through a potential difference of 13.6 volts.

Thus, ionization potential is the minimum potential to be applied in order to remove the electron completely from its ground state to infinity.

Emission Spectra

When the excited atoms make transitions from the excited state to the lower lying energy levels, then the emission spectra is obtained. Emission spectra are classified into continuous, line and a band spectrum visible from hot solid is an example of the continuous spectrum. A continuous spectrum is produced by incandescent solids, liquids, and compressed gasses. Line spectra are discontinuous lines produced by excited atoms and ions as they fall back to the lower energy level.

Absorption spectra

Absorption spectra are obtained when electrons are taken from lower energy states to the higher energy states. Various absorption series are Lyman, Balmer, Paschen, Bracket, and Pfund.

Limitations of Bohr’s Theory of Hydrogen Atom

Elliptical orbits are possible for the electron orbits, but Bohr’s theory does not tell us why only elliptical orbits are possible.
Bohr’s theory does not explain the spectra of only simple atoms like hydrogen but fails to explain the spectra of multi-electron atoms.
The fine structure of certain spectral lines of hydrogen could not be explained by Bohr’s theory.
It does not explain the relative intensities of spectral lines.
This theory does not account for the wave nature of electrons.

reference

Manu Kumar Khatry, Manoj Kumar Thapa et al. Principle of Physics. Kathmandu: Ayam publication PVT LTD, 2010.

S.K. Gautam, J.M. Pradhan. A text Book of Physics. Kathmandu: Surya Publication, 2003.

Lesson

Quantisation of Energy

Subject

Physics

Grade

Grade 12

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