Term Paper on Atoms | Molecules | Elements | Biochemistry

Here is a term paper on ‘Atoms’ for class 9, 10, 11 and 12. Find paragraphs, long and short term papers on the ‘Atoms’ especially written fro school and college students.

Term Paper on Atoms

Term Paper Contents:

1. Term Paper on the Introduction to Atoms
2. Term Paper on Isotopes
3. Term Paper on Electrons and Orbitals
4. Term Paper on Electrons and Energy
5. Term Paper on Electronegativity

---

ADVERTISEMENTS:

1. Term Paper on the Introduction to Atoms:

There are 92 naturally occurring chemical elements, each differing from the others in the structure of its atoms. Each different type of atom has a different number of protons in its nucleus, ranging from the lightest, hydrogen, which has 1 proton, to the heaviest, uranium, which has 92. The number of protons in the nucleus of a particular atom is called the atomic number.

The universe began, astronomers tell us, with an explosion that filled all space, with every particle of matter hurled away from every other particle. The temperature at the time of the explosion—some 20 billion years ago-was about 100,000,000,000 degrees Celsius (10¹¹ °C). At this temperature, not even atoms could hold together; all matter was in the form of subatomic, elementary particles.

Moving at enormous velocities, even these particles had fleeting lives. Colliding with great force, they annihilated one another, creating new particles and releasing more energy. As the universe cooled, two types of stable particles, previously present only in relatively small amounts, began to assemble themselves. (By this time, 100,000 years after the “big bang” is believed to have taken place, the temperature had dropped to a mere 2500°C, about the temperature of a white-hot wire in an incandescent light bulb).  

These, particles-protons and neutrons-are very heavy as subatomic particles go. Held together by forces that are still little understood, they formed the central core, or nuclei, of atoms. These nuclei, with their positively charged protons, attracted small, light, negatively charged particles-electrons-which moved rapidly around them. Thus, atoms came into being. (Perhaps atoms existed before the explosion, but how will one ever know?)

According to current theory, it is from these atoms-blown apart, formed, and re-formed over 20 billion years-that all the stars and planets of the universe are formed, including our particular star and planet. And it is from the atoms present on this planet that living systems assembled themselves and evolved.

Each atom in our own bodies had its origins in this explosion of some 20 billion years ago. You and I are flesh and blood, but we are also stardust. This text begins where life begins, with the atom. At first, the universe aside, it might appear that lifeless atoms have little to do with biology. Bear with us, however.

A closer look reveals that the activities we associate with being alive depend on combinations and exchanges between atoms, and the force that binds the electron to the atomic nucleus stores the energy that drives living systems.

Outside the nucleus of the atom are electrons, attracted by the positive charge of the protons. The electrons determine the chemical properties of atoms, and chemical reactions involve changes in the numbers and relative positions of these electrons. Atoms also contain neutrons, which are uncharged particles about the same weight as protons.

These, too, are found in the nucleus of the atom, where they seem to have a stabilising effect. The atomic weight of an element is essentially equal to the number of protons and neutrons in the nucleus. (Electrons are so light by comparison that their weight is usually disregarded. When you weigh yourself, only about 30 grams-approximately 1 ounce-of your total weight is made up of electrons.)

---

2. Term Paper on Isotopes:

Atoms with the same number of protons but different numbers of neutrons are known as isotopes; they differ from one another in their atomic weights but not in their atomic numbers. For example, the common form of hydrogen, with its one proton, has an atomic weight of 1 and is symbolised as ¹H, or simply H. Deuterium, ²H, is an isotope of hydrogen that contains one proton and one neutron and so has an atomic weight of 2. Tritium, ³H, the third isotope of hydrogen, has one proton and two neutrons and so has an atomic weight of 3.

Like many, but not all of the less common isotopes, tritium is radioactive, which means that its nucleus is unstable and emits energy when changing into a more stable form. The next heaviest atom is helium (He), which has an atomic number of 2 (two protons) and an atomic weight of 4 (two protons and two neutrons).

Hydrogen, deuterium, and tritium are all similar in their chemical properties because each can attract only a single electron, but helium with its two electrons (attracted by its two protons) is very different chemically from any of the isotopes of hydrogen. Thus, to repeat, the protons determine the number of electrons attracted to an atomic nucleus and those electrons determine the chemical properties of the atom.

---

3. Term Paper on Electrons and Orbitals:

The concept of the atom as the indivisible unit of the chemical elements is almost 200 years old; however, our ideas about its structure have undergone many changes. These ideas, or hypotheses, are usually presented in the forms of models, as are many scientific hypotheses.

The earliest model, emphasizing the indivisibility of the atom, resembled a billiard ball. As it came to be realised that electrons could be removed from the atom, the billiard ball gave way to the plum- pudding model, in which the atom was represented as a solid, positively charged mass with negatively charged particles, the electrons, embedded in it. Subsequently, however, physicists found that an atom is, in fact, mostly open space.

The distance from electron to nucleus, experiments indicated, is about 1,000 times the diameter of the nucleus; the electrons are so exceedingly small that the space is almost entirely empty. Thus the more familiar planetary model of the atom came into being, in which the electrons were depicted as moving in orbits around the nucleus. More recently, the Bohr model (named after physicist Niels Bohr) became the most popular one.

It emphasizes the fact that electrons are found outside the nucleus at different energy levels; this concept of energy levels is, as you will see, of great importance in the chemistry of living systems. The current model of electron configurations is quite different from all previous ones and more accurate in terms of what we know about the behaviour of electrons.

According to this model, the electron moves unpredictably around the nucleus, and its position at any given moment cannot be known with certainty. For convenience, its pattern of motion is defined as the volume in which the electron will be found 90 percent of the time. This volume is known as the electron’s orbital. Each orbital can hold a maximum of two electrons. Orbitals vary in shape.

The first two electrons occupy a single spherical orbital. (Thus, for instance, hydrogen’s single electron moves about the nucleus-90 percent of the time-within a single spherical orbital, and so do the two electrons of helium.) This single spherical orbital, with its maximum of two electrons, makes up the first energy level. At the second energy level, there are four orbitals, each of which, as we noted, can hold two electrons. One of these orbitals is spherical, and the other three are dumbbell-shaped.

The axes of the dumbbell orbitals are perpendicular to one another. The spherical orbitals are filled first, and then the dumbbell-shaped ones. The second energy level can hold a total of eight electrons, and so can the third. Atoms tend to complete their energy levels, and the chemical behaviour of atoms is governed by this tendency.

For instance, helium (atomic number 2), neon (atomic number 10), and argon (atomic number 18) all have completely filled outer energy levels and so tend to be unreactive; they are thus called the “noble” gases because of their disdain for reacting with other elements. Hydrogen (atomic number 1), lithium (atomic number 3), sodium (atomic number 11), and potassium (atomic number 19) each has a single electron in its outermost energy level, and each tends to lose this electron.

As a consequence of such a loss, each has one more proton than electron and therefore acquires a positive charge- H⁺, Li⁺, Na⁺, K⁺ Fluorine and chlorine, by contrast, with atomic numbers of 9 and 17, tend to gain an electron in order to complete an outer energy level and so become negatively charged- F^– and CI^–. Similarly, an atom with two electrons in its outer energy level may lose both of them, acquiring a double positive charge. Magnesium (atomic number 12) and calcium (atomic number 20) become Mg²⁺ and Ca²⁺, and so on. Such charged atoms are known as ions.

Ions make up less than 1 percent of the weight of most living matter, but they play crucial roles, K⁺ is the principal positively charged ion in most cells, and many essential biological reactions do not proceed in its absence. Both Na⁺ and K⁺ are involved in the production and propagation of the nerve impulse. Ca²⁺ is required for the contraction of muscles and Mg²⁺ forms a part of the chlorophyll molecule, the molecule that traps the energy from the sun.

---

4. Term Paper on Electrons and Energy:

Electrons, which are negatively charged, are attracted to the atomic nucleus because of the positive charge of the protons. The orbital occupied by an electron is determined by the amount of energy of the electron. This energy is in the form of potential energy. An analogy may be useful.

A rock on flat ground may be said to have no energy. If you push it up a hill, you give it energy-potential energy. So long as it sits on the peak of the hill, it neither gains nor loses energy. If it rolls down the hill, however, it loses its potential energy as it rolls back toward its original level ground.

Similarly, water that has been pumped up to a water tank for storage has potential energy that will be released when the water runs back down.

The electron is like the boulder, or the water, in that an input of energy can raise it to a higher energy level-farther away from the nucleus. As long as it remains at this higher level, it possesses the added energy. Also, like the boulder or water, the electron tends to go to its lowest possible energy level, just as the rock rolls downhill, and not up.

In a given atom, the first spherical orbital is the lowest energy level-the ground state. The four orbitals of the second level are occupied by electrons with more energy, and so on. It takes energy to move a negatively charged electron farther away from the positively charged nucleus, just as it takes energy to position a boulder at the top of a hill.

However, unlike the boulder on the hill, the electron cannot be pushed part way up. With an input of energy, electrons may move from a lower energy level to any one of several higher ones, but they cannot move to somewhere in between. For an electron to move from one level to another, the atom must absorb a discrete packet of energy, known as a quantum, which contains just the precise energy needed for the transition and no more or no less.

Thus the study of electron movements is known as quantum mechanics, and the term quantum jump, which has invaded our everyday discourse, refers to an abrupt, discontinuous movement from one level to another.

---

5. Term Paper on Electronegativity:

For the atoms of any particular element, all the electrons at any given energy level have about equal amounts of energy. However, the atomic nuclei of different elements have various degrees of attraction for electrons. The strength of the attraction depends on the number of protons in the nucleus, the closeness of the electrons to the nucleus, and the number of electrons outside the nucleus.

The affinity of an atom for electrons is called electronegativity. Electronegativity is expressed on a scale of 0 to 4. Helium and the other unreactive noble gases have electronegativity’s of 0. At the other end of the scale is fluorine with an electronegativity of 4. Oxygen, the next most electronegative, is 3.5. Electronegativity values for some of the elements are given in Table 1.2.

When an electron moves from an atom that is less electronegative to one that is more electronegative, it moves downhill, energetically speaking, and energy is released, as it is released when the boulder moves downhill.

In the green cells of plants and algae, the radiant energy of sunlight raises electrons to a higher energy level. In the course of a series of electron-transfer reactions, the electrons are passed slowly downhill until they are finally accepted by oxygen. During this transition, the radiant energy of sunlight is changed to the chemical energy on which all life on earth depends.