Atomic Physics

General Science Topic:

Atomic Physics Presenter:

Adnan Mirza Facilitator:

Afsheen Khalil

Agenda o Introduction o History o Achievements o Theories o Disadvantages o Conclusion

Introduction Atomic physics (or atom physics) is the field of physics that studies atoms as isolated systems comprised of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and the processes by which these arrangements change.

Introduction The term atomic physics is often associated with nuclear power and nuclear bombs, due to the synonymous use of atomic and nuclear in standard English. However, physicists distinguish between atomic physics - which deals with the atom as a system of electron(s) and a nucleus and nuclear physics - which considers atomic nuclei alone.

Atom o Atom is the smallest particle of an element. o Atoms are made up of 3 types of particles electrons, protons and neutrons. o These particles have different properties.

Electron

Proton

Neutron

Atom Electrons are tiny, very light particles that have a negative electrical charge (-). Protons are much larger and heavier than electrons and have the opposite charge, protons have a positive charge. Neutrons are large and heavy like protons, however neutrons have no electrical charge. An atom that carries an electrical charge is called an ion.

Atom o A major characteristic of an atom is its atomic number, which is defined as the number of protons. The chemical properties of an atom are determined by its atomic number and is denoted by the symbol Z. o The total number of nucleons (protons and neutrons) in an atom is the atomic mass number. This value is denoted by the symbol A. The number of neutrons in an atom is denoted by N. o Thus the mass of an atom is A = N + Z.

Isotopes o Two atoms with different numbers of neutrons are called isotopes. o Atoms with the same atomic number but with different atomic masses are called isotopes. o They have identical chemical properties, yet have very different nuclear properties.

Isotopes

Hydrogen Atomic Mass = 1 Atomic Number = 1

Deuterium Atomic Mass = 2 Atomic Number = 1

History The earliest steps towards atomic physics was the recognition that matter was composed of atoms, in the modern sense of the basic unit of a chemical element . This theory was developed by the British chemist and physicist John Dalton in the 18th century.

History o The true beginning of atomic physics is marked by the discovery of spectral lines and attempts to describe the phenomenon, most notably by Joseph von Fraunhofer. The study of these lines led to the Bohr atom model and to the birth of quantum mechanics itself. In seeking to explain atomic spectra an entirely new mathematical model of matter was revealed. o Since the Second World War , both theoretical and experimental fields have advanced at a great pace.

Early Models of Atoms The theory: Thomson “jellybean” model of the atom. The positive charge occupies most of the volume of the atom. Charged particles shot at this atom should be deflected slightly as they pass through.

Early Models of Atoms The Experiment (Rutherford):

o Most of the atom is empty space! o All of the positive charge is concentrated in a very small space!

Atomic Spectra

o Each element has its own characteristic “fingerprint”. o A heated gas emits emission lines. o The same gas, when placed between a bright continuous background source and the observer produces absorption lines at those same wavelengths.

Bohr’s Atomic Model Figure 28.1: Planetary model of the atom

o In 1913, Bohr applied the quantum theory of Planck and Einstein to the nuclear atom of Rutherford and formulated the well-known planetary model of atom.

Bohr’s Atomic Model o Bohr reasoned that Planck’s quantized electron energy states corresponded to electrons orbiting at different distances from the nucleus. o He reasoned that light is emitted when electrons makes a transitions from a larger to a smaller orbit. o Bohr realized that the frequency of emitted radiation is given by E = hf, where E is the difference in the atoms energy when the electrons is in the different orbit and f is the frequency of the emitted spectral lines and h is the Planck's constant and its value is 6.6*10-34 joules. second

Radioactivity o Radioactivity is the result of an atom trying to reach a more stable nuclear configuration. The process of radioactive decay, can be achieved via three primary methods.   

A nucleus can change one of its neutrons into a proton with the simultaneous emission of an electron (beta decay). By emitting a helium nucleus (alpha decay). By spontaneous fission (splitting) into two fragments.

Alpha Decay o In alpha decay, a positively charged particle, identical to the nucleus of helium 4, is emitted spontaneously. This particle, also known as an alpha particle, consists of two protons and two neutrons. o It was discovered and named by Sir Ernest Rutherford in 1899. o Alpha decay usually occurs in heavy nuclei such as uranium or plutonium.

Beta Decay o

o

o  

Beta decay occurs when an atom has either too many protons or too many neutrons in its nucleus. This form of radioactive decay was discovered by Sir Ernest Rutherford in 1899, although the neutrino was not observed until the 1960s. Two types of beta decay can occur. Positive beta decay releases a positively charged beta particle called a positron, and a neutrino. Negative beta decay releases a negatively charged beta particle called an electron.

Spontaneous Fission Another type of radioactive decay is spontaneous fission. In this decay process, the nucleus will split into two nearly equal fragments and several free neutrons. A large amount of energy is also released. Most elements do not decay in this manner unless their mass number is greater than 230.

Disadvantages o One of the main disadvantage of the study of the atomic physics is the formation of atom bomb or atomic weapons. o The two main examples of them are Hiroshima and Nagasaki o At this time every single country want to be a atomic power which is a sign of third world war

Cont o Its because of the atomic weapons that still the coming generation of the people of Nagasaki and Hiroshima is not fully normal o The effect of the attack last as long as the single particle of those deadly missiles floating in the air of those targeted areas.

Conclusion Atomic advancement is very much important today it is something through which any country can protect the citizens but on the other hand being an atomic power and make wrong use of it may results in the distraction of an entire state. The value of human life is ranked lower and lower. The examples of Hiroshima and Nagasaki explain us that what really happen when an atomic explosion take place. In a nutshell, power doesn’t mean that to be aggressive but it’s a source which makes you familiar with more responsibilities.