Isotope PDF

Isotope - Are atoms of the same element that have the same atomic number (Z) but different mass number (A). Isotopic Notation One way to identify the different isotopes of an element is through a symbol called isotope notation. It has four parts: X= element symbol A = mass number (protons +...

Isotope - Are atoms of the same element that have the same atomic number (Z) but different mass number (A). Isotopic Notation One way to identify the different isotopes of an element is through a symbol called isotope notation. It has four parts: X= element symbol A = mass number (protons + neutrons) Z = atomic number (number of protons) E = atomic charge (protons- neutrons) In general, the isotope notation for neutral uranium atom with 146 neutrons can be written as follows: For example, the isotope for neutral uranium atom with 146 neutrons can be written as follows: 238 U 92 Another way of expressing the isotope notation is to write the name or symbol of the element followed by mass of the isotope: uranium-238 Or U-238. Remember that if the charge on the atom is zero, then the zero is not written. Also, if the number of electrons is not stated, then it is presumed to be equal to the number of protons. Isotopes and Mass Numbers of Elements Hydrogen has the simplest nucleus among all the elements. It has only one proton of its nucleus. Thus, its atomic mass just 1.008 atomic mass unit (amu). Some hydrogen atoms have an additional neutron in their nuclei. One of these exists with additional neutron and also called deuterium. It has an atomic mass of 2.014 amu. The one exists with two additional neutrons and is called tritium. It has an atomic mass of 3.016 amu. Deuterium and tritium are isotopes of hydrogen, but they behave chemically, like any other hydrogen atoms. Atomic Mass and Isotopic Abundance Carbon has three fundamental isotopes: carbon 12, carbon -13, and Carbon-14. Carbon 12 or C-12 is the most common and the lightest among the carbon isotopes. It has six protons, six electrons, and six neutron per atom. Carbon- 13 or C-13 has medium- weight structure. It has six protons, six electrons and seven neutrons per atom. Carbon -14 or C-14 is the rarest heaviest among the three. It has six protons, six electrons, and eight neutrons per atom. Carbon has an atomic mass of 12,011 amu. This mass refers to the average relative atomic mass of the three Example There are two stable isotopes of nitrogen: nitrogen -14 and nitrogen -15. Nitrogen -14 has an atomic of 14.0031 amu, while nitrogen -15 has an atomic mass of 15.0001 amu. Nitrogen has an atomic weight of 14.0067 amu. Calculate the percent abundance of each isotope. 1) Write the following equation: (14,0031)(X)+(15.0001)(1-x)=14.0067 Note: The sum of x and 1-x is equal to 1. 2) Solve for x. X= 0.9959 (This calculation technique works only for an element with two isotopes.) The Development of the atomic structure The discovery of protons, electrons and Neutrons Eugen Goldstein (1850-1930)- discovered the positively charged subatomic particle as a component of anode rays (canal rays) Ernest Rutherford (1871-1937)- who coined term proton for the positively charged particle in an atom. J.J. Thomson (1856-1940)-discovered that an atom is also composed of negatively charged particles which named electrons. Another model of an atom is mostly an empty space that has a nucleus and electrons revolving around the nucleus. In 1932, James Chadwick (1891-1974) discovered the neutral particles, which are called neutrons, in the nucleus of an atom. Ernest Rutherford Verified Thomson's atomic model by conducting his gold foil experiment using naturally occurring radioactive substances that emitted alpha rays. Most alpha particles would pass through the thin gold foil with very slight deflections because of positively charged subatomic particles were diffused. His observations were the following: 1. Most alpha particles pass through the gold foil undeflected 2. Some alpha particles passed through the gold foil with large angles of deflection. 3. A smaller number of alpha particles bounced back in the direction from which they came.  What are the similarities and differences between Thomson's and Rutherford's atomic models? The number of protons determines the atomic number (Z) of an element. Generally, the number of protons is equivalent to the number of electrons, except in ion formation, where an atom may donate or accept an electron. Thus, the difference in the number of protons and electrons determines the charge of an atom. The Modern Periodic Table In 1913, Henry Moseley (1887-1915)- Published his measurements on the wavelengths of spectral lights of 39 elements showing the order of frequencies of wavelengths emitted by X - rays correspond to the atomic number Rutherford's model of an atom conflicted with the theory of electric fields as proposed by James Maxwell (1831-1879) states that when a body moves in an orbit around an oppositely charged body, the particles will gradually lose energy by emitting radiation. This loss of energy will cause electrons to move inward until they have direct contact with the nucleus, which is opposite their charge. If this theory applies to atoms, then atoms cannot be stable Niels Bohr(1885-1962) He incorporates the quantum concept of Max Planck (1858-1957) and Albert Einstein (1879-1955) in Rutherford's planetary model of the atom to describe the electrons. Bohr proposed the following postulates: 1. An electron can revolve around an atom following its specified orbital. 2. An electron does not emit radiation if it revolves only around its allowed orbital. 3. Moving from one orbital to another, which is called a quantum leap, will allow the electron to gain or lose energy. Alchemists' Contributions to Modern Chemistry Alchemy- is a medieval practice which aims to transform a metal into gold. 16th 17th centuries, alchemy played a role in the scientific revolution particularly in the development of the atomic structure. Daniel Sennert (1572-1637) Experimented on how precious metals could be dissolved in acid and then precipitated using an alkali. This experiment paved the way of the mechanical philosophy of Robert Boyle and Rene Descartes. In the early 17 century Andreas Libavius (1555 -1616) said that each atom is a perfect Aristotelean mix in that the elements are like shells that hide the secret" first principles" or seeds (i.e..., atoms). Dalton's Atomic theory Dalton's formulated his theory based on Antoine Lavosier's (1743 - 1794) law of conservation of mass and Joseph Proust,s (1754-1826) Law of definite proportion. The following are the major postulates of Dalton's atomic theory 1. Matter is composed of small invisible particles called atoms. 2. Atoms of the same elements are identical 3. Compounds contain atoms of more than one element. 4. In a compound, atoms of different elements always combine in the same way