Each element has a unique atomic number that identifies the number of protons. The atomic number of an atom is the number of protons in its nucleus. If the atomic symbol has two letters, the first letter is capitalized and the second is in lower case. The atoms of all the elements are represented by a unique atomic symbol which is a one or two lettered notation used to represent an atom corresponding to an element. Electrons revolve around positively charged nucleus which is made of protons and neutrons. Electron is negatively charged, proton is positive and neutron is neutral. Each atom is consists of the fundamental particles. The extremity of this space comparison is highlighted by the fact that for an atom with equal numbers of neutrons and protons, the nucleus comprises about 99.97% of the mass of the atom!Įxperimental evidence suggests that nuclear matter is almost of uniform density, so that the size of a nucleus can be estimated from its mass number.An atom is a basic building block of matter around us.

This great disparity in size was first discovered by Rutherford scattering of alpha particles off a thin gold foil. Scaling the gold nucleus suggests that the atomic radius is some 18,000 times the size of the nucleus. For example, the space inside an atom can be compared to the space in the solar system in a scale model. The size of the nucleus compared to the size of the atom in which it resides is so small that it has invited a number of interesting comparisons. But two protons touching each other would feel a repulsive force over 100 million times stronger!! So how can such protons stay in such close proximity? This may give you some feeling for the enormity of the nuclear strong force which holds the nuclei together. The electron in a hydrogen atom is attracted to the proton nucleus with a force so strong that gravity and all other forces are negligible by comparison. When the balance is broken, the resultant radioactivity yields particles of enormous energy. Within the incredibly small nuclear size, the two strongest forces in nature are pitted against each other. The nuclear radius of carbon-12 is 2.7 x 10 -15 m while the size of the atom from the periodic table is about 0.9 x 10 -10 m, about 33,000 times larger! Nuclear notation Examination of a scale model of the atom makes it evident that the nucleus is extremely tiny compared ot the size of the atom. It should not be surprising that an extra neutron or two in the nucleus has almost no effect on that interaction with the world. The dominant contributer to the interactions between atoms and their environment is the electromagnetic force. But for practical purposes the chemical behavior of the isotopes of any element are identical. A tiny difference in the spectral frequencies of hydrogen and deuterium comes from an essentially mechanical source, the slight change in the ' reduced mass' associated with the orbiting electron. It is significant to note that the three isotopes of hydrogen change in mass by a factor of three, but their chemical properties are virtually identical.

Isotopes are (almost) Chemically Identical Information about the isotopes of each element and their abundances can be found by going to the periodic table and choosing an element. The element tin (Sn) has the most stable isotopes with 10, the average being about 2.6 stable isotopes per element. For stable isotopes of light elements, the number of neutrons will be almost equal to the number of protons, but a growing neutron excess is characteristic of stable heavy elements. The chemical properties of the different isotopes of an element are identical, but they will often have great differences in nuclear stability. The different isotopes of a given element have the same atomic number but different mass numbers since they have different numbers of neutrons.

This is useful in calculating the cross section for nuclear scattering. If the density ρ of the material is known, then the number of nuclei per unit volume n can be calculated from n =ρN A/A. The mass of an element that is numerically equal to the atomic mass A in grams is called a mole and will contain Avogadro's number N A of nuclei. Carbon 14 is radioactive and thebasis for carbon dating. Carbon-12 is thecommon isotope,with carbon-13as another stableisotope which makes up about1%. The element is determined bythe atomic number 6. Standard nuclear notation shows the chemical symbol, the mass number and the atomic number of the isotope.Įxample: the isotopes of carbon.

Atom symbol