Atomic Structure

Objective Know the atomic structure Know the orbital electrons and its shells Know the forces that binds the electron to the nucleus. Know the relationship between the electron and the periodic table.

Nucleus of Atom The nucleus of an atom is very small. Less than 0.001% of the volume of an atom is occupied by matter. The nucleus containing the neutrons and protons of the atom contains most of its mass. Atom is mostly empty space. The proton and neutron of the atom is in the nucleus which contains most of its mass. Classical representations of the atom were oversimplified like Bohr atom are mostly empty space. Example: element of uranium contains 99.998% of the entire mass of the atom.

Orbits Electron orbits are grouped into different shells. specifically, the number and arrangement of electrons in the outermost shell determine the chemical behavior of an atom. The outermost shell is called valence shell or valence electron. Orbital has two type of orbits or shell. Shell Subshell the arrangement of electrons in these shells determines how an atom reacts chemically( that is how it combines with other atoms.)

Shell and Subshell Shell and Subshell are defined by the quantum number, not by the distance of its electron from the nucleus or even their overall energy. Shells are labeled as K, L, M, N, O, P and Q or 1, 2, 3, 4, 5, 6 and 7. Going from innermost shell to the outermost shell. Electron in outer shells have higher average energy and travel further from the nucleus than those in the inner shells. The outermost shell is important because the pull of the nucleus upon them is weak and more easily broken.

Subshells Each shell is composed of subshells labeled s, p, d, f and g. The maximum number of electrons in shell 1 is 2 x 12 = 2 x 1 = 2. The maximum number of electrons in shell 2 is 2 x 22 = 2 x 4 = 8. The maximum number of electrons in shell 3 is 2 x 32 = 2 x 9 = 18. The maximum number of electrons in shell 4 is 2 x 42 = 2 x 16 = 32. Note the increase in the limit of the different subshell increases by four. The problem with that answer is that they do not account for the law of dimishing returns and the maximum number of prototypical eternal forms available to the universe. they stop at the number N = 4 because they have a problem when N = 5. They have only observed 32 electrons in the fifth orbital shell. then they have only observed 18 electrons in the sixth orbital shell, they have only observed 8 electrons in the seventh orbital shell. They have not observed any elecrons in the eighth orbital shell. 118 in total. It may be that there are 120 in total where the Law of Symmetry allows for 2 electrons in the eighth orbital shell.thus the numbers are 2, 8, 18, 32, 32, 18, 8, 2.

Electron Arrangement The maximum number of electrons that can exist in each shell increases with the distance of the shell from the nucleus. The electron limit per shell can be calculated from the following formula, where (n) is the shell number. Electron limit per shell = 2xn2 Physicist call the shell number (n) the principal quantum number (the shell number e.g. K,L,M,N,O,P and Q or 1,2,3,4,5,6 and 7). Every electron in every atom can be precisely identified by the principal quantum number. It has a relationship with the periodic table and the number of shells in an atom in its position on the periodic table. Example: Oxygen (O) has 8 electrons. 8O – 2 K shell – 6 L shell

Periodic table 8O – 2 K shell – 6 L shell The number of the outermost occupied electron shell of an atom is equal to its period in the periodic table. The number of electron in the outermost shell is equal to its group. Oxygen (O) has 8 electrons. 8O – 2 K shell – 6 L shell Means that Oxygen is in the second period and in the sixth group.

Aluminum (13Al) has the following electron configuration: Example Aluminum (13Al) has the following electron configuration: K shell = 2 L shell = 8 M shell = 3

Maximum number of electrons that can occupy each electron shell. Shell Number Shell Symbol Number of Electrons 1 K 2 L 8 3 M 18 4 N 32 5 O 50 6 P 72 7 Q 98

Orbital Names Orbital are given names in the form of X typey Where as X is the energy level corresponding to the principal quantum number n(it is the shell symbol of an electron or orbits in layman's term). type is a lower-case letter denoting the shape or subshell of the orbital ( s, p, d and f subshell). y is the number of electron in that orbital. Example: 1s2 which means that the orbital has two electrons and is the lowest energy level (n=1) with a subshell “s”.

Atomic structure Examples Hydrogen (H) 1 p, 1 e K shell 1 Helium (He) 2 p, 2 e, 2 n K shell 2 Lithium (Li) 3 p, 3 e, 4 n K shell 2, L shell 1

Periodic table All atoms having one electron in the outer shell lie in group I of the periodic table. Atoms with two electrons in the outer shell falls in group II etc. Atoms with eight electrons in its outer shell are in group VIII and are very stable chemically. No outermost shell can contain more than 8 electrons. The orderly scheme of atomic progression from smallest to largest atom is interrupted in the fourth period. Instead of adding atom to the next outer shell, electrons are added to an inner shell. Atoms associated with this phenomenon are called transitional elements or transitional metals. Transitional elements tends to have high tensile strength, density and melting and boiling point. Due to the d orbital electrons ability to delocalize within the metal lattice.

Force that binds the electron to the nucleus The closer an electron is to the nucleus, the more tightly it is bound. The attraction of electron and protons are due to the law of electricity, which states that opposite charges attract each other. The opposing forces cause electron to maintain their distance from the nucleus, and thus electrons travel in a circular or elliptical path. Electrons can exist only in certain shells, which represent different electron binding energies or energy levels. Due to the attractions of charges an electrostatic attraction produces centripetal force. Centripetal force is a center seeking force that just matches the force of motion or velocity.

Electron binding energy K shell is the closes to the nucleus which in turn has a high electron binding energy. While Q shell is the farthest which has low electron binding energy. The complexity of the electron configuration of atoms increases as one progresses through the periodic table to the most complex naturally occurring element. Electron orbital shells are given codes K,L,M,N,O,P and Q to represent the relative binding energies of electrons from closest to the nucleus to farthest from the nucleus. Electron binding energy – is the attachment of an electron to the nucleus (Eb). The closer an electron to the nucleus, the higher its binding energy the more tightly it is bound. The greater the total number of electrons in an atom, the more tightly each is bound.

Ionized Atoms If an atom has an extra electron or has an electron removed, it is ionized. An ionized atom is not electrically neutral but carries a charge equal in magnitude to the difference between the number of electrons and protons. Atoms cannot be ionized by addition or subtraction of protons, since that changes the atom from one element to another. In their normal state, atoms are electrically neutral. The electric charge of atoms is 0. The number of electrons is equal to the number of protons. An alteration in the number of neutron does not ionize an atom because the neutron is electrically neutral. Ionization is when the x-ray photon transfers its energy to an orbital electron and ejects that electron from the orbit of the atom. Ionization of an atom carbon by an x-ray leaves the atom with a net electric charge of +1. The ionized atom and the released electron are called an ion pair.