The organization of the periodic table leads to recurring properties or periodic table trends. These properties and their trends are:
- Electron Configuration
The electron configuration or organisation of electrons orbiting neutral atoms shows a recurring pattern or periodicity. The electrons occupy a series of electron shells which numbered 1, 2, and so on. Each shell consists of one or more sub-shells named as s, p, d, f and g. As atomic number increases, electrons progressively fill these shells and sub-shells more or less according to the energy ordering rule, as shown in the diagram.
The electron configuration for neon, for example, is 1s², 2s², 2p⁶. With an atomic number of ten, neon has two electrons in the first shell, and eight electrons in the second shell; there are two electrons in the s sub-shell and six in the p sub-shell.
In periodic table terms, the first time an electron occupies a new shell corresponds to the start of each new period, these positions being occupied by hydrogen and the alkali metals. Since the properties of an element are mostly determined by its electron configuration, the properties of the elements likewise show recurring patterns or periodic behavior.
- Atomic Radii
Atomic radii vary in a predictable and explainable manner across the periodic table. For instance, the radii generally decrease along each period of the table, from the alkali metals to the noble gases. Moving left to right across a period, atomic radius usually decreases. This occurs because each successive element has an added proton and electron, which causes the electron to be drawn closer to the nucleus. But from top to bottom in a group, the atomic radii of the elements increase down each group. Since there are more filled energy levels, the valence electrons are found farther from the nucleus. The radius increases sharply between the noble gas at the end of each period and the alkali metal at the beginning of the next period.
- Ionization Energy
It is the energy needed for an atom of an element to remove an electron from its gaseous atom or ion. The first ionization energy is the energy it takes to remove one electron from an atom, the second ionization energy is the energy it takes to remove a second electron from the atom, and so on. Ionization energy increases moving left to right and decreases moving down a group. The ionization energy increase when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron. Whereas, from the top to bottom in a group, each successive element has a lower ionization energy because it is easier to remove an electron since the atoms are less tightly bound.
- Electronegativity
Electronegativity is the tendency of an atom to form a chemical bond in order to attract a shared pair of electrons. An atom's electronegativity is affected by both its atomic number and the distance between the valence electrons and the nucleus. The higher its electronegativity, the more an element attracts electrons. Electronegativity increases when moving from left to right across a period. The more tightly bound an element is, the more energy is required to remove an electron because of the pull exerted on the electrons by the nucleus. The noble gases are an exception, with an electronegativity approaching zero. Electronegativity decreases moving from top to bottom in a group due to an increasing distance between valence electrons and the nucleus.
- Electron Affinity
The electron affinity of an atom is the amount of energy released when an electron is added to a neutral atom to form a negative ion. It is the tendency of an atom that how readily an atom accepts an electron. Electron affinity increases moving across a period and decreases moving down a group. Generally, metals (left side of a period) generally have a lower electron affinity than nonmetals (right side of a period), with the exception of the noble gases. Electron affinity is nearly zero for noble gases. Chlorine most strongly attracts an extra electron. Electron affinity generally increases across a period while moving from left to right. This is caused by the filling of the valence shell of the atom; a group 17 atom releases more energy than a group 1 atom on gaining an electron because it obtains a filled valence shell and is therefore more stable.
Comments
Post a Comment