The notorious bongo-playing physicist Richard Feynman is said to have invoked relativity to predict the end of the periodic table at element His calculations showed that electrons in elements beyond would have to move faster than the speed of light, and thus violate the rules of relativity, to avoid crashing into the nucleus.
More recent calculations have since overturned that limit. Feynman treated the nucleus as a single point. Allow it to be a ball of particles, and the elements can keep going until about Then all hell breaks loose.
Atoms beyond this limit may exist but only as strange creatures capable of summoning electrons from empty space. Relativity isn't the only problem. Positively charged protons repel each other, so the more you pack into a nucleus, the less stable it tends to be.
Uranium, with an atomic number of 92, is the last element stable enough to occur naturally on Earth. Every element beyond it has a nucleus that falls apart quickly, and their half-lives—the time it takes for half of the material to decay—can be minutes, seconds or even split seconds.
There are 18 groups in the standard periodic table, including the d-block elements but excluding the f-block elements. A physical property of a pure substance can be defined as anything that can be observed without the identity of the substance changing. The observations usually consist of some type of numerical measurement, although sometimes there is a more qualitative non-numerical description of the property. Physical properties include such things as:.
Within a group of the periodic table, each element has the same valence electron configuration. For example, lithium, sodium, potassium, rubidium, cesium, and francium all have a single electron in an s orbital, whereas every element in the group including fluorine has the valence electron configuration ns 2 np 5 , where n is the period.
This means the elements of a group often exhibit similar chemical reactivity, and there may be similarities in physical properties as well. Before a discussion of the melting points of various elements, it should be noted that some elements exist in different forms. For example, pure carbon can exist as diamond, which has a very high melting point, or as graphite, whose melting point is still high but much lower than that of diamond.
Different groups exhibit different trends in boiling and melting points. For Groups 1 and 2, the boiling and melting points decrease as you move down the group. For the transition metals, boiling and melting points mostly increase as you move down the group, but they decrease for the zinc family.
In the main group elements, the boron and carbon families Groups 13 and 14 decrease in their boiling and melting points as you move down the group, whereas the nitrogen, oxygen, and fluorine families Groups 15, 16, and 17 tend to increase in both.
The noble gases Group 18 decrease in their boiling and melting points down the group. These phenomena can be understood in relation to the types of forces holding the elements together.
For metallic species, the metallic bonding interaction electron-sharing becomes more difficult as the elements get larger toward the bottom of the table , causing the forces holding them together to become weaker. As you move right along the table, however, polarizability and van der Waals interactions predominate, and as larger atoms are more polarizable, they tend to exhibit stronger intermolecular forces and therefore higher melting and boiling points.
Metallic elements are shiny, usually gray or silver in color, and conductive of heat and electricity. They are malleable can be hammered into thin sheets and ductile can be stretched into wires. Some metals, such as sodium, are soft and can be cut with a knife. Others, such as iron, are very hard. Non-metallic atoms are dull and are poor conductors.
They are brittle when solid, and many are gases at STP standard temperature and pressure. Metals give away their valence electrons when bonding, whereas non-metals tend to take electrons. A metal and a non-Metal : On the left is sodium, a very metallic element ductile, malleable, conducts electricity.
On the right is sulfur, a very non-metallic element. Metallic character increases from right to left and from top to bottom on the table.
Non-metallic character follows the opposite pattern. This is because of the other trends: ionization energy, electron affinity, and electronegativity. You will notice a jagged line running through the periodic table starting between boron and aluminum — this is the separation between metallic and non-metallic elements, with some elements close to the line exhibiting characteristics of each. The metals are toward the left and center of the periodic table, in the s, d, and f blocks.
Poor metals and metalloids somewhat metal, somewhat non-metal are in the lower left of the p block. Non-metals are on the right of the table. The electron configuration of a given element can be predicted based on its location in the periodic table.
The periodic table does more than just list the elements. This is because the elements are listed in part by their electron configuration. Blocking in the periodic table : The periodic table can be broken into blocks, corresponding to the highest energy electrons. The alkali metals and alkaline earth metals have one and two valence electrons electrons in the outer shell , respectively; because of this, they lose electrons to form bonds easily and so are very reactive.
These elements comprise the s block of the periodic table. The p block, on the right, contains common non-metals, such as chlorine and helium. The noble gases, in the column on the right, almost never react, since they have eight valence electrons forming a stable outer shell.
The halogens, directly to the left of the noble gases, readily gain electrons and react with metals. The s and p blocks make up the main- group elements, also known as representative elements. The d block, which is the largest, consists of transition metals, such as copper, iron, and gold. The f block, on the bottom, contains rarer metals, including uranium. Elements in the same group or family have the same configuration of valence electrons, so they behave in chemically similar ways. Periodic table of the elements : This image is color-coded to show the s, p, d, and f blocks of the periodic table.
In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule in atomic or molecular orbitals. For example, the electron configuration of the neon atom Ne is 1s 2 2s 2 2p 6. According to the laws of quantum mechanics, a certain energy is associated with each electron configuration.
Under certain conditions, electrons can move from one orbital to another by emission or absorption of a quantum of energy, in the form of a photon. Knowledge of the electron configurations of different atoms is useful in understanding the structure of the periodic table. The concept is also useful for describing the chemical bonds that hold atoms together. In bulk materials, this same idea helps explain the peculiar properties of lasers and semiconductors. As electrons are added, they assume their most stable positions electron orbitals with respect to the nucleus and the electrons that are already there.
According to the principle, electrons fill orbitals starting at the lowest available energy state before filling higher states e. The number of electrons that can occupy each orbital is limited by the Pauli exclusion principle. Atomic orbitals ordered by increasing energy : Order in which orbitals are arranged by increasing energy according to the Madelung rule.
Magnetism is a property of materials that respond to an applied magnetic field. Permanent magnets have persistent magnetic fields caused by ferromagnetism, the strongest and most familiar type of magnetism. Valence Electrons. Across A Group — Across a group, valence electrons remain constant.
It means elements present in the same group have the same number of valence electrons. For example, hydrogen, lithium, and sodium elements are present in the 1 st group and have the same number of valence electrons which is one. Valency is the combining capacity of an atom.
Across a Period — on moving left to right across a period in the periodic table, first valency increases then decreases. Across A Group — There is no change in valency across a group. Elements of the same groups show the same valency. Across a Period — As we move left to right across a period in the periodic table, metallic character of elements decreases.
Metallic Character. Across a Group — As we move top to bottom in a group of the periodic table, the metallic character of elements increases. Across a Period — As we move left to right across a period in the periodic table, nonmetallic character of elements increases. Nonmetallic Character. Across a Group — As we move top to bottom in a group of periodic table non metallic character decreases.
Group Reactivity of metals depends on its electropositive character. So, more is the metallic character, more is the electropositive nature of the element and more is its reactivity. As metallic character decreases across a period left to right, so reactivity also decreases. Although reactivity of nonmetals increases on moving left to right across a period.
Thus, we can conclude, as we move left to right in a period, the reactivity of elements gradually decreases up to the group thirteen and then starts increasing.
Ionization energy IE is the amount of energy required to remove an electron from an atom in the gas phase:. It is always positive because the removal of an electron always requires that energy be put in i. IE also shows periodic trends. As you go down the periodic table, it becomes easier to remove an electron from an atom i.
However, as you go across the periodic table and the electrons get drawn closer in, it takes more energy to remove an electron; as a result, IE increases:. IE also shows an interesting trend within a given atom. This is because more than one IE can be defined by removing successive electrons if the atom has them to begin with :.
Each successive IE is larger than the previous because an electron is being removed from an atom with a progressively larger positive charge. However, IE takes a large jump when a successive ionization goes down into a new shell.
For example, the following are the first three IEs for Mg, whose electron configuration is 1 s 2 2 s 2 2 p 6 3 s 2 :. The second IE is twice the first, which is not a surprise: the first IE involves removing an electron from a neutral atom, while the second one involves removing an electron from a positive ion. The third IE, however, is over five times the previous one. Why is it so much larger? Thus, it takes much more energy than just overcoming a larger ionic charge would suggest.
It is trends like this that demonstrate that electrons are organized in atoms in groups. Electron Affinity The opposite of IE is described by electron affinity EA , which is the energy change when a gas-phase atom accepts an electron:. EA also demonstrates some periodic trends, although they are less obvious than the other periodic trends discussed previously.
Generally, as you go across the periodic table, EA increases its magnitude:. There is not a definitive trend as you go down the periodic table; sometimes EA increases, sometimes it decreases.
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