The elements other than carbon, hydrogen and oxygen are known as extra elements. Detection of the extra elements is an important step in the investigation of an unknown organic compound. Thus, nitrogen in presence of carbon gets converted to cyanide ions, sulphur to sulphide ions and halogens to halide ions.

Of these 118 elements, 94 occur naturally on Earth. Six of these occur in extreme trace quantities: technetium, atomic number 43; promethium, number 61; astatine, number 85; francium, number 87; neptunium, number 93; and plutonium, number 94.

Already 118 elements are now known on the periodic table. There are no naturally occurring elements on Earth with more than 92 protons in the nucleus of their atoms – a feature denoted by the atomic number in the periodic table. It is possible, however, to synthesise atoms with more in the laboratory.

Ununennium, also known as eka-francium or element 119, is the hypothetical chemical element with symbol Uue and atomic number 119. It is the lightest element that has not yet been synthesized.

Helium

Lithium

173 pm

143 pm

In other words, K+ has bigger effective nuclear charge than Cl− , which translates to a bigger net positive charge felt by the outermost electrons. This will compress the energy levels a bit and make the ionic radius smaller for the potassium cation.

Na,Z=11 ; Al,Z=13 . Aluminum has greater nuclear charge. While aluminum has more electrons, valence electrons are known to shield each other very imperfectly. The increased effective nuclear charge tends to decrease atomic radii across the Period from left to right.

Due to the addition of electrons in the same shell in Aluminum, the nuclear charge on Aluminium is more than that of Na and thus the atom tends to shrink a little in size. Hence, Al has a smaller atomic size than Na.

Normally, phosphorous has a larger atomic radius compared to sulfur and sulfur has a larger atomic radius compared to chlorine. Even though you are adding electrons to the atoms, the atomic radius of phosphorus is still larger than sulfur and same thing with chlorine.

Atomic radii of oxygen is 48 pm. In moving from left to right across a period, the atomic radius decreases as the effective nuclear charge increases. Hence, fluorine has smaller atomic radius than oxygen.

Fluorine has a smaller atomic radius than oxygen. This means that the size of fluorine’s electron cloud is smaller, and it has a greater ability/tendancy to attract a bonding pair of electrons (thus a higher electronegativity) than oxygen as it has a higher nuclear charge and a smaller atomic radius.

Since fluorine is a relatively small atom with a large electronegativity, its covalent radius is difficult to evaluate. The covalent radius is defined as half the bond lengths between two neutral atoms of the same kind connected with a single bond. By this definition, the covalent radius of F is 71 pm.

The atomic radii of nitrogen is larger than oxygen.