periodic table

• The elements are arranged by increasing atomic number, with the exception of hydrogen.
• Elements that have similar chemical properties are grouped together into vertical columns called groups or families.
• Groups contain elements with similar electron configurations in their outermost shells.
• Periodic trends refer to patterns observed when comparing the physical and chemical properties of elements within a period (row) on the periodic table.
• Atomic radius decreases across a period due to an increase in nuclear charge attracting electrons closer to the nucleus.
• Anything that influences the valence electrons will affect the chemistry of the element.
• Ionization enthalpy increases for each successive electron.
• Each block contains a number of columns equal to the number of electrons that can occupy that subshell.
• The d-block has 8 columns, because a maximum of 8 electrons can occupy all the orbitals in a d-subshell.
• The greatest increase in ionization enthalpy is experienced on removal of electron from core noble gas configuration.
• Considering the elements B, Al, Mg, and K, the correct order of their metallic character is: B > Al > Mg > K.
• Considering the elements B, C, N, F, and Si, the correct order of their non-metallic character is: F > N > C > B > Si.
• Removal of electron from orbitals bearing lower n value is easier than from orbital having higher n value.
• The block indicates value of azimuthal quantum number (l) for the last subshell that received electrons in building up the electronic configuration.
• Considering the elements F, Cl, O and N, the correct order of their chemical reactivity in terms of oxidizing property is: F > Cl > O > N.
• End of valence electrons is marked by a big jump in ionization enthalpy.
• The size of isoelectronic species — F–, Ne and Na+ is affected by nuclear charge (Z).
• Highly reactive elements do not occur in nature in free state; they usually occur in the combined form.
• The physical and chemical properties of elements vary periodically with their atomic numbers.
• Periodic trends are observed in atomic sizes, ionization enthalpies, electron gain enthalpies, electronegativity and valence.
• Electronegativity also shows a similar trend.
• Elements which lie at the border line between metals and non-metals, such as Si, Ge, As, are called metalloids or semi-metals.
• There is some periodicity in valence, for example, among representative elements, the valence is either equal to the number of electrons in the outermost orbitals or eight minus this number.
• Oxides of elements in the centre are amphoteric or neutral.
• Oxides formed of the elements on the left are basic and of the elements on the right are acidic in nature.
• Metallic character increases with increasing atomic number in a group whereas decreases from left to right in a period.
• Non-metals, which are located at the top of the periodic table, are less than twenty in number.
• The atomic radii decrease while going from left to right in a period and increase with atomic number in a group.
• Ionization enthalpies generally increase across a period and decrease down a group.
• Chemical reactivity is highest at the two extremes of a period and is lowest in the centre.
• Hydrogen with one electron in the 1 s orbital occupies a unique position in the periodic table.
• The reactivity on the left extreme of a period is because of the ease of electron loss (or low ionization enthalpy).
• Electron gain enthalpies, in general, become more negative across a period and less negative down a group.
• Metals comprise more than seventy eight per cent of the known elements.
• The normal oxide formed by the element on extreme left is the most basic (e.g., Na 2 O), whereas that formed by the element on extreme right is the most acidic (e.g., Cl 2 O 7 ).
• The chemical reactivity of an element can be best shown by its reactions with oxygen and halogens.
• The change in atomic radii is still smaller among inner-transition metals (4 f series).
• In a group, the increase in atomic and ionic radii with increase in atomic number generally results in a gradual decrease in ionization enthalpies and a regular decrease (with exception in some third period elements as shown in section 3.7.1(d)) in electron gain enthalpies in the case of main group elements.
• The change in atomic radii is much smaller as compared to those of representative elements across the period among transition metals (3 d series).
• In the case of transition elements, a reverse trend is observed.