How are periods on the periodic table organized?

Answer 1

it is organized by how you go in a library is organized by its books it is organized by how you go in a library is organized by its books

Answer 2

Groups of elements are organized by the number of valence electrons in the outer shell.

The valence number i.e. the number of electrons in the outer shell is the most important factor determining the chemical behaviour of any given element. The other major factors are the amount of positive charge in the nucleus (=atomic number) and how "far away" from the nucleus the outer electron shell is. Taken together these factors all determine how likely the atom is to lose its outer electrons, or to gain electrons from other electron donors if its outer shell is nearly full.

This behaviour is only strongly characteristic for the very left- and right- hand edges of the Periodic Table where you'll find the groups marked Ia & IIa (on the left) and VIIa & VIIIa (on the right). Groups IIIa-VIa don't exhibit such consistent behaviour all the way down to the heaviest elements that "should" be in the same valence group, which actually behave more like metals. This is partly because of the shielding effect that the higher number of inner, filled-up electron shells afford against the positive charge in the nucleus, and partly because of the larger distance from it - or so my high school chemistry teacher told me anyway (to put it another way, the higher the shell number, the higher the energy level the electrons in it are forced to occupy). This "shielding" for the larger atoms means that the tendency to attract a third or fourth electron is somewhat attenuated (or to put it another way, the total energy of the electrons in these higher orbitals is quite large compared to the energy lost by adjusting the population of the outer shell).

The central section consisting of the transition metals IIIb-VIIIb, Ib & IIB (plus the Actinides and the Lanthanides), represents metals whose outer shell is neither nearly empty nor nearly full. These elements don't have a particularly strong or weak electronegativity and so don't possess a compulsion to either gain or lose electrons. In metals, electrons are freely exchanged between atoms without any major net energy change, and this is what makes them good electrical conductors.

Please note this account only takes account of the rudimentary classical "Bohr atom", which is good enough for most high school chemistry. For the rest - unless you are doing advanced research in quantum chemistry - you don't have to be an expert in quantum electrodynamics; even up to college undergraduate level chemistry it's enough to have an appreciation of the shape of the orbitals (these equate to the sub-shells 1s, 2s, 2p and so on) and how they interact physically within a molecule*. The research chemists have figured all that out for you and you'll find pretty pictures in your college textbook. When you find yourself dealing with these you'll need a more modern periodic table which uses a different categorization of blocks (rather than groups) named after these orbitals/sub-shells.

• see for instance delocalization of electrons in aromatic compounds eg benzene, and reaction mechanisms such as electrophilic attack, nucleophilic attack etc.

Answer 3

They are organized into rows and columns. Anyone knows that!

Answer 4

The Periodic Table is organized in rows and columns called Periods and Groups respectively.

Answer 5

The elements are arranged in the increasing order of their atomic number (number of protons).

Answer 6

Elements on the periodic table are placed in groups and periods according the number of protons in the atomic nucleus and chemical properties.

Answer 7

Because it is number lil