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What is a period in chemistry?

In chemistry, the term period indicates the energy level of an atom and is used to name the horizontal lines of the periodic table of elements. There are 7 periods, and the elements that are included in each one have common characteristics.

period definition

In the periodic table, the elements are ordered according to their characteristics and properties, divided into groups, periods, and blocks with different colors. Therefore, the elements share similar qualities with those closest to them.

The period indicates the energy levels of the atoms of the elements and are the seven rows that appear in the periodic table; that is, the horizontal ordering . They are numbered from 1 to 7, numbers that not only indicate the order from lowest to highest, but also indicate the number of main energy level that the electrons occupy in ascending order.

Elements that are within the same period have electrons in the same number of energy levels. That is, each atom has the same number of electron shells. For example, period 2 indicates that the elements that compose it have electrons distributed in two energy levels.

Characteristics of the periods

As one progresses through a period, one atom of each element gains one electron and exhibits fewer metallic characteristics than the element before it. In this way, the elements that are on the left hand side of a period are characterized by being metallic and highly reactive. Instead, the elements on the right hand side are non-metallic. Halogens are non-metallic and non-reactive.

Elements that are in the same period also show similar trends with respect to atomic radius, electronegativity, ionization energy, and electron affinity.

Generally, the atomic radius decreases in the same period when we move to the right of the periodic table; at the same time, it causes the ionization energy and electronegativity to increase from left to right. This is due to the attraction that the nucleus exerts on the electrons.

Likewise, metals, which are to the left of the period, usually have a lower affinity than nonmetals, which are to the right of the period. The exception is the noble gases.

The periods of the periodic table of the elements

The different periods of the periodic table of elements are:

period 1

It is the first row of the periodic table. This period indicates that the atom has electrons in only one energy level.

The elements that belong to this period are: hydrogen (H) and helium (He).

period 2

Period 2 is the second row of the periodic table and includes 8 elements, which have electrons distributed in two energy levels: lithium (Li), beryllium (Be), boron (B), carbon (C), nitrogen ( N), oxygen (O), fluorine (F) and neon (Ne).

period 3

Period 3 is the third row of the periodic table and indicates that the electrons of the atom are divided into three energy levels. The 8 elements of period 3 are: sodium (Na), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), chlorine (Cl) and argon (Ar).

period 4

Period 4 is the fourth row of the periodic table and indicates that the atom has electrons located in four energy levels. In this period there are 18 elements: potassium (K), calcium (Ca), scandium (Sc), titanium (Ti), vanadium (V), chromium (Cr), manganese (Mn), iron (F), cobalt (Co ), nickel (Ni), copper (Cu), Zinc (Zn), gallium (Ga), germanium (Ge), arsenic (As), selenium (Se), bromine (Br) and krypton (Kr).

period 5

Period 5 is the fifth row of the periodic table and indicates that the included elements have electrons distributed in five energy levels. Within this period there are 18 elements: rubidium (Rb), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), technetium (Tc), ruthenium (Ru), rhodium ( Rh), palladium (Pd), silver (Ag), cadmium (Cd), indium (In), tin (Sn), antimony (Sb), tellurium (Te), iodine (I), and xenon (Xe).

period 6

Period 6 is the sixth row of the periodic table. It represents the elements whose atoms have electrons divided into six energy levels. In this period are the following elements: cesium (Cs), barium (Ba), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os), iridium (Ir), platinum ( Pt), gold (Au), mercury (Hg), thallium (Tl), lead (Pb), bismuth (Bi), polonium (Po), astatine (At) and radon (Rn).

Also included in this period are the lanthanides: lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu).

period 7

Period 7 is the seventh row of the periodic table and indicates the elements that have electrons distributed in seven energy levels. Within this period are the following elements: francium (Fr), radium (Ra), rutherfordium (Rf), dubnium (Db), seaborgium (Sg), bohrium (Bh), hasium (Hs), meitnerium (Mt), darmstatium (Ds), roentgenium (Rg), copernicium (Cn), flerovium (Fl) and livermorium (Lv).

Also included in this period are the actinides actinium (Ac), thorium (Th), protactinium (Pa), uranium (U), neptunium (Np), plutonium (Pu), americium (Am), curium (Cm), berkelium (Bk), californium (Cf), einsteinium (Es), fermium (Fm), mendelevium (Md), nobelium (No) and lawrencium (Lr). There are also the elements nihonium (Nh), muscovium (Mc), teneso (Ts) and oganeson (Og).

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