The periodic table

Cells with text in red are gaseous at room temperature.
Cells with text in green are liquid at room temperature.
Cells with text in black are solid at room temperature.
Cells with a dashed red outline are not found naturally on earth.
Elements 43, 61, and 84 and greater are only known as radioactive.

Subject classification: this is a chemistry resource.

The periodic table lists all the known elements. As of 2016, following the IUPAC's (International Union of Pure and Applied Chemists) naming of nihonium, moscovium, tennessine, and oganesson (elements 113, 115, 117, and 118 respectively), there are 118 elements currently known and officially named. Many of them are naturally occurring, but some were made in a laboratory and are not present in nature.

The periodic table arranges the elements according to their atomic number and fits them into a logical pattern (made by Henri Moseley in 1910), while when Russian scientist Dimitri Mendeleev (1870) created the periodic table, he arranged it by atomic mass.

There are 18 columns that divide the elements into groups with closely related chemical properties. Rows, or periods, help list elements in order of mass and atomic number. Properties of elements change in systematic ways throughout the periodic table.

The periodic table is arranged into groups (columns) and periods (rows).

Elements in the same group, or family, have similar chemical properties. Elements from the same group are found in vertical columns. Elements in the same group act similarly because they have the same valence electron configuration.

Each elements in the same period have the same number of electron shells. For example, the first period consists of Hydrogen and Helium, which both have one electron shell. While the second period have elements that have two electron shells (the first electron shell contains two electrons, and the second shell can hold up to eight). As you read across the period, the elements in the period increase with electrons on their electron shell (they do not increase in electron shell if you go left to right on a period in the periodic table, only the electrons on the electron shell increase).

So, Lithium has one electron on the outer shell while Beryllium has two electrons on its outer shell (while the 1st shell is full). By the time you get to Neon, the electron shells are completely full!

Non-metals are found on the top-right corner of the p-block elements. These elements tend to gain electrons when forming a bond with metals or share electrons between two non-metals to form a covalent bond.

Alkaline metals are known as the most reactive metals. This can be especially observed by their reaction with water, for example. Their reactivity is attributed to the low ionization energy of the outermost electron in the atom (one valence electron). Their most common oxidative state is +1. They tend to lose 1 electron to complete their outer shells. Reactivity increases down the group, which explains why Francium is the most reactive metal. Francium reacts easily due to its low ionization energy. In the electron configuration of Francium the valence electron is at very far distance so that's why electron need very less energy to emit that electron (due to less attraction force) . And this is also a reason for its lowest ionisation energy.

Alkali-Earth Metals have the second lowest ionization energy. Their most common oxidation state is +2. According to Moseley's Period table, These elements are found in 2nd Group.

The atoms of the transition metals have more complicated electron arrangements than other atoms. These metals have varying valence electrons, can have more than 1 oxidation state, and are always positive. The d orbitals of these elements are being filled. This group contains many well-known metals, such as iron (Fe), nickel (Ni), copper (cu), Chromium (Cr), mercury (Hg), and Gold (Au).

The Inner transition metals - the separated rows at the bottom of the periodic table, "f block", are mostly synthetic:

• The Lanthanides metals - Shiny (luster), metallic elements with atomic numbers #57-71 that fill 4f orbitals.
• The Actinidies metals - Metallic elements with atomic numbers #89-103 that fill 5f orbitals; all are very radioactive, such as Uranium. Their radioactivity is due to the fact that any nucleus with greater than 82 protons cannot be stable.

The poor metals consist of aluminum, gallium, indium, thallium, tin, lead, and bismuth.

Metalloids roughly form a staircase line in the periodic table. This line divides metals and nonmetals. The elements around this partition have intermediate metal- and non-metal-like properties. Many of them can be used as semiconductors.

All halogens are missing just one electron to fill their valence electron shell. For this reason, in most chemical reactions, halogens tend to gain one electron.

Halogens always exist as diatomic molecules (live in pairs). Going down the group, the color of elements increase; due to decreasing effective nuclear charge, atomic radius increase, and electronegativity decreases.

Hydrogen also shows property like Halogens but exceptionally According to electron configuration it's placed in 1st group of the period table.

Halogens are not always in -1 oxidation state (but can be -1 oxidation state in order to be isoelectronic with their respective noble gases); when reacting with other more electronegative atoms, they give positive oxidation states. Examples are Cl₂O₇, and BrO^-.

This group consists of the elements helium, neon, argon, krypton, and xenon. The noble gases have a full valence electron shell. For this reason, noble gases do not normally react with other elements (unreactive/stable), hence their former title inert gases. In fact, until 1962, they were thought completely nonreactive. (But flourides and oxides are known for Xenon, and a lesser extent for Krypton.)

Noble gas elements form monatomic molecules, and do not form ionic compounds or solutions. They can be ionized in an electrified gas plasma, though.

All members of this group are colourless gases (nonmetals). If you look at any periodic table, the density of these gases increases as you go downwards. This is because the mass of the atoms gets larger due to increasing nuclear charge.

There are some undiscovered elements on the periodic table. However, due to the understanding of periodic table positions, their descriptions can be estimated.

• Iridium and Osmium have the greatest density
• Francium is the least electronegative element and Fluorine is the most electronegative element

• The Periodic Table
• Periodic Trends
• List of Elements and their Symbols
• List of Elements and their Symbols 2

• Periodic videos