Chemical Elements with Atomic Mass

As of now, there are 118 officially recognized chemical elements that complete the first seven rows of the periodic table. While elements up to 94 exist naturally on Earth, elements from 95 to 118 have only been synthesized in laboratories. Scientists are actively working on creating heavier elements (like element 119 and beyond), which would begin a new, eighth row of the periodic table.

The first element is Hydrogen (H), which holds the atomic number 1. This means it has just one proton in its nucleus, making it the simplest and lightest of all elements. It's also the most abundant element in the universe, making up about 75% of all baryonic mass and serving as the primary fuel for stars like our Sun.

The last known element is Oganesson (Og), with atomic number 118. It is a synthetic, superheavy element created in a laboratory and is extremely unstable, with its most stable known isotope having a half-life of less than a millisecond. It is named after the nuclear physicist Yuri Oganessian and is classified as a noble gas, although its properties are expected to differ significantly from others in the group due to relativistic effects.

Hydrogen (H) is the lightest element, with an atomic mass of about 1.008 atomic mass units (u). Its most common isotope, protium, consists of only a single proton and a single electron, with no neutrons. This simple structure gives it the lowest density of any element.

The heaviest known element is Oganesson (Og), with an atomic number of 118. Its atomic mass is approximately 294 u. It's a synthetic element, meaning it doesn't occur naturally and has only been produced in a lab. Due to its extreme instability, only a few atoms have ever been created, making it difficult to study its properties directly.

The periodic table has 18 vertical columns known as groups. Elements within the same group share similar chemical properties because they have the same number of valence electrons (electrons in the outermost shell). For example, all elements in Group 1 (the alkali metals) are highly reactive and have one valence electron.

There are 7 horizontal rows in the periodic table, called periods. As you move from left to right across a period, the atomic number of each element increases by one. All elements in the same period have the same number of electron shells.

The Lanthanide series (elements 57-71) and the Actinide series (elements 89-103) are two special rows of elements usually placed at the bottom of the periodic table to keep it from becoming too wide. They are both part of the f-block elements. Lanthanides are known as rare-earth metals, while Actinides are all radioactive.

Several alkali metals are less dense than water and can float on it, most notably Lithium (Li), Sodium (Na), and Potassium (K). However, they also react very vigorously and often violently with water, so this is a dangerous experiment to perform without proper safety precautions.

The Noble Gases are the elements in Group 18 of the periodic table: Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and the radioactive Oganesson (Og). They are known for their extreme stability and low reactivity because their outermost electron shells are completely full.

Many element symbols are derived from their Latin names, especially for elements known since ancient times. For example, the symbol for Sodium is Na (from Natrium), Gold is Au (from Aurum), and Iron is Fe (from Ferrum). Other symbols come from Greek, English, or are named after people or places.

Francium (Fr) is considered the most reactive metal. As an alkali metal at the bottom of Group 1, it has a very low ionization energy, meaning it gives up its outermost electron very easily. However, it is extremely rare and radioactive, so its chemistry is not widely studied. Cesium (Cs), just above it, is the most reactive stable metal.

The least reactive metals are often called the noble metals. Gold (Au) and Platinum (Pt) are prime examples. Their low reactivity is why they do not corrode or tarnish easily, making them highly valued for jewelry and long-lasting applications.

Oxygen (O) is the most abundant element by mass in the Earth's crust, making up about 46.6%. It is mostly found combined with other elements in minerals like silicates and carbonates. The second most abundant is Silicon (Si).

Oxygen is also the most abundant element in the human body by mass, accounting for about 65% of our body weight. This is primarily because our bodies are about 60% water (H₂O), and oxygen is a major component of water, as well as organic molecules like proteins and fats.

At standard temperature and pressure (STP: 0°C and 1 atm), eleven elements are gases. These include Hydrogen (H₂), Nitrogen (N₂), Oxygen (O₂), Fluorine (F₂), Chlorine (Cl₂), and all the noble gases: Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe), and Radon (Rn).

No. Many elements have isotopes that are radioactive, meaning their atomic nuclei are unstable and decay over time, emitting radiation. All elements with an atomic number greater than 83 (Bismuth) are entirely radioactive, meaning they have no stable isotopes. Elements like Technetium (43) and Promethium (61) are also notable for having no stable isotopes.

The main difference lies in how atoms are bonded. Ionic compounds are typically formed between a metal and a non-metal where electrons are transferred from the metal to the non-metal, creating charged ions that attract each other (e.g., NaCl). Covalent compounds are formed between two non-metals where electrons are shared between atoms to form a stable molecule (e.g., H₂O).

Several elements that exist in their native form were known to ancient civilizations, though they weren't understood as elements in the modern sense. These include Carbon (C), Sulfur (S), Iron (Fe), Copper (Cu), Silver (Ag), Tin (Sn), Gold (Au), Mercury (Hg), and Lead (Pb).

Yes, but today "discovery" usually means "creation." New elements are synthesized in particle accelerators by bombarding heavy elements with lighter ones. These new elements are typically superheavy, highly radioactive, and exist for only fractions of a second. Scientists are currently trying to create elements 119 and 120.

Elements are broadly classified based on their properties into three main categories: Metals (which are typically shiny, conductive, and malleable), Non-metals (which are generally dull, poor conductors, and brittle), and Metalloids (which have properties intermediate between metals and non-metals). They are further organized into groups (like Alkali Metals, Halogens, Noble Gases) in the periodic table based on their electron configurations and chemical behavior.

An element is considered radioactive if all its isotopes are unstable. The most well-known radioactive elements are the actinides, such as Uranium (U), Thorium (Th), and Plutonium (Pu). Other key examples include Radium (Ra), Francium (Fr), Polonium (Po), Astatine (At), Radon (Rn), Technetium (Tc), and Promethium (Pm). In reality, many other elements have at least one radioactive isotope, but they also have stable ones.