Periodic tableTabular arrangement of the chemical elementsPeriodic table of the chemical elements showing the most or more commonly named sets of elements (in periodic tables), and a traditional dividing line between metals and nonmetals.
Chemical elementChemical substance not composed of simpler onesThe chemical elements ordered in the periodic table, as shown in the 32-column formatA chemical element is a species of atom defined by its number of protons. The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8: each oxygen atom has 8 protons in its nucleus.
MetalType of materialIron, shown here as fragments and a 1 cm cube, is an example of a chemical element that is a metal.Metal in the form of a gravy boat made from stainless steel, an alloy largely composed of iron, chromium and nickelA metal (from Ancient Greek μέταλλον (métallon) 'mine, quarry, metal') is a material that, when polished or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well.
ElectronegativityElectronegativity, symbolized as χ, is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the distance at which its valence electrons reside from the charged nucleus. The higher the associated electronegativity, the more an atom or a substituent group attracts electrons.
MetalloidThe word metalloid comes from the Latinmetallum ("metal") and the Greekoeidḗs ("resembling in form or appearance"). However, there is no standard definition of a metalloid and no complete agreement on which elements are metalloids. Despite the lack of specificity, the term remains in use in the literature. The six commonly recognised metalloids are boron, silicon, germanium, arsenic, antimony and tellurium.
HeliumHelium (from Ancient Greek: ἥλιος, romanized: helios, lit. 'sun') is a chemical element; it has symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is the lowest among all the elements, and it does not have a melting point at standard pressures. It is the second-lightest and second-most abundant element in the observable universe, after hydrogen.
HydrogenChemical element with atomic number 1 (H)–↑H↓Li(none) ← hydrogen → helium
OxygenChemical element with atomic number 8 (O)–↑O↓Snitrogen ← oxygen → fluorine
Nitrogen–↑N↓Pcarbon ← nitrogen → oxygen
AcidAn acid is a molecule or ion capable of either donating a proton (i.e. hydrogen cation, H+), known as a Brønsted–Lowry acid, or forming a covalent bond with an electron pair, known as a Lewis acid. The first category of acids are the proton donors, or Brønsted–Lowry acids. In the special case of aqueous solutions, proton donors form the hydronium ion H3O+ and are known as Arrhenius acids.
IodineBr↑I↓Attellurium ← iodine → xenon
Observable universeThe observable universe is a spherical region of the universe consisting of all matter that can be observed from Earth; the electromagnetic radiation from these astronomical objects has had time to reach the Solar System and Earth since the beginning of the cosmological expansion. The radius of this region is about 14.26 gigaparsecs (46.5 billion light-years or 4.40×10 m).*As an Amazon Associate I earn from qualifying purchases.