Helium Project

Alkali metals
any of the elements lithium, sodium, potassium, rubidium, cesium, and francium, occupying group IA. They are very reactive electropositive, monovalent metals forming strongly alkaline hydroxides
Alkaline earth metals
any of the divalent strongly basic metals of group II of the periodic table comprising beryllium, magnesium, calcium, strontium, barium, and radium. Comprise group 2 on the periodic table.
Valence electrons
an electron that is associated with an atom, and that can participate in the formation of a chemical bond; in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.
Noble gases
any of the gaseous elements: helium, neon, argon, krypton, xenon, and radon occupying group 18 on the PT. they were once called inert gases.
Halogens
The halogens are five nonmetallic elements found in group17 of the periodic table. The term “halogen” means “salt-former” and compounds containing halogens are called “salts”. All halogens have 7 electrons in their outer shells.
Ionization energy
element is the energy needed to remove the outermost, or highest energy, electron from a neutral atom in the gas phase.
Electronegativity atomic radius
Ability of an atom to attract electrons when the atom is in a chemically combined compound
Mendeleev
Russian chemist: he help develop the periodic law.
Periodic law
law in chemistry: the elements when arranged in the order of their atomic numbers show a periodic variation of atomic structure and of most of their properties.
Groups
Each vertical column is called a group. The elements in each group have the same number of electrons in the outer orbital.
Periods
Rows left to right are called periods. The periodic table has 7 rows.
Metals
Elements that form cations when compounds of it are in solution and oxides of the elements form hydroxides rather than acids in water. Most metals are conductors of electricity, have crystalline solids with a metallic luster and have a high chemical reactivity.
Non-metals
element that doesn’t have the characteristics of metal including: ability to conduct heat or electricity, luster, or flexibility. An example of a nonmetal element is carbon.
Diatomic molecules
molecules composed of only two atoms, of either the same or different chemical elements. The prefix di- is of Greek origin, meaning “two”. If a diatomic molecule consists of two atoms of the same element, such as hydrogen (H2) or oxygen (O2), then it is said to be homonuclear.
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