Periodic table - review

Halogens are a group of elements in Group 17 of the periodic table, known for being highly reactive nonmetals. They include fluorine, chlorine, bromine, iodine, and astatine.

Metalloids are also known as semiconductors, as they have properties of both metals and nonmetals.

Xenon and silver have the same number of energy levels, which is 5.

Mendeleev first ordered the periodic table of elements by increasing atomic mass.

False. Not all elements are solid at 20°C; for example, mercury is a liquid at this temperature.

Alkali metals are the elements in Group 1 of the periodic table, known for being highly reactive and having one valence electron.

Alkaline Earth Metals are the elements in Group 2 of the periodic table, characterized by having two valence electrons and being less reactive than alkali metals.

Transition metals are the elements found in Groups 3-12 of the periodic table, known for their ability to form various oxidation states and colored compounds.

Noble gases are the elements in Group 18 of the periodic table, known for being inert and having a full valence shell, making them very stable.

The atomic number is the number of protons in the nucleus of an atom, which determines the element's identity.