#separator:tab #html:false #tags column:4 Group A column of the periodic table; elements in it act alike chem-periodic-table-groups Period A row of the periodic table chem-periodic-table-groups How many groups are in the standard periodic table? 18 chem-periodic-table-groups How many periods are in the standard periodic table? 7 chem-periodic-table-groups Alkali metals Group 1 (except hydrogen): very reactive soft metals like sodium chem-periodic-table-groups Alkaline earth metals Group 2: reactive metals like calcium and magnesium chem-periodic-table-groups Transition metals The block in the middle, like iron, copper and gold chem-periodic-table-groups Halogens Group 17: reactive nonmetals like chlorine and iodine chem-periodic-table-groups Noble gases Group 18: very unreactive gases like helium and neon chem-periodic-table-groups Metalloids Elements with properties of both metals and nonmetals, like silicon chem-periodic-table-groups Nonmetals Elements that are usually dull, brittle and poor conductors chem-periodic-table-groups Metals Shiny elements that conduct heat and electricity and can be shaped chem-periodic-table-groups Lanthanides Row of 15 elements shown below the main table, from lanthanum chem-periodic-table-groups Actinides Row of 15 elements shown below the main table, from actinium chem-periodic-table-groups Atomic number The number of protons in an atom's nucleus chem-periodic-table-groups Atomic mass The average mass of an element's atoms, in atomic mass units chem-periodic-table-groups Element symbol One or two letters standing for an element; the first is capital chem-periodic-table-groups Who created the first widely used periodic table in 1869? Dmitri Mendeleev chem-periodic-table-groups How did Mendeleev arrange the elements? By atomic mass, leaving gaps for undiscovered elements chem-periodic-table-groups How is the modern table arranged? By increasing atomic number chem-periodic-table-groups Valence electrons Electrons in an atom's outermost shell chem-periodic-table-groups How many valence electrons do halogens have? 7 chem-periodic-table-groups How many valence electrons do alkali metals have? 1 chem-periodic-table-groups How many valence electrons do most noble gases have? 8 (helium has 2) chem-periodic-table-groups Which group contains carbon? Group 14 chem-periodic-table-groups Which group contains oxygen? Group 16 chem-periodic-table-groups Which group contains nitrogen? Group 15 chem-periodic-table-groups Which element is placed alone at the top-left, and is not an alkali metal? Hydrogen chem-periodic-table-groups Which side of the table holds mostly metals? The left side and middle chem-periodic-table-groups Which side of the table holds the nonmetals? The upper right chem-periodic-table-groups What is the zigzag line on the right side of the table for? It separates metals from nonmetals; metalloids sit along it chem-periodic-table-groups Why are noble gases unreactive? Their outer electron shell is full chem-periodic-table-groups Why do elements in a group act alike? They have the same number of valence electrons chem-periodic-table-groups Which period 1 elements exist? Hydrogen and helium chem-periodic-table-groups Which is the lightest metal, atomic number 3? Lithium chem-periodic-table-groups Synthetic element One made in a lab and not found in nature in large amounts chem-periodic-table-groups Radioactive element An element whose atoms break down and give off energy chem-periodic-table-groups Which element has the lowest atomic number? Hydrogen (1) chem-periodic-table-groups Isotope Atoms of the same element with different numbers of neutrons chem-periodic-table-groups