‍ The groups are the vertical columns. The modern periodic table consists of 18 groups and 7 periods. Periods of the Periodic Table. The modern periodic table of the elements contains 18 groups, or vertical columns. If you can locate an element on the Periodic Table, you can use the element's position to figure out the energy level of the element's valence electrons. Like PERIODic table.). There are seven rows, or periods, in the Periodic Table of Elements. Period 1 has just two elements (Hydrogen & Helium). i) Down the group, the atomic size and metallic character of elements increase. For example, the elements sodium (\(\ce{Na}\)) and magnesium (\(\ce{Mg}\)) are both in period 3. The first periodic table. How many periods are there in the periodic table ... A.Li B.Si C.Br D.Ne Br, along with F, a halogen (column 7 of the periodic table) Look at the periodic table. Groups are given a number to show where they are in the periodic table and also to identify the group of elements in them. Chemestry. For example, every element in the top row (the first period) has one orbital for its electrons. Elements in a group have similar chemical and physical properties because they have the same number of outer electrons. A period is a horizontal row of elements on the periodic table. ii) On moving from left to right in a period, the atomic size and metallic character of elements decreases. For atoms with atomic numbers less than about 20, the octet rule of electron addition and orbital filling applies. Mendeleyev’s periodic table of 1869 contained 17 columns, with two nearly complete periods (sequences) of elements, from potassium to bromine and rubidium to iodine, preceded by two partial periods of seven elements each (lithium to fluorine and sodium to chlorine), and followed by three incomplete periods. When you look at the periodic table, each row is called a period (Get it? The periods vary in length. Period 1 has only two elements (hydrogen and helium), while periods 2 and 3 have 8 elements. The periodic table consists of seven periods. Periods 2&3 have 8 each (Lithium to Argon). A new period begins when a new principal energy level begins filling with electrons. 2 elements (H and He) How many elements does Period 2 have? 18 elements (K, Ca, Sc, etc.) In the periodic table, there are 2 electrons in period 1, while both periods 2 and 3 have 8 electrons in the filled level. How many elements does Period 1 have? There are seven periods in the periodic table, with each one beginning at the far left. asked Jun 7, 2018 in Class X Science by priya12 ( -12,630 points) All of the elements in a period have the same number of atomic orbitals. The periodic table today is arranged with two different parts, the groups and the periods. 7 periods and 18 groups. There are seven periods currently. 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