‍ The groups are the vertical columns. 2 elements (H and He) How many elements does Period 2 have? When you look at the periodic table, each row is called a period (Get it? For example, every element in the top row (the first period) has one orbital for its electrons. A new period begins when a new principal energy level begins filling with electrons. There are seven rows, or periods, in the Periodic Table of Elements. The first periodic table. The periodic table consists of seven periods. Like PERIODic table.). asked Jun 7, 2018 in Class X Science by priya12 ( -12,630 points) For atoms with atomic numbers less than about 20, the octet rule of electron addition and orbital filling applies. All of the elements in a period have the same number of atomic orbitals. There are seven periods in the periodic table, with each one beginning at the far left. The modern periodic table of the elements contains 18 groups, or vertical columns. The elements Be, 12Mg and 20Ca, each having two valence electrons in their valence shells, are in periods 2, 3 and 4 respectively of the modern periodic table. Period 1 has only two elements (hydrogen and helium), while periods 2 and 3 have 8 elements. Periods 4&5 have 18 elements each (Potassium to Xenon). How many elements does Period 1 have? The periodic table today is arranged with two different parts, the groups and the periods. The periods vary in length. In the periodic table, there are 2 electrons in period 1, while both periods 2 and 3 have 8 electrons in the filled level. 7 periods and 18 groups. 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. The modern periodic table consists of 18 groups and 7 periods. A period is a horizontal row of elements on the periodic table. Periods of the Periodic Table. There are seven periods currently. Period 1 has just two elements (Hydrogen & Helium). 18 elements (K, Ca, Sc, etc.) i) Down the group, the atomic size and metallic character of elements increase. 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. Periods 2&3 have 8 each (Lithium to Argon). Elements in . ii) On moving from left to right in a period, the atomic size and metallic character of elements decreases. Elements in a group have similar chemical and physical properties because they have the same number of outer electrons. Chemestry. The columns are called groups. Groups are given a number to show where they are in the periodic table and also to identify the group of elements in them. 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