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