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