Which group of elements will have similar chemical properties or reactivity? a.) Cd, Ca, C b.) Mg, Sr, Ba
Elements that are positioned in the same column (or group) of the periodic table exhibit similar properties. This is due to the similar electronic configuration (more importantly the number of valence electrons).
Among the two groups given here, choice (b) Mg, Sr and Ba are alkaline earth elements (part of group IIA) in the periodic table. Other elements of this group are Be, Ca and Ra. All these elements form the alkaline earth metal group of the periodic table. All these elements have 2 valence electrons, which they can give up to attain a +2 charge as cations. They have certain common properties, including shiny and silver-white appearance.
In comparison, the choice (a) consists of elements Cd, Ca and C which are part of different groups. Ca is from group IIA, Cd is from group 12 and C is from group VI and hence have different properties.
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The periodic table is organized according to atomic number, groups, and periods. As you move from left to right, top to bottom, along the periodic table, the atomic number of each element increases by 1. The periodic table is also organized in groups (vertical columns) and periods (horizontal rows). Elements that are in the same group or column will have the same number of valence electrons and therefore will have similar properties and will react similarly.
While the atomic number (number of protons in an atom) is the identity of an element, the number of valence electrons is the element's personality and will determine how reactive the atom will be with other atoms.
Answer choice B. Mg, Sr, Ba are all in the same column or group (group 2 or 2A) and therefore will have 2 valence electrons in their atoms. They will all react similarly- but not identically. These elements in group 2A are called the Alkaline Earth Metals and are highly reactive (although not as reactive as group 1A Alkali Metals). For example, these elements in the Alkaline Earth Metal Group are reactive with water and are shiny in appearance.
Answer choice A. Cd, Ca, and C are not a part of the same column/group. They are in groups 12B, 2A, and 4A respectively and therefore will not have similar properties based on their valence electrons and reactivity.