20) An element has atomic number 12. In which period and group should it be placed?
21) The electronic configuration of an atom is 2,8,8,2. To which period and group does it belong?
22) The molecular formula of a certain ionic compound is xyz and 'x' is a metal. State the groups to which elements 'x' and 'y' belong in the periodic table.
23) Write any two differences between Mendeleev's periodic table and the modern periodic table.
24) Clarify the relation between the size of the atoms of metals and their chemical reactivity.
25) Clarify the relation between the size of the atoms of non-metals and their chemical reactivity.
Answer (2)
Magnesium, with an atomic number of 12, is in Period 3 and Group 2. The atom with an electronic configuration of 2, 8, 8, 2 is calcium, located in Period 4 and Group 2. Metals tend to be larger and more reactive, while smaller non-metals often exhibit higher reactivity by gaining electrons.
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An element has atomic number 12. In which period and group should it be placed?
An element with an atomic number of 12 is magnesium (Mg). Its electronic configuration is 2, 8, 2.
Period: This element is in the 3rd period because it has three electron shells.
Group: It belongs to Group 2, which is the alkali earth metals group.
The electronic configuration of an atom is 2,8,8,2. To which period and group does it belong?
The electronic configuration 2, 8, 8, 2 corresponds to calcium (Ca).
Period: Calcium is in the 4th period because it has four electron shells.
Group: It belongs to Group 2, which is also the alkali earth metals group.
The molecular formula of a certain ionic compound is xyz and 'x' is a metal. State the groups to which elements 'x' and 'y' belong in the periodic table.
Since 'x' is a metal, it is usually from a group that contains metals. While we don't have specific details about elements 'x' and 'y', typically:
Metals like sodium, potassium (usually represented as 'x') are from Group 1 (the alkali metals), and the non-metals like chlorine, oxygen (usually represented as 'y') are from Group 17 (the halogens) or Group 16 (the chalcogens).
Write any two differences between Mendeleev's periodic table and the modern periodic table.
Basis of organization: Mendeleev's periodic table was arranged by increasing atomic weight, whereas the modern periodic table is arranged based on increasing atomic number.
Gaps for undiscovered elements: Mendeleev left gaps in his table for elements that were not yet discovered, predicting their properties. The modern periodic table has no such gaps due to increased knowledge and discovery of elements.
Clarify the relation between the size of the atoms of metals and their chemical reactivity.
In metals, chemical reactivity tends to increase with increasing atomic size. This is because larger metal atoms have their outer electrons farther from the nucleus, which means that they can lose these electrons more easily to form positive ions during chemical reactions. For example, reactivity increases as you move down Group 1 (alkali metals).
Clarify the relation between the size of the atoms of non-metals and their chemical reactivity.
For non-metals, chemical reactivity typically decreases with increasing atomic size. Smaller non-metal atoms are more reactive because the nucleus can attract additional electrons more effectively to form negative ions. For instance, in Group 17 (halogens), reactivity decreases as you move down the group.
