The horizontal rows in the modern periodic table are called:
A. Groups
B. Blocks
C. Periods
D. Families
Answer: Option C
Solution (By JKSSB Mock Tests)
The periodic table has 7 horizontal rows called periods. Elements in the same period have the same number of electron shells. Properties change gradually across a period. Groups are vertical columns (18), where elements have similar valence electron configurations and thus similar chemical properties. Families are informal group names (e.g., halogens). Blocks (s, p, d, f) are based on the orbital in which the last electron enters.
Explanation:
In H₂, two hydrogen atoms share their electrons equally because they have the same electronegativity. Thus, a non-polar covalent bond is formed. Ionic bonds form between metals and non-metals. Polar covalent bonds involve unequal sharing (e.g., HCl). Coordinate bonds involve one atom donating both electrons (e.g., NH₄⁺).
Explanation:
The modern periodic law states that the physical and chemical properties of elements are periodic functions of their atomic numbers. This was proposed by Henry Moseley, correcting Mendeleev's periodic table which was based on atomic mass. Atomic number determines the electronic configuration and thus chemical properties.
Explanation:
A bomb calorimeter burns a known mass of fuel in excess oxygen inside a sealed bomb immersed in water. The temperature rise of water is measured to calculate heat released. Thermometer is part of it but not the device itself.
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