Dalton proposed that all atoms of a given element are identical in mass and properties. The discovery of isotopes (atoms of same element with different mass) contradicted this. Dalton's theory explained the three laws of chemical combination. Later models modified the theory. Subatomic particles and radioactivity also could not be explained by Dalton.
Explanation:
Atomic radius increases down a group due to addition of shells. Lithium (Z=3, 2 shells) is the first element in Group 1 and has the smallest radius. Cesium has the largest. The effective nuclear charge also plays a role, but shell number dominates. Trend: Li < Na < K < Rb < Cs.
Explanation:
Electronegativity is the tendency of an atom to attract shared electrons in a chemical bond. It increases across a period and decreases down a group. Fluorine, located at the top right of the periodic table (Group 17, Period 2), has the smallest atomic radius and highest effective nuclear charge, giving it the highest electronegativity (3.98 on Pauling scale).
Explanation:
HCl + NaOH → NaCl + H₂O. This is a neutralization reaction producing sodium chloride (common salt). NaNO₃ from HNO₃, Na₂SO₄ from H₂SO₄, Na₂CO₃ from H₂CO₃ (weak acid).
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