Atomic Structure — Important Questions

Thomson's model

Thomson's model is called the 'plum pudding' model. Step 1: After discovering electrons, Thomson needed to explain how positive and negative charges were arranged in atoms. Step 2: He proposed atoms were spheres of uniform positive charge with electrons embedded throughout. Step 3: This resembled a plum pudding where the pudding represents positive charge and plums represent electrons. Step 4: The model explained electrical neutrality but was later disproved by Rutherford's experiments. Dalton's model had no internal structure, Rutherford's had a nucleus, and Bohr's had orbital shells.

2, 8, 1

Sodium's electronic configuration is 2, 8, 1. Step 1: Sodium has atomic number 11, meaning 11 electrons in a neutral atom. Step 2: Electrons fill shells in order: K shell first (maximum 2), then L shell (maximum 8), then M shell. Step 3: First 2 electrons go to K shell: 2 electrons remaining = 11-2 = 9. Step 4: Next 8 electrons fill L shell: 9-8 = 1 electron remaining for M shell. Therefore: K=2, L=8, M=1 or (2,8,1). This configuration makes sodium highly reactive as it has 1 valence electron.

Neutron

Neutron has no electrical charge (neutral). Step 1: Atoms contain three fundamental subatomic particles with different charges. Step 2: Electrons carry negative charge (-1), discovered through cathode ray experiments. Step 3: Protons carry positive charge (+1), discovered through canal ray experiments. Step 4: Neutrons carry no charge (0), discovered by Chadwick in 1932, which explained why atomic mass was greater than expected from protons alone. Alpha particles are helium nuclei with +2 charge. Neutrons are essential for nuclear stability.

1

The valency is 1. Step 1: Electronic configuration 2,8,7 means 7 electrons in the outermost (valence) shell. Step 2: For elements with more than 4 valence electrons, valency = 8 - number of valence electrons. Step 3: Valency = 8 - 7 = 1. Step 4: This element (chlorine) needs 1 electron to complete its octet and achieve stability, so it can form 1 bond. Elements try to achieve stable configuration of 8 electrons in outermost shell (octet rule). Valency indicates combining capacity, not the number of valence electrons.