Sodium has 11 electrons. Two fit in its first shell, but remember that the second shell can only carry 8 electrons. Sodium's 11th electron cannot fit into either its first or its second shell. This electron takes up another orbit, a 3rd electron shell in sodium. The reason that there is a dramatic shift in chemical properties when moving from neon to sodium is because there is a dramatic shift in electron configuration between the two elements. But why is sodium similar to lithium? Look at the electron configurations. 