How many of the following have greater `7_(eff)` than silicon atom:
`Na, Mg, AI, P, CI, S, N, O, C, F`

Answer

To determine how many of the given elements have a greater effective nuclear charge (Z_eff) than silicon, we can follow these steps:

### Step 1: Understand Z_eff
Z_eff (effective nuclear charge) is the net positive charge experienced by an electron in a multi-electron atom. It accounts for the actual nuclear charge (Z) and the shielding effect caused by other electrons. Z_eff generally increases across a period (left to right) and decreases down a group (top to bottom).

### Step 2: Locate Silicon in the Periodic Table
Silicon (Si) is located in Group 14 (IV) and Period 3 of the periodic table. Its atomic number is 14.

### Step 3: Analyze Each Element
We will analyze each element in the list to determine if they have a greater Z_eff than silicon:

- **Na (Sodium)**: Group 1, Period 3. Z_eff < Si (due to being in the same period but to the left).
- **Mg (Magnesium)**: Group 2, Period 3. Z_eff < Si (same reason as Na).
- **Al (Aluminum)**: Group 13, Period 3. Z_eff < Si (same period, further left).
- **P (Phosphorus)**: Group 15, Period 3. Z_eff > Si (to the right in the same period).
- **Cl (Chlorine)**: Group 17, Period 3. Z_eff > Si (to the right in the same period).
- **S (Sulfur)**: Group 16, Period 3. Z_eff > Si (to the right in the same period).
- **N (Nitrogen)**: Group 15, Period 2. Z_eff > Si (higher period, but to the left).
- **O (Oxygen)**: Group 16, Period 2. Z_eff > Si (higher period, but to the left).
- **C (Carbon)**: Group 14, Period 2. Z_eff > Si (higher period, same group).
- **F (Fluorine)**: Group 17, Period 2. Z_eff > Si (higher period, to the right).

### Step 4: Count Elements with Greater Z_eff
From the analysis:
- Elements with greater Z_eff than silicon: P, Cl, S, N, O, C, F.
- Total count: 7 elements.

### Final Answer
**7 elements have a greater Z_eff than silicon.**

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