Tuesday, October 6 — Day 26
Valence. Short day. Start at 10:10.
The clock
Late start, so two work blocks instead of three.
| NY time | What | |
|---|---|---|
| Work | 10:10–10:50 | Read this. The column number. |
| Break | 10:50–11:10 | No phone. |
| Work | 11:10–11:50 | Printed sheet. Filled side down. |
| Break | 11:50–12:10 | No phone. |
| Exam | 12:10–12:40 | 18 questions. A or B. |
Phones off until 1:10. The sheet is on the desk. Put it away before the exam. The bar mitzvah reading is 20 minutes and is not part of this block.
The idea
Valence is the electrons on the outside. It is not the proton count. Sodium has 11 protons and 1 valence electron.
Same column, same valence. Across row 2 or row 3 the numbers go 1, 2, 3, 4, 5, 6, 7, 8.
| Column | Examples | Valence |
|---|---|---|
| 1 | Lithium, sodium | 1 |
| 2 | Beryllium, magnesium | 2 |
| 3 | Boron, aluminum | 3 |
| 4 | Carbon, silicon | 4 |
| 5 | Nitrogen, phosphorus | 5 |
| 6 | Oxygen, sulfur | 6 |
| 7 | Fluorine, chlorine | 7 |
| 8 | Neon, argon | 8 |
Helium is the exception. Its shell is full at 2, not 8. Hydrogen is 1.
A few questions are divide-by-flipping: flip the second fraction, then multiply. 1/2 ÷ 1/4 = 2.
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