Multiple choiceQuestion 1 · Recall
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By the end you can take a set of observations about an unknown element and deduce four things: whether it is a metal or non-metal, its group, its period, and which element it is.
"Deduce" questions hand you a data table and an unknown element. Do not guess the name first. Work through three questions:
Each answer must be justified by a specific observation. "It is a metal because it conducts electricity when solid and its oxide is basic" is a deduction. "It is probably sodium" is a guess.
| Observation | What it tells you |
|---|---|
| Conducts electricity when solid | Metal (delocalised electrons) |
| Does not conduct when solid | Usually a non-metal (or a metalloid such as silicon) |
| Oxide solution is alkaline | Metal — a basic oxide |
| Oxide solution is acidic | Non-metal — an acidic oxide |
| Oxide is amphoteric | Aluminium, or a transition metal such as zinc |
| Reacts with cold water | Group 1 or Group 2 metal |
| Formula of oxide or chloride | Number of outer electrons → group |
| Number of occupied shells | Period |
| Relative atomic radius or ionisation energy | Confirms the period by comparison |
The first four rows settle the nature. The last four settle the position.
In a compound with oxygen or chlorine, the element is usually showing all of its outer electrons in bonding. Count them, and you have the group.
| Compound | Charge or oxidation state of X | Outer electrons | Group |
|---|---|---|---|
| +1 | 1 | 1 | |
| , | +2 | 2 | 2 |
| , | +3 | 3 | 13 |
| , | +4 | 4 | 14 |
| , | +5 | 5 | 15 |
| +6 | 6 | 16 | |
| +7 | 7 | 17 |
Two cautions. First, the group number is not the same as the number of outer electrons once you pass Group 2: three outer electrons means Group 13, not Group 3. Second, a metal can show a lower oxidation state in a different compound (iron forms both and ), so use the highest oxide or chloride the question gives you.