These questions ask you to read a location, direction or region of the periodic table and infer one broad property. Identify whether the movement is across a period or down a group before choosing the quantity and its trend.
Read the table in layers
Begin with orientation. Rows are periods and vertical columns are groups. Atomic number rises from left to right and continues rising when table order moves to the next row. For a ground-state main-group atom, the period gives the number of occupied principal shells. A main-group column groups elements with similar outer-electron patterns, so it supports a broad prediction of similar chemical behaviour rather than identical mass or physical state.
| Position or movement | Inference |
|---|---|
| Left side and centre | Mainly metals; many nonmetals occupy the upper right, with hydrogen as a nonmetal on the left. |
| Near the zigzag boundary | Core metalloid examples lie near the broad divide between metals and nonmetals. |
| Main-group groups 1 and 2 | The usual valence counts are one and two respectively. |
| Main-group groups 13 through 18 | Subtract ten from the group number for the usual valence count; helium is the exception with two. |
| Left to right across a period | Atomic radius generally decreases, while first ionization energy generally increases. |
| Down a group | Atomic radius generally increases, while first ionization energy generally decreases. |
A useful sketch is two opposing arrows for the two trends. Across a row, stronger overall attraction draws the occupied electron region inward and makes an outer electron harder to remove. Down a column, added shells increase distance and shielding, so the atom is larger and the outer electron is generally easier to remove. For example, an element below another family member has an extra occupied shell, not a reset atomic number.
Keep the table signals separate
| Trap | How to reject it |
|---|---|
| Putting metals only in one corner, row or column | Use broad regions: metals fill most of the left and centre, while core metalloids trace a boundary rather than a complete row or group. |
| Treating every left-side element as a metal | Remember the hydrogen exception while keeping the broad upper-right concentration of nonmetals. |
| Reading a period number as proton or valence count | For the school shell model, period answers occupied shells. Group position supplies the usual valence rule. |
| Making radius grow across because atomic number grows | Within one period, stronger attraction generally pulls the electron region inward, so the radius trend points left rather than right. |
| Giving ionization energy the radius direction | The general arrows oppose each other: where atoms become smaller across a period, first ionization energy generally rises; added shells down a group reverse both changes. |
Try it
A learner follows the numbered cells across one period and then continues onto the next row. How do atomic numbers change in standard table order?
- They increase and do not restart on a new row.
- They decrease across every row.
- They restart at 1 in each period.
- They remain constant within a period.
Which statements correctly apply the usual main-group valence-electron rule for groups 13 through 18? Select all that apply.
- A group 16 main-group atom usually has 16 valence electrons.
- A group 16 main-group atom usually has 6 valence electrons.
- Helium has 8 valence electrons.
- Helium has 2 valence electrons.
An element is compared with the element directly below it in the same group. What is the general change in atomic radius?
- It increases only among nonmetals.
- It remains identical.
- It generally increases.
- It generally decreases.