What is the First Row of the Periodic Table?
The first row of the periodic table consists solely of two elements: hydrogen (H) and helium (He). This row is unique because it contains only these two elements, unlike other rows that include many more. Hydrogen has one electron in its first shell, while helium has two electrons, filling its shell.
Composition of the First Row
The periodic table is arranged in rows called periods, representing the filling of electron shells. The first row, often called the first period, includes just hydrogen and helium.
- Hydrogen has one electron (1s1 configuration).
- Helium has two electrons (1s2 configuration), filling the first shell completely.
No other elements are part of this initial row because the first electron shell can hold a maximum of two electrons.
Variability in Defining the First Row
Some sources differ in defining the “first row.” While many agree it includes only H and He, some consider the first row to span from lithium (Li) to neon (Ne), starting the second period instead.
This difference arises because of the periodic table’s shape and the small size of the first row. Since it contains only two elements, it’s sometimes overlooked or grouped differently.
Clarifying Terminology for Periods and Rows
To avoid confusion, the term “period” is preferred over “row” when discussing the horizontal arrangement of elements. This term clearly relates to electron shell filling and reduces ambiguity.
If necessary, specifying “H-row” or “Li-row” can clarify which set of elements one refers to.
Key Points to Remember
- The first row (period 1) contains only hydrogen and helium.
- These elements fill the first electron shell (1s orbital).
- Different textbooks may define the first row variably, sometimes including Li to Ne.
- Using the term “period” instead of “row” improves clarity.
What elements make up the first row of the periodic table?
The first row contains only hydrogen and helium. Hydrogen has one electron and helium has two, filling their 1s orbitals.
Why do some sources list lithium to neon as the first row?
Some books treat the first row as lithium to neon. This variation arises because the tiny first row is sometimes overlooked or deemed less important.
Is there confusion about the term “first row” in the periodic table?
Yes. The shape of the table causes inconsistency. It’s clearer to say “period” rather than “row,” or specify, like “H-row,” to avoid confusion.
How many electrons do first-row elements have in their outer shell?
Hydrogen has 1 electron in its 1s shell, helium has 2. These are the only elements in the first row.
Should we always call the first horizontal row a “period” instead of “row”?
Using “period” is recommended for clarity. “Row” can be vague, so specifying “period 1” or naming elements helps clear misunderstandings.
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