what are the horizontal rows on the periodic table called
What are the horizontal rows on the periodic table called?
Answer: The horizontal rows on the periodic table are called periods. There are seven periods in the modern periodic table, each corresponding to the highest energy level an electron in that element can occupy at ground state. Here is a more detailed overview:
1. Definition of Periods:
- Periods are the horizontal rows in the periodic table. Each period indicates the highest principal energy level that electrons occupy in the elements of that period. For example, elements in the second period have electrons in the second energy level (n=2).
2. Characteristics of Elements in a Period:
- Electron Configuration: As you move across a period from left to right, the atomic number increases, meaning each subsequent element has one more proton and electron than the previous one. This results in electrons filling the same energy level until a new period begins.
- Properties: The properties of elements change gradually across a period. For example, metals are on the left side of a period, metalloids are in the middle, and non-metals are on the right.
- Reactivity: The reactivity of elements changes across a period. For example, in Period 3, sodium (Na) is highly reactive, while argon (Ar), a noble gas, is inert.
3. Examples of Periods:
- Period 1: Contains only hydrogen (H) and helium (He).
- Period 2: Includes lithium (Li) to neon (Ne).
- Period 3: Ranges from sodium (Na) to argon (Ar).
- And so on, up to Period 7 which includes the lanthanides and actinides series.
Understanding periods helps in predicting the properties of elements, their reactivity, and their role in chemical bonding and compounds formation. The concept of periods is fundamental in the study of chemistry and helps in organizing the elements systematically.