Problem 15 Which periods are called the sho... [FREE SOLUTION]

Chapter 3: Problem 15

Which periods are called the short periods and which periods are called long periods? Why?

Short Answer

Expert verified

Answer: Short periods in the periodic table, such as Period 1 and Period 2, contain fewer elements than long periods, like Periods 3 to 7. This difference is due to the electron configuration of the elements, as there are fewer orbitals available for electrons to occupy in the first and second energy levels (principal quantum numbers 1 and 2). In contrast, higher energy levels (principal quantum numbers 3, 4, 5, 6, and 7) have more orbitals available, allowing for the accommodation of more elements in each period, resulting in long periods having more elements than short periods.

Step by step solution

Identifying Short and Long Periods

In the periodic table, periods are numbered from top to bottom, starting with Period 1 and ending with Period 7. Short periods are those with fewer elements, while long periods contain more elements.

Short Periods: Period 1 and Period 2

Period 1 contains only two elements, hydrogen and helium. Period 2 contains eight elements, starting with lithium and ending with neon. These periods are shorter than the other periods, hence they are called the short periods.

Long Periods: Periods 3 to 7

Periods 3 to 7 are the long periods in the periodic table. In Period 3, there are 8 elements; Period 4 and Period 5, have 18 elements each; and Period 6 and Period 7 contain 32 elements each. These periods are longer because they contain more elements than the short periods.

Reason behind the classification

The short periods and long periods classification is due to differences in the electron configuration of the elements. The first two periods contain a small number of elements, as there are fewer orbitals available for electrons to occupy in the first and second energy levels (principal quantum numbers 1 and 2). As we move to higher energy levels (principal quantum numbers 3, 4, 5, 6, and 7), there are more orbitals available, allowing for the accommodation of more elements in each period. This is why long periods have more elements than short periods.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Short Periods

In the periodic table, some periods are referred to as "short periods." These include Period 1 and Period 2. These periods have fewer elements compared to others on the table.
Period 1 holds only two elements: hydrogen and helium. This makes it the smallest period. The reason it only has two elements is because it can only hold electrons in the 1s orbital.
Period 2, though slightly longer, still only contains eight elements, starting with lithium and ending with neon. The main reason they are categorized as short periods is due to their limited number of elements which directly relates to available electron orbitals.

Long Periods

In contrast to short periods, there are long periods in the periodic table. These start from Period 3 and go up to Period 7. Each of these periods contains more elements than the short periods, due to more available orbitals for electrons.
For instance:

Period 3 has 8 elements.
Period 4 and Period 5 each have 18 elements.
Period 6 and Period 7 contain the maximum number with 32 elements each.

These periods are longer because as you move down the table, higher energy levels and additional electron subshells become available.

Electron Configuration

The concept of electron configuration is crucial in determining why some periods are short and others are long. Electron configuration describes the arrangement of electrons in an atom across different orbitals.
Each orbital can only host a certain number of electrons, and each element fills these orbitals according to defined rules like the Aufbau principle. This principle helps us understand why the initial periods have fewer elements. In Periods 1 and 2, there are fewer orbitals (just s and p) to fill compared to the extended range of orbitals available in the long periods.

Principal Quantum Numbers

The principal quantum number is a number that indicates the relative size and energy of atomic orbitals. It is closely tied to the periods on the periodic table.
In short periods, the principal quantum numbers are lower, which means there are fewer orbitals and electrons to accommodate. For example, Period 1 is represented by principal quantum number 1, while Period 2 corresponds to principal quantum number 2.
As we move to long periods with higher principal quantum numbers (3, 4, 5, 6, and 7), more orbitals are available. This results in longer periods with more elements.

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Which periods are called the short periods and which periods are called long periods? Why?

Short Answer

Step by step solution

Identifying Short and Long Periods

Short Periods: Period 1 and Period 2

Long Periods: Periods 3 to 7

Reason behind the classification

Key Concepts

Short Periods

Long Periods

Electron Configuration

Principal Quantum Numbers

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