Problem 25 - Chemistry and Chemical Reactivity

Question

How many periods of the periodic table have 8 elements, how many have 18 elements, and how many have 32 elements?

Step-by-Step Solution

Answer

2 periods have 8 elements, 2 have 18 elements, and 2 have 32 elements.

Step 1: Identify Periods with 8 Elements

The periods with 8 elements in the periodic table are Period 2 and Period 3. Each of these periods has a full set of s and p orbitals, making a total of 8 elements.

Step 2: Identify Periods with 18 Elements

Period 4 and Period 5 have 18 elements each. These periods utilize s, p, and d orbitals, resulting in a total of 18 elements in each period.

Step 3: Identify Periods with 32 Elements

The periods with 32 elements are Period 6 and Period 7. These periods include s, p, d, and f orbitals, which accommodate 32 elements in each period.

Key Concepts

Periods of the Periodic Table

The Periodic Table is organized into horizontal rows known as periods. Each period signifies a new principal energy level for electrons. The number of periods in the periodic table is seven. Each period corresponds to a higher principal quantum number. Hence, as you move from top to bottom through the periods, the number of electron shells for elements increases.

• Period 1 has the fewest elements with only 2, while higher periods can have more, showing the changes in orbital types that electrons fill.
• The variation in the number of elements per period is because of the differences in the electron filling sequence.

Understanding periods is fundamental for locating elements and predicting their behaviors based on electron configuration.

Elements Per Period

The periods in the periodic table feature different numbers of elements based on the filled electron orbitals:

• Period 1 has 2 elements. This is because it only fills the 1s orbital.
• Periods 2 and 3 contain 8 elements each. They fill the 2s and 2p, and 3s and 3p orbitals, respectively.
• Periods 4 and 5 have 18 elements each. The full range of orbitals from this level, including the 4s, 4d, 4p, and 5s, 5d, 5p, allow for more elements.
• Periods 6 and 7 contain 32 elements. These periods even include the 4f and 5f orbitals, accommodating more electrons.

This pattern is crucial in understanding how elements are grouped and how the table expands with more complex atomic structures.

Electron Orbitals

Electron orbitals are regions around the nucleus where electrons are likely to be found. Each type of orbital has a different shape and energy level. Orbital names combine energy levels and types, like the "1s" or "3p" notation.

• The s orbital is spherical and can hold up to 2 electrons.
• The p orbitals are dumbbell-shaped and can hold up to 6 electrons.
• The d orbitals can hold up to 10 electrons, having a more complex shape.
• The f orbitals are even more complex and can hold up to 14 electrons.

Understanding orbitals is key to predicting how elements will interact, combining the number and type to define where electrons reside.

s, p, d, f Orbitals

Each of the orbital types contributes differently to the structure of the periodic table.

• **s orbitals**: Always filled first in any new energy level. They have a maximum of 2 electrons.
• **p orbitals**: Start filling after the s orbitals at each energy level from the second period onward, with a capacity to hold 6 electrons.
• **d orbitals**: Begin filling from the fourth period, and align strongly with transition metals, involving significant electron configuration changes and can hold up to 10 electrons.
• **f orbitals**: These become significant from the sixth period and are associated with the lanthanides and actinides, accommodating up to 14 electrons.

These orbitals explain the electron distribution across elements, describing the electron configuration and chemical behavior of elements in the periodic table.