Question

Which is the largest atom in the third period of the periodic table?

Short answer

Sodium (Na) is the largest atom in the third period.

Step-by-step solution

Understanding the Periodic Table

The periodic table is arranged in periods and groups. Periods run horizontally across the table, and atoms in the same period have the same number of electron shells. We are interested in the third period, which runs from sodium (Na) to argon (Ar).

Examining Atomic Size Trends

As you move from left to right across a period, atomic size generally decreases. This trend occurs because electrons are added to the same energy level while protons are added to the nucleus, increasing the nuclear charge and pulling electrons closer.

Identifying the Elements

The elements in the third period are: sodium (Na), magnesium (Mg), aluminum (Al), silicon (Si), phosphorus (P), sulfur (S), chlorine (Cl), and argon (Ar). Since we determined that atomic size decreases across a period, the first element should be the largest.

Finding the Largest Atom

Sodium (Na) is the first element in the third period. Since atomic size decreases across a period, sodium is the largest atom in the third period.

Key concepts

Atomic Size Trend

The trend of atomic size is a fundamental concept in chemistry, as it helps us understand how atoms change in size across the periodic table. Atomic size, often referred to as atomic radius, can be thought of as the distance from the center of an atom's nucleus to the outermost electron shell. One key trend is that atomic size generally decreases as you move from left to right across a period in the periodic table. This happens because as you go across a period, electrons are added to the same energy level, while protons are simultaneously added to the nucleus. This increase in nuclear charge pulls the electrons closer to the nucleus, resulting in a smaller atomic size.

• As electrons are added to the same energy level without an increase in shielding, they are pulled in more tightly.
• Increased protons in the nucleus lead to a stronger attraction between the nucleus and the electron cloud.

On the other hand, as you move down a group (which are the vertical columns), atomic size increases. This occurs due to the addition of new energy levels or shells to the atoms. Thus, understanding these trends is crucial for predicting and explaining the chemical behavior of different elements.

Third Period Elements

The third period of the periodic table includes the elements from sodium (Na) to argon (Ar). These elements represent a complete series containing eight elements in total. Each element in this period has electrons filling the 3rd electron shell. As we move across the third period from left to right, the atomic number increases from 11 to 18.
Sodium, being the first element in this period, begins with just one electron in its outer shell. As we progress to argon, the number of outer electrons increases, and the outer shell becomes fully occupied, making argon a noble gas that is chemically inert.

• Elements in the third period show a variety of physical and chemical properties.
• The transition from metals to nonmetals is evident as one moves across the period.
• Understanding these elements helps illustrate trends in atomic size, electronegativity, and reactivity.

The third period is particularly important for studying trends in atomic properties.

Nuclear Charge Effect

The effect of nuclear charge is a crucial factor in determining the behavior and properties of atoms. The nuclear charge is essentially the total charge of all the protons in the nucleus. As you add more protons to the nucleus when moving across a period, the nuclear charge increases. This increase has significant effects on atomic size and other properties.
One primary effect of increasing nuclear charge is that it leads to a stronger pull on the electrons surrounding the nucleus. Because the electrons are attracted more strongly to the nucleus, they are drawn closer, effectively reducing the atomic radius. This explains why we observe a decrease in atomic size from left to right across a period despite the same number of electron shells.

• The greater the nuclear charge, the stronger the attractive force on the electrons.
• Higher nuclear charge also affects ionization energy and electronegativity, increasing them across a period.

Understanding how nuclear charge influences atomic properties is essential for grasping atomic structure and reactivity.