Question

In what region of the periodic table are the largest atoms found? Where are the smallest atoms found?

Short answer

The largest atoms are found in the bottom left region of the periodic table, while the smallest atoms are located in the upper right region, excluding the noble gases.

Step-by-step solution

Understanding Periodic Trends

The size of an atom, also known as its atomic radius, varies in a predictable way across the periodic table. As you move from left to right across a period, the atomic size decreases due to the increasing nuclear charge which pulls electrons closer to the nucleus. As you move down a group, the atomic size increases because each row adds an additional electron shell.

Identifying the Region for Largest Atoms

Since the atomic size increases as you move down a group, the largest atoms will be found at the bottom of the periodic table. Moreover, since atomic size also increases as one moves from right to left across a period, the largest atoms will be found on the leftmost side of the bottom rows of the periodic table.

Locating the Region for Smallest Atoms

The atomic size decreases as you move from left to right across a period because of the increase in the positive charge of the nucleus, which attracts electrons more strongly. Therefore, the smallest atoms can be found in the upper right corner of the periodic table, excluding the noble gases, because they have a complete valence shell that prevents them from forming bonds under standard conditions.

Key concepts

The Periodic Table and Atomic Size

The periodic table is an arrangement of all known elements in an order that reflects patterns in their properties, including atomic radius. The atomic radius is defined as the distance from the center of the nucleus of an atom to the boundary of its electron cloud. Understanding the layout of the periodic table helps students to grasp why the largest and smallest atoms are found in specific regions.

The table is organized into rows called periods, and columns known as groups. When assessing the size of atoms, a clear trend is observed: atoms increase in size as you move down a group and decrease in size as you move across a period from left to right. This is because new electron shells are added as you descend the groups, increasing the atom's volume, while the rightward movement across a period signifies an increase in the number of protons and electrons within the same shell, which doesn't significantly change the size of the electron shell but does increase the nuclear charge, pulling electrons in more tightly and reducing the size of the atom.

Understanding Electron Shells

Electron shells are like layers around the nucleus of an atom where electrons are most likely to be found. Each shell can hold a fixed number of electrons, and these shells are filled in a specific order. The innermost shell is filled first, followed by the next level out, and so forth. This concept is crucial because the number of electron shells influences the size of an atom.

Electron Capacity of Shells

Each electron shell has a different capacity for electrons. The first shell can hold up to 2 electrons, while the second can hold up to 8, and the third, 18, and so on, following a pattern based on the quantum mechanical model of the atom. As elements in a group on the periodic table have similar properties due to their valence shell electron configuration, those lower down in a group will have more electron shells, resulting in a larger atomic radius.

The Role of Nuclear Charge

Nuclear charge is the total charge of the nucleus, equal to the number of protons it contains, which is characteristic of each element. A greater nuclear charge means that the nucleus has a stronger attractive force on the electrons surrounding it.

Influence on Atomic Radius

Nuclear charge plays a pivotal role in determining atomic size. Within a period, as the nuclear charge increases, electrons are pulled closer to the nucleus due to the stronger attraction. This greater pull overcomes the repulsion among electrons and results in a smaller atomic radius. Conversely, although the nuclear charge also increases as you move down a group, the addition of electron shells outweighs the increased nuclear charge, resulting in a larger atomic size. Hence, the smallest atoms, with the highest nuclear charge in relation to their number of electron shells, are found at the upper right side of the periodic table, except for the noble gases.