Question

Challenge Determine which element in each pair has the largest atomic radius: a. the element in period \(2,\) group \(1 ;\) or the element in period \(3,\) group 18 b. the element in period \(5,\) group \(2 ;\) or the element in period \(3,\) group 16 c. the element in period \(3,\) group \(14 ;\) or the element in period \(6,\) group 15 d. the element in period \(4,\) group \(18 ;\) or the element in period \(2,\) group 16

Short answer

In each pair: a. Lithium (Li) has a larger atomic radius than Argon (Ar). b. Strontium (Sr) has a larger atomic radius than Sulfur (S). c. Bismuth (Bi) has a larger atomic radius than Silicon (Si). d. Krypton (Kr) has a larger atomic radius than Oxygen (O).

Step-by-step solution

Pair A: Period 2 Group 1 vs Period 3 Group 18

Period 2 Group 1 element is Lithium (Li), whereas Period 3 Group 18 element is Argon (Ar). Moving from top to bottom in a group, the atomic radius increases, while moving from left to right in a period, the atomic radius decreases. In this case, Li is above and to the left of Ar in the periodic table. Therefore, the atomic radius of Li is larger than that of Ar.

Pair B: Period 5 Group 2 vs Period 3 Group 16

Period 5 Group 2 element is Strontium (Sr), while Period 3 Group 16 element is Sulfur (S). Since Sr is below and to the left of S in the periodic table, the atomic radius of Sr is larger than that of S.

Pair C: Period 3 Group 14 vs Period 6 Group 15

Period 3 Group 14 element is Silicon (Si), and Period 6 Group 15 element is Bismuth (Bi). In this pair, Bi is below and to the right of Si on the periodic table. Even though moving from left to right in a period results in a decreasing atomic radius, moving from top to bottom in a group results in an increasing atomic radius. The effect of moving down a group dominates the effect of moving right in a period. Hence, the atomic radius of Bi is larger than that of Si.

Pair D: Period 4 Group 18 vs Period 2 Group 16

Period 4 Group 18 element is Krypton (Kr), whereas Period 2 Group 16 element is Oxygen (O). In this case, Kr is below and to the right of O in the periodic table. Similar to pair C, moving from top to bottom in a group results in an increasing atomic radius, which is more dominant than the effect of moving from left to right in a period. Thus, the atomic radius of Kr is larger than that of O.

Key concepts

Periodic Table

The periodic table is a systematic layout of all known chemical elements. It organizes elements based on their atomic number, which is the number of protons in an atom's nucleus. This table helps scientists predict the properties of elements and their compounds. Each box on the table represents an element and contains its chemical symbol, atomic number, and sometimes additional information such as atomic mass.
The periodic table is arranged in rows called periods and columns called groups.

• Periods: These are horizontal rows, and there are seven periods in the current periodic table. Elements in the same period have the same number of atomic orbitals. As you move from left to right across a period, elements gain more protons and electrons, which causes a decrease in atomic radius due to the increased nuclear charge pulling the electron cloud closer.
• Groups: These are vertical columns, and each group contains elements with similar chemical properties. This similarity arises because elements in a group have the same number of valence electrons.

Understanding the layout and properties of the periodic table is crucial for predicting atomic radius and understanding elemental behavior.

Element Groups

Element groups, also known as families, are columns within the periodic table that display similar properties among the elements. There are 18 groups in the periodic table, each marked by a group number at the top.
The similarities within a group are primarily due to the elements having the same number of valence electrons, which determines how they interact with other elements. This results in them following similar chemical trends.
For instance, elements in Group 1, known as the alkali metals, have one valence electron and are highly reactive, especially with water. Meanwhile, Group 18 elements, the noble gases, have full valence electron shells, making them very stable and unreactive.
Recognizing the properties of each group can help predict how an element will behave in chemical reactions, as well as its atomic radius.

Periodic Trends

Periodic trends are patterns in the periodic table that arise due to the arrangement of electrons in atoms. These trends can help predict and explain the properties of elements. Some key periodic trends include atomic radius, ionization energy, and electronegativity.

• Atomic Radius: This is a measure of the size of an atom. As you move down a group, the atomic radius increases because additional electron shells are added. Conversely, as you move from left to right across a period, the atomic radius decreases because the increased nuclear charge pulls the electrons more tightly towards the nucleus.
• Ionization Energy: This is the energy required to remove an electron from an atom. Typically, ionization energy decreases down a group due to increased distance between the nucleus and valence electrons, and increases across a period as atomic size decreases.
• Electronegativity: This measures an atom's ability to attract electrons in a bond. Like ionization energy, electronegativity tends to increase across a period and decrease down a group.

Understanding these trends is essential for predicting the chemical behavior of elements and comparing atomic radii in exercises.

Atomic Structure

The atomic structure refers to how different components of an atom are arranged. Atoms are made up of three essential particles: protons, neutrons, and electrons.

• Protons: These are positively charged particles found in the nucleus that define the identity of the element, known as the atomic number.
• Neutrons: Neutron particles also reside in the nucleus alongside protons and help stabilize the atomic nucleus. The number of neutrons can vary within atoms of the same element, creating different isotopes.
• Electrons: These are negatively charged particles found in various energy levels around the nucleus. Their arrangement is what determines an atom's size and is crucial for defining atomic radius.

The interplay between protons, neutrons, and electrons not only determines the atom's overall charge and stability but also influences its chemical properties and interaction with other atoms. Hence, understanding atomic structure is fundamental when discussing atomic radius and reactivity within the periodic table.