Question

Consider \(S, C 1,\) and \(K\) and their most common ions. (a) List the atoms in order of increasing size. (b) List the ions in order of increasing size. (c) Explain any differences in the orders of the atomic and ionic sizes.

Short answer

The increasing order of atomic sizes is Cl < S < K, determined by their positions in the periodic table. In contrast, the increasing order of ionic sizes is K^(+) < Cl^(-) < S^(2-), primarily due to electron gain/loss and changes in electron shielding and effective nuclear charge. K^(+) is smaller than its neutral atom, while Cl^(-) and S^(2-) are larger than their neutral atoms.

Step-by-step solution

Identify the positions of the elements in the periodic table

Start by identifying the positions of the given elements (S, Cl, and K) in the periodic table. This will help us determine their relative sizes. - S (sulfur) is in group 16 and period 3 - Cl (chlorine) is in group 17 and period 3 - K (potassium) is in group 1 and period 4

List atoms in order of increasing size

The size of atoms typically increases from top to bottom within a group and decreases from left to right across a period in the periodic table. Since S and Cl are in the same period (period 3) and K is in period 4, K will be the largest of the three atoms. Comparing S and Cl, which are in the same period, Cl is to the right of S, so Cl will be smaller than S. Therefore, the order of increasing atomic size will be: Cl < S < K.

Identify the most common ions of the elements

Now, let's identify the most common ions for each of these elements: - Sulfur (S) typically forms a 2- ion (S^(2-)) - Chlorine (Cl) typically forms a 1- ion (Cl^(-)) - Potassium (K) typically forms a 1+ ion (K^(+))

List ions in order of increasing size

When atoms lose or gain electrons to form ions, their sizes will change. Cations (positive ions) are typically smaller than their neutral atoms, while anions (negative ions) are generally larger than their neutral atoms. So, K^(+) will be smaller than neutral K, and both S^(2-) and Cl^(-) will be larger than their neutral atoms. The order of increasing ionic size will be: K^(+) < Cl^(-) < S^(2-).

Explain the differences in atomic and ionic sizes' orders

The difference in the orders of atomic and ionic sizes is mainly due to electron gain/loss, and the changes in electron shielding and effective nuclear charge. In the case of the atoms, the size increases as we move down the periodic table (K is the largest) and decreases as we move across a period (Cl is smaller than S). In the case of the ions, K loses one electron to form a cation, resulting in a smaller ionic size compared to its neutral atom. Cl and S gain electrons to form anions, resulting in their ionic sizes being larger than their neutral atoms. As S^(2-) gains two more electrons than Cl^(-), the repulsion between electrons is greater and so its size will be larger than Cl^(-). In summary, the increasing order of atomic sizes is Cl < S < K, while the increasing order of ionic sizes is K^(+) < Cl^(-) < S^(2-).

Key concepts

Understanding Atomic Size

Atomic size refers to the distance from an atom's nucleus to the outermost shell of electrons. In the periodic table, atoms generally increase in size as you move down a group due to the addition of electron shells. Conversely, as you move across a period from left to right, atomic size decreases because the increasing positive charge on the nucleus pulls the electron shells closer.

• Sulfur (S): Located in group 16 and period 3. S has three electron shells.
• Chlorine (Cl): Found in group 17 and period 3. Cl also has three electron shells but a higher nuclear charge.
• Potassium (K): In group 1 and period 4, K has four electron shells and a comparatively lower nuclear charge than S and Cl.

In our example, as Cl is to the right of S, it is smaller than S, and K is the largest because it is in the next period with an extra shell of electrons. The order of increasing atomic size: Cl < S < K.

Ionic Size Explained

Ionic size is the size of ions, which are atoms that have lost or gained electrons. Cations, or positive ions formed by the loss of electrons, are smaller than the neutral atom due to reduced electron-electron repulsion and a stronger pull from the nucleus. Anions, negative ions formed when atoms gain electrons, are larger due to increased electron-electron repulsion.

In this context:

• Potassium (K+): Loses an electron and forms a smaller cation.
• Chlorine (Cl-): Gains an electron to form a larger anion.
• Sulfur (S2-): Gains two electrons, leading to a larger increase in size compared to Cl- because of the increased repulsion with two additional electrons.

The order of increasing ionic size is K+ < Cl- < S2-.

Periodic Table Groups and Periods

Groups (columns) and periods (rows) structure the periodic table, influencing element properties. Groups contain elements with similar chemical properties and the same number of valence electrons. Elements in the same period have their valence electrons in the same shell.

Key points to remember when considering groups and periods:

• Elements in the same group typically have similar chemical reactivity.
• Moving down a group, elements have more electron shells and are larger.
• Moving across a period, nuclear charge increases, drawing electron shells closer and reducing atomic size.

This framework is crucial for predicting element behavior during chemical reactions.

Cation and Anion Comparison

Cations and anions differ notably in size and formation. Cations (positive ions) form when an atom loses one or more electrons, which reduces repulsion among the remaining electrons and pulls them closer to the nucleus. This makes cations smaller than their parent atoms.

Anions (negative ions) form by gaining one or more electrons, increasing the electron-electron repulsion, which pushes electrons apart and enlarges the ion size compared to the neutral atom.

For instance, K+ is a smaller cation because it loses an electron, while Cl- and S2-, gain electrons to become larger anions. The contrast in size often significantly influences how ions interact in chemical reactions and the solids' structure they form.