Question

Name and give the symbol for the element with the characteristic given below: (a) Its electron configuration is \(1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{5}\). (b) Lowest ionization energy in Group 14. (c) Its \(+2\) ion has the configuration \(\left[{ }_{18} \mathrm{Ar}\right] 3 \mathrm{~d}^{5}\). (d) It is the alkali metal with the smallest atomic radius. (e) Largest ionization energy in the fourth period.

Short answer

Question: Based on the analysis and solution provided, identify the elements for the following: (a) The element with electron configuration \(1s^{2} 2s^{2} 2p^6 3s^{2} 3p^5\) (b) The element with the lowest ionization energy in Group 14 (c) The element corresponding to the +2 ion with electron configuration \(\left[{ }_{18} \mathrm{Ar}\right] 3 \mathrm{~d}^{5}\) (d) The smallest alkali metal by atomic radius (e) The element with the largest ionization energy in the fourth period Answer: (a) Chlorine (Cl) (b) Lead (Pb) (c) Calcium (Ca) (d) Lithium (Li) (e) Krypton (Kr)

Step-by-step solution

(a) Identifying the element by electron configuration

First, note the given electron configuration: \(1s^{2} 2s^{2} 2p^6 3s^{2} 3p^5\). The electron configuration gives information on the distribution of electrons in the shells and orbitals of a particular atom. To determine the element, you must count the total number of electrons, as this corresponds to the atomic number. In this case, there are: \(2 + 2 + 6 + 2 + 5 = 17\) electrons. So, the atomic number is 17, which corresponds to the element Chlorine (Cl).

(b) Identifying the element with the lowest ionization energy in Group 14

Ionization energy refers to the energy required to remove an electron from an atom. Within a group of the periodic table, ionization energy generally decreases down the group. Group 14 elements include C, Si, Ge, Sn, and Pb. Among these elements, lead (Pb) is the lowest and therefore has the lowest ionization energy.

(c) Identifying the element by the configuration of its +2 ion

The electron configuration for the +2 ion is given as \(\left[{ }_{18} \mathrm{Ar}\right] 3 \mathrm{~d}^{5}\). Argon (Ar) has an atomic number of 18. Since this ion has lost two electrons, it has an atomic number of 20, which corresponds to the element Calcium (Ca).

(d) Identifying the smallest alkali metal by atomic radius

Atomic radius generally increases down a group and decreases across a period. Alkali metals are found in Group 1 of the periodic table and include Li, Na, K, Rb, Cs, and Fr. Since atomic radius decreases across a period, the smallest alkali metal is lithium (Li), which is located in the first period of Group 1.

(e) Identifying the element with the largest ionization energy in the fourth period

Since ionization energy increases across a period, the element with the largest ionization energy will be found towards the right end of the fourth period. In the fourth period, the most electronegative element is krypton (Kr). Due to its high electronegativity, it has the largest ionization energy within the fourth period.

Key concepts

Ionization Energy

Understanding the concept of ionization energy is critical when studying the behavior of elements. Ionization energy, the energy required to remove an electron from an atom in the gas phase, plays a significant role in determining an element's chemical reactivity and its tendency to form bonds. As you go across the periodic table from left to right, the ionization energy generally increases because the additional protons in the nucleus create a stronger attraction for the electrons, making them harder to remove.

When it comes to groups, the trend is the opposite; as you move down a group, the ionization energy decreases. This is because the electrons are further away from the nucleus due to more shells, and thus, they are less tightly held and easier to remove. The element with the lowest ionization energy in a particular group is typically the one with the highest atomic number within that group, due to its larger atomic radius and electron shielding effects.

Atomic Radius

The atomic radius is essentially half the distance between the nuclei of two atoms of the same element when joined together by a chemical bond. It's a fundamental concept when discussing the size of an element and has implications for the element's properties and its place on the periodic table. Atomic radius tends to increase as you go down a group since new electron shells are added, creating a larger 'orbit' for electrons. Conversely, the radius tends to decrease as you move from left to right across a period, due to the increasing nuclear charge pulling electrons closer to the nucleus.

A practical example of this concept is when comparing alkali metals. Lithium, being at the top of Group 1, exhibits the smallest atomic radius within its group. This impacts properties such as density and melting point, which are relevant to the element's behavior in various chemical reactions.

Alkali Metals

Alkali metals, located in Group 1 of the periodic table, are known for being highly reactive due to their single valence electron which they can easily lose to form +1 ions. This group includes familiar elements such as Lithium (Li), Sodium (Na), and Potassium (K). These metals are characterized by their softness, low density, and low ionization energies, which decrease further down the group. As the size increases, their reactivity also increases, because the valence electron becomes more and more distant from the pull of the nucleus and is more readily lost.

When we look for the alkali metal with the smallest atomic radius, we turn to lithium. Amongst its peers in Group 1, lithium's compact size means it has a higher melting and boiling point, making it unique in its group. These special properties have practical implications, such as its use in lithium batteries because of its high electrochemical potential.

Periodic Table

The periodic table is a tabular arrangement of the chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties. Elements are presented in order of increasing atomic number, and the table has a grid-like structure with rows called periods and columns called groups. The elements within a group often share similar characteristics, like those we see in alkali metals with their single outer electron and their characteristic reactivity.

The table is not just a display of information; it’s a powerful tool that enables predictions about the behavior of elements based on their position. Key trends, such as the changes in ionization energy and atomic radius, guide us in understanding the chemical reactivity and bonds that atoms can form. For instance, the element with the highest ionization energy in a given period is typically found at the far right end, such as the noble gases, known for their lack of reactivity due to their full valence electron shells.