Question

Consider the elements \(\mathrm{O}, \mathrm{Ba}, \mathrm{Co}, \mathrm{Be}, \mathrm{Br}\), and Se. From this list select the element that (a) is most electronegative, (b) exhibits a maximum oxidation state of \(+7\), (c) loses an electron most readily, (d) forms \(\pi\) bonds most readily, (e) is a transition metal.

Short answer

(a) Most electronegative: Oxygen (O) (b) Maximum oxidation state of +7: Selenium (Se) (c) Loses an electron most readily: Barium (Ba) (d) Forms π bonds most readily: Oxygen (O) (e) Is a transition metal: Cobalt (Co)

Step-by-step solution

Element positions in the periodic table

For reference, let's locate each element in the periodic table: - Oxygen (O): Group 16 (or 6A), Period 2 - Barium (Ba): Group 2 (or 2A), Period 6 - Cobalt (Co): Group 9 (or 7B), Period 4 - Beryllium (Be): Group 2 (or 2A), Period 2 - Bromine (Br): Group 17 (or 7A), Period 4 - Selenium (Se): Group 16 (or 6A), Period 4

Electronegativity

(a) Electronegativity is highest in the upper right corner of the periodic table, excluding noble gases. From our list, the most electronegative element would be Oxygen (O), as it is in the upper right corner among the given elements.

Maximum oxidation state

(b) An element with a maximum oxidation state of +7 can be found among the nonmetals in higher period numbers. Selenium (Se) belongs to group 16, and its highest oxidation state is +6. However, an exception occurs where Selenium can exhibit a maximum oxidation state of +7 in certain compounds. Therefore, Selenium (Se) is the element that exhibits a maximum oxidation state of +7.

Losing electrons

(c) Alkali metals and alkaline earth metals lose electrons most readily because they have only one or two electrons in their valence shell. Among the elements in our list, Barium (Ba) and Beryllium (Be) belong to the alkaline earth metals. Barium (Ba) is in the sixth period, and its valence electrons are more weakly attracted to the nucleus due to the greater distance compared to Beryllium (Be) in the second period. Therefore, Barium (Ba) is the element that loses an electron most readily.

Forming π bonds

(d) Elements that can form π bonds readily are usually nonmetals with small atomic size in the higher periods. Oxygen (O) and Carbon (C) are well-known for their ability to form π bonds. In our current list, the only option that can form π bonds readily is Oxygen (O).

Transition metal

(e) Transition metals are elements in groups 3-12 (or 3B-2B) and have incomplete d orbitals. From our list, the only transition metal is Cobalt (Co), which is in Group 9. To summarize: (a) Most electronegative: Oxygen (O) (b) Maximum oxidation state of +7: Selenium (Se) (c) Loses an electron most readily: Barium (Ba) (d) Forms π bonds most readily: Oxygen (O) (e) Is a transition metal: Cobalt (Co)

Key concepts

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons. It is an important concept used to predict how atoms will interact and form molecules. Electronegativity values increase from left to right across a period and decrease down a group in the periodic table. This trend is because atoms have more protons in their nuclei as you move across a period, increasing their ability to attract electrons. Meanwhile, as you go down a group, the outer electrons are further from the nucleus and experience greater electron shielding, reducing their attraction to the nucleus.

In our list of elements (O, Ba, Co, Be, Br, Se), Oxygen is the most electronegative. Oxygen is located in the upper right of the periodic table, which is characteristic of elements with high electronegativity. This property makes Oxygen highly reactive and a common participant in the formation of polar covalent bonds, especially with hydrogen and carbon.

Oxidation States

The oxidation state of an element in a compound is the hypothetical charge it would have if all bonds were ionic. This concept is crucial in understanding redox reactions and the transfer of electrons between species. Each element has a range of possible oxidation states, but some have specific maximum values. Elements like Selenium, found in group 16, typically exhibit a +6 oxidation state, but certain compounds can push its maximum oxidation state to +7.

When examining oxidation states, keep in mind that nonmetals in higher periods can exhibit these maxima due to the availability of additional d-orbitals, which can accommodate more electrons or pairs.

Electron Affinity

Electron affinity is the energy change that occurs when an electron is added to a neutral atom. High electron affinity indicates an atom's strong tendency to gain an electron, thus forming an anion. This property varies across the periodic table, generally increasing across a period and decreasing down a group.

In our selection of elements, the alkaline earth metal Barium, which is in group 2, has a low electron affinity, making it more prone to losing an electron rather than gaining one. This tendency is due to its larger atomic size and the lower effective nuclear charge experienced by its outermost electrons, reducing the atom’s overall electron affinity.

Pi Bonds

Pi (\( \pi \)) bonds are a type of covalent bond which occur due to the sideways overlap of p orbitals. They are integral to the formation of double and triple bonds in molecules. Unlike sigma bonds, which are strong and result from head-on orbital overlap, pi bonds are weaker due to the diffraction of sideways orbital overlaps.

Oxygen is known for its capacity to form pi bonds. Due to its small size and high electronegativity, it forms these bonds readily, particularly in compounds like carbon dioxide (\( \text{CO}_2 \)) and molecular oxygen (\( \text{O}_2 \)). Pi bonds play a critical role in determining the reactivity and geometry of molecules, influencing properties like bond angles and the shape of the molecules they form.

Transition Metals

Transition metals are a group of elements located in groups 3-12 of the periodic table. They are characterized by their ability to form variable oxidation states, and the presence of partially filled d orbitals. These metals are well known for their unique properties, such as forming colored compounds, being good conductors of heat and electricity, and having high melting and boiling points.

Cobalt, from our list, is a transition metal positioned in group 9. This element showcases the variability in oxidation states typical of transition metals, due to the possibility of electrons being removed from both the s and d orbitals. Cobalt and other transition metals are important in various industrial processes, serving as catalysts in reactions and playing a key role in metallurgy and the production of alloys.