Question

Among the elements with atomic numbers 9,12, 16 and 36 which is highly electropositive? (a) Element with atomic number (b) Element with atomic number (c) Element with atomic number (d) Element with atomic number

Short answer

The element with atomic number 12 (Magnesium) is the most electropositive among the given elements.

Step-by-step solution

Identify the Electropositivity Trend On the Periodic Table

Electropositivity is the tendency of an atom to donate electrons to form positive ions. In the periodic table, electropositivity increases as you move from right to left across a period and increases as you move down a group. Elements on the left side and the bottom of the periodic table are more electropositive.

Determine the Group and Period of Each Element

Locate each element with the given atomic numbers on the periodic table. Element with atomic number 9 (Fluorine) is in group 17 and period 2, element with atomic number 12 (Magnesium) is in group 2 and period 3, element with atomic number 16 (Sulfur) is in group 16 and period 3, and element with atomic number 36 (Krypton) is in group 18 and period 4.

Compare the Position of Each Element in the Periodic Table

Since electropositivity increases as we move to the left and down the periodic table, we can compare the elements' positions to determine which is the most electropositive. Fluorine is in group 17 (halogens), which are very electronegative, and Krypton is in group 18 (noble gases), which are typically unreactive and not known for forming ions. Sulfur is closer to the right side of the table, which makes it less electropositive compared to elements on the left side. Magnesium is in group 2, which is on the left side of the periodic table and has a tendency to lose its two outer electrons and form a positive ion.

Choose the Most Electropositive Element

Comparing group and period positions, Magnesium (atomic number 12) in group 2 is the most electropositive among the given elements, as it is furthest to the left and lower than Sulfur and Fluorine, and Krypton does not readily form ions.

Key concepts

Understanding Periodic Table Trends

When exploring the periodic table, one will notice several predictable trends that are key to understanding the properties of elements, including their electropositivity. Electropositivity reflects an element's ability to donate electrons and form positive ions. As we move left across a period (row), elements tend to become more electropositive. This trend is due to the decreasing electronegativity, which is the pull that an atom has on shared electrons. Similarly, moving down a group (column), electropositivity increases because atoms have more electron shells, making their outer electrons easier to lose. This is because the increased distance and the added inner electrons shield the outer electrons from the nucleus's pull.

It's crucial to note that the most electropositive elements are found at the bottom left corner of the periodic table. The alkali metals, in group 1, are typically the most electropositive elements because they have a single electron in their outermost shell that they can easily lose to form a cation or a positive ion. Recognizing these trends can significantly aid in predicting the chemical behavior of elements in different contexts.

The Role of Atomic Number

Atomic number is a fundamental property that identifies each element uniquely. Defined as the number of protons found in the nucleus of an atom, the atomic number also determines an element's position in the periodic table. As the atomic number increases, new electron shells may begin to fill, or electrons may be added to the same shell but experience greater nuclear charge. This can either increase or decrease electropositivity, depending on whether an element is moving across a period or down a group.

In the context of the exercise, elements with atomic numbers 9, 12, 16, and 36 represent Fluorine, Magnesium, Sulfur, and Krypton, respectively. These atomic numbers help us to locate these elements on the periodic table and to evaluate their tendencies to form positive ions. Remembering that a lower atomic number does not necessarily mean an element is more electropositive, as the position in period and group must also be considered, is key to understanding chemical reactivity.

Group and Period in the Periodic Table

Groups and periods are the vertical and horizontal classifications in the periodic table that categorize elements by shared characteristics and properties due to their electron configurations. Elements in the same group often exhibit similar chemical behavior because they have the same number of valence electrons. For example, all elements in group 1 have one valence electron and are similarly electropositive.

When we talk about periods, this refers to the horizontal rows on the periodic table. As you move from left to right within a period, the electropositivity generally decreases due to the increasing nuclear charge and the associated increase in electronegativity. This trend is why, within a period, metals (found on the left side) tend to be more electropositive than nonmetals (found on the right side). The understanding of these periodic trends helps to explain the reactivity and formation of ions among different elements.

Formation of Positive Ions

The formation of positive ions, also known as cations, is a process intrinsic to elements that exhibit high electropositivity, primarily metals. An ion is formed when an atom gains or loses electrons, and it becomes charged. In the case of cations, this occurs when an electropositive atom loses one or more of its valence electrons, resulting in a positively charged ion. The ease with which an atom can lose electrons and the number of electrons lost depends on the element’s position in the periodic table.

For instance, alkali metals in group 1 easily lose their single valence electron, forming ions with a +1 charge. The element Magnesium, which was highlighted in the exercise as the most electropositive among the given options, tends to lose two electrons due to its placement in group 2, thereby forming a +2 charged ion. This behavior underpins many chemical reactions and is fundamental to various applications, from forming salts to conducting electricity in ionic compounds.