Question

Predict which element in each of the following pairs is more electronegative according to the general trends in the periodic table: (a) Br or Cl (b) O or S (c) Se or As (d) \(N\) or \(F\)

Short answer

(a) Cl, (b) O, (c) Se, (d) F

Step-by-step solution

Understanding Electronegativity

Electronegativity is the tendency of an atom to attract electrons toward itself in a chemical bond. In the periodic table, electronegativity generally increases across a period from left to right and decreases down a group from top to bottom.

Comparison of Elements in Pair (a)

For pair (a), we need to compare bromine (Br) and chlorine (Cl). Both elements are in the same group, but chlorine is above bromine. According to periodic trends, since chlorine is higher up in the group, it is more electronegative than bromine.

Comparison of Elements in Pair (b)

For pair (b), the elements are oxygen (O) and sulfur (S). They belong to the same group as well. Oxygen is located above sulfur in the periodic table, making it more electronegative than sulfur due to its higher position in the group.

Comparison of Elements in Pair (c)

Looking at pair (c), selenium (Se) and arsenic (As) are from the 4th period, where selenium is a group VI element and arsenic is a group V element. Electronegativity increases across a period, so selenium, being to the right of arsenic, is more electronegative.

Comparison of Elements in Pair (d)

In pair (d), consider nitrogen (N) and fluorine (F). These two are in the same period, but fluorine is on the far right. Since electronegativity increases across a period from left to right, fluorine is more electronegative than nitrogen.

Key concepts

Periodic Table Trends

The periodic table is a powerful tool to predict how elements behave chemically, especially when it comes to electronegativity. Electronegativity is the ability of an atom to attract electrons when it forms a chemical bond. In the periodic table, we observe several trends that help us quickly determine the electronegativity of elements.
Electronegativity increases from left to right across a period. This is because as we move across a period, the number of protons in the nucleus increases, pulling the electrons more strongly towards the nucleus. Conversely, electronegativity tends to decrease as we move down a group. This is due to an increase in the number of electron shells, which causes a shielding effect. This effect reduces the nucleus's pull on the bonding electrons due to the distance and inner electrons blocking the attractive force.
Understanding these trends is key to predicting and comparing the electronegativity of elements located in different positions on the periodic table.

Chemical Bonding

Chemical bonding involves atoms joining together, and electronegativity plays a crucial role in this. When atoms form bonds, their relative electronegativities determine how electrons are shared or transferred between them, giving rise to different types of bonds.

• Ionic Bonds: If one atom is significantly more electronegative than another, it can completely transfer an electron to the more electronegative atom, resulting in ionic bonding.
• Covalent Bonds: If two atoms have similar electronegativity, they share electrons to achieve a stable electron configuration, leading to covalent bonds.
• Polar Covalent Bonds: If there's a moderate difference in electronegativity, the shared electrons are more closely associated with the more electronegative atom, creating a polar covalent bond.

Electronegativity not only influences the type of bond formed but also affects the molecule's shape, reactivity, and interactions with other molecules.

Periodic Groups

The periodic table is organized into vertical columns known as groups or families. Elements in the same group have similar properties because they have the same number of valence electrons. The placement of an element within a group aids in predicting its electronegativity relative to other elements within the same group.
In any given group, elements higher up generally exhibit higher electronegativity than those placed lower. For example, chlorine (Cl) is more electronegative than bromine (Br) because it is positioned above bromine in the same group. This trend occurs because elements positioned higher have fewer electron shells, leading to less shielding and a stronger pull on bonding electrons by the nucleus.
Recognizing these group trends helps in comparing elements' electronegativity within the same column in the periodic table.

Element Comparison

Comparing elements is essential to determining how they interact chemically, especially in terms of electronegativity. By using periodic table trends as a guide, we can effectively compare the electronegativities of elements.
For example, in comparing pairs of elements like chlorine (Cl) and bromine (Br), or oxygen (O) and sulfur (S), understanding their positions within their groups or periods will tell us which one is more electronegative. Elements that are higher up in their groups, like Cl over Br, are typically more electronegative. Additionally, elements further to the right within a period, such as selenium (Se) compared to arsenic (As), reflect an increasing electronegativity.
Before making such comparisons, identifying whether the compared elements belong to the same group or period is crucial. Following this approach yields more precise and logical predictions regarding which element in each pair has a stronger tendency to attract electrons.