Question

Give some similarities that exist among the elements of Group 7.

Short answer

Group 7 elements, also known as halogens, have several similarities, including their electron configuration (ns^2 np^5), high reactivity, ability to form halide ions and ionic compounds, diatomic molecular structure, and electronegativity. These similarities can be attributed to their shared outer energy level containing seven valence electrons, which results in high reactivity and a tendency to form halide ions and ionic compounds. Moreover, their physical states differ along the group, with fluorine and chlorine being gases, bromine being a liquid, and iodine and astatine being solids at room temperature.

Step-by-step solution

1. Overview of Group 7 Elements (Halogens)

Group 7 elements, which are commonly referred to as halogens, consist of fluorine (F), chlorine (Cl), bromine (Br), iodine (I), and astatine (At). These elements share some similarities in terms of their physical and chemical properties, electron configurations, and reactivity.

2. Valence Electron Configuration

All halogens have seven valence electrons in their outer energy level. This characteristic electron configuration can be written as ns^2 np^5, where n represents the energy level of the outermost shell. Because they are just one electron short from achieving a stable noble gas configuration, halogens tend to be highly reactive, often gaining one electron to complete their valence shell.

3. High Reactivity

Group 7 elements are known for being very reactive, especially with alkali metals (Group 1) and alkaline earth metals (Group 2). This high reactivity is due to their electron configuration, which allows them to easily gain one electron to form a negatively charged ion, or a halide. The reactivity generally decreases as you go down the group, meaning that fluorine is the most reactive, while astatine is the least reactive.

4. Formation of Halide Ions and Ionic Compounds

Halogens readily form halide ions (X-) by gaining one electron from other atoms, which results in the formation of ionic compounds. For example, when a halogen reacts with an alkali metal, it forms an ionic compound called a metal halide: \[M + X_2 \longrightarrow MX_2\] Where M is a metal atom, X is a halogen atom, and X_2 is a diatomic halogen molecule.

5. Diatomic Molecules and Physical States

In their elemental form, halogens are diatomic molecules, meaning that they consist of two atoms bonded together (F_2, Cl_2, Br_2, I_2, At_2). Their physical states vary along the group - fluorine and chlorine are gases, bromine is a liquid, and iodine and astatine are solids at room temperature.

6. Electronegativity

Halogens are highly electronegative elements, meaning they have a strong tendency to attract electrons. Fluorine has the highest electronegativity of any element, with a value of 3.98 on the Pauling scale. The electronegativity values decrease as you go down the group due to increasing atomic size and decreasing effective nuclear charge experienced by the outer shell electrons. In summary, the elements in Group 7 share several key similarities, such as their valence electron configuration, high reactivity, formation of halide ions and ionic compounds, diatomic molecular structure, and electronegativity.

Key concepts

Halogens

Group 7 elements, also known as halogens, include fluorine, chlorine, bromine, iodine, and astatine. These elements are unique due to their ability to form salts when they react with metals, which is reflected in their name "halogen," meaning "salt-former."
They exhibit a range of physical states: from gaseous fluorine and chlorine, to liquid bromine, and solid iodine and astatine. This variety is tied to their increasing molecular weights and dispersion forces as you move down the group.
Halogens are crucial in both industrial and biological processes. For instance, chlorine is widely used in water purification, while iodine is essential for thyroid health in humans.

Valence Electron Configuration

The valence electron configuration of halogens is characterized by having seven electrons in the outermost shell: expressed as ns\(^2\) np\(^5\).
This configuration is close to the stable configuration of noble gases, which have eight valence electrons. Halogens, therefore, need to gain only one more electron to reach a stable, energy-efficient state.
Because of this, halogens are typically very keen on accepting electrons, which plays a key role in their chemical reactivities.

Reactivity of Halogens

Halogens are some of the most reactive elements in the periodic table. Their reactivity arises from their desire to achieve a full outer electron shell.
This makes them extremely reactive with metals such as those in Group 1 (alkali metals) and Group 2 (alkaline earth metals), often forming ionic compounds.
The reactivity of the halogens decreases down the group; for example, fluorine is the most reactive, whereas astatine is the least. This is because the atomic size increases, making it harder for the nucleus to attract additional electrons.

Diatomic Molecules

In nature, halogens do not exist in isolated atoms. Instead, they exist as diatomic molecules. This means they pair up to form molecules like F\(_2\), Cl\(_2\), Br\(_2\), I\(_2\), and At\(_2\).
This diatomic arrangement is favored because it allows the atoms to share electrons through a covalent bond, filling their outer electron shells.
The physical state of these diatomic molecules changes down the group from gases to liquids, and eventually to solids, as atomic and molecular weights increase.

Electronegativity

Electronegativity measures an atom's ability to attract and hold onto electrons. Halogens are among the most electronegative elements, with fluorine leading the pack due to its small size and high nuclear charge.
This high electronegativity means that halogens have a strong tendency to attract electrons and form negative ions (anions).
As you move down the group, the electronegativity decreases due to the increasing atomic size and the corresponding shielding effect, which reduces the nuclear attraction experienced by incoming electrons.