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(a) As described in Section \(7.7\), the alkali metals react with hydrogen to form hydrides and react with halogens-for example, fluorine-to form halides. Compare the roles of hydrogen and the halogen in these reactions. In what sense are the forms of hydrogen and halogen in the products alike? (b) Write balanced equations for the reaction of fluorine with calcium and for the reaction of hydrogen with calcium. What are the similarities among the products of these reactions?

Short Answer

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In the reactions with alkali metals, both hydrogen and halogens act as electronegative elements forming ionic bonds. Hydrogen forms hydrides (H-) and halogens form halides (such as F-). The balanced equations for the reactions of fluorine and hydrogen with calcium are: \(Ca + F_2 \rightarrow CaF_2\) and \(Ca + H_2 \rightarrow CaH_2\). The products, calcium fluoride (CaF2) and calcium hydride (CaH2), are both ionic compounds with similar chemical structures. The calcium ion (Ca2+) bonds with the halide ion (F-) in CaF2 and the hydride ion (H-) in CaH2, both resulting from the transfer of electrons from calcium to the electronegative elements.

Step by step solution

01

(a) Comparing roles of hydrogen and halogens in reactions with alkali metals

Hydrogen and halogens have similar roles when they react with alkali metals. They both act as electronegative elements that form ionic bonds with the electropositive alkali metals. The products of these reactions are hydrides for hydrogen and halides for halogens.
02

Similarities between forms of hydrogen and halogens in the products

In the products, hydrogen and halogens exist in the form of negatively charged ions (anions). The hydrogen takes the form of a hydride ion (H-) and the halogen takes the form of a halide ion (such as F- for fluorine). In both cases, they are negatively charged because they have gained an electron from the alkali metal.
03

(b) Reaction of fluorine with calcium

The balanced equation for the reaction of fluorine with calcium is: \[Ca + F_2 \rightarrow CaF_2\] Calcium forms an ionic bond with the two fluorine atoms, resulting in a calcium fluoride compound (CaF2).
04

Reaction of hydrogen with calcium

The balanced equation for the reaction of hydrogen with calcium is: \[Ca + H_2 \rightarrow CaH_2\] Calcium forms an ionic bond with the two hydrogen atoms, resulting in a calcium hydride compound (CaH2).
05

Similarities among the products

The products of these reactions, calcium fluoride (CaF2) and calcium hydride (CaH2), are both ionic compounds that have the same chemical structure. The electropositive calcium ion (Ca2+) bonds with the electronegative halide ion (F-) in CaF2 and the hydride ion (H-) in CaH2. The ionic bonding in both compounds is the result of the transfer of electrons from calcium to the electronegative elements, hydrogen, and fluorine.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Hydrides
Hydrides are compounds formed when hydrogen combines with other elements, typically metals. When talking about ionic hydrides, these usually involve hydrogen's reaction with alkali metals. Hydrogen acts as an electronegative element in these reactions. It forms an ionic bond by accepting an electron from the electropositive metal, becoming a negatively charged hydride ion, represented as \(H^-\).
  • This ion has a full, stable electron configuration, similar to helium.
  • Hydrides are often found in compounds like \(CaH_2\), where hydrogen bonds with calcium.
Hydrides showcase how hydrogen's versatility allows it to form various chemical bonds, particularly the ionic bond in such contexts.
Halides
Halides are similar to hydrides in that they are also ionic compounds, but these involve halogens: fluorine, chlorine, bromine, and iodine. Halogens are highly electronegative and readily accept electrons. Like hydrides, when halogens react with metals, they form negatively charged ions called halide ions.
  • An example is fluorine, which forms the fluoride ion \(F^-\) when it gains an electron.
  • Calcium fluoride \(CaF_2\) is an example of a halide where fluorine has combined with calcium.
Halides are notable for their strong ionic bonds due to the significant difference in electronegativity between the involved elements.
Electron Transfer
An essential aspect of forming ionic compounds is electron transfer. This process involves the movement of electrons from one atom to another, resulting in the formation of ions. In the reactions with calcium to form \(CaH_2\) and \(CaF_2\), calcium donates electrons to hydrogen and fluorine.
  • Calcium gives away two electrons, adopting a \(Ca^{2+}\) charge, which stabilizes the new ionic compound.
  • The hydrogen and fluoride ions receive these electrons, becoming stable negatively charged ions \(H^-\) and \(F^-\).
Electron transfer is crucial in chemical bonding, as it determines how ions bond together to form stable ionic compounds.
Chemical Bonding
Chemical bonding refers to the process where atoms combine to form compounds. In the case of hydrides and halides, the type of chemical bond formed is ionic. This bonding type occurs between metals and non-metals, like calcium with hydrogen or fluorine. Here, ionic bonding results from the electron transfer: one atom loses electrons while another gains them.
  • In \(CaH_2\) and \(CaF_2\), the ionic bond is formed between \(Ca^{2+}\) ions and \(H^-\) or \(F^-\) ions.
  • This results in the strong electrostatic forces that hold the compound together, giving ionic compounds their characteristic high melting and boiling points.
Understanding chemical bonding, especially the ionic type, is fundamental to grasping how different substances interact and form new compounds.

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