File Name: chemical structure and bonding .zip
This chapter provides a review of material covered in a standard freshman general-chemistry course through a discussion of the following topics:. Organic chemistry studies the properties and reactions of organic compounds.
1: Structure and Bonding
Chemical bonding describes a variety of interactions that hold atoms together in chemical compounds. Chemical bonds are the connections between atoms in a molecule. These bonds include both strong intramolecular interactions, such as covalent and ionic bonds. They are related to weaker intermolecular forces, such as dipole-dipole interactions, the London dispersion forces, and hydrogen bonding. The weaker forces will be discussed in a later concept. Chemical bonds : This pictures shows examples of chemical bonding using Lewis dot notation.
Hydrogen and carbon are not bonded, while in water there is a single bond between each hydrogen and oxygen. Bonds, especially covalent bonds, are often represented as lines between bonded atoms. Acetylene has a triple bond, a special type of covalent bond that will be discussed later. Chemical bonds are the forces of attraction that tie atoms together.
The nature of the interaction between the atoms depends on their relative electronegativity. Atoms with equal or similar electronegativity form covalent bonds, in which the valence electron density is shared between the two atoms. The electron density resides between the atoms and is attracted to both nuclei.
This type of bond forms most frequently between two non- metals. When there is a greater electronegativity difference than between covalently bonded atoms, the pair of atoms usually forms a polar covalent bond. The electrons are still shared between the atoms, but the electrons are not equally attracted to both elements. As a result, the electrons tend to be found near one particular atom most of the time.
Again, polar covalent bonds tend to occur between non-metals. Finally, for atoms with the largest electronegativity differences such as metals bonding with nonmetals , the bonding interaction is called ionic, and the valence electrons are typically represented as being transferred from the metal atom to the nonmetal.
Once the electrons have been transferred to the non-metal, both the metal and the non-metal are considered to be ions. The two oppositely charged ions attract each other to form an ionic compound. Covalent interactions are directional and depend on orbital overlap, while ionic interactions have no particular directionality. Each of these interactions allows the atoms involved to gain eight electrons in their valence shell, satisfying the octet rule and making the atoms more stable.
These atomic properties help describe the macroscopic properties of compounds. For example, smaller covalent compounds that are held together by weaker bonds are frequently soft and malleable. On the other hand, longer-range covalent interactions can be quite strong, making their compounds very durable. Ionic compounds, though composed of strong bonding interactions, tend to form brittle crystalline lattices.
Ionic bonds are a subset of chemical bonds that result from the transfer of valence electrons, typically between a metal and a nonmetal. Ionic bonds are a class of chemical bonds that result from the exchange of one or more valence electrons from one atom, typically a metal, to another, typically a nonmetal. This electron exchange results in an electrostatic attraction between the two atoms called an ionic bond. An atom that loses one or more valence electrons to become a positively charged ion is known as a cation, while an atom that gains electrons and becomes negatively charged is known as an anion.
This exchange of valence electrons allows ions to achieve electron configurations that mimic those of the noble gases, satisfying the octet rule. The octet rule states that an atom is most stable when there are eight electrons in its valence shell. Atoms with less than eight electrons tend to satisfy the duet rule, having two electrons in their valence shell. By satisfying the duet rule or the octet rule, ions are more stable. An anion is indicated by a negative superscript charge - something to the right of the atom.
Similarly, if a chlorine atom gains an extra electron, it becomes the chloride ion, Cl —. Both ions form because the ion is more stable than the atom due to the octet rule. Once the oppositely charged ions form, they are attracted by their positive and negative charges and form an ionic compound. Ionic bonds are also formed when there is a large electronegativity difference between two atoms. This difference causes an unequal sharing of electrons such that one atom completely loses one or more electrons and the other atom gains one or more electrons, such as in the creation of an ionic bond between a metal atom sodium and a nonmetal fluorine.
Formation of sodium fluoride : The transfer of electrons and subsequent attraction of oppositely charged ions. To determine the chemical formulas of ionic compounds, the following two conditions must be satisfied:. This is because Mg has two valence electrons and it would like to get rid of those two ions to obey the octet rule. Fluorine has seven valence electrons and usually forms the F — ion because it gains one electron to satisfy the octet rule.
Therefore, the formula of the compound is MgF 2. The subscript two indicates that there are two fluorines that are ionically bonded to magnesium. On the macroscopic scale, ionic compounds form crystalline lattice structures that are characterized by high melting and boiling points and good electrical conductivity when melted or solubilized.
Fluorine has seven valence electrons and as such, usually forms the F — ion because it gains one electron to satisfy the octet rule. Covalent bonds are a class of chemical bonds where valence electrons are shared between two atoms, typically two nonmetals. The formation of a covalent bond allows the nonmetals to obey the octet rule and thus become more stable. For example:. Covalent bonding requires a specific orientation between atoms in order to achieve the overlap between bonding orbitals.
Sigma bonds are the strongest type of covalent interaction and are formed via the overlap of atomic orbitals along the orbital axis. The overlapped orbitals allow the shared electrons to move freely between atoms. Pi bonds are a weaker type of covalent interactions and result from the overlap of two lobes of the interacting atomic orbitals above and below the orbital axis. Unlike an ionic bond, a covalent bond is stronger between two atoms with similar electronegativity. For atoms with equal electronegativity, the bond between them will be a non- polar covalent interaction.
In non-polar covalent bonds, the electrons are equally shared between the two atoms. For atoms with differing electronegativity, the bond will be a polar covalent interaction, where the electrons will not be shared equally. Ionic solids are generally characterized by high melting and boiling points along with brittle, crystalline structures. Covalent compounds, on the other hand, have lower melting and boiling points. Unlike ionic compounds, they are often not soluble in water and do not conduct electricity when solubilized.
Key Takeaways Key Points Chemical bonds are forces that hold atoms together to make compounds or molecules. Chemical bonds include covalent, polar covalent, and ionic bonds. Atoms with relatively similar electronegativities share electrons between them and are connected by covalent bonds.
Atoms with large differences in electronegativity transfer electrons to form ions. The ions then are attracted to each other. This attraction is known as an ionic bond. Key Terms bond : A link or force between neighboring atoms in a molecule or compound.
This attraction usually forms between a metal and a non-metal. This interaction typically forms between two non-metals.
Ionic Bonds Ionic bonds are a subset of chemical bonds that result from the transfer of valence electrons, typically between a metal and a nonmetal. Learning Objectives Summarize the characteristic features of ionic bonds. Key Takeaways Key Points Ionic bonds are formed through the exchange of valence electrons between atoms, typically a metal and a nonmetal. The loss or gain of valence electrons allows ions to obey the octet rule and become more stable.
Ionic compounds are typically neutral. Therefore, ions combine in ways that neutralize their charges. Key Terms valence electrons : The electrons of an atom that can participate in the formation of chemical bonds with other atoms. They are the furthest electrons from the nucleus. Covalent Bonds Covalent bonding involves two atoms, typically nonmetals, sharing valence electrons. Learning Objectives Differentiate between covalent and ionic bonds.
Key Takeaways Key Points Covalent bonds involve two atoms, typically nonmetals, that share electron density to form strong bonding interactions.
Covalent bonds include single, double, and triple bonds and are composed of sigma and pi bonding interactions where 2, 4, or 6 electrons are shared respectively. Covalent compounds typically have lower melting and boiling points than ionic compounds. Key Terms electronegativity : The tendency of an atom or molecule to attract electrons and thus form bonds. Licenses and Attributions.
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covalent bonds. Origins of Organic Chemistry. Page 3. ▫ Review ideas from general chemistry: atoms.
Structure and Bonding
A chemical bond is a lasting attraction between atoms , ions or molecules that enables the formation of chemical compounds. The bond may result from the electrostatic force of attraction between oppositely charged ions as in ionic bonds or through the sharing of electrons as in covalent bonds. The strength of chemical bonds varies considerably; there are "strong bonds" or "primary bonds" such as covalent, ionic and metallic bonds, and "weak bonds" or "secondary bonds" such as dipole—dipole interactions , the London dispersion force and hydrogen bonding. Since opposite charges attract via a simple electromagnetic force , the negatively charged electrons that are orbiting the nucleus and the positively charged protons in the nucleus attract each other.