4. Chemical Bonds

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Chapter four of our Chemistry course e-book for the ENEM test is dedicated to the study of Chemical Bonds. This is an essential topic for understanding chemistry as it describes how atoms combine to form molecules and chemical compounds.

Chemical bonds are the forces that hold atoms together in molecules. There are three main types of chemical bonds: ionic bonds, covalent bonds, and metallic bonds. Each type of bond has its own unique properties, which are determined by how electrons are shared or transferred between atoms.

Ionic Bonds

Ionic bonds occur when an atom transfers one or more electrons to another atom. This results in ions (charged atoms) being attracted to each other due to their opposite charge. For example, table salt (NaCl) is formed by an ionic bond between sodium (Na) and chlorine (Cl). Sodium donates an electron to chlorine, forming a Na+ ion and a Cl- ion. These ions are attracted to each other, forming an ionic bond.

Covalent Bonds

Covalent bonds occur when two atoms share one or more pairs of electrons. This usually occurs between atoms that have high electronegativity, such as carbon (C), nitrogen (N), and oxygen (O). For example, the water molecule (H2O) is formed by covalent bonds between two hydrogen atoms (H) and an oxygen atom (O).

Metallic Connections

Metallic bonds occur between metal atoms. In a metallic bond, electrons are shared by all atoms in a three-dimensional structure. This results in unique properties such as high electrical and thermal conductivity.

Molecular Geometry and Polarity

In addition to understanding bond types, it is important to understand molecular geometry and polarity. Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. Polarity refers to the distribution of electrical charge in a molecule. Both are determined by how electrons are shared or transferred between atoms.

For example, the water molecule has an angular geometry and is polar, because oxygen attracts electrons more strongly than hydrogen. This results in a partial negative charge on oxygen and a partial positive charge on hydrogen.

Intermolecular Forces

Finally, intermolecular forces are the forces that hold molecules together. There are three main types: dipole-dipole forces, London dispersion forces, and hydrogen bonds. Dipole-dipole forces occur between polar molecules, while London dispersion forces occur between non-polar molecules. Hydrogen bonds are a special type of dipole-dipole force that occurs between hydrogen atoms and nitrogen, oxygen, or fluorine atoms.

Understanding chemical bonds is fundamental to understanding chemistry and is a topic frequently covered in ENEM. This chapter will provide you with a solid understanding of chemical bonds, preparing you for related questions on the exam.

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454.1. Chemical Bonds: Octet Theory