2.1 Atoms, Molecules, and Chemical Bonds
3 min read•august 7, 2024
Atoms, molecules, and chemical bonds form the foundation of life's chemistry. These tiny building blocks combine in countless ways, creating the diverse substances that make up our world.
Understanding atomic structure and chemical bonding is key to grasping how living things function. From DNA to proteins, these concepts explain how biological molecules form and interact within organisms.
Atomic Structure
Subatomic Particles
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- Atoms are the basic units of matter and the defining structure of elements
- Atoms consist of three subatomic particles: protons, neutrons, and electrons
- Protons have a positive charge, are located in the nucleus, and determine the of an
- Neutrons have no charge, are located in the nucleus, and contribute to the mass of an atom
- Electrons have a negative charge, occupy the space outside the nucleus, and are involved in chemical bonding
- Electrons are arranged in energy levels or shells around the nucleus (1s, 2s, 2p, 3s, etc.)
- The configuration of an atom determines its chemical properties and bonding behavior
Atomic Models
- The Bohr model of the atom depicts electrons orbiting the nucleus in fixed circular paths or shells
- This model is useful for understanding the basic structure of an atom but has limitations
- The quantum mechanical model describes the probability of finding an electron in a certain region around the nucleus
- This model uses complex mathematical equations to represent the behavior of electrons as wave functions
Chemical Building Blocks
Elements and Atoms
- An element is a pure substance composed of one type of atom
- Elements are represented by unique chemical symbols (H for hydrogen, O for oxygen, etc.)
- The periodic table organizes elements based on their atomic number and chemical properties
- Atoms of the same element have the same number of protons but may vary in the number of neutrons (isotopes)
- Isotopes of an element have different masses but similar chemical properties (carbon-12 and carbon-14)
Molecules and Compounds
- A is a group of two or more atoms held together by chemical bonds
- Molecules can be composed of the same type of atom (O₂) or different types of atoms (H₂O)
- A is a substance made up of two or more different elements chemically combined in a fixed ratio
- Compounds have properties that differ from those of their constituent elements (NaCl, table salt)
- The chemical formula of a compound indicates the number and type of atoms present (CH₄, methane)
Chemical Bonds
Covalent Bonds
- A is a type of chemical bond formed by the sharing of electrons between atoms
- Covalent bonds form when atoms share one or more pairs of to achieve a stable electron configuration
- Single covalent bonds involve the sharing of one pair of electrons (H₂)
- Double and triple covalent bonds involve the sharing of two or three pairs of electrons, respectively (O₂, N₂)
- Covalent bonds are common in molecules and compounds composed of nonmetals (CH₄, H₂O)
Ionic Bonds
- An is a type of chemical bond formed by the electrostatic attraction between oppositely charged ions
- Ionic bonds form when one atom (typically a metal) transfers one or more electrons to another atom (typically a nonmetal)
- The atom that loses electrons becomes a positively charged cation (Na⁺)
- The atom that gains electrons becomes a negatively charged anion (Cl⁻)
- Ionic compounds are held together by the strong electrostatic forces between the cations and anions (NaCl, table salt)
Hydrogen Bonds
- A hydrogen bond is a type of intermolecular force that occurs between a hydrogen atom bonded to a highly electronegative atom (N, O, or F) and another electronegative atom
- Hydrogen bonds are weaker than covalent or ionic bonds but play a crucial role in the properties of many substances
- is responsible for the unique properties of water (high boiling point, surface tension, and cohesion)
- Hydrogen bonds are important in the structure and function of biological molecules (DNA, proteins)
Key Terms to Review (19)
Atomic number: The atomic number is the number of protons found in the nucleus of an atom, which uniquely identifies an element and determines its position on the periodic table. Each element has a distinct atomic number, which not only defines the type of element but also influences its chemical properties and behavior in reactions. The atomic number is crucial for understanding how atoms interact to form molecules and establish chemical bonds.
Avogadro's Law: Avogadro's Law states that equal volumes of gases, at the same temperature and pressure, contain an equal number of molecules. This principle connects the concepts of moles, molecular volume, and gas behavior, establishing a foundational understanding of the relationship between gas quantities and their properties in chemistry.
Compound: A compound is a substance formed when two or more different elements chemically bond together in fixed proportions. Compounds can have properties that are very different from the individual elements that make them up, and they play a crucial role in forming the diverse range of materials and substances found in nature. Understanding compounds is essential for grasping how molecules interact and how chemical reactions occur.
Covalent Bond: A covalent bond is a type of chemical bond where two atoms share one or more pairs of electrons in order to achieve stability. This sharing allows each atom to attain a full outer shell of electrons, typically following the octet rule, which states that atoms are most stable when they have eight electrons in their valence shell. Covalent bonds can form between identical or different elements and are crucial for the formation of molecules in biological systems.
Electron: An electron is a subatomic particle with a negative electric charge, typically found in the outer regions of an atom. Electrons play a crucial role in chemical bonding, as their interactions with other electrons and atomic nuclei determine how atoms connect and form molecules. These tiny particles are fundamental to the structure of matter, influencing the behavior of atoms in various chemical reactions.
Electronegativity: Electronegativity is the measure of an atom's ability to attract and hold onto electrons when it is part of a compound. This property plays a crucial role in determining how atoms interact, bond, and form molecules, influencing the polarity of bonds and the behavior of substances in chemical reactions.
Element: An element is a pure substance made up of only one type of atom, distinguished by its atomic number, which represents the number of protons in its nucleus. Elements are the fundamental building blocks of matter, and they combine in various ways to form compounds and molecules, which are essential for life and chemical reactions.
Homogeneous mixture: A homogeneous mixture is a combination of two or more substances that are evenly distributed throughout the mixture, resulting in a uniform composition. In these mixtures, the individual components cannot be distinguished from one another, even under a microscope. This uniformity occurs at the molecular level and is crucial for understanding how different substances interact in chemical processes.
Hydrogen Bonding: Hydrogen bonding is a weak attraction between a hydrogen atom covalently bonded to an electronegative atom and another electronegative atom. This interaction is crucial for many biological processes and contributes significantly to the unique properties of water, as well as the structure and function of biomolecules like DNA. The specific nature of hydrogen bonds allows for the stabilization of complex molecular structures, influencing both physical properties and biological functions.
Ionic bond: An ionic bond is a type of chemical bond formed through the electrostatic attraction between oppositely charged ions. This occurs when one atom donates an electron to another atom, resulting in a positive ion (cation) and a negative ion (anion), which are held together by their opposite charges. Ionic bonds are typically formed between metals and nonmetals, showcasing the transfer of electrons as a key feature of their interaction.
Law of Conservation of Mass: The law of conservation of mass states that matter cannot be created or destroyed in a chemical reaction. This principle means that the total mass of reactants before a reaction is equal to the total mass of products after the reaction. This law is fundamental to understanding how atoms and molecules interact during chemical reactions, emphasizing that all atoms present at the start must be accounted for in the products formed.
Molecule: A molecule is a group of two or more atoms bonded together, representing the smallest fundamental unit of a chemical compound that retains its chemical properties. Molecules can consist of the same type of atoms, like oxygen (O2), or different types, such as water (H2O). Understanding molecules is crucial because they are the building blocks of all matter and play a key role in chemical reactions and biological processes.
Neutron: A neutron is a subatomic particle found in the nucleus of an atom, which has no electrical charge and a mass slightly greater than that of a proton. Neutrons play a critical role in stabilizing the nucleus by offsetting the repulsive forces between positively charged protons. They also influence the atomic mass and are essential in nuclear reactions, including fission and fusion processes.
Polarity: Polarity refers to the distribution of electrical charge around atoms and molecules, which affects their interactions and behaviors. Molecules can be polar or nonpolar depending on the arrangement of atoms and the electronegativity differences between them. This concept is crucial for understanding how substances interact with each other, particularly in biological systems.
Products: In chemistry, products are the substances that result from a chemical reaction, created when reactants undergo a transformation. Understanding products is crucial because they demonstrate how atoms and molecules interact and change during reactions, providing insight into the conservation of mass and energy transformations involved in these processes.
Proton: A proton is a subatomic particle found in the nucleus of an atom, carrying a positive electric charge. Protons, along with neutrons, make up the atomic nucleus, and they play a crucial role in determining the identity and properties of an element. The number of protons in an atom defines its atomic number, which directly influences its chemical behavior and bonding characteristics.
Reactants: Reactants are the starting substances in a chemical reaction that undergo transformation to form products. They are crucial because they provide the necessary atoms and molecules that interact during the reaction, leading to new compounds. Understanding reactants is key to grasping how chemical bonds break and form, as well as how energy changes throughout the process.
Solution: A solution is a homogeneous mixture composed of two or more substances, where one substance (the solute) is dissolved in another (the solvent). This concept is essential in understanding how substances interact at the molecular level and how chemical reactions occur, as solutions provide an environment where solutes can be uniformly distributed and chemically react with other compounds.
Valence Electrons: Valence electrons are the electrons located in the outermost shell of an atom and are crucial in determining how an atom interacts with others during chemical bonding. These electrons play a key role in the formation of molecules and the types of chemical reactions that an atom can undergo. The number of valence electrons directly influences an element's reactivity, electronegativity, and the nature of the bonds it forms.