7.3 Lewis Symbols and Structures
3 min read•june 25, 2024
and structures are essential tools for understanding chemical bonding and . They provide a visual representation of and atomic arrangements, helping chemists predict molecular shapes and reactivity.
The guides electron distribution in , but exceptions exist. predicts molecular shapes based on electron repulsion, while explains equivalent bond formation. These concepts are crucial for understanding molecular behavior and properties.
Lewis Symbols and Structures
Lewis structures for molecules
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- Lewis symbols represent of an atom using dots around the , one dot per valence electron
- Valence electrons are the electrons in the outermost shell of an atom that participate in chemical bonding
- Lewis structures show the arrangement of atoms and in a molecule or ion using lines to represent bonds
- represented by a single line (-), by two lines (=), by three lines (≡)
- Atoms arranged with the least atom (usually the ) in the center, other atoms connected to it with single bonds
- Remaining electrons distributed as to satisfy the , each atom (except H) should have 8 electrons in its valence shell
- If not enough electrons for each atom to have an octet, rearrange electrons to form double or triple bonds
- Drawing Lewis structures involves determining total valence electrons, arranging atoms and connecting with single bonds, distributing remaining electrons as , and rearranging to form multiple bonds if needed
- can be calculated to determine the most stable Lewis structure
Octet rule and exceptions
- Octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable electron configuration with 8 electrons in their valence shell, similar to the nearest noble gas
- Exceptions to the octet rule include:
- Molecules with an odd number of electrons (NO, NO2) that cannot have an even number of electrons to satisfy the octet rule
- Molecules with less than 8 electrons around the central atom (BF3, BeH2) that are electron-deficient and highly reactive
- Molecules with more than 8 electrons around the central atom (SF6, PCl5) that have expanded octets and are stable due to the presence of empty d-orbitals
- Ions also follow the octet rule, with cations losing electrons and anions gaining electrons to achieve a stable electron configuration
- Some molecules can have multiple valid Lewis structures called
Molecular shapes from electron domains
- Electron domain theory () predicts molecular shapes based on the number of electron domains (bonds and lone pairs) around the central atom
- Electron domains repel each other and arrange themselves to minimize repulsion, resulting in specific geometries
- 2 domains: , 3 domains: , 4 domains: tetrahedral, 5 domains: , 6 domains:
- Molecular geometries are determined by the arrangement of atoms, not considering lone pairs, which affect bond angles and overall shape
- Examples: linear (2 bonding domains, 0 lone pairs), (3 bonding domains, 0 lone pairs), tetrahedral (4 bonding domains, 0 lone pairs)
- (3 bonding domains, 1 lone pair), (2 bonding domains, 2 lone pairs)
Molecular Structure and Bonding
- Electron-pair geometry describes the arrangement of all electron domains (bonding and non-bonding) around the central atom
- Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule, which can differ from the electron-pair geometry due to lone pairs
- Hybridization explains the formation of equivalent bonds in molecules by mixing atomic orbitals to create new hybrid orbitals
Key Terms to Review (44)
Bent: The term 'bent' refers to the angular shape or geometry of a molecule, particularly in the context of Lewis symbols and structures, as well as hybrid atomic orbitals. It describes the non-linear arrangement of atoms within a molecule, which is a crucial aspect of understanding molecular structure and bonding.
Bonds: Bonds refer to the chemical interactions that hold atoms together in a molecule. They are the fundamental forces that determine the stability and properties of chemical compounds.
Central Atom: The central atom is the main atom in a molecule or complex ion that is bonded to other atoms or ligands. It is the focal point around which the molecular structure is organized and plays a crucial role in determining the overall shape and properties of the chemical species.
Chemical symbol: A chemical symbol is a one- or two-letter abbreviation used to represent an element. Each symbol is derived from the element's name, often in Latin.
Chemical Symbol: A chemical symbol is a one- or two-letter abbreviation used to represent a specific chemical element. These symbols are the building blocks of chemical formulas and equations, providing a concise way to communicate the identities and quantities of elements involved in chemical processes.
Coordinate covalent bond: A coordinate covalent bond is a type of covalent bond in which one atom provides both electrons for the shared pair. This often occurs between a Lewis base and a Lewis acid.
Covalent Bond: A covalent bond is a chemical bond formed by the sharing of one or more pairs of electrons between two atoms. This type of bond is responsible for the stability and structure of many molecules and is a fundamental concept in understanding the topics of 7.2 Covalent Bonding, 7.3 Lewis Symbols and Structures, 7.4 Formal Charges and Resonance, 7.5 Strengths of Ionic and Covalent Bonds, 7.6 Molecular Structure and Polarity, and 8.1 Valence Bond Theory.
Diatomic molecule: A diatomic molecule is a molecule that consists of two atoms, which can be either of the same element or different elements. These molecules are significant in chemistry because they can form covalent bonds and are fundamental in understanding molecular structures and interactions. Common examples include hydrogen (H$_2$), oxygen (O$_2$), and nitrogen (N$_2$), which play essential roles in various chemical reactions and processes.
Double bonds: Double bonds are a type of chemical bond that involves the sharing of four electrons between two atoms, resulting in a stronger connection than a single bond. This occurs when two pairs of valence electrons are shared, typically between nonmetals, and is represented in structural formulas by two lines connecting the bonded atoms. Understanding double bonds is crucial for predicting molecular shapes, reactivity, and properties of compounds.
Electron domain theory: Electron domain theory is a model used to predict the geometry of molecules based on the arrangement of electron domains around a central atom. Each electron domain, which can be a bonding pair of electrons, a lone pair, or a multiple bond, exerts a repulsive force on other domains, leading to specific spatial arrangements that minimize these repulsions. This theory is essential for understanding molecular shapes and the behavior of atoms in chemical bonding.
Electronegative: Electronegativity is a chemical property that describes the ability of an atom to attract shared electrons in a chemical bond. Atoms with high electronegativity values are considered electronegative, meaning they have a strong tendency to attract and hold onto electrons.
Formal charge: Formal charge is a theoretical charge assigned to an atom in a molecule, calculated based on the number of valence electrons minus the sum of non-bonding electrons and half of the bonding electrons. It helps determine the most stable Lewis structure for a molecule.
Formal Charge: Formal charge is a concept in chemistry that helps determine the distribution of electrons in a molecule or ion. It is a way to assign a partial charge to each atom in a molecule based on the difference between the number of valence electrons an atom would have in an isolated, neutral state and the number of electrons it appears to have in the molecule.
Free radicals: Free radicals are molecules or atoms that possess an unpaired electron in their outermost shell, making them highly reactive. They can engage in various chemical reactions, often causing damage to other molecules.
Gilbert N. Lewis: Gilbert Newton Lewis was an American physical chemist who made significant contributions to the understanding of chemical bonding and the nature of matter. He is best known for his development of the Lewis dot structure, which provides a visual representation of chemical bonding and the arrangement of valence electrons in atoms and molecules.
Hybridization: Hybridization is the concept in chemistry where atomic orbitals combine to form new hybrid orbitals that are suitable for the pairing of electrons to form chemical bonds. This idea helps explain molecular geometry and bonding properties, linking the arrangement of atoms in a molecule to their electron configurations and the types of bonds formed.
Hypervalent molecules: Hypervalent molecules are species in which a central atom forms more than four bonds or has more than eight electrons in its valence shell. These molecules defy the octet rule, common examples include sulfur hexafluoride (SF_6) and phosphorus pentachloride (PCl_5).
Ionic bond: An ionic bond is a type of chemical bond formed through the electrostatic attraction between oppositely charged ions, typically resulting from the transfer of electrons from one atom to another. This bond occurs mainly between metals and nonmetals, where metals lose electrons to become positively charged cations and nonmetals gain those electrons to become negatively charged anions. Understanding ionic bonds is crucial for visualizing how atoms interact and create stable compounds.
Lewis Structures: Lewis structures, also known as Lewis dot diagrams, are a visual representation of the bonding between atoms in a molecule. They depict the arrangement of atoms and the sharing or transfer of valence electrons, providing insights into the structure and properties of chemical compounds.
Lewis symbol: A Lewis symbol is a notation that represents the valence electrons of an atom as dots around the element's symbol. It helps visualize the bonding capacity of an element in molecules.
Lewis Symbols: Lewis symbols, also known as electron dot diagrams, are a graphical representation of the valence electron configuration of an atom or molecule. They depict the arrangement of valence electrons around the nucleus of an atom, which is crucial for understanding chemical bonding and reactivity.
Linear: In the context of Lewis symbols and structures, the term 'linear' refers to a molecular geometry where the atoms are arranged in a straight line, with two substituents or bonding pairs of electrons around a central atom.
Lone pairs: Lone pairs are pairs of valence electrons that are not involved in chemical bonding. They are typically represented as dots in Lewis structures.
Lone Pairs: Lone pairs, also known as unshared electron pairs, are pairs of valence electrons that are not involved in the formation of covalent bonds between atoms. They occupy space around the central atom and contribute to the overall geometry and reactivity of a molecule.
Molecular Geometry: Molecular geometry refers to the three-dimensional arrangement of atoms in a molecule. It is a fundamental concept in chemistry that describes the spatial configuration of atoms bonded together and plays a crucial role in understanding the properties and reactivity of molecules.
Octahedral: Octahedral is a molecular geometry where a central atom is surrounded by six atoms or ligands placed at the vertices of an octahedron. This arrangement results in 90° bond angles between adjacent atoms.
Octahedral: Octahedral is a geometric shape in which a central atom or ion is surrounded by six other atoms or ions arranged in a three-dimensional, octagonal configuration. This shape is commonly observed in the context of Lewis Symbols and Structures, Hybrid Atomic Orbitals, and Coordination Chemistry of Transition Metals.
Octet rule: The octet rule states that atoms tend to form bonds in such a way that they achieve eight electrons in their valence shell, gaining a stable electron configuration similar to noble gases. This rule is fundamental for understanding molecular structures and chemical bonding.
Octet Rule: The octet rule is a fundamental concept in chemistry that states that atoms tend to form stable configurations by attaining a full outer electron shell, typically containing eight electrons. This principle helps explain the formation of ionic and covalent bonds, as well as the stability of various chemical compounds.
Polyatomic Ion: A polyatomic ion is a charged species composed of two or more covalently bonded atoms. These ions carry an overall positive or negative charge and play a crucial role in chemical nomenclature and Lewis symbol representations.
Polyatomic ions: Polyatomic ions are charged particles composed of two or more covalently bonded atoms. They act as a single unit in chemical reactions and possess a net charge due to the loss or gain of electrons.
Resonance Structures: Resonance structures are a set of contributing structures that represent the delocalization of electrons in a molecule, allowing for the stabilization of the overall structure. This concept is crucial in understanding the behavior and properties of various organic compounds, particularly those involving conjugated systems and aromatic rings.
Single bond: A single bond is a chemical bond between two atoms involving the sharing of one pair of electrons. It is represented by a single line between the two atoms in Lewis structures.
Single bonds: Single bonds are a type of chemical bond where two atoms share one pair of electrons, resulting in a stable connection between them. This bond is represented by a single line between the atomic symbols in Lewis structures, indicating the sharing of one electron from each atom. Single bonds are crucial in forming stable molecules and play a significant role in understanding molecular geometry and reactivity.
Smalley: Richard Smalley was an American chemist who won the Nobel Prize in Chemistry in 1996 for his discovery of fullerenes, a new form of carbon. His work significantly advanced the understanding of molecular structures and bonding.
Trigonal bipyramidal: Trigonal bipyramidal is a molecular geometry where a central atom is surrounded by five atoms or groups of atoms. This shape consists of three atoms in an equatorial plane and two atoms in axial positions above and below this plane.
Trigonal Bipyramidal: Trigonal bipyramidal is a molecular geometry in which five atoms or groups of atoms are arranged around a central atom in a three-dimensional shape consisting of a triangular base and two pyramids at the top and bottom. This geometry is commonly observed in certain chemical compounds and is an important concept in the study of Lewis Symbols and Structures, as well as Hybrid Atomic Orbitals.
Trigonal planar: A trigonal planar molecular geometry occurs when a molecule has three atoms bonded to a central atom with no lone pairs, resulting in a flat, triangular shape. The bond angles are typically 120 degrees.
Trigonal Planar: Trigonal planar is a molecular geometry in which a central atom is bonded to three other atoms, with all the atoms lying in the same plane and forming a triangular arrangement around the central atom.
Trigonal Pyramidal: Trigonal pyramidal is a molecular geometry in which a central atom is bonded to three atoms and one lone pair of electrons, resulting in a pyramid-like shape. This geometry is commonly observed in molecules and is an important concept in the understanding of Lewis Symbols and Structures as well as Hybrid Atomic Orbitals.
Triple Bonds: A triple bond is a type of covalent bond where three pairs of electrons are shared between two atoms. This strong bond occurs when atoms, typically nonmetals, share three electrons to achieve greater stability and complete their valence shells. Triple bonds result in a linear molecular geometry, which influences the properties and reactivity of the molecules that contain them.
Valence electrons: Valence electrons are the outermost electrons of an atom and are involved in forming chemical bonds. They determine an element's chemical properties and reactivity.
Valence Electrons: Valence electrons are the outermost electrons in an atom that participate in chemical reactions and bonding. They are the electrons in the highest occupied energy level of an atom and are responsible for an element's chemical properties and behavior.
VSEPR theory: VSEPR theory, or Valence Shell Electron Pair Repulsion theory, is a model used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shell of central atoms. This theory emphasizes that the shape of a molecule is determined by the spatial arrangement of electron pairs, including both bonding and lone pairs, which minimizes the repulsive forces between them.