Covalent Bonds and Lewis Formulas
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Questions and Answers

What type of bonds are formed from the head-on overlap of atomic orbitals?

  • Pi bonds
  • Sigma bonds (correct)
  • Delta bonds
  • Phi bonds

    • A single covalent bond can be a pi bond.

    False

    Describe where the electron density is concentrated in a sigma bond.

    Along the bond axis between the two nuclei.

    Pi bonds are formed from the _____ combination of adjacent p orbitals.

    <p>lateral</p> Signup and view all the answers

    Match the following bond types to their characteristics:

    <p>Sigma bond = Head-on overlap of atomic orbitals Pi bond = Lateral overlap of p orbitals Double bond = One sigma bond and one pi bond Triple bond = One sigma bond and two pi bonds</p> Signup and view all the answers

    In which type of bonds are pi bonds found?

    <p>Double and triple bonds</p> Signup and view all the answers

    The electron density in a pi bond is symmetrical about the bond axis.

    <p>False</p> Signup and view all the answers

    What type of atomic orbitals combine to form sigma bonds?

    <p>s orbitals and p orbitals.</p> Signup and view all the answers

    What is the purpose of sharing electrons in a covalent bond?

    <p>To achieve an electron configuration similar to a noble gas</p> Signup and view all the answers

    The octet rule states that atoms prefer to have 10 electrons in their valence shell.

    <p>False</p> Signup and view all the answers

    What is meant by 'expanding the octet'?

    <p>It refers to the ability of a central atom to accommodate more than 8 electrons in its outer shell.</p> Signup and view all the answers

    In drawing Lewis formulas, the total number of ______ electrons must be counted first.

    <p>valence</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Covalent bond = Sharing of electron pairs between non-metal atoms Lewis structure = Diagram showing electron pairs around atoms Octet rule = Atoms' tendency to have 8 electrons in their valence shell Electron deficient = When a central atom has less than 8 electrons in its outer shell</p> Signup and view all the answers

    Which of the following is NOT a characteristic of Lewis formulas?

    <p>They must show only one type of atom</p> Signup and view all the answers

    A Lewis formula can be represented only by lines and cannot use dots or crosses.

    <p>False</p> Signup and view all the answers

    How many electrons does a stable atom generally aim to have in its valence shell?

    <p>8</p> Signup and view all the answers

    What is the bond angle in a linear molecule?

    <p>180 degrees</p> Signup and view all the answers

    Lone pairs repel less than bonding pairs according to VSEPR theory.

    <p>False</p> Signup and view all the answers

    What is the abbreviation for Valence Shell Electron Pair Repulsion Theory?

    <p>VSEPR</p> Signup and view all the answers

    In three electron domains, the molecular shape is referred to as __________.

    <p>triangular planar</p> Signup and view all the answers

    According to VSEPR theory, which of the following statements is true?

    <p>All lone pairs and bonding pairs spread out to minimize repulsion.</p> Signup and view all the answers

    Name one example of a molecule that has a linear shape.

    <p>BeCl2, CO2, or HC≡CH</p> Signup and view all the answers

    Match the following molecular shapes with their corresponding electron domains:

    <p>Linear = Two electron domains Triangular Planar = Three electron domains Tetrahedral = Four electron domains Trigonal Bipyramidal = Five electron domains</p> Signup and view all the answers

    The regions of negative cloud charge are known as __________.

    <p>domains</p> Signup and view all the answers

    What is the bond angle in a tetrahedral arrangement observed in diamond?

    <p>109.5 degrees</p> Signup and view all the answers

    Diamond is known to be the second hardest substance after graphite.

    <p>False</p> Signup and view all the answers

    Name one application of diamond due to its hardness.

    <p>Drills or glass-cutting tools</p> Signup and view all the answers

    In giant covalent structures, bonds between atoms continue ______, forming a lattice.

    <p>indefinitely</p> Signup and view all the answers

    Match the following allotropes of carbon with their characteristics:

    <p>Graphite = Good conductor of electricity Diamond = Hardest known natural material Buckminsterfullerene = Molecular form consisting of 60 carbon atoms Graphene = Single layer of carbon atoms arranged in a 2D lattice</p> Signup and view all the answers

    What elements form the triple bond in hydrogen cyanide?

    <p>Carbon and Nitrogen</p> Signup and view all the answers

    Hydrogen cyanide contains two sigma bonds.

    <p>True</p> Signup and view all the answers

    What is the hybridization of nitrogen in hydrogen cyanide?

    <p>sp</p> Signup and view all the answers

    The triple bond in hydrogen cyanide consists of one ______ and two _____ bonds.

    <p>sigma, pi</p> Signup and view all the answers

    Match the following components with their contributions in hydrogen cyanide:

    <p>Hydrogen (H) = Forms a sigma bond with Carbon Carbon (C) = Forms a sigma bond with Nitrogen Nitrogen (N) = Contributes to the triple bond Triple bond = Consists of one sigma and two pi bonds</p> Signup and view all the answers

    What happens to the energy needed to overcome the forces of attraction between noble gas atoms as the number of electrons increases?

    <p>It increases</p> Signup and view all the answers

    A larger surface area of a molecule results in lower melting and boiling points.

    <p>False</p> Signup and view all the answers

    What type of forces are increased by larger surface areas in molecules?

    <p>London (dispersion) forces</p> Signup and view all the answers

    The attraction between a permanent dipole on one molecule and a permanent dipole on another is known as __________.

    <p>dipole-dipole bonding</p> Signup and view all the answers

    Which statement best describes the interaction between the delta negative end of one polar molecule and the delta positive end of another?

    <p>Attraction</p> Signup and view all the answers

    Match the types of molecular interactions with their descriptions:

    <p>London forces = Attraction due to temporary dipoles Permanent dipole-dipole = Attraction between permanent dipoles Hydrogen bonding = Strong attraction involving hydrogen bonds</p> Signup and view all the answers

    All molecules have permanent dipoles.

    <p>False</p> Signup and view all the answers

    What effect does a permanent dipole have on molecular interactions compared to temporary dipoles?

    <p>It creates additional attraction through dipole-dipole bonding.</p> Signup and view all the answers

    Study Notes

    Covalent Bonds

    • Covalent bonds form between non-metals
    • Electrons are shared, not transferred
    • Atoms form covalent bonds to achieve a stable electron configuration, similar to noble gases
    • Covalent bonds occur when atomic orbitals overlap, forming a molecular orbital

    Lewis Formulas

    • Lewis formulas are simplified diagrams showing electron pairs around atoms
    • Electron pairs can be represented by dots, crosses, or lines
    • The octet rule states that atoms tend to gain a valence shell of 8 electrons

    Multiple Bonds

    • Non-metals can share more than one pair of electrons forming multiple bonds
    • Single bonds share 2 electrons
    • Double bonds share 4 electrons
    • Triple bonds share 6 electrons
    • Bond energy and bond length are inversely related, stronger bonds have higher energy and shorter lengths.

    Coordinate Bonds (Dative Covalent Bonds)

    • Coordinate bonds occur when one atom donates both electrons in a bond
    • Electron deficient atom accepts the pair
    • The donating atom has a lone pair of electrons
    • Example: ammonium ion (NH4+)

    Shapes of Molecules (VSEPR Theory)

    • Valence Shell Electron Pair Repulsion theory predicts molecular shapes
    • Electron pairs (bonding and lone pairs) arrange themselves as far apart as possible
    • Lone pairs repel more strongly than bonding pairs
    • Common shapes: linear, trigonal planar, tetrahedral, trigonal pyramidal, bent, and others

    Molecular Polarity

    • Electronegativity is the ability of an atom to attract electrons in a bond
    • Polar bonds occur when atoms with different electronegativities are bonded
    • A dipole moment is a measure of bond polarity
    • Polar molecules in 3D space have an unequal distribution of charge.

    Giant Covalent Structures

    • Giant covalent structures have strong covalent bonds throughout a lattice
    • Diamond, graphite, silicon(IV) oxide are examples

    Intermolecular Forces

    • Intermolecular forces are attractive forces between molecules
    • London dispersion forces: temporary fluctuations in electron distribution causing temporary dipoles
    • Dipole-dipole forces: attraction between permanent dipoles
    • Hydrogen bonds: strong dipole-dipole forces involving hydrogen bonded to a highly electronegative atom (N, O, F).

    Physical Properties of Covalent Substances

    • Physical properties (melting point, boiling point, solubility, conductivity) are determined by intermolecular forces
    • Stronger forces lead to higher melting/boiling points.
    • Larger molecules have stronger London dispersion forces therefore higher boiling point.
    • Polar molecules have stronger dipole-dipole interactions
    • Polarity and molecular size affect solubility.

    Chromatography

    • Chromatography is used to separate mixtures
    • Paper chromatography and thin-layer chromatography (TLC) utilise a stationary phase (paper/silica gel) and a mobile phase (solvent)
    • Different substances travel at different speeds, depending on their interactions with the stationary phase.
    • Rf values (retardation factors) are used to identify substances by comparing their relative mobility to the solvent front.

    Resonance Structures (HL)

    • Resonance structures represent possible electron arrangements in a molecule, which are more stable.
    • True structure lies somewhere between the extremes showing delocalisation of electrons and bonds
    • Examples: nitrate ion (NO3-), carbonate ion (CO32-), carboxylate ion (RCOO-), ozone (O3), benzene (C6H6)

    Expansion of the Octet (HL)

    • Some molecules (periods 3 and above) can have more than eight valence electrons around the central atom.
    • This is possible because of the availability of d orbitals to accommodate extra electrons.
    • Examples: PCl5, SF4, CIF3, I3-, SF6, BrF5, XeF4

    Sigma and Pi Bonds (HL)

    • Covalent bonds are formed by overlap of atomic orbitals.
    • Sigma (σ): Head-on, direct overlap, resulting in electron density concentrated along the bond axis
    • Pi (π): Sideways overlap, resulting in electron density above and below the bond axis
    • Multiple bonds (double/triple) involve one o bond and one/two π bonds.

    Hybridisation (HL)

    • Hybridisation involves mixing of atomic orbitals to form new hybrid orbitals
    • Common hybridisations: sp³, sp², sp
    • These hybrid orbitals lead to specific molecular shapes and bond angles.

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    HL IB Chemistry - The Covalent Model PDF

    Description

    This quiz explores the concept of covalent bonds, focusing on their formation, types, and the significance of Lewis formulas. It delves into the sharing of electrons between non-metals and the implications of bond energy and length. Test your understanding of atomic structures and bond interactions in this engaging quiz!

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