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 (B)

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 (B)</p> Signup and view all the answers

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

<p>False (B)</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 (C)</p> Signup and view all the answers

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

<p>False (B)</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 (C)</p> Signup and view all the answers

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

<p>False (B)</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 (B)</p> Signup and view all the answers

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

<p>False (B)</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. (A)</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 (A)</p> Signup and view all the answers

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

<p>False (B)</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 (B)</p> Signup and view all the answers

Hydrogen cyanide contains two sigma bonds.

<p>True (A)</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 (A)</p> Signup and view all the answers

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

<p>False (B)</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 (D)</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 (B)</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

Flashcards

Sigma Bond Formation

Sigma (σ) bonds are formed by the direct head-on/end-to-end overlap of atomic orbitals, concentrating electron density along the bond axis.

Sigma Bond Axis

The imaginary line between the two atomic nuclei where the electron density of a sigma bond is concentrated.

Types of Sigma Bonds

Sigma bonds can form from the overlapping of s orbitals, p orbitals, or a combination of s and p orbitals.

Pi Bond Formation

Pi (Ï€) bonds are formed from the lateral (side-to-side) overlap of adjacent p orbitals, with electron density concentrated above and below the sigma bond plane.

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Pi Bond Location

Pi bonds are located within double and triple bonds, not single bonds.

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Single Covalent Bond

A single covalent bond is always a sigma bond.

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Bonding Electrons

The electrostatic attraction between the electrons and the nuclei creates the bond that holds atoms together.

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Electron Density Symmetry

The electron clouds in sigma bonds exhibit symmetry around the bond axis.

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Covalent Bonding

The sharing of electron pairs between nonmetal atoms to achieve stable electron configurations.

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Octet Rule

Atoms tend to gain a full outer electron shell (8 electrons) to achieve stability.

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Lewis Formulas

Simplified diagrams showing electron pairs around atoms in molecules.

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Electron Deficient

Central atom in a molecule with fewer than 8 electrons in its outer shell.

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Expanding the octet rule

Central atoms accommodating more than 8 electrons in their outer shell.

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Valence Electrons

Electrons in the outermost shell of an atom, involved in chemical bonding.

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Skeletal Structure

A simplified representation showing the connectivity of atoms in a molecule.

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Electron Charge Clouds

Representations of regions where electrons are likely to be found around an atom.

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Lewis Dot Structure Steps

Steps to create Lewis structure: counting valence electrons, drawing skeletal structure, and arranging pairs.

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VSEPR Theory

Valence Shell Electron Pair Repulsion Theory; predicts molecular shapes by minimizing repulsion of electron pairs around a central atom.

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Electron Domains

Regions of negative charge around a central atom, formed by bonding pairs or lone pairs of electrons.

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Linear Shape

A molecular shape with two electron domains around the central atom, resulting in a 180° bond angle.

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Two Electron Domains

A central atom bonded to two other atoms, with no lone pairs.

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Triangular Planar Shape

A molecular shape with three electron domains around the central atom, resulting in a 120° bond angle.

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Three Electron Domains

A central atom bonded to three other atoms, with no lone pairs.

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Lone Pairs

Pairs of electrons that are not involved in bonding.

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Bond Angle

The angle between two adjacent bonds in a molecule.

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Giant Covalent Structures

Substances with repeating covalent bonds forming a large, continuous lattice, with no individual molecules.

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Diamond

A giant covalent structure of carbon atoms, where each carbon atom is bonded to four others in a tetrahedral arrangement.

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Tetrahedral Arrangement

A molecular geometry where atoms are arranged around a central atom at the corners of a tetrahedron.

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Bond Angle in Diamond

109.5 degrees, the angle between the bonds connecting each carbon atom to its neighbors.

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Allotropes of Carbon

Different forms of carbon, each with a unique structure and properties, including diamond, graphite, etc.

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Intermolecular Forces

Forces that exist between molecules, determining properties like boiling point.

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London Dispersion Forces

Temporary intermolecular forces caused by temporary dipoles in molecules.

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Surface Area (Molecules)

Larger surface area leads to greater intermolecular interactions.

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Dipoles

Separation of positive and negative charges within a molecule.

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Permanent Dipole-Dipole Forces

Attraction between permanent dipoles on molecules.

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Boiling Points (Isomers)

Molecules with similar electron count but different shapes have varying boiling points.

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Electron Number & Intermolecular Forces

More electrons result in stronger London forces.

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Isomers

Molecules with identical molecular formulas but different structures.

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Triple bond in HCN

A triple bond in hydrogen cyanide (HCN) is formed by one sigma bond and two pi bonds between the carbon and nitrogen atoms.

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Sigma bond (σ)

A direct head-on overlap of atomic orbitals creating electron concentration along the bond axis.

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Pi bond (Ï€)

A side-to-side overlap of p orbitals, creating electron density above and below the sigma bond plane.

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HCN bonding

Hydrogen cyanide (HCN) has a triple bond between carbon (C) and nitrogen (N), plus a single bond between hydrogen (H) and carbon.

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Triple bond formation in HCN

H-C triple bonded to N is formed by one sigma and two pi bonds.

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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 (Ï€): Sideways overlap, resulting in electron density above and below the bond axis
  • Multiple bonds (double/triple) involve one o bond and one/two Ï€ 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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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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