Chemical Bonding and the Octet Rule
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Questions and Answers

What characterizes a double bond between two atoms?

  • Three single bonds
  • One sigma bond and one pi bond (correct)
  • Two sigma bonds
  • Two pi bonds

Which of the following is a property of ionic compounds?

  • Soft and malleable
  • Contain individual molecules
  • Low melting and boiling points
  • Conduct electricity when molten or dissolved in water (correct)

According to the VSEPR Theory, what primarily determines the shape of a molecule?

  • The total mass of the molecule
  • The types of atoms involved in the molecule
  • The number of electron pairs around the central atom (correct)
  • The number of bonds formed with other atoms

What type of bond is formed by the overlap of two orbitals head-on?

<p>Sigma bond (C)</p> Signup and view all the answers

Which characteristic is NOT typical of covalent compounds?

<p>High melting and boiling points (B)</p> Signup and view all the answers

What is the three-dimensional arrangement of ions in Sodium Chloride called?

<p>Crystal Lattice (C)</p> Signup and view all the answers

How many chloride ions surround each sodium ion in Sodium Chloride?

<p>6 (B)</p> Signup and view all the answers

What is the total charge contributed by aluminium in Aluminium Oxide?

<p>+3 (C)</p> Signup and view all the answers

To obtain a neutral compound of Aluminium Oxide, what is the lowest common multiple of the charges of Aluminium and Oxygen?

<p>6 (C)</p> Signup and view all the answers

Which groups of elements typically form ionic compounds?

<p>Groups I and II with Groups VI and VII (A)</p> Signup and view all the answers

What distinguishes the bonding in PH3 from that in H2O, NH3, and HCl?

<p>PH3 is virtually non-polar due to tiny electronegativity difference. (A)</p> Signup and view all the answers

Which hydrides exhibit hydrogen bonding between their molecules?

<p>H2O and NH3 (B)</p> Signup and view all the answers

What effect does hydrogen bonding have on the boiling point of H2O and NH3?

<p>It increases the boiling point due to stronger intermolecular attractions. (B)</p> Signup and view all the answers

How does the symmetry of BCl3 affect its polarity?

<p>It cancels out the unequal sharing of electrons, making it non-polar. (B)</p> Signup and view all the answers

What is the molecular shape of PH3 and how does it arise from electron-pair repulsion?

<p>Pyramidal, due to repulsion between three bond pairs and one lone pair. (B)</p> Signup and view all the answers

What type of bonding is characterized by temporary dipoles that induce attraction between non-polar molecules?

<p>Van der Waals forces (D)</p> Signup and view all the answers

Which type of intermolecular force is considered stronger than Van der Waals forces but weaker than ionic bonds?

<p>Dipole-Dipole forces (C)</p> Signup and view all the answers

What primarily determines the strength of Van der Waals forces in a molecule?

<p>The size and number of electrons in the molecule (C)</p> Signup and view all the answers

Which atoms, when bonded to hydrogen, can create strong hydrogen bonds?

<p>Nitrogen, Oxygen, Fluorine (A)</p> Signup and view all the answers

Which intermolecular force is primarily responsible for the higher boiling points of polar molecules compared to non-polar molecules?

<p>Dipole-Dipole forces (D)</p> Signup and view all the answers

What occurs when the partial positive charge of a hydrogen atom bonded to an electronegative atom is attracted to another electronegative atom?

<p>Hydrogen bond (C)</p> Signup and view all the answers

What type of forces exist between molecules characterized by permanent dipoles?

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

Which relationship between Van der Waals forces and molecular size is true?

<p>Van der Waals forces strengthen with larger molecules due to more electrons. (D)</p> Signup and view all the answers

What is the reason that water is a polar molecule?

<p>The positive poles are attracted to negatively charged objects. (C)</p> Signup and view all the answers

How does the electronegativity difference define the type of bonding in a compound?

<p>An E.N difference greater than 1.7 indicates ionic bonding. (B)</p> Signup and view all the answers

What happens when a polar liquid is exposed to a charged plastic rod?

<p>It spins so that the positively charged end faces the negatively charged rod. (D)</p> Signup and view all the answers

Which of the following is a characteristic of a non-polar liquid?

<p>It does not exhibit attraction when in the presence of a charged rod. (A)</p> Signup and view all the answers

What occurs to ionic substances like sodium chloride when dissolved in water?

<p>The strong attraction from polar water molecules overcomes ionic bonding. (A)</p> Signup and view all the answers

What type of covalent bond is indicated by an electronegativity difference of 0.35?

<p>Non-polar covalent bond (D)</p> Signup and view all the answers

What bonding characteristics are associated with ionic compounds?

<p>They have high melting and boiling points due to strong ionic bonds. (D)</p> Signup and view all the answers

Which statement about intramolecular bonding is true?

<p>It refers to bonding that occurs within a molecule. (D)</p> Signup and view all the answers

What is the strongest form of intermolecular force?

<p>Hydrogen bonding (D)</p> Signup and view all the answers

How many sigma and pi bonds are present in a molecule of nitrogen?

<p>1 sigma bond and 2 pi bonds (C)</p> Signup and view all the answers

What defines electronegativity?

<p>The relative attraction of an atom for a shared pair of electrons (C)</p> Signup and view all the answers

Which molecule has hydrogen bonding between its molecules?

<p>Ammonia (NH3) (D)</p> Signup and view all the answers

What is the bond angle in a molecule of ammonia (NH3)?

<p>107.3° (A)</p> Signup and view all the answers

Why does hydrogen have a lower boiling point compared to oxygen?

<p>Hydrogen is smaller, resulting in weaker intermolecular forces (B)</p> Signup and view all the answers

What describes intramolecular bonding?

<p>Forces between atoms in molecules (B)</p> Signup and view all the answers

How can a molecule with polar bonds be non-polar?

<p>Polar bonds cancel each other out (D)</p> Signup and view all the answers

Flashcards

Ionic Compound Formula

Represents a compound using element symbols and counts for each element.

Crystal Lattice Structure

The 3D arrangement of ions in an ionic compound.

Ionic Compound Formation

Occurs between metal (groups I & II) and non-metal (groups VI & VII) elements.

Aluminium Oxide Formula

Al2O3, shows the ratio of aluminium and oxygen atoms to achieve neutrality.

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Finding Lowest Common Multiple

Find the smallest common number when dealing with multiple charges to get a neutral compound

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Sigma Bond

A covalent bond formed by the head-on overlap of atomic orbitals.

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Pi Bond

A covalent bond formed by the sideways overlap of atomic orbitals.

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Triple Bond

A covalent bond consisting of one sigma bond and two pi bonds.

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VSEPR Theory

Valence Shell Electron Pair Repulsion Theory; predicts the shape of molecules based on electron pair repulsion.

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Ionic vs. Covalent Compounds

Ionic compounds have high melting/boiling points, are usually solid, and conduct electricity in molten or dissolved states, while covalent compounds have low melting/boiling points, are often gases or soft solids and usually are poor conductors.

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Polar Covalent Bond

A covalent bond where electrons are shared unequally between atoms due to electronegativity difference. This results in a partial positive and partial negative charge on the atoms.

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Non-polar Covalent Bond

A covalent bond where electrons are shared equally between atoms due to negligible electronegativity difference. This results in no partial charges on the atoms.

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Electronegativity Difference

The difference in electronegativity values between two atoms in a bond. This difference indicates the degree of polarity in the bond.

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How to Determine Bond Type

To determine the type of bond, calculate the electronegativity difference between the two atoms. If the difference is greater than 1.7, the bond is ionic. If the difference is less than or equal to 1.7, the bond is covalent. If the difference is greater than 0.4 and less than 1.7, the bond is polar covalent. If the difference is less than or equal to 0.4, the bond is non-polar covalent.

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Water as a Solvent

Water is an excellent solvent due to its polar nature. The partial positive and negative charges on water molecules attract ions and polar molecules, allowing them to dissolve.

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Intramolecular Bonding

The forces within a molecule that hold atoms together. It includes covalent and ionic bonds.

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Intermolecular Bonding

The forces between molecules that hold them together. These forces are weaker than intramolecular bonds.

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How to Identify a Polar Liquid

To identify a polar liquid, test its attraction to a charged rod. A charged rod will attract a stream of a polar liquid due to the alignment of its polar molecules with the rod's charge.

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Intermolecular Forces

Attractive forces between molecules that influence their physical properties like boiling point and melting point.

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Van der Waals Forces

Weak, temporary attractive forces between non-polar molecules arising from temporary dipoles.

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Dipole-Dipole Forces

Attractive forces between permanent dipoles of polar molecules.

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Hydrogen Bonding

Strong type of dipole-dipole force specifically between molecules containing H bonded to N, O, or F.

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What are the weakest intermolecular forces?

Van der Waals forces are the weakest intermolecular forces.

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What effect do stronger intermolecular forces have on boiling point?

Stronger intermolecular forces lead to higher boiling points.

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What are the strongest intermolecular forces?

Hydrogen bonds are the strongest intermolecular forces.

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How do dipole-dipole forces compare to Van der Waals forces?

Dipole-dipole forces are stronger than Van der Waals forces because they involve permanent dipoles.

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Boiling Point & Intermolecular Forces

The strength of intermolecular forces determines a substance's boiling point. Stronger forces require more energy (heat) to break, resulting in a higher boiling point.

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Electronegativity

The relative ability of an atom to attract electrons in a covalent bond.

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Polar Bond

A covalent bond where electrons are shared unequally, creating a partial positive and partial negative charge on the atoms.

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Lone Pair Repulsion

Lone pairs of electrons on a central atom exert a greater repulsive force than bonding pairs, affecting the bond angles of a molecule.

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Non-polar Molecule

A molecule with symmetrical shape where the centers of positive and negative charges coincide, resulting in no overall dipole moment.

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Polar vs. Non-polar Molecules

Polar molecules have uneven charge distribution due to unequal electron sharing, resulting in partial positive and negative ends. Non-polar molecules have even charge distribution due to equal electron sharing.

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Electron-Pair Repulsion Theory (VSEPR)

VSEPR predicts the shape of molecules by minimizing repulsions between electron pairs around a central atom.

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Why is PH3 Non-polar?

PH3 has very small electronegativity difference between phosphorus and hydrogen, leading to almost equal sharing of electrons, making it non-polar.

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Why is BCl3 Non-polar?

BCl3 has polar B-Cl bonds but the molecule itself is non-polar due to its symmetrical shape. The polarities of the B-Cl bonds cancel out.

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Study Notes

Chemical Bonding

  • A compound is a substance made of two or more different elements combined chemically.
  • Attractive forces hold atoms together in a compound, called chemical bonds.

The Octet Rule

  • Atoms tend to gain, lose, or share electrons to achieve an electron arrangement with eight electrons in their outermost energy level (octet rule).
  • Noble gases are unreactive because they already have a stable octet.
  • Elements in the same group have similar properties.

Exceptions to the Octet Rule

  • Transition metals frequently do not follow the octet rule.
  • Hydrogen, lithium, and beryllium tend to achieve two electrons in their outermost shell instead of eight.

Ionic Bonding

  • An ion is a charged atom or group of atoms.
  • Atoms gain or lose electrons to have the electron configuration of a noble gas.
  • Atoms in group 1 lose one electron, forming a positive ion.
  • Atoms in group 2 lose two electrons, forming a positive ion.
  • Atoms in group 6 or 7 gain electrons, forming a negative ion (anion).
  • Ionic bonds result from the attraction between oppositely charged ions.
  • Ionic compounds form crystal lattices.

How to Write Formulas for Ionic Compounds

  • Chemical formulas show the atoms in a compound and their quantities.
  • Ionic compounds are typically composed of metals in groups 1 and 2 and nonmetals in groups 6 and 7.
  • The overall charge of an ionic compound must be zero; the charges on the ions balance.

Dot and Cross Diagrams

  • Used to represent the bonding in simple compounds.
  • Dots represent the outer electrons of one atom.
  • Crosses represent the outer electrons of another atom.
  • Arrows show the transfer of electrons.

Sodium Chloride Crystal Structure

  • X-ray studies reveal the arrangement of ions in a crystal lattice.
  • Sodium chloride has a cubic structure.
  • Each sodium ion is surrounded by 6 chloride ions, and vice-versa.

Common Polyatomic Ions

  • Memorize common polyatomic ions or groups of atoms which carry a net charge.

Transition Metals

  • Transition metals have variable valencies (charges).
  • Predicting charges for transition metal compounds requires knowledge of common charges for these metals.

Covalent Bonding

  • Atoms share electrons to achieve a stable electron configuration.
  • Bond pairs are pairs of electrons shared between atoms.
  • Lone pairs are electron pairs that are not involved in bonding.
  • Covalent bonds can be nonpolar or polar covalent.

Molecules

  • A molecule is a group of atoms bonded together.
  • Molecules can be represented by dot and cross diagrams.

Sigma and Pi bonds

  • Sigma bonds: formed by head-on overlap of orbitals.
  • Pi bonds: formed by sideways overlap of p orbitals.
  • Single bonds are only sigma bonds.
  • Double bonds have one sigma and one pi bond.
  • Triple bonds have one sigma and two pi bonds.

Electronegativity

  • Electronegativity measures an atom's ability to attract electrons in a bond.
  • Differences in electronegativities determine bond polarity (polar or nonpolar).
  • Significant difference in electronegativity (greater than 1.7) indicates ionic bonding.
  • Smaller differences (less than 1.7) suggest covalent or polar covalent bonding.

Types of Intermolecular Forces

  • Van der Waals: weak forces between all molecules (including nonpolar).
  • Dipole-dipole: attractive forces between polar molecules.
  • Hydrogen bonding: strong type of dipole-dipole force between molecules containing hydrogen bonded to nitrogen, oxygen, or fluorine.

Properties of Ionic and Covalent Compounds

  • Ionic compounds: high melting/boiling points, hard and brittle, conduct electricity in molten or dissolved states.
  • Covalent compounds: low melting/boiling points, varying physical states, usually soft, do not conduct electricity.

Shapes of Molecules

  • Molecular shape is critical in determining properties.
  • Used Valence Shell Electron Pair Repulsion (VSEPR) Theory to determine molecular shapes.

Prediction of Intermolecular Forces

  • Consider bond polarity and types of atoms involved to predict the intermolecular forces.

Predicting Bond Type

  • Large electronegativity differences predict ionic bonding.
  • Smaller differences predict covalent bonding.
  • Moderate differences predict polar covalent bonding.

Exam Questions

  • Students should study example questions and practice applying concepts.

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Chemical Bonding PDF

Description

Explore the essential concepts of chemical bonding, including the formation of compounds and the significance of the octet rule in achieving electron stability. Delve into exceptions and the mechanisms of ionic bonding. This quiz will test your understanding of these fundamental chemistry topics.

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