Chemistry Unit 4: Covalent Bonds

Questions and Answers

What primarily influences the covalent character of ionic bonds?

The size of the cation only

The electronegativity of the cation

The temperature at which the ionic compound is formed

The polarising power of the cation and polarisability of the anion (correct)

Which theory serves as a better predictor of molecular shapes than the Lewis concept?

Crystal Field Theory

Molecular Orbital Theory

Valence Shell Electron Pair Repulsion (VSEPR) Theory (correct)

Hybridization Theory

What did Fajans' rules primarily explain regarding ionic bonds?

The partial covalent character of ionic bonds (correct)

The polarisation of cations in solutions

The complete ionic nature of ionic bonds

The exact bond lengths in ionic compounds

Which of the following factors is NOT mentioned as influencing the extent of ionic bond distortion?

Ionic radii of the cation Signup and view all the answers

What character do all covalent bonds exhibit to some extent?

Partial ionic character Signup and view all the answers

What type of bond is formed between the two carbon atoms in an ethene molecule?

Double bond Signup and view all the answers

How do the charges in the CO32– ion affect its total valence electron count?

It includes the negative charges as additional electrons. Signup and view all the answers

What does a positive charge on the NH4+ ion signify about its electron count?

It has lost one electron compared to neutral nitrogen. Signup and view all the answers

What type of bond exists between two chlorine atoms?

Covalent bond Signup and view all the answers

In a CO2 molecule, what type of bond exists between the carbon and oxygen atoms?

Covalent bond Signup and view all the answers

What is the angle of the distorted tetrahedron shape described?

104.5° Signup and view all the answers

Which arrangement is more stable based on the provided information?

Arrangement with lp at equatorial position Signup and view all the answers

How many lp—bp repulsions occur when the lp is in an axial position?

3 Signup and view all the answers

What is the shape described in arrangement (b)?

Distorted tetrahedron Signup and view all the answers

Which term best describes the configuration when the lp is in a more stable position?

See-saw Signup and view all the answers

What type of molecular structure is indicated by the presence of lone pairs impacting bond angles?

Distorted geometry Signup and view all the answers

In a molecular structure with lone pairs, what is the effect on bond angles?

They decrease due to repulsion Signup and view all the answers

What effect does position have on the stability of the molecular arrangements discussed?

Axial position creates instability Signup and view all the answers

What determines the type of overlap between atomic orbitals?

The sign and orientation of the amplitude of orbital wave functions Signup and view all the answers

Which statement accurately describes positive overlap between atomic orbitals?

It is characterized by the orbitals having the same sign and orientation. Signup and view all the answers

What is the significance of the 90° angle between the C-H bonds in methane (CH4)?

It is a result of the tetrahedral geometry of the molecule. Signup and view all the answers

Which type of molecules are affected uniformly by the criterion of orbital overlap for bond formation?

Both homonuclear and heteronuclear diatomic molecules Signup and view all the answers

In the context of atomic orbital overlap, what do positive and negative signs represent?

The phase of the wave function of the orbital Signup and view all the answers

What is the geometric arrangement of hydrogen atoms around a carbon atom in methane (CH4)?

Tetrahedral Signup and view all the answers

Which of the following statements regarding the overlap of s and p atomic orbitals is true?

Overlapping s and p orbitals may have varied spatial orientation. Signup and view all the answers

Which of the following molecular shapes results from the arrangement of the three p orbitals in conjunction with hydrogen in CH4?

Tetrahedral Signup and view all the answers

What distinguishes odd-electron molecules from other molecules in relation to the octet rule?

They can have unpaired electrons that do not complete the octet. Signup and view all the answers

Which statement about formal charges is correct?

Formal charges help track valence electrons within a molecule. Signup and view all the answers

In which situation is the octet rule typically not applicable?

In molecules with more than eight valence electrons. Signup and view all the answers

Which of the following is an example of a compound that exhibits an expanded octet?

PF5 Signup and view all the answers

What characteristic of elements in the third period of the periodic table allows them to form expanded octets?

The participation of d orbitals in bonding. Signup and view all the answers

Which of the following best describes the nature of molecules with an odd number of electrons?

They possess free radical characteristics due to unpaired electrons. Signup and view all the answers

What role do formal charges play in the Lewis structure of a molecule?

They assist in tracking valence electrons around atoms. Signup and view all the answers

Which of the following is NOT a characteristic of the expanded octet?

It is common among elements in the second period of the periodic table. Signup and view all the answers

Study Notes

Chemical Bonding Concepts

Ethene consists of two carbon atoms bonded by a double bond.
Covalent bonds involve the sharing of electrons, demonstrated in molecules like Cl2 and CO2, where Cl-Cl, and double bonds respectively exist.

Valence Electrons and Ions

Valence electrons are crucial for understanding molecular structures; additional electrons may indicate negative charges (e.g., CO32–) while lost electrons suggest a positive charge (e.g., NH4+).
Odd-electron molecules such as nitric oxide (NO) and nitrogen dioxide (NO2) do not satisfy the octet rule for all atoms due to their odd number of electrons.

Expanded Octet Rule

Elements from the third period and beyond can utilize d orbitals in bonding, allowing for more than eight valence electrons around a central atom.
The octet rule is not applicable for compounds like PF5, SF6, and H2SO4, which exhibit expanded octets.

Covalent and Ionic Bonds

Both covalent and ionic bonds exhibit partial characters of the other type; the extent of covalent character in ionic bonds can be influenced by the polarizing ability of cations and polarizability of anions.
Fajans' rules aid in understanding the nature of ionic bonds and their covalent character.

VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) Theory predicts molecular shapes based on electron pair repulsion.
Non-bonding electron pairs (lone pairs) significantly alter molecular geometry, as seen with bond angles, e.g., reducing tetrahedral angles from 109.5° to 104.5° due to lone pair-bond pair interactions.

Atomic Orbital Overlap

Orbital overlap is fundamental for covalent bond formation; positive overlap occurs when orbitals align with the same phase.
Different overlap types (positive, negative, zero) affect the resulting chemical bond and orientation in space.

Molecular Geometry Examples

CH4 has a tetrahedral shape with bond angles of 109.5°; NH3 presents a pyramidal shape; H2O shows a bent configuration due to its distinct lone pair arrangements and bond angles.
In carbon's bonding with hydrogen, four atomic orbitals overlap with hydrogen’s 1s orbitals, resulting in four C-H bonds, although the arrangement is influenced by the shape and angles of the orbitals.

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Description

This quiz covers the concepts of covalent bonds as discussed in Chemistry Unit 4. Participants will explore double bonds between carbon atoms in ethene and other examples, such as chlorine and carbon dioxide. Test your understanding of molecular structures and bonding types.