What is the main goal that atoms try to achieve when they form chemical bonds?
To achieve a stable electron arrangement, usually a duplet or octet.
Why are noble gases generally unreactive?
Because they have stable duplet or octet configurations.
What is an ionic bond?
A bond formed by the transfer of electrons between a metal and non-metal, resulting in ions.
What are the two types of ions that form in ionic bonding?
Cations and anions.
What force holds ions together in an ionic compound?
Strong electrostatic forces.
Do ionic compounds usually have high or low melting and boiling points?
High.
Under what conditions can ionic compounds conduct electricity?
When molten or in aqueous solution.
What is a covalent bond?
A bond formed by the sharing of electrons between non-metal atoms.
Can a covalent bond be single, double or triple?
Yes.
Do covalent compounds usually conduct electricity?
No.
What is a hydrogen bond?
An attractive force between hydrogen and highly electronegative atoms like oxygen, fluorine, or nitrogen.
Are hydrogen bonds stronger or weaker than covalent bonds?
Weaker.
What type of bond is present in molecules like water, ammonia and hydrogen fluoride?
Hydrogen bonds.
What is a dative bond also known as?
A coordinate bond.
What type of bonding is present in metals?
Metallic bonding.
What is meant by delocalised electrons in metals?
Valence electrons are free to move.
Are metals good conductors of electricity?
Yes.
What is a giant molecular structure?
A covalently bonded network that forms a large, continuous structure.
Do giant molecular structures typically have high or low melting points?
High.
What is an example of a giant molecular structure?
Diamond or graphite.
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Explanation Questions
Explain how ionic bonds are formed, using sodium chloride (NaCl) as an example.
Ionic bonds are formed by the transfer of electrons from a metal to a non-metal. In NaCl, sodium (Na), with one valence electron, transfers this electron to chlorine (Cl), which has seven valence electrons. This forms a positively charged sodium ion (Na⁺) and a negatively charged chloride ion (Cl⁻). The oppositely charged ions are held together by strong electrostatic forces, resulting in the formation of NaCl.
Explain the formation of a covalent bond using a chlorine molecule (Cl₂) as an example.
Covalent bonds involve the sharing of electron pairs between non-metal atoms. In Cl₂, each chlorine atom has seven valence electrons. To achieve a stable octet, each Cl atom shares one of its valence electrons with the other, forming a single covalent bond. This shared pair of electrons is attracted to both nuclei, holding the atoms together in the molecule.
How does the concept of ‘delocalised electrons’ explain the conductivity of metals?
In metals, valence electrons are not bound to individual atoms but are free to move throughout the structure. This creates a 'sea of electrons'. These delocalised electrons can move freely when an electrical potential is applied, allowing metals to conduct electricity.
Explain why ionic compounds generally have high melting and boiling points, and why covalent compounds generally have lower melting and boiling points.
Ionic compounds have high melting and boiling points due to the strong electrostatic forces between oppositely charged ions in a lattice structure. A large amount of energy is required to overcome these forces. Covalent compounds have lower melting and boiling points because they are held together by weaker intermolecular forces such as van der Waals forces.
Explain the formation of a hydrogen bond and why water has a relatively high boiling point.
Hydrogen bonds are formed when hydrogen is bonded to a highly electronegative atom like oxygen, fluorine, or nitrogen. These bonds are stronger than van der Waals forces. Water (H₂O) has hydrogen bonding between the hydrogen and oxygen atoms of different molecules. The relatively strong hydrogen bonds between water molecules mean water has a higher boiling point than similar-sized molecules that do not have hydrogen bonding, such as hydrogen chloride.
Describe the difference in electrical conductivity between ionic and covalent compounds in different states (solid, liquid).
Ionic compounds do not conduct electricity in the solid state because their ions are fixed in a lattice structure. When melted or dissolved in a solution, the ions are free to move, allowing them to conduct electricity. Covalent compounds generally do not conduct electricity, as they do not have free-moving charges.
What is a dative bond, and in what types of molecules do they occur?
A dative bond (also called a coordinate bond) occurs when both electrons in a shared pair come from the same atom. Dative bonds can occur in molecules such as the ammonium ion (NH₄⁺), where a hydrogen ion (H⁺) bonds to the nitrogen atom of ammonia, using a lone pair of electrons from nitrogen.
Compare and contrast the properties of ionic and covalent compounds related to solubility in water and organic solvents.
Ionic compounds are generally soluble in water because the polar water molecules can interact with and stabilise the charged ions. Ionic compounds are typically insoluble in nonpolar organic solvents. Covalent compounds are generally insoluble in water because they are nonpolar, but they can dissolve in organic solvents.
Explain the concept of a giant molecular structure and give an example.
Giant molecular structures consist of a large number of atoms held together by covalent bonds in a continuous network, rather than discrete molecules. An example is diamond, where each carbon atom is covalently bonded to four other carbon atoms, forming a large three-dimensional structure. These substances usually have very high melting and boiling points.
Describe the role of van der Waals forces in covalent compounds.
Van der Waals forces are weak intermolecular forces that exist between covalent molecules. These forces arise from temporary fluctuations in electron distribution, creating temporary dipoles that result in attractions between molecules. They are responsible for the states (solid, liquid, gas) and physical properties such as melting and boiling points in many covalent compounds. The strength of these forces is related to the size of the molecule: larger molecules generally have stronger van der Waals forces.