Unit 1 : Topic 3 Flashcards
Bonding and Structure
How is an ion formed?
An ion forms when an atom gains or loses at least one electron.
How does electrolysis provide evidence for the existence of ions?
Electrolysis demonstrates the existence of ions by showing the movement of positively charged ions toward the negative electrode and negatively charged ions toward the positive electrode. This is evident in a solution where one end turns blue and the other fades to yellow, indicating ion migration.
How do electron density maps provide evidence for the existence of ions?
Electron density maps offer proof of ions by revealing regions of electron probability. For instance, in sodium chloride, ions are shown in a regular pattern with no electron density between them, clearly depicting distinct ions.
What is an ionic bond?
An ionic bond is the strong electrostatic attraction between positively and negatively charged ions.
How is a dot-and-cross diagram for the ionic compound NaCl drawn?
In sodium chloride, the sodium atom loses an electron to become a sodium ion (Na+), and the chlorine atom gains this electron to become a chloride ion (Cl−).
What is an ionic crystal?
An ionic crystal is a large lattice of ions held together by the electrostatic forces between oppositely charged ions.
What is the trend in ionic radius down a group, and why does this occur?
Ionic radius increases down a group due to a higher nuclear charge, increased shielding, and reduced electrostatic attraction, leading to a larger atomic radius.
How do ionic radius and ionic charge affect the strength of ionic bonding?
The strength of ionic bonding increases with higher ionic charge or smaller ionic radius, as this raises the charge density and strengthens the electrostatic attraction.
What is an isoelectronic species?
Isoelectronic species are atoms or ions with the same electronic configuration.
What is the trend in ionic radius for a set of isoelectronic species such as N³⁻ to Al³⁺?
For isoelectronic species, the ionic radius decreases as nuclear charge increases while the number of electrons remains constant, enhancing nuclear attraction.
What is polarisation?
Polarisation refers to the distortion of an ionic bond when a cation strongly attracts the electrons of an anion, potentially leading to a charge cloud resembling a covalent bond.
What does the polarising power of a cation depend upon?
The polarising power of a cation depends on its charge density, which is influenced by the cation’s charge and ionic radius. A higher charge density results in greater polarising power.
What does the polarising power of an anion depend upon?
The polarising power of an anion depends on its ionic radius. A larger ionic radius makes the anion more easily polarised because its electrons are held less tightly by the nucleus.
What is a covalent bond?
A covalent bond is formed by the sharing of electron pairs between atoms, due to the electrostatic attraction between the positive nuclei of the bonded atoms and the shared negative electrons.
What are some properties of giant covalent structures?
Giant covalent structures have high melting and boiling points because breaking the strong covalent bonds requires a large amount of energy. They do not conduct electricity, as they lack free charge carriers.
What are some properties of simple molecular covalent structures?
Simple molecular covalent structures have low melting and boiling points due to weak intermolecular forces, and they cannot conduct electricity because they do not have free charge carriers.
What is a dative covalent bond?
A dative covalent bond is a covalent bond in which both electrons in the shared pair are donated by a single atom.
How is a dot-and-cross diagram for Cl₂ drawn?
A chlorine molecule is represented with a shared pair of electrons between the two chlorine atoms, with each atom also having three lone pairs.
How is a dot-and-cross diagram for NH₄⁺ drawn?
In the ammonium ion, each hydrogen atom is covalently bonded to the nitrogen atom. One of these bonds is a dative covalent bond where both electrons are donated by the nitrogen atom.
What is the structure of graphite?
Graphite consists of layers of hexagonal rings of carbon atoms, with each carbon atom bonded to three others. Weak intermolecular forces exist between the layers, and each carbon atom has one delocalised electron.
What are the properties of graphite, and how are they explained?
Graphite is soft and slippery because the layers can slide over one another due to weak intermolecular forces. It conducts electricity because its delocalised electrons can move and carry charge.
What is the structure of diamond?
Diamond is composed of carbon atoms, each covalently bonded to four others in a rigid, repeating structure. It has no delocalised electrons.
What are the properties of diamond?
Diamond is extremely hard due to its strong covalent bonding. It has a very high melting point and does not conduct electricity because it lacks charged particles.
What are the uses of graphite, and why is it suitable?
Graphite is used as electrodes because it conducts electricity and has a high melting point. It is also used as a lubricant due to its slippery layers.
