Essential Chem. Questions (Set 10-14) (Test 1&2) Flashcards
Why are metals good conductors of electricity?
Metals are good conductors of electricity due to their 3D metallic lattice that has cations and a delocalised sea of electrons, the cations (metallic ions) are in a fixed position whereas the electrons are delocalised and become a sea of electrons that move within the structure. When voltage is applied, it is carried through the mobile electrons, thus metals are good conductors of electricity.
Why are metallic elements both malleable & ductile?
Metals are malleable and ductile due to the bonding between cations (metal ions) and the sea of electrons that are non-directional. Meaning that metal ions can move into relation with each other without breaking bonds between them and the sea of electrons. Allowing metals to bend, stretch or dent.
Why are metals good conductors of heat?
Metals are good conductors of heat as the delocalised (valence) electrons are mobile throughout the metal lattice, the vibration of metallic ions also contribute to the flow of heat as well.
Describe the formation of the ionic solid sulfide (CaS) from separate neutral atoms of calcium (Ca) and sulfur (S). Consider the following:
- electron transfer
- formation of the ionic bond
- structure of the ionic lattice
Ionic bonding is the transfer of valence electrons from a metal to a non-metal for both to become stable. Which in this case each calcium loses 2 electrons forming Ca^2+ ion while each sulfur atom gains these 2 electrons to form S^2- ion. The products sulfide and calcium ions experience strong electrostatic attraction (opposite ions/charges attract) within the 3D lattice.
All ionic substances are known to be brittle. Describe this property and show with the aid of a diagram and how the structure of these substances give rise to their brittle nature.
Ionic substances are brittle when force is applied to the 3D lattice of oppositely charged ions, layers of ions will be forced to move. Like charged ions will be forced to be aligned with one another and no longer have unlike charged ion patterns. The like charges will come closer together than unlike charges resulting in repulsive forces to exceed attractive forces, making the 3D lattice break apart rather than bend or dent.
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Covalent molecular substances typically have low melting & boiling points. This occurs despite covalent bonding being a very strong form of chemical bond. Account for this observation. Your answer should clearly refer to intermolecular forces and intramolecular forces.
When a molecular substance melts or boils, only weak intermolecular forces need to be broken. Thus the weakly bonded lattice of molecules in solid phase is easily disrupted to form a liquid or gas.
(Remember: Strong covalent bonds occurring between atoms within molecule (intramolecular forces) are unaffected when a substance melts or boils.)
Carbon dioxide (CO2) is a gaseous substance present in low concentrations in the Earth’s atmosphere. The substance silicon dioxide (SiO2) is present in vast quantities in the Earth’s crust. It’s commonly known as quartz or sand. Despite their similar-looking formula, these substances are quite different. Compare the structure and bonding of carbon dioxide (CO2) with that of silicon dioxide (SiO2). Thus account for the different phase of carbon dioxide and silicon dioxide.
- Covalent bonding is present in both.
- Their different phases CO2 being a gas at room temp. while SiO2 is a high melting point solid, is due to their different structure.
- Carbon dioxide has a molecular structure, consists of molecules of formula CO2. Each molecule consists of two oxygen atoms covalently bonded by double bonds to a single carbon atom. Strong INT’RA’MOLECULAR FORCES (covalent bonds) occur within the CO2 molecule to keep the three atoms strongly bonded as a single cluster known as a molecule. Weak INT’ER’MOLECULAR FORCES occur between the molecules making up a sample of CO2. It’s the result of WEAK INT’ER’MOLECULAR FORCES that result in CO2 is a gas under normal conditions.
- Silicon dioxide however consists of a single vast array of Si and O atoms that are covalently bonded to neighbouring Si and O atoms. Each Si atom bonds to four neighbouring O atoms while each O atom is bonded to two neighbouring Si atoms. As the strong bond extends throughout the SiO2 structure all atoms are held tightly in their fixed array. Very high temps. are needed to disrupt (melt) this arrangement and so the substance SiO2 will be solid at room conditions.
Distinguish between the terms ‘covalent bond’ and ‘covalent molecular’
A covalent bond is a type of chemical bond where two atoms share one or more pairs of electrons in order to become stable. The bond is a result of electrostatic attraction between the shared pair of electrons and the positive nuclei.
Covalent molecular is the type of structure where atoms bond by covalent bonds to form small clusters of two or more atoms. The cluster is referred to as a molecule. Weak bonding forces may occur between these molecules.
What bonding is… Nal
Ionic
Mg
Metallic
SO2
Covalent molecular
Al2o3
Ionic
SiO2
Covalent network
CO2
Covalent Molecular
C
Covalent Network
