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Flashcards by mysticalfirefox, updated more than 1 year ago
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Created by mysticalfirefox
about 10 years ago
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| Question | Answer |
| Define a Covalent Bond | A covalent bond is formed when two atoms (non-metals) share a pair of electron by the overlapping of orbitals in the outer shell, each carrying 1 electron. They are held together by the electrostatic attraction between the nuclei of the atoms and the electron pair. |
| Define the term 'sigma bond' | This is formed by the overlapping of the overlap of s, sp, sp2 or sp3 hybridised orbitals resulting in the electrons being shared in the internuclear axis. |
| Define the term 'pi-bond' | This is formed by the sideways overlap of p-orbitals resulting in the electrons being shared to be above or below the plane. |
| Define the term 'non-polar covalent bond' | This occurs when the electrons in a covalent bond, which is joining two (2) identical atoms or atoms of a similar electronegativity are shared equally and thus neither of the atoms develops a permanent charge. |
| Define the term 'polar covalent bond' | This occurs when the two (2) atoms are different as one atom will be more electronegative than the other and thus the electrons will not be shared equally. The electrons will be closer and more readily attracted to the more electronegative element. This results in a higher electron density around the more electronegative atom. The molecules develops a permanent dipole, which is a slight positive charge (ℴ+) on the less electronegative atom and a slight negative charge (ℴ-) on the more electronegative atom. |
| Define the term 'electron deficiency; | Not all atoms achieve a noble gas configuration when they form a covalent compound. When an atom in a covalent compound is electron deficient, it has less than eight (8) electrons in its outer shell. This makes the structure unstable so that it usually forms other types of bonds. |
| Define the term 'dative covalent bond' | This is a covalent bond (a shared pair of electrons) in which both electrons come from the same atom. It is formed by the overlap of two (2) atomic orbitals, one (1) of which carries an electron pair while the other is empty. |
| Define the term 'valency shell expansion' | In certain cases an atom shares electrons and finishes off with more than 8 electrons in its outer shell. This is due to valency shell expansion. |
| Why is it some atoms are restricted from forming more bonds? | Forming bonds requires energy if too much energy is required to form that bond without it being compensated for by the formation by the extra bonds formed then the bonds to not form. This is due to shell restriction (the electron shells are labeled K, L, M, N, O, P, and Q; or 1, 2, 3, 4, 5, 6, and 7; going from innermost shell outwards) |
| What are the properties of covalent compounds? | 1. The compounds can either be in a gaseous, liquid, or solid state of matter (they are made up of molecules). 2. The compounds tend to have low melting and boiling points. 3. The compounds have poor electrical conductors in all phases. 4. The compounds are usually soluble in nonpolar liquids but not in water. |
| What is a macromolecular structure? | A macromolecular solid structure is made up of a large number of atoms held together by strong covalent bonds |
| In diamond each carbon atom is the centre of what kind of structure? | Tetrahedral structure. |
| What type of hybdridisation does the carbon atoms have in diamond? | sp3 hybridised |
| What type of hybridisation does carbon have in graphite? | sp2 hybridisation |
| Why is Graphite more reactive than Diamond? | Graphite is more reactive than diamond is since the close structure of diamond results in a higher atomisation. |
| Which has the higher melting point Graphite or Diamond? Why? | Graphite has the higher melting point and this is because the carbon-carbon covalent bonds in graphite are slightly shorter than those in diamond. As a result, they are slightly stronger which explains why the melting point of graphite is slightly higher than that of diamond. |
| Why is Graphite less dense than that of Diamond? | The weak bonds between the layers are the reason why the density of graphite is lower than that of diamond and thus the structure is not as tightly packed as that of diamond. |
| Why can Graphite conduct electricity? | Graphite conducts electricity because of its free electrons which conduct electricity along its layers. |
| What are the uses of Diamond? | Diamond is the hardest naturally occurring substances with a very high melting point due to its giant covalent structure, having strong covalent bonds. As a result it is widely used in industry for diamond-edged tools and in oil-rig drills. Its hardness also makes it suitable for use as an abrasive. Its high reflective index and high reflectivity makes it suitable for jewellery. |
| What are the uses of Graphite? | It is suitable as an inert solvent, as lead pencils and as a dry, high temperature lubricant due to its high melting point and the layers of hexagons sliding over each other as the Van der Waals forces between them are easily broken. . It is also used as a moderator in nuclear reactors as it slows down neutrons but it is inefficient in absorbing them. |
| Describe the structure of Silicon Dioxide | The silicon atom is the centre of a tetrahedral structure and it is covalently bonded to 4 atoms of oxygen and each oxygen atom is covalently bonded to 2 atoms of silicon. |
| What are the properties of simple covalent compounds? | In simple molecular structures, a lattice of covalently bonded molecules is held together by weak intermolecular forces. 1. They are usually soft and brittle 2. They usually have a low melting and boiling points as the intermolecular forces between the molecules are weak 3. They are usually insoluble in water because it is energetically unfavourable for the water molecules to break their hydrogen bonds and form weaker bonds with the particles. 4. They do not conduct electricity as they have no free ions or free electrons. |
| Define the term 'ionic bonding' | This is also known as electrovalent bonding. It is the electrostatic attraction between oppositely charged ions. Loss and gain of electrons takes place so that the atoms are changed into ions which have a noble gas electronic structure. |
| What are the properties of ionic compounds? | 1. These compounds form crystals or crystalline structures 2. These compounds have high melting and boiling points 3. These compounds conduct electricity when in solution or molten 4. These compounds are usually soluble in water but not in nonpolar liquids |
| How does polarisation (partial covalency) arise? | Covalent character in an ionic bond is due to the polarisation of the anion by the cation. The extent of polarisation depends on the polarising power of the cation and the polarisability of the anion. |
| What do Fajan's Rules involve regarding the factors which result in high covalent character? | The cation must have a high positive charge and a small size while the anion must have a high negative charge and a large size |
| Characteristics of ionic compounds with appreciable covalent character? | There show abnormally low melting points and boiling points and are soluble in covalent solvents. |
| Define the term 'metallic bonding' | This is the type of bonding which occurs in metals. A metallic lattice is made up of metal cations held together by delocalised electrons which form an electron cloud, or a sea of electrons. There is an attractive force between the nuclei of the cations and the delocalised electrons. |
| What is the strongest kind of metallic bond? | The strongest metallic bond is formed between the cations having the highest charge density and the electron cloud with the high charge density as there is a very large attraction. |
| What are the properties of metallic bonds? | 1. Shiny Appearance 2. Generally high melting & boiling points 3. Good conductors of heat & electricity 4. Strong 5. Malleable & ductile 6. Metals are readily soluble in each other when molten and on cooling an alloy is formed |
| Define the term 'hydrogen bond' | This is the attraction between the lone pair of a highly electronegative atom of fluorine, oxygen or nitrogen and a hydrogen atom covalently bonded to a fluorine, oxygen or nitrogen atom in another molecule or chemical group and vice versa. It is an especially strong dipole-dipole interaction. |
| Define the term 'dipole-dipole interaction' | These intermolecular forces are present between unsymmetrical molecules which has a permanent dipole. The partially positive atom of one molecule is attracted to the partially negative atom of another molecule |
| Define the term 'Van der Waals forces' | This is the force which exists between closely positioned non-polar molecules. |
| Define the term 'Valency Shell Electron Pair Repulsion Theory (VSEPR Theory) | The molecular shape is determined largely by the number of different sets of electrons in the valency shell of the central atom. Since electrons are negatively charged, they repel each other and arrange themselves in space so as to minimise the repulsive forces. |
| Electron Pairs around central atom: 2 Bonding Pair around central atom: 2 Lone Pairs around the central atom: 0 | Name Of Shape: Linear Bond Angle: 180 |
| Electron Pairs around central atom: 3 Bonding Pair around central atom: 3 Lone Pairs around the central atom: 0 | Name Of Shape: Trigonal Planar Bond Angle: 120 |
| Electron Pairs around central atom: 4 Bonding Pair around central atom: 4 Lone Pairs around the central atom: 0 | Name Of Shape: Tetrahedral Bond Angle: 190 |
| Electron Pairs around central atom: 4 Bonding Pair around central atom: 4 Lone Pairs around the central atom: 0 | Name Of Shape: Tetrahedral Bond Angle: 190 |
| Electron Pairs around central atom: 4 Bonding Pair around central atom: 3 Lone Pairs around the central atom: 1 | Name Of Shape: Trigonal Pyramidal Bond Angle: 107 |
| Electron Pairs around central atom: 4 Bonding Pair around central atom: 2 Lone Pairs around the central atom: 2 | Name Of Shape: V-shape (Bent) Bond Angle: 104.5 |
| Electron Pairs around central atom: 5 Bonding Pair around central atom: 5 Lone Pairs around the central atom: 0 | Name Of Shape: Trigonal Bipyramidal Bond Angle: 107 |
| Electron Pairs around central atom: 5 Bonding Pair around central atom: 4 Lone Pairs around the central atom: 1 | Name Of Shape: See-saw Bond Angel: 90, 120, 180 |
| Electron Pairs around central atom: 5 Bonding Pair around central atom: 3 Lone Pairs around the central atom: 2 | Name Of Shape: T-shape Bond Angle: 90, 180 |
| Electron Pairs around central atom: 5 Bonding Pair around central atom: 2 Lone Pairs around the central atom: 3 | Name Of Shape: Linear Angle: 180 |
| Electron Pairs around central atom: 6 Bonding Pair around central atom: 6 Lone Pairs around the central atom: 0 | Name Of Shape: Octahedral Bond Angle: 90, 180 |
| Electron Pairs around central atom: 6 Bonding Pair around central atom: 5 Lone Pairs around the central atom: 1 | Name Of Shape: Square Pyramidal Bond Angle: 90 |
| Electron Pairs around central atom: 6 Bonding Pair around central atom: 4 Lone Pairs around the central atom: 2 | Name Of Shape: Square Planar Bond Angle: 90 |
| What is a dipole moment? | A molecule has a dipole moment if it turns in an electric field. It is a covalent molecule with polar bonds in which the dipoles do not cancel out. The bigger the dipole is the bigger the dipole moment. |
| What are delocalised orbitals? | Delocalised orbitals contain electrons which are not located between any 2 specific nuclei in a molecule, but are free to move between 3 or more nuclei. |
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