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Karteikarten von Lizzy Crockatt, aktualisiert more than 1 year ago
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Erstellt von Lizzy Crockatt
vor fast 8 Jahre
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| Frage | Antworten |
| When are ions formed in ionic bonding? | when electrons are transferred |
| What are valence electrons? | Outer electrons |
| Are metals cations or anions? | cations |
| Are non-metals cations or anions? | anions |
| Why do elements in group 14 have a tendency not to form ions? | Because they have 4 electrons in their outer shell => the energy to lose/gain/transfer 4 electrons is generally too large to be favourable. Therefore, they do not form ions. |
| What are polyatomic ions? | Ions made up of more than one atom |
| Give some examples of polyatomic ions and their charge, with an example of a compound containing that ion. | Any from: 1. Nitrate= 1- = lead nitrate 2. Hydroxide= 1- = barium hydroxide 3. hydrogencarbonate = 1- = potassium hydrogencarbonate 4. carbonate = 2- = magnesium carbonate 5. sulfate = 2- = copper sulfate 6. phosphate= 3- = calcium phosphate 7. ammonium = 1+ = ammonium chloride |
| What is ionization? | Ionization happens when an atom that loses electrons passes them directly to an atom that gains them. The atom is then said to be ionized. |
| Explain ionic lattices | The forces of electrostatic attraction between the ions in a compound cause them to surround themselves with ions of the opposite charge. As a result of this, the ionic compound takes on a predictable 3D crystalline structure called an ionic lattice. |
| What is a coordinate number? | This is what is used to describe or express the umber of ions surrounding an ion in an ionic lattice |
| What is a formula unit? | An expression of the simplest ratio of ions present |
| What is lattice energy? | A measure of the strength of attraction between the ions in an ionic lattice |
| When is lattice energy the greatest? Why? | The smaller the ions, the greater the lattice energy. This is because they have a larger charge density and so are highly charged. |
| The physical properties of ionic compounds reflect their ___ structure? | lattice |
| Do ionic compounds have high or low mp/bp? Why? | high. This is because their electrostatic forces of attraction are strong so they require more heat energy in order to break. |
| Are ionic compounds solid at room temperature? | yes |
| What is volatility? | The tendency of a substance to vaporize |
| What is solubility? | The ease with which a solide (the solute) becomes dispersed through a liquid (the solvent) to become a solution. |
| How is solubility determined? | by the degree to which the separated particles of solute are able to form bonds or attractive forces with the solvent. |
| Are water molecules polar or non-polar? Why? | Polar, because they have some separation of charge in their structure=> at the contact surface, the partial charges in the water molecules are attracted to ions of opposite charge in the lattice |
| When does a water molecule become hydrated? | When an ion separates from the lattice due to polarity, they become surrounded by water molecules |
| What is solubility based on? | The similar chemical nature of the solute and the solvent. |
| When do ionic compounds conduct electricity? | When in molten or in aqueous solution (i.e. not in solid) |
| A general expression to describe the notion of solubility trends? | "_ dissolves like _" |
| What does the ability of a compound to conduct electricity depend on? | The availability of the ions to carry a charge and move. |
| Are ionic compounds brittle or nah? Give an example | yes. Crystal tends to shatter when force is applied. |
| Why are ionic compounds usually brittle? | movement of the ions within the lattice, places ions of the same charge next to/alongsid each other and the repulsive forces cause it to split. |
| What is a binary compound? | A compound containing only 2 elements. |
| Describe the tendencies to lose or gain electrons referring to the periodic table. | The tendency to LOSE electrons and form POSITIVE ions increases DOWN a GROUP. So, the tendency to GAIN electrons and form NEGATIVE ions increases UP a GROUP |
| On the pauline scale, what does a difference of genereally 1.8 or more mean? | A compound which is predominantly ionic will be formed. |
| How is a covalent bond formed? | By sharing electrons |
| What is a group of atoms held together by covalent called? | a molecule |
| The formation of a covalent bond stabilizes the atoms so.... | energy is released as the bond forms. |
| How are the atoms in a covalent bond held at a fixed distance apart? | The forces between the two nuclei and shared electrons are balanced by the forces of repulsion between the 2 nuclei. |
| What is the octet rule? | the tendency of atoms to form a stable arrangement of 8 electrons in their outer shell. |
| What is a lone electron pair? | the electrons NOT involved in forming the bond. However, they play an important role in determining the shape of more complex molecules. |
| How are multiple bonds formed? | when multiple pairs of electrons are shared |
| How many electrons are shared in single, double and triple bonds? | single=2 (one pair) double=4 (2 pairs) triple=6 (3 pairs) |
| What is a diatomic molecule? Give examples. | Diatomic molecules are molecules composed of only two atoms, of the same or different chemical elements. The prefix di- is of Greek origin, meaning "two". If a diatomic molecule consists of two atoms of the same element, such as hydrogen (H2) or oxygen (O2), then it is said to be homonuclear. |
| Every covalent bond is characterized by two values, What are they? | Bond strength and Bond enthalpy |
| What is bond length? | A measure of the distance between the two bonded nuclei |
| What is Bond Strength? | Usually described in terms of bond enthalpy - effectively a measure of the energy required to break the bond. |
| Explain trend in atomic radius referring to periodic table and explain what this means. | Atomic radius increases as we go down a group. The atoms forms molecules with longer bonds. => The shared electron pair is further from the pull of the nuclei in the larger molecules, the bond however, gets weaker. |
| As the bond length ___ The bond enthalpy ___ | increases/decreases decreases/increases |
| Why do multiple bonds have stronger forces of electrostatic attraction between the bonded nuclei? | They have a greater number of shared electrons => greater pulling power on the nuclei => brings them closer together => results in shorter and stronger bonds |
| name the two types of bonds which double bonds are made up of. | sigma and pi |
| ___ bonds, ___ bonds, ___ bonds, respectively increase in length and decrease in strength | single, double, triple |
| Polar bonds result from __________ | unequal sharing of electrons |
| Why can the sharing of electrons be unequal? Explain in detail. | They can be unequal due to a difference in electronegativities. => Whichever atom in the bond has a higher electronegativity, exerts the greatest pulling power on the shared electrons and therefore gains more "possession". It is now said to be a polar bond as the bond is now unsymmetrical in respect to electron distribution. |
| What is a dipole? | This term is used to indicate the fact that a polar bond has two separated opposite electric charges. |
| More electronegative= slightly___ Less electronegative= slightly___ | negative postive |
| Describe electronegativity trends referring to th periodic table. | INCREASES across a period. INCREASES UP as group |
| The greater the difference in electronegativities in a covalent bond, the ___ polar the bond. | more |
| What is a pure covalent bond? | A bond that has 0 polarity- so a bond that is between two or more of the SAME atom. Since the atoms are the same, their electronegativities are identical and therefore there is no polarity. |
| How does the presence of a polar bond affect a molecule's properties? | The partial separation of charges introduces some ionic nature into covalent bonds... The more polar the bond, the more it's properties are similar to those of ionic. |
| Synonym for dot and cross diagram? | Lewis Structure |
| Many, though not all, ionic solids dissolve in water. This property depends on whether...... | the forces of attraction between the water molecules and the constituent ions of the crystal are strong enough to overcome the attractions between the ions themselves |
| Explain how ions become hydrated (Hint: refer to polarity and water ions) | Water molecules are polar as there is some separation of charge in their structure - note the ð+ and δ- charges on the water molecules. This polarisation occurs, because oxygen is more electronegative than hydrogen. At the surface of the crystal, where it is in contact with the water solvent, the partial charges in the water molecules are attracted to the oppositely charged ions in the lattice. This results in the ions being dislodged from their position. These ions break off from the lattice, becoming surrounded by water molecules. The ions become hydrated - surrounded by a hydration shell of water molecules. When this happens, the solid dissolves. |
| Why is the solubility of ionic substances in solvents, such as hexane and propanone, very limited? | Non-polar solvents cannot disrupt the crystal lattice in the same ways as polar solvents can. |
| Explain the electrolytic conductivity of sodium chloride in detail and what this means etc.. | Sodium chloride doesn't conduct electricity when solid because there are no electrons in the structure that are free to move. However, when it melts, sodium chloride can undergo electrolysis. This involves the flow of electricity caused by the movement and discharge of the ions. In the molten substance the ions are free to move laterally to the electrodes - this is known as electrolytic conductivity. In the process, the compound is split into its constituent elements.sodium and chlorine are produced. This is a chemical change rather than a physical process. |
| The ability of a compound to conduct electricity depends on what? | It depends on whether it has ions that are able to move and carry a charge. |
| Explain the brittleness of ionic crystals | -they tend to shatter if force is applied -They fracture across a plane when the layers of ions become incorrectly aligned =>This arises because the movement of the ions within the lattice when the force is applied places ions of the same charge next each other, so the repulsive forces cause the crystal to split. |
| Give an overview of the general properties of ionic compounds. (Give explanations) | Enter text here... |
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