2023097
| Pregunta | Respuesta |
| Define ionic bond | An ionic bond is the electrostatic attraction between oppositely charged ions |
| What is an ionic bond? | When atoms combine, they do so by trying to achieve an inert gas configuration Ionic compounds are formed when electrons are transformed from one atom to another to form ions, with full outer shells in ionic compounds, the +ve and -ve ions are attracted to each other by strong electrostatic forces, building into a strong lattice Atoms aim to get a full outer shell |
| What does an ionic bond from between? | Ionic bonding occurs between METALS and NON METALS to from anions and cations The metal will loose or gain the electrons |
| What are the properties of ionic compounds? | - High melting and boiling points (due to strong attraction between ions) but still depends on size and charge of ions - Crystalline solids with ions organised into regular lattices - Conducts electricity when molten or in aqueous solutions, but NOT when solid, as ions are fixed in the lattice and cannot move - Brittle - Often soluble in water- polar molecules can attract opposite charges and pull them into solution, surrounding them Na+/Cl- Mg2+/ Cl- (NB 2:1 ratio) |
| How to write an ionic compound | Overall charge on the compound must equal 0 Lithium Fluoride - Li+/ F- = LiF Calcium Phosphate - Ca2+/ P3- = Ca3P2 Aluminium Bromide - Al3+/Br- = AlBr3 |
| What happens to ions containing more than one element? | In ions formed from more than one element, the charge is often spread (delocalised) throughout the ion POSITIVE ION: e.g. NH4+ in which all 4 N-H bonds are identical NEGATIVE ION: (Acid radicals) as they form when an acid looses one or more H+ ions e.g. OH- / NO3- / SO42-/ CO32-/ CH3COO- The formulas are then constructed in the same way e.g. Sodium Nitrate = Na+NO3- Ammonium Sulphate = (NH4+)2SO42- |
| When is a molecule ionic or covalent? | Ionic compounds are formed from metals of the left of the periodic table and non-metals of the right - Groups 1,2,3 (low electronegativity) - Groups 4,5,6 (high electronegativity) Generally the difference between electronegativities needs to be above 1.8 for ionic bonding to occur |
| Define covalent bond | A covalent bond is the sharing of electrons between two or more atoms with attraction between a pair of electrons and positively charged nuclei |
| What happens with single covalent bonds? Structure/ names/ examples | Covalent bonds can be shown using dot and cross diagrams where the atomic orbitals overlap Covalently bonded structures are called molecules The simplest covalent molecule is hydrogen Chlorine is another diatomic molecule with a single covalent structure. The outer lone electrons are shared and are electrostatically attracted by the positive nuclei |
| How do Lewis structures show single covalent bonds? | In Lewis structures, all valence electrons are shown - bonding and non- bonding A line represents an electron pair Dots and crosses can represent single electrons The carbon atom (2.4) has fewer electrons in its outer shell and requires a share in 4 more electrons, forming 4 single bonds with elements that only require a share in one more electron Nitrogen (2.5) forms 3 single bonds with hydrogen in ammonia, leaving one non-bonded pair of electrons In water, there are two lone pairs and in hydrogen fluoride, 3 lone pairs |
| Draw some Lewis structures with multiple covalent bonds | In some compounds, atoms can share more than one pair of electrons to achieve inert gas configuration Oxygen has a double bond and 2 lone pairs on each oxygen atom Nitrogen has a triple bond and 2 lone pairs on each atom |
| What is meant by a dative covalent (co -ordinate) bond? | The electrons in the shared pair originate from the same atom (both electrons from the same atom) The dative bond is indicated with an arrow coming from the donor atom (Carbon monoxide) |
| What is meant by covalent bond length and bond strength? | The strength of attraction that two nuclei have for the shared electrons affects both the length and strength of the bond There is considerable variation in the bond lengths/ strengths in single bonds of different compounds Double bonds are generally shorter and stronger than single bonds and triple bonds are the strongest covalent bond |
| What is meant by covalent bond polarity? | In diatomic molecules containing the same element (H2 or Cl2), the electron pair will be shared equally, as both atoms exert the same attraction When the atoms are different, the more electronegative atom exerts a greater attraction for the electron pair One end of the molecule will be more electron rich, resulting in a polar bond This relatively small difference in charge is represented by a delta -ve or +ve sign The bigger the difference in electronegativites, the more polar the bonds |
| What is the rule of HONC? | H - Hydrogen and halogens have 1 bond O - Oxygen forms 2 bonds N - Nitrogen forms 3 bonds C - Carbon forms 4 bonds |
| What is VESPR theory? | - The shapes of covalently bonded molecules are determined by the Valence Shell Electron Pair Repulsion theory - It states that electron pairs (charge centres) arrange themselves around a central atom to be as far apart as possible to minimise repulsion - Lone pairs repel more than bonded pairs - Single, double and triple bonds repel equally |
| What is the shape, bond angles, name of the shape and type of bonds in two charge centres | With two bonding pairs, the molecule is linear with 180 bond angles |
| What is the shape, bond angles, name of the shape and type of bonds in three charge centres | 3 bonding pairs = trigonal planer = 120 2 bonding pairs, 1 lone pairs = bent = 120 |
| What is the shape, bond angles, name of the shape and type of bonds in four charge centres | 4 bonding pairs = tetrahedral = 109.5 3 bonding pairs , 1 lone pair = trigonal pyramidal = 107 2 bonding pairs, 2 lone pairs = bent = 104.5 |
| What is the shape, bond angles, name of the shape and type of bonds in five charge centres | 5 bonding pairs = trigonal bipyramidal = axcial = 90 and equatorial = 120 4 bonding pairs, 1 lone pair = distorted tetrahedral/ k-shaped = 119 and 89 3 bonding pairs, 2 lone pairs = trigonal planer/ t-shape = 120 and 89 |
| What is the shape, bond angles, name of the shape and type of bonds in six charge centres | 6 bonding pairs = octahedral = 90 4 bonding pairs, 2 lone pairs = square planer = 180 5 bonding pairs, 1 lone pair = square pyramidal = 90 and 180 |
| How would you work out the shape? | To work out the actual shape of the molecule, count the number of pairs of electrons around the central atom and the number of each bonding and lone pairs |
| What happens to the shapes of ions? | Ions are formed when molecules loose or gain electrons and the shape/ structure is then shown in square brackets with the charge The types of ion usually involve dative covalent bonds |
| What is molecular polarity? | Whether a molecule is polar or not depends on its relative electronegativities of the atoms in the molecule and on its shape If the individual bonds are polar, then it doesn't necessarily mean that the molecule will be polar, as the resultant dipole may cancel out individual dipoles |
| Define electronegativity | The ability of an atom to attract electrons in a covalent bond The order of electronegativity is F > O > N > Cl |
| What are the types of intermolecular forces? | 1. Van der Waals (induced dipole/dipole) 2. Permanent dipole - dipole 3. Hydrogen bonding |
| What is Van der Waals forces? | Even in molecules with no polar bonds, there are temporary dipoles due to uneven distribution due to the constant movement of electrons (all molecules have VDW's, but they are the only forces between non-polar molecules) It induces a temporary dipole in a neighbouring molecule, producing dipole-dipole attraction The bigger the molecule (the more electrons, the greater VDWs The higher the Mr, the closer the molecules pack and therefore the stronger the VDWS |
| What are permanent dipole- dipole forces? | - Some molecules with polar bonds have an overall dipole - Polar molecules are attracted to each other by electrostatic forces - There are attractions between these permanent dipoles and the neighbouring molecules - The more polar the bond, the stronger the attraction and the higher the melting point |
| What is hydrogen bonding forces? | - Hydrogen bonding occurs when hydrogen is bonded directly to F,O or N - It is a special case of dipole-dipole attraction - The polar bond leaves hydrogen nucleus exposed and hydrogen only has one electron - There is therefore a strong attraction from the lone pair on the F, O or N of one molecule to the exposed hydrogen nucleus of another molecule - IT IS NOT A BOND - just a strong intermolecular force |
| In what order or strength are the three types of intermolecular force? | Hydrogen bonding the strongest, then permanent dipole dipole ad then VDWs * hydrogen bonds are in order of 1/10th the strength of covalent bonds, VDWs are in order of 1/00th of a covalent bond |
| Define allotrope | An allotrope is when an element can exist in different crystalline forms |
| What are 3 allotropes of carbon? | 1. Diamond 2. Graphite 3. Buckminsterfullerene |
| What is the structure and relating functions of diamond? | - Each carbon atom is covalently bonded to 4 others, to form a giant covalent structure - All the bonds are equally strong, meaning no panes of weakness in the molecule, making diamond exceptionally hard - All electrons are localised, so it doesn't conduct electricity *(silicon and silicon dioxide have a similar tetrahedral structure!) |
| What is the structure and relating functions and properties of graphite? | - Each carbon atom has very strong bonds to three others, giving layers of hexagonal rings (like a honeycomb) - There are only weak bonds between the layers, meaning layers can slide over each other, making graphite an excellent lubricant - Electrons are delocalised, meaning graphite can conduct electricity |
| What is the structure and relating function and properties of buckminsterfullerene? | - 60 carbon atoms are arranged in hexagons and pentagons to give a geodesic spherical structure - The discovery of buckminsterfullerene has lead to other similar carbon molecules being found, leading to a new branch of science - NANOTECHNOLOGY |
| What is metallic bonding? | - The valence electrons in metals become detached from individual atoms, so that the metals consist of a close packed lattice of positive ions in a sea of electrons - This happens when the atomic orbitals of the atoms overlap and loose their outer shell electrons to form cations |
| Define metallic bonding | The electrostatic attraction between positive ions and negative, delocalised electrons |
| Name 5 properties of metals | 1. Conductivity 2. Ductile 3. Malleable 4. Hard and high tensile strength 5. Soluable |
| Explain the property of conductivity in metals | - Metals contain delocalised (free) electrons so is an excellent conductor - Molten (ionic) salts can conduct electricity, but are chemically decomposed in the process - Metals conduct heat, as the ions are packed tightly, so vibrate in the lattice |
| Explain the property of ductability in metals | Metals are ductile (can form into a wire) as the bonding forces of attraction aren't broken, the metal ions can slide over each other to form a new lattice position and the delocalised electrons can continue to hold them together |
| Explain the property of malleability in metals | Metals are malleable (can be bent, reshaped and moulded under pressure) as the bonding forces of attraction are not broken, it is purely that the metal ions in the lattice can slide over each other, forming a new lattice position and delocalised electrons keep them together |
| Explain the property of hard and high tensile strength in metals | Metals have high and hard tensile strength because of the strong attractive forces within the lattice between the delocalised electrons and the positive metal cations |
| Explain the property of solubility in metals | Like tends to make like soluble Polar substances will tend to dissolve in polar solvents Non - polar substances tend to dissolve in non- polar solvents (heptane or tetrachloromethane) |
| What happens to melting point with in the metals going down a group? | Going down the group, the melting points decrease, as the size of the cation increase *The charge on the ion and the number of delocalised electrons stays the same |
| What happens to melting point with in the metals going across a period? | Going across a period, melting point increase, as the atomic radius, charge on the cation and number of delocalised electrons per atom increases |
| What does the strength of a metallic bond depend upon? | CHARGE DENSITY Consisting of 1. charge on the ion 2. Size of the ion |
| Define volatility | Volatility is how easily a substance turns into a gas |
| How does melting and boiling points relate to the type of bond? | When a liquid turns to a gas, the attractive forces between the particles are completely broken, so the boiling point is a good indication of the strength of IM forces When solids melt, the crystalline structure is broken down, but there are still some attractive forces between particles *Melting points are affected by impurities, weakening the structure and lowering melting points* |
| What type of melting and boiling points do covalent macromolecular structures and metals and ionic compounds have? | Covalent macromolecular structures have extremely high melting and boiling points Metals and ionic compounds also have high boiling points, due to the strong ionic attractions |
| What is the relationship between volatility and type of force? | The weaker the force, the more volatile the substance is |
| what is meant by "expanding the octet"? | Expanding the octet can occur in elements in period 3 or below, as the electrons can go into the d-subshell |
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