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Description
Flashcards by Beth Ritchie, updated more than 1 year ago
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Created by Beth Ritchie
almost 12 years ago
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| Question | Answer |
| Define covalent bonding | The sharing of pairs of electrons, usually between non-metal atoms, to form molecules or giant structures |
| What holds covalently bonded atoms together? | The electrostatic attraction between the positive nuclei and the negative electron pairs shared between those nuclei |
| Define ionic bonding | The net electrostatic attractions between oppositely charged ions in a 3D lattice, which usually occurs between metal and non-metal atoms |
| How are ions formed? | By atoms losing or gaining electrons. More electronegative atoms gain electrons from less electronegative atoms |
| How are ions arranged? | In a giant lattice structure, with cations and anions arranged alternatively |
| How stron is the lattice? | Very strong due to strong electrostatic attractions |
| What is the melting point of ionic compounds, and how does it's structure explain this? | Ionic compounds have very high melting points, as the strong electrostatic forces need to be broken |
| What is the conductivity of ionic compounds, and how does it's structure explain this? | In solid form, ionic compounds cannot conduct as charged ions cannot move. However, when molten or in solution, ionic compounds can conduct |
| What is the bonding in metals, and how to they remain bonded together? | Metallic - each atom is detached from it's outer electrons, forming metal cations and a sea of delocalised electrons between which there is an electrostatic attraction |
| How does the metallic bonding model explain the conductivity of metal? | The delocalised electrons can carry charge when the metal is in solid or liquid state |
| How does conductivity change from Na to Mg to Al? | Because Na has 1 delocalised electron, Mg has 2 and Al has 3, they are more conductive respectively as there are more delocalised electrons to carry charge |
| How does the metallic bonding model explain the mallebility of metal? | Because layers of cations can slide over eachother without breaking the bonds as the delocalised electrons keep them bonded |
| What is the melting point trend down metal groups? | It decreases, as there is a larger atomic radius and therefore a weaker electrostatic attraction |
| What is the melting point trend across metal periods? | Increase, due to an increased number of delocalised electrons and an increased charge, so stronger electrostatic attraction to hold the atom together |
| What acronym explains the 3-D shapes of molecules? | VSEPR - Valance Shell Electron Pair Repulsion |
| What does the acronym mean? | Electron pairs repel eachother and get as far apart as possible to minimise repulsions |
| What happens to a molecules shape if only bond pairs are present? | The shape will be totally symetrical |
| When two atoms are bonded to a central atom with no lone pairs, what is it's shape and bond angle? | Linear, 180 degrees |
| When three atoms are bonded to a central atom with no lone pairs, what is it's shape and bond angle? | Trigonal planar (meaning it is on one plane), 120 degrees |
| When four atoms are bonded to a central atom with no lone pairs, what is it's shape and bond angle? | Tetrahedral, 109.5 degrees |
| When five atoms are bonded to a central atom with no lone pairs, what is it's shape and bond angle? | Trigonal bipyramid, 90 degrees and 120 degrees |
| When six atoms are bonded to a central atom with no lone pairs, what is it's shape and bond angle? | Octahedral, 90 degrees |
| Where are lone pairs relative to bond pairs? | Closer to the nucleus due to electrostatic attraction |
| What happens to 'normal' (symmetrical) angles when lone pairs are present? | Reduced by about 2.5 degrees per lone pair present |
| When three atoms are bonded to a central atom with a lone pair, what is it's shape and bond angle? | Trigonal pyramid, 107 degrees (109.5-2.5) |
| When two atoms are bonded to a central atom with two lone pairs (eg. Water), what is it's shape and bond angle? | V-shape, 104.5 (109.5 - 5) |
| What IMF's are between ionic compounds? | None |
| What IMF's are between metallic? | None |
| What IMF's between giant covalent? | None |
| What IMF's are between molecular covalent? | Van der Waals (for all), dipole dipole (for polar molecules) and hydrogen bonds (for H-F, H-N or H-O) |
| What is the melting point of ionic compounds and why? | Very high, because strong electrostatic attractions must be overcome |
| What is the melting point of metallic? | Very high (except Hg) and lots of energy is needed to overcome strong electrostatic attractions between cations and delocalised electrons |
| What is the melting point of giant covalent? | Very high, as they need lots of energy to break strong covalent bonds |
| What is the melting point of molecular covalent? | Low, as generally very little energy is needed to overcome weak IMF's but melting point varies on type of IMF and molecular size |
| What is the conductivity of ionic? | None, unless molten or in solution |
| What is the conductivity of metallic? | Very high, because delocalised electrons move |
| What is the conductivity of giant covalent? | Insulators, as there are no charged particles present, except for graphite which has delocalised electrons |
| What is the conductivity of molecular covalent? | Insulators - no charged particles present |
| What bonds are present in diamond? | 4 strong covalent bonds ber carbon atom |
| What shape is diamond? | Tetrahedral |
| What is diamond's bond angle? | 109.5 degrees |
| What are 3 properties of diamond? | High melting point, hard and non-conducting |
| What type of structure is diamond? | Giant covalent |
| What type of structure is graphite? | Giant covalent |
| What kind of bonds are in graphite? | 3 strong covalent bonds per carbon atom, leading to 1 delocalised electron per carbon atom |
| What is the shape of graphite? | Trigonal planar, with planes of carbon atoms in hexagons |
| What is the bond angle in graphite? | 120 degrees |
| What are 3 properties of graphite? | High melting point, soft due to sliding layers and conductive due to delocalised electrons |
| What is the structure of NaCl? | Giant ionic |
| What is the shape of NaCl? | Cubic |
| What is the coordination of NaCl? | 6:6 |
| What are 3 properties of NaCl? | High melting point, non conducting when solid, but conducts when molten or in solution |
| What is the trend in first ionisation energies across period 3? | General increase as nuclear charge increases, but decreases between Mg-Al as outer electron is in more distant and shielded 3p orbital, and decrease P-S due to e- pair causing repulsions |
| What is the trend in melting points across period 3? | Increases Na-Al as metallic bonds with more delocalised electrons, Si is higher due to strong covalent bonds, then P-Ar lower due to VW forces |
| What is the trend in boiling points across period three? | Increases Na to Al, as delocalised electrons increases, decreases Al-Si because vaporisation occurs when enough covalent bonds are broken to create Si2 and Si3 molecules, then VW forces |
| What is the trends in conductivities across period three? | Increase due to metals with more delocalised electrons, Si is a semi conductor, others are non-conducting |
| What are the trends in atomic radii across period three? | Decrease, as greater nuclear charge and same atomic radius and shielding |
| What are the trends in first ionisation energies down group two? | Decrease as electrons are more distant and more shielded |
| What are the trends in atomic radii down group two? | Increase as energy levels are added |
| What are the trends in electronegativities down group two? | Decrease as bond electron is more distant and more shielded from nucleus |
| What are the trends in melting points down group two? | Decreasae as metallic bonding is weaker because radius and mass of 2+ ions increase, reducing strength of electrostatic attraction |
| What are the trends in electronegativities across period three? | Increase due to increasing nuclear charge |
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