152830
Description
Flashcards by eimearkelly3, updated more than 1 year ago
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Created by eimearkelly3
almost 13 years ago
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| Question | Answer |
| Compound | Two or more elements chemically combined |
| Give one way in which compounds can be broken down into their elements. | Electrolysis |
| Hydrated substances contain | molecules of water in definite proportions |
| How can water of crystallisation be driven off? | Heating |
| Water of crystallisation | Water chemically combined in definite proportions in a crystalline compound. |
| Valency | The number of bonds an atom forms when it reacts. |
| Octet rule | Atoms on reaction tend to a stable electron arrangement with eight electrons in its outer shell. |
| Exceptions to the octet rule | Beryllium and boron Sulfur and phosphorous D-block elements Hydrogen, helium, lithium (2 in outer shell) |
| Valency of group 1 | I |
| Valency of group 2 | II |
| Valency of group 3 | III |
| Valency of group 4 | IV |
| Valency of group 5 | III |
| Valency of group 6 | II |
| Valency of group 7 | I |
| Valency of group 0 | 0 |
| Why is helium safer than hydrogen in balloons and blimps although they both have low densities? | Helium is not flammable |
| Why is argon added to light bulbs? | To prevent the tungsten filament for melting or reacting |
| Ionic bonding typically happens between | Metals and non-metals |
| Ionic bond | The electrostatic force of attraction between oppositely charged ions. |
| Positively charged ions | Cations |
| Is the cation generally larger or smaller than the corresponding atom? | Smaller |
| Do the metals or the non-metals become cations? | Metals |
| Negatively charged ions | Anions |
| Do metals or non-metals generally become anions? | Non-metals |
| Is the anion generally larger or smaller than the corresponding atom? | Larger |
| Electrons are ...... in ionic bonding | Transferred |
| Everyday examples of ionic substances | Table salt (food preservation and flavouring) Brine (a solution of sodium chloride used for curing bacon --> preservation) Salt tablets (taken to replace salt lost by the body through sweat) Fluoride compounds (sodium fluoride - prevents food decay - added to water and occasionally toothpaste) |
| Characteristics of ionic substances | Solids - high melting and boiling points Conduct electricity when molten or in aqueous solution (electrolytes) Soluble in water |
| Electrons in a covalent bond are | Shared |
| Each shared pair is | A covalent bond |
| Electron pairs involved in bonding are called | Bonding pairs |
| Electron pairs not involved in bonding are called | Lone pairs |
| Ionic bonding results in the formation of | A rigid 3D crystal lattice |
| Covalent bonding results in the formation of | Molecules |
| Covalent bonds form between | Non-metals |
| Double covalent bonds form between | oxygen atoms |
| Triple covalent bonds form between | Nitrogen atoms |
| Two s orbitals overlapping | sigma bond |
| Pi bond | Two p orbitals overlapping sideways |
| The strength of covalent bonds can be measured by | Bond dissociation energies |
| Electrons shared equally | Non-polar / pure covalent bond |
| What two factors dictate the extent to which the shared electrons are attracted by different nuclei | Size of the atom The nuclear charge |
| Electrons shared unequally | Polar covalent |
| Characteristics of covalent compounds | Liquids or gases at room temperature Low melting and boiling points Not soluble in water (except polar covalent) Do not conduct electricity (neutral molecules) |
| Examples of covalent compounds | Polar solvent = water Polar = glucose Non-polar solvent = cyclohexane Non-polar = petrol or oil |
| Electronegativity | A measure of the relative attraction an atom has for the shared pair of electrons in a covalent bond. |
| What is the most common scale of electronegativity? | Pauling scale |
| The higher the electronegativity value | The better it is at attracting the shared electrons towards itself |
| 3 factors responsible for the variation in electronegativity values | Nuclear charge Atomic radius Screening effect of inner shell electrons |
| Difference of more than 1.7 | Ionic |
| Difference of 0 or very little | Pure covalent / non-polar covalent |
| less than 1.7 | polar covalent |
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