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Erstellt von eimearkelly3
vor etwa 11 Jahre
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Frage | Antworten |
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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