Ionic and Covalent Bonding

eimearkelly3
Flashcards by , created almost 6 years ago

Leaving Certificate Chemistry (Ionic and Covalent Bonding) Flashcards on Ionic and Covalent Bonding, created by eimearkelly3 on 07/24/2013.

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eimearkelly3
Created by eimearkelly3 almost 6 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