Structure and Bonding Unknown Information

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Is ammonium chloride ionic or covalent? Why?
Ionic because it is an interaction between the ammonium ion and chloride ions
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What sort of bonding is within ammonium ions?
Covalent
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Elements close together in the periodic table (groups 14,15,16 and 17) form...
Covalent compounds
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Elements far apart in the periodic table form...
Ionic compounds
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A covalent compounds is how many non-metal elements?
2 or more
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What are elements trying to do in forming ions?
Noble gas configuration and isoelectronic with nearest noble gas
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What does isoelectronic mean?
Same number of electrons
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Do transition metals try to gain a full outer shell of electrons?
No - variable states and d orbitals
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What sort of metals can form multiple ions?
Transition metals
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Where are electrons lost first when transition metals form ions?
4S
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What determines the number of electrons lost or gained in an atom?
Its electron configuration
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What charge does a silver ion form?
Ag+
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What is a hydrogencarbonate ion?
HCO3 -
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What is a nitrate ion?
NO3 -
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What is the charge of a nitride ion?
N 3-
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What is the charge of a phosphate ion?
PO4 3-
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What is a shortcut for calculating ionic formulae?
Swap over charges
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What is an ionic bond?
An electrostatic attraction between oppositely charged ions
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Are there individual ionic bonds? Explain
No because the electrostatic attractions extend throughout the whole structure in all directions
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What are rubies and sapphire mainly made of?
Aluminium oxide
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What is an exception to ionic compounds having high melting and boiling points?
Ethylammonium nitrate is a liquid at room temperature not a solid (low melting points)
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Force between ions is proportional to...
The products of the charges
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What allows conduction of electricity when an ionic compound is molten?
Ions are free to move to the electrodes allowing conduction
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Why are ionic compounds soluble?
Enthalpy of hydration and energy released when ions are surrounded by water molecules is enough to pay back enthalpy to break the lattice
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Why are ionic compounds not soluble in non-polar solvents?
Energy to break the lattice is not paid back by the formation of weak London dispersion forces with the solvent
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What is a covalent bond?
The electrostatic attraction between a shared pair of electrons and the positive nuclei of atoms that are bonded
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How many pairs of electrons are shared in a double and triple bond?
2 pairs in a double bond and 3 pairs in a triple bond
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Why is a triple bond stronger than a double bond?
The attraction of the two nuclei for 3 pairs of electrons is greater than for 2 pairs of electrons
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Why are triple bonds shorter than double and single bonds?
Stronger attraction between two nuclei and electron pairs
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Why are bonds weaker down a group?
Atomic radii are larger so electron pairs are further from the nuclei so less attraction
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What does electronegativity depend on?
The size of atoms and their nuclear charge
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What is electronegativity?
A measure of the attraction of an atom in a molecule for the electron pair in the covalent bond for which it is a part
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Who created the most commonly used electronegativity scale?
Linus Pauling
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What must we bear in mind with electronegativity values?
They have no physical quantity although they were derived from physical quantities (bond energies etc) or units and are for comparative purposes only
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Which group has electronegativity values of 0? Why?
Noble gases because they do not form compounds
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What has a higher electronegativity value, metals or non-metals?
Non-metals
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Name 4 highly electronegative atoms
Fluorine, chlorine, oxygen and nitrogen
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What must the difference in electronegativity be for a bond to be ionic?
More than 1.7
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What must the difference in electronegativity be for a bond to be covalent?
Less than 1.7
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What are exceptions to the electronegativity rule?
NaI and KI have electronegativity differences of 1.6 and 1.7 respectively but behave ionically
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What ions tend to obey the octet rule?
Polyatomic ions
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Name two exceptions to the octet rule?
Beryllium chloride (4 valence electrons) and boron fluoride ( 6 valence electrons)
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Can elements in period 3 expand their octet?
Yes
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What is an adduct?
Two molecules bonded together
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What bonding occurs in carbon monoxide?
Two covalent bonds and one coordinate covalent bond. Both atoms have a lone pair of electrons
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When are coordinate covalent bonds important?
Transition metal complexes
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When drawing Lewis structures, what is the outer atom (s)?
Normally the more electronegative atoms
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Where do the electrons come from to form a carbonate ion?
The metal it was attached to. The carbonate ion cannot just be formed on its own
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In ozone, no matter where the double bond is positioned, how many lone pairs of electrons is on that oxygen atom?
2
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How many lone pairs of electrons are on the oxygen atoms in ozone not connected by a double bond?
3
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What must you always do when drawing the Lewis structure of a charged ion?
Square brackets with charge on outside
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How many lone pairs are always on the central carbon in ozone?
1
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Are bond lengths equal or different in the carbonate ion, ozone and benzene molecules? Why?
They are all the same because the actual molecule is considered to be a hybrid of resonance structures
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Why can elements in period 3 or more expand their octets?
They have d orbitals available for bonding
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What method can be used for covalent structures consisting of period 2 atoms and period 3 if no expanded octet?
Add up total valence electrons and divide by two. That is how many lines you have. Assign each atom a single bond and give the rest as lone pairs. Move lone pairs around to make double bonds and ensure the octet rule is obeyed for all atoms
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What is the valence shell electron pair repulsion theory?
Pairs of electrons (electron domains) in the valence shell of an atom repel each other and will therefore take up positions in space to minimise these repulsions (far apart as possible)
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Do multiple bonds count as multiple electron domains?
No just one
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If sulfur dioxide was drawn with an expanded octet would it make any difference to the shape?
No
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What shape is carbon dioxide?
Linear
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If sulfur dioxide was drawn with an expanded octet would it make any difference to the shape?
No
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What shape is carbon dioxide?
Linear
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Polarity only occurs it what sort of compounds?
Covalent
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Although bonds might be polar, when might a molecule not be polar?
If symmetry is expressed so the individual dipole moments cancel out
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What is a dipole moment?
The product of one of the charges making up a dipole and the distance between the charges
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What value for dipole moment do non-polar molecules have?
Zero
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What is an allotrope?
Different forms of the same element
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Name four allotropes of carbon
Diamond, graphite, graphine and fullerenes
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What makes allotropes different?
How the atoms are bonded together
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What sort of array is diamond? Why?
Tetrahedral because each carbon atom is bonded to four other carbon atoms
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What sort of structure is diamond?
One giant covalent structure (macromolecule)
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What is the melting point of diamond?
4000 degrees celcius
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Why is diamond hard and has a strong melting/ boiling point?
Strong covalent bonds require lots of energy to break
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Why does diamond not conduct electricity?
Electrons are fixed in the covalent bonds in the molecule and are not free to move
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Why is diamond insoluble in water?
Strong covalent forces means more energy is used to break them than is paid back to solvate the carbon atoms
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How many other carbon atoms are bonded to each carbon atom in graphite?
3
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What sort of intermolecular forces exist between layers of graphite? How is this useful?
Weak London dispersion forces so layers can be easily separated. This is good for a lubricant and pencil leads
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Does graphite have a low or high melting/ boiling point?
High because it still has strong covalent bonds between carbon atoms
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Is graphite soluble in water or non-polar solvents?
No because of strong covalent bonds
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Why can graphite conduct electricity?
Carbon has only 4 electrons on its outer shell but uses only 3 to form bonds in graphite with 3 other carbon atoms. This leaves a spare p orbital containing one electron and they overlap to form a pi delocalised system allowing electrons to move
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What are properties of graphene?
High tensile strength, thermal conductor, electrical conductor and high melting/ boiling points
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What sort of structure is buckminsterfullerene compared to all the other allotropes of carbon?
Molecular
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What is the C60 fullerene composed of?
Individual C60 molecules composed of covalent bonds and bonded to each other by weak London forces
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Why is the C60 fullerene insoluble in water but soluble in organic solvents?
Energy used to break weak London dispersion forces is paid back making London forces between solvent and individual C60 molecules
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Why can C60 fullerene not conduct electricity despite having a pi delocalised system?
The shape of individual molecules means electrons cannot move from one molecule to another
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What shapes are the C60 fullerene molecules composed of?
Hexagons and pentagons
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How many atoms are each carbon atom attached to in C60 fullerene molecules?
3
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What is the structure of silicon dioxide?
A giant covalent structure. Each silicon atom is attached to 4 oxygen atoms and each oxygen atom is bonded to 2 silicon atoms. In a tetrahedral array but bent structure for a single oxygen atom
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Why is the molecular structure of silicon dioxide SiO2 not SiO4?
Each silicon has a half share of the electrons from the four oxygen atoms
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Does silicon dioxide have high or low melting and boiling points?
High due to strong covalent bonds
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Why is quartz used as a material in clocks and watches?
It is a piezoelectric material
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London dispersion forces act between...
Non-polar atoms/ molecules
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Melting and boiling points depend on...
Intermolecular forces
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What defines Van der Waal's forces?
London dispersion forces, dipole-dipole interactions and dipole-induced dipole interactions
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In what states of matter do London dispersion forces exist?
Solids and liquids
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Why do temporary (instantaneous) dipole- induced dipole interactions occur?
Electrons are constantly moving and at any one point, may not be evenly distributed in the atom nuclei. This results in a temporary induced dipole to create the opposite dipole in a neighbouring atom. These dipoles attract each other
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If dipole - induced dipole interactions constantly appear and disappear, how do atoms still stay together?
Overall force is attractive because dipole always induces opposite dipole
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Why do dipole-induced dipole interactions increase as molecular mass increases?
Increased number of electrons so stronger dipole moments. Outer electrons less strongly held in larger molecules so more polarisable
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Why do longer hydrocarbon chains have higher melting and boiling points?
More atoms, more electrons leading to more and stronger dipole-induced dipole interactions and more points of contact between chains
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Are dipole-dipole interactions temporary or permanent?
Permanent
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When comparing molecules, what must we keep the same to see the intermolecular forces and effects?
Molecular mass
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Aldehydes are...
Polar
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Hydrogen bonds are still weaker than...
Covalent bonds
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Which atoms when connected to a hydrogen atom show hydrogen bonding?
Nitrogen, oxygen and fluorine
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As well as a very electronegative atom, what must there also be on the electronegative atom?
At least one lone pair of electrons
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Why do cis dioic acids have a lower melting point that trans dioic acids?
More intramolecular hydrogen bonding as COOH groups are closer so less intermolecular hydrogen bonding. Trans forms have less intramolecular hydrogen bonding as COOH groups are further away
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Melting and boiling covalent molecules, do the covalent bonds break?
No
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What allows dissolving to occur?
If the intermolecular forces of the solvent and solute are similar
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Why is pentane not soluble in water?
Energy released to form London dispersion forces with water does not pay back energy put in to break strong hydrogen bonds between water molecules
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Why are longer chain hydrocarbons less soluble in water?
Longer chain prevents water molecules on either side hydrogen bonding with each other. Energy needed to break hydrogen bonds but not paid back to form weaker London forces with the hydrocarbon
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What sort of interactions form between water and ions?
Ion-dipole interactions
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When is an ionic substance soluble in water?
If the energy released to hydrate ions is equal to the energy used to break apart the lattice
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Are covalent molecules volatile or non-volatile?
Volatile (weaker intermolecular forces can be broken)
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When might some covalent molecules dissolve in water?
Ionisation so they form ions
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How is a metallic bond electrostatic in nature?
Attraction between positive ions and delocalised negatively-charged electrons
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What holds a metallic lattice together?
Each electron is attracted by all positive ions
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Give three reasons why magnesium has stronger metallic bonding than sodium
Forms a 2+ charge compared to a 1+ charge so stronger electrostatic attraction between ions and electrons. Magnesium is smaller than sodium so electrons are closer to the positive nuclei and are more strongly attracted. Two electrons per magnesium
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What is metallic bonding?
An electrostatic attraction between positive ions in the lattice and the delocalised electrons
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Give some properties of metals
Lustrous (shiny when freshly scratched/cut), malleable, ductile, good conductors of heat and electricity
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Is diamond a good conductor of heat?
Yes because vibrations can travel through atoms
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Why are metals malleable and ductile?
The electrostatic attractions are non-directional and positive ions attract electrons in all directions so when two layers slide, the bonding is identical unlike ionic solids where repulsion between like-charges would occur
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Why is mild steel used for car bodies?
Malleable
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What composes steel?
Iron and carbon
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What is brass composed of?
Copper and zinc
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What is bronze composed of?
Copper and tin
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What is pewter composed of?
Copper, tin and antimony
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What are alloys?
Homogeneous mixtures of two or more metals or a metal and a non-metal
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Why are alloys stronger and stiffer than pure metals?
Differently-sized atoms prevent planes of atoms/ ions sliding over each other
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What is combined when you make alloys?
The desirable qualities of the metals
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How can alloying not be useful?
Alloys of aluminium are more susceptible to corrosion. Alloys of copper have their electrical conductivity reduced
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What is duralumin made of and used for?
Aluminium and copper for aeroplane parts because aluminium on its own is too soft but it keeps its low density
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What is formal charge?
The charge of an atom in a molecule we would expect if electrons were shared equally in the covalent bond atoms are bonded by
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What assumption is made when calculating formal charge?
Atoms have the same electronegativity
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How can atoms in a molecule gain a formal charge?
Coordinate covalent bond or molecule is an ion
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How do you calculate formal charge?
Number of valence electrons on atom - (1/2 no. bonding electrons) - no. non-bonding electrons
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Which Lewis structure is preferred by the formal charges?
The one closest to zero
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What is it called if an atom has less than an octet of electrons?
Incomplete octet
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Give examples of molecules with an incomplete octet
BF3, BCl3, BeCl2 (g)
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How can you draw molecules with an expanded octet to not have an expanded octet?
Use coordinate covalent bonds instead of double bonds
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Compounds composed of what normally have an expanded octet?
Noble gases
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Why are there two bond angles in a trigonal bipyramidal structure?
Not possible to give positions evenly spaced around a sphere
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What are the equatorial and axial planes in trigonal bipyramidal structures?
Equatorial is where lone pairs position around the middle plane. Axial are above and below the central triangle
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How do you make xenon fluoride?
Heat with excess fluorine gas at high temperature and pressure in nickel container. White, crystalline solid at room temperature
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What orientation must orbitals be for a sigma bond to occur?
Head-on/ axial
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What is a coordinate covalent bond in terms of orbitals?
When an orbital containing two electrons overlaps with an empty orbital
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What is the linear combination of atomic orbitals (LCAO)?
A mathematical approximation that assumes molecular orbitals can be described as linear functions (adding or subtracting wave functions). aka adding or subtracting s or p orbitals
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In sigma bonds, where does the electron distribution lie?
On the axis joining the two nuclei
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Where is the electron distribution in a pi bond?
Above and below the internuclear axis
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As well as p orbitals overlapping side-on, how else can pi bonds be created?
a p and d orbital overlapping or two d orbitals
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Is a pi bond stronger or weaker than a sigma bond?
Weaker
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Why are sigma bonds stronger than pi bonds?
More direct attraction between electron pair and nuclei
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Why are the bonds equal lengths in ozone?
Resonance hybrids
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How do you show two resonance structures?
Double-headed arrow
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What is delocalisation?
Sharing a pair of electrons between three or more atoms
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What are the bond orders of single, double and triple bonds?
1, 2 and 3
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How can the bond lengths in ozone be explained by delocalisation?
Pi delocalised system so electron pair shared across 3 oxygen atoms. Each O-O bond has half share of the electrons so both have a bond order of 1.5 and are identical
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If you can draw resonance structures where the only difference is the position of the double bond (lone pair)...
There is a delocalised structure
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If you are asked to draw the delocalised structure of a molecule, what do you not include?
Lone pairs of electrons
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The lower the bond order...
The longer the bond
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What is the bond order of benzene? Why?
1.5 because pi component of each double bond is shared between 2 C-C bonds
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UV-C has the shortest wavelength. What length?
Less than 280nm
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What wavelength range is UV-B?
280-320nm
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What wavelength range is UV-A?
320-400nm
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How many unpaired electrons in an oxygen free radical?
2 per atom
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Which UV radiation is required to break an oxygen molecule?
UV-C - less than 242nm
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Radiation up to what wavelength can break ozone molecules?
330nm - bond order 1.5 so weaker than a double bond and less radiation needed
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When O3 is broken by UV-B, what is formed?
Oxygen free radical and an oxygen molecule
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Which UV reaches the Earth's surface?
UV-A which is least harmful
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How can ozone molecules be destroyed?
Free radicals in nitrogen oxides or CFCs when broken down by UV light
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What does CFC stand for?
Chlorofluorocarbons
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What is homolytic fission?
One electron goes back to each atom making the bond
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Why does hybridisation occur?
So bonding orbitals can be at the correct orientation for bonding
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What is required for hybridisation?
Energy to promote an electron
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Do characteristics of original orbitals remain in hybridisation?
Yes
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sp3 orbitals are closer in energy to which orbitals?
p orbitals
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Hybrid orbitals are...
Degenerate (same energy)
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What forms sigma bonds in methane?
sp3 orbitals on central carbon overlap with s orbitals on hydrogen atoms
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How is a pi bond created in ethene?
One hydrogen atom is not involved in hybridisation
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The number of hybrid orbitals corresponds to what?
The shape of the molecule
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To tell the hybridisation, what should you look at?
Shape of the molecule (how many domains to how many orbitals there must be)
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Card 2

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What sort of bonding is within ammonium ions?

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Covalent

Card 3

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Elements close together in the periodic table (groups 14,15,16 and 17) form...

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Card 4

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Elements far apart in the periodic table form...

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Card 5

Front

A covalent compounds is how many non-metal elements?

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