Topic 3: Bonding (physical chemistry) Flashcards
what is metallic bonding defined as
electrosatic force of attraction between cations and delocalised electrons in a lattice structure
describe covalent bonding
shared pair of electrons between non metals. Attraction between nucleus and electrons
describe metallic bonding
giant lattice. Positive cations with a sea of delocalized electrons
describe ionic bonding
Giant lattice. Metal and non metal. Donation and loss of electrons. Electrostatic attraction between oppositely charged ions
what is the bonding like for noble gases (group 8)
no bonding (stable full outer shell)
what are some similarities between ionic and metallic bonding
-Both have cations
-Giant lattices
-Both have strong electrosatic forces of attraction between opposite charges
ionic bonding
Ionic bonding:
-Non metal anion and metal cation
-Dot and cross diagrams are used to depict this
Formation of ions:
-A sodium ion would loose one electron to form a cation with a singly positive charge
-A chlorine atom would have to gain an electron to form an anion with a singly negative charge
state one observation when magnesium reacts with steam
white powder forms
Mg (s) + H2O (g) –> MgO (s) + H2
describe the bonding in magnesium
attraction between the lattice of Mg2+ ions and delocalised electrons
Explain why magnesium chloride has a high melting point
-giant ionic lattice
-strong electrostatic forces of attraction
-between Mg2+ and Cl- ions
give one medical use for MgOH2
indigestion relief
what does a single covalent bond contain
a shared pair of electrons
how many electrons are shared in a single, double and triple covalent bond
single - 2
double - 4
triple -6
what does a dative bond contain
a shared pair of electrons with both electrons supplied by one atom
define metallic bonding
Metallic bonding involves attraction between delocalised electrons and positive ions arranged in a lattice.
what is an ionic bond
the electrostatic force of attraction between oppositely charged ions
what is the structure of an ionic compound
giant lattice of metal cation and non metal anions held together by strong electrostatic forces of attraction between oppositely charged ions
what does it mean if ionic bonding is strong
which means that a large amount of energy is required to overcome the electrostatic force of attraction between oppositely charged ions
what does it mean if a lot of ions are present in an ionic lattice
each ion is attracted to many oppositely charged ions so a large amount of energy is required to overcome the electrostatic force of attraction
what is bond strength dependent on
-Radii is the size of the ion (radius) –> distance between the nucleus and the outer electron
-High charges and small radii have the strongest force of attraction
-The greatest attraction and strongest ionic bond forms small highly charged ions –> nuclear charge, atomic radius, shielding, attraction
how are dative covalent bonds indicated
using an arrow from the lone electron pair
how are covalent bonds held together
weak van der waals forces
true or false simple covalent molecules are poor conductors
true –> structure contains no charged particles
Explain how the ions are held together in a solid sodium metal
electrostatic forces of attraction between positive lattice and delocalised electrons
explain how the ions are held together in solid sodium chloride
strong electrostatic forces of attraction between oppositely charged ions
Why can metallic compounds conduct electricity
delocalised electrons flow through the structure and carry charge
why is sodium metal malleable
layers in lattice can slide over eachother
what statement about inorganic ionic compounds is always correct
they form giant structures
which molecule is not able to form a co-ordinate bond with another species
NH3 (permanent dipole)
Explain why flouride ion is larger than a sodium ion
flouride ion has lower nuclear charge so weaker attraction between nucleus and outer electron
Name the type of bond formed when HF reacts with H+
Dative covalent bond –> lone pair of electrons is donated from flourine
true or false - graphite has delocalised electrons
true
name the strongest attractive force between two ammonia molecules
hydrogen bonds
define electronegativity
the power of an atom to attract a pair of electrons in a covalent bond
Do group 1 or group 2 ions has stronger bonding
Group 2
-high nuclear charge
-smaller ionic radius
-stronger electrostatic forces of attraction
what ion is larger Na+ or Li+
Na+ –> more shielding
What ion has a larger radius K+ or Ca2+
-K+ has a larger radius than Ca2+ due to weaker nuclear charge
what happens as ionic radius decreases
attraction increases
why do ionic compounds have a high melting and boiling point
-high nuclear charge
-smaller ionic radius
-stronger electrostatic forces of attraction
why are ionic compounds brittle
-As force is applied the structure will move so that like ions are next to eachother. This results in repulsion of the ions
Suggest why MgO has a higher boiling point than NaCl
-Mg2+ has a greater nuclear charge than Na+
-MgO has a smaller ionic radius
-Therefore stronger electrostatic forces of attraction between Mg2+ and O2-
-This means that more energy is required to overcome forces of attraction
can ionic compounds conduct electricity
-Only conduct when molten or aqueous as ions become free to move when a potential difference is applied
-cannot conduct when solid as ions are in a fixed lattice so cannot move freely
define covalent bonding
the sharing of a pair of electrons between two non-metal atoms. There is a force of attraction present between the nuclei and both atoms of the electron pair
H—-H –> what does this line represent?
the line represents the covalent bond which is the shared pair of electrons
what do dot and cross diagrams show
the bonding pairs of electrons in a compound, we can use these to represent ionic and covalent bonding
what is the success criteria for dot and cross diagrams
-outer shell electrons
-how many electrons are required
-draw bonding pair
-draw lone pairs
what do lone pair of electrons do
Lone pairs of electrons:
–> They affect the shape of molecules
–> are important in chemical reactions of some compounds
–> are used to form dative covalent bonds
the melting point of sodium chloride is much higher than that of sodium metal. why?
ionic bonding is stronger than metallic bonding. this means that a lot of electron is required to overcome strong electrostatic forces of attraction
explain why the boiling point of water is much higher than the boiling point of hydrogen sulfide
-hydrogen bonding is stronger than intermolecular forces of attraction
what are the features of sodium chloride
-ionic crystal structure
-high melting and boiling points
-brittle
structure/features of diamond
-tetrahedral substance
-4 carbon bonds
-high melting points
why is lone pair repulsion present
-lone pairs around the central atom provide additional repulsive forces
-for every lone pair present the bond angle between covalent bonds is reduced by 2.5 degrees
v - shaped structure
-2 bonding pairs
-2 lone pairs
-104.5 degrees
pyramidal
-3 bonding pairs
-1 lone pair
-107 degrees
Explain what causes molecules to have shapes
-Molecules have shapes as the bonding and lone pairs repel each other as far apart as possible to reach a position of minimum repulsion and maximum separation
which has a bond angle of 109.5 degrees
Diamond
Explain why CF4 has a bond angle of 109.5 degrees
the central atom is surrounding 4 bonding pairs of electrons, Therefore they reach positions of maximum separation and minimum repulsion forming a tetrahedral shape
Explain how the electron pair repulsion theory can be used to deduce the shapes of the bond angle in PF3
-P has 5 electrons in the valence shell so needs 3 electrons to have a full outer shell
-the central atom of P is surrounding 3 fluorine bonds and has 1 lone pair
-this repels to positions of maximum separation and minimum repulsion
-the angle is 120 degrees and the shape is trigonal planar
what is the shape of an molecule with 2 lone pairs
104.5 degrees
-bent shape / v-shaped
what is the shape of a molecule with 1 lone pair
107 degrees
pyramidal
what are electron pairs
clouds of negative charge, so there is repulsion between them, forcing them as far apart as possible thus causing molecules to have a shape
(equal replusion between electron pairs)
what is the order of repulsion strength in terms of lone and bonding pairs
Lone pair–lone pair repulsion is greater than lone pair–bond pair repulsion, which is greater than bond pair–bond pair repulsion.
what are bond angles and when do they stop repelling
-the extent to which bonding pairs repel eachother results in a certain angle between them
-Bonds will stop repelling each other when there is maximum separation between bonds and minimum repulsion between pairs of electrons
linear
180 degrees
2 bonding pairs
trigonal planar
120 degrees
3 bonding pairs
tetrahedral
109.5 degrees
4 bonding pairs
trigonal bipyramidal
90 and 120 degrees
5 bonding pairs
octahedral
90 and 90 degrees
6 bonding pairs
what is VSEPR
valence shell electron pair repulsion theory
steps to calculating shapes of molecules
1) identify central atoms
2) count the central atom’s valence electrons
3) Add one electron for each bonding atom
4) Divide number of electrons by 2 to find total
5) number each electron pair
6) use this to predict the shape
what are double and triple bonds considered as
single bonds
–> called bonding groups
why do lone pairs have a stronger repulsion than bonding pairs
-lone pairs are held closer to the central atom than bonding pairs. This means that they have a stronger repelling effect than bonding pairs
what is the shape of ammonia
pyramidal
when calculating shapes of molecules what do you do when there is a positive ion
subtract 1electron
can ionic compounds dissolve in water (soluble aq) and why
yes because of the polarity of water that attract the positive and negative ions thus breaking up the structure
features of graphite
-low density
-layers can slide
-high melting point
-insoluble
-can conduct electricity
what shape is formed with 3 bond pairs and 2 lone pairs
trigonal planar
what shape is formed with 4 bond pairs and 2 lone pairs
square planar
What shape if H2F+
v-shaped
Explain the bond angle of H2O
104.5
-2 lone pairs which repel more than bonding pairs so bond angle reduces by 5 degrees
which is the most likely bond angle around the oxygen atom in ethanol
104.5 degrees
explain the bond angle in PF3
-central atom P has 5 electrons in valence shell
-needs 3 electrons from 3 F atoms
-PF3 has 3 bond pairs and one lone pairs
-lone pairs repel more than bonding pairs
-shape is tetrahedral with bond angle of 107
suggest one reason why electron pair repulsion theory cannot be used to predict shape of Cobalt chloride ion
too many electrons in d subshell
true or false when drawing molecules that are ions brackets have to been drawn
true
how can dative covalent bonds be demonstrated
dot and cross
line diagram
how is a normal bond shown
bond lies in the plane of the paper
how is a dashed bond shown
bond extends backwards away from the viewer
how is a wedged bond shown
bond protrudes towards the viewer
tetrahedral shape (drawing)
1 dashed line
1 wedge
2 normal lines
trigonal bipyramid (drawing)
1 wedge
3 normal lines
1 dashed
octahedral (drawing)
2 wedges
2 dashed
2 normal
trigonal planar (drawing)
3 normal
when does dative covalent occur
Dative covalent bonding occurs when one atom in a bonding molecule donates a pair of electrons to another atom. The other atom’s electrons are not involved in the bonding
steps for drawing dative covalent bonds
1) identify where the lone pair is donated from
2) draw the dot and cross diagram between carbon and oxygen
what does an electron dense map indicate
the region where you are most likely to find an electron
When the electron cloud is polarised, the electron cloud moves towards a positive region
define polarisation
the distortion of an electron cloud towards a region of positive charge
true or false - same atoms in a molecule are polarised
false - only different atoms in a molecule are polarised
define polar covalent bonding
bonding between atoms with different values of electronegativity
define ionic bonding with polarisation
small, highly charged cations causing partial covalency
factors that influence polarisation in ionic bonds
small cation that is highly charged, large anion that is easily polarised
-most ionic = lowest polarisation + larger radius
why does polarisation occur
-In a covalent bond between two different elements, the electron density is not shared equally
-polarisation is due to a difference in each elements electronegativity
define electronegativity
the ability of an atom to attract the bonding electron pair in a covalent bond
what does it mean if an element has a greater electronegativity
greater ability to attract the electron cloud and bonding pair of electrons
what element has the greatest electronegativity
Flourine
what is the trend in electronegativity down a group
decreases
trend in electronegativity across a period
increases
why do noble gases have no electronegativity
do not form covalent bonds
how is a bond considered polar
bond must have a difference in electronegativity greater than 0.5and less than 1.7
how is a bond considered non-polar
difference in electronegativity is less than 0.5
what is the difference in electronegativity for ionic bonds
more than 1.7
charges of electronegative atoms
the more electronegative atom has a partial negative charge
-the less electronegative atom has a partial positive charge
molecule polarity
-A molecule which has symmetrical polar bonds cancel out the dipoles and the molecule is non-polar
-A molecule which has asymmetrical polar bonds are polar
-The presence of lone pairs makes a molecule polar e.g water
predicting which molecule is polar
1) Does it contain polar bonds or not
2) Are there lone pairs on the central atom
3) Are atoms bonded to the same central atom
what causes a permanent dipole
a polar molecule
define a dipole
a difference in charge between two atoms caused by a shift in electron density
what are the most common elements for increasing electronegativity
H - C - N - Cl - O - F
what shape is carbon dioxide
linear
180 degrees
what does a higher difference in electronegatvity mean
molecule is more ionic
complete the sentence
the larger the electronegativity difference
the larger the dipole
what scale is used for electronegativity
the pauling scale
what does a larger difference in electronegativity mean
The greater the difference in electronegativity, the more polarized the electron distribution and the larger the partial charges of the atoms.
correlation between bond strength and length
single bond = weakest (longer)
double bond = stronger (shorter)
bonding in covalent molecules
Covalent bonds between atoms in a molecule are relatively strong however, the intermolecular forces between molecules are weak.
what are the 3 types of intermolecular forces
-hydrogen bonding
-permanent dipole-permanent dipole
-van der waal forces
van der waal forces
-exist between ALL covalent molecules (polar and non-polar except diamond)
-When two atoms in a molecule meet there will be an attraction between the electron cloud and nuclei of the atoms. There will also be repulsion between both of the nuclei and clouds of electrons
-dipole –> a bond whose ends have opposite charges
-van der waal forces are the weakest intermolecular forces
how do van der waal forces form
1) A non-polar molecule has an uneven distribution of electron cloud
2) The electron cloud has temporarily been displaced to one end
3) An instantaneous dipole is formed
4) A dipole in one molecule induces a dipole in another due to electrostatic attraction
5) Van der waal forces are formed
factors affecting van der waal forces
-number of electrons (more electrons = stronger forces)
-Points of contact (straight chain rather than branched)
why would there be a higher possibility of temporary induced dipoles
The larger the atom, the higher the polarizability. As the molecules get bigger there are more electrons so have a higher polarizability and therefore a higher possibility for temporary induced dipoles.
Permanent dipole-permanent dipole
-Only found in polar molecules
-If a molecule is polar due to its shape, it is said to have a permanent dipole due to a difference in electronegativity
-Between the molecules of HCl there is a difference in electronegativity due to bond polarity. Dipoles dont cancel out and therefore molecules have an overall dipole.
-If molecules contain bonds with a permanent dipole, the molecules may align so there is electrostatic attraction between the opposite charges on neighboring molecules
key features of a permanent dipole-permanent dipole interaction
-Polar molecules
-strong electrostatic attraction
-stronger than van der waal forces as it is permanent not temporary
-if van der waal forces have a larger boiling point than permanent dipole forces then the van der waal forces exerts the greater influence in this case
Explain why only van der waal forces exist in SiF4
-SiF4 is a non-polar molecule so has a symmetrical arrangement which means dipoles cancel out
-Temporary dipole is formed by an instantaneous dipole
-dipole induces in a neighbouring molecule due to electrostatic attraction
explain how permanent dipole-dipole forces arise between HCl molecules
-Difference in electronegativitiy leads to bond polarity
-permanent dipole forms between opposite charges on neighbouring molecules
Lone pairs for electronegative atoms
N = one lone pair
F = one lone pair
O = two lone pairs
what is the strongest intermolecular force
hydrogen bonding
what elements does hydrogen bonding only occur between
-Can only form with Nitrogen, Flourine and Oxygen as there is a significant difference in electronegativity
why can only N,O,F form hydrogen bonds with hydrogen
-very electronegative
-have a small atomic radius
-therefore makes a more polar bond
how are hydrogen bonds formed
The more electronegative atom e.g oxygen will attract the electrons more strongly away from the hydrogen. The covalent bond becomes polarised.
When the polarised bond is near a neighbouring molecule that has also been polarised by hydrogen will cause the two molecules to become attracted to eachother thus forming a hydrogen bond.
what are the steps to drawing hydrogen bonds
1) draw O H O in a straight line
2) Draw hydrogen bonding and one full covalent
3) Add in lone pairs and partial charges
4) Add in rest of the molecule
what do temporary dipoles cause
an attraction
state the strongest intermolecular force in an ice crystal
hydrogen bonding (water)
explain why iodine has a higher melting point than flourine
-iodine = larger atomic radius
-therefore has more electrons = stronger van der waal forces
-more energy required to overcome
what is the shape of NH2-
v-shaped/bent
104.5
why does magnesium have a much greater liquid range
forces of attraction in a molten metal are stronger
Describe the structure and bonding of graphite and explain why the melting point is very high
-each carbon atom covalently bonded to 3 other forming layers of hexagonal rings
-layers held by van der waal forces
-delocalised electrons able to flow through layers
-high melting point to overcome covalent bonds
define allotropes
different forms of the same element
what are the allotropes of carbon
diamond, graphite, graphene, fullerene, buckminister fullerene, nanotubes
what affects physical properties
bonding
crystal structure
Diamond
-Giant covalent structure
-each carbon atom bonded by covalent bonds to 4 other carbon atoms
-Rigid 3D structure
-Very strong
-Does not conduct electricity
Graphite
-macromolecular crystal
-each carbon atom is covalently bonded to 3 other in the same 2D plane thus forming hexagonal rings in layers
-Layers of graphite held weakly together by van der waal forces
-conducts electricity as for each carbon atom there is 1 delocalised electron
-delocalized electrons flow within a layer
-120 degrees bond angle (trigonal planar)
Graphene
-thinnest (1 layer of graphite)
-no van der waal forces only covalent bonds
-light weight and transparent
-good conductor (delocalised electrons for each C atom)
-3 carbon covalent bonds for each carbon
-120 degrees bond angle (trigonal planar)
fullerenes
-buckministerfullerene contains 60 carbon atoms –> each of which is bonded to 3 others by two single bonds and one double bond
-carbon nanotubes are another type of fullerene –> used to transport drugs to cells in the body and as components in electrical transistors
name the type of bond formed between N and Al
dative covalent bond
metallic structure
-Electrostatic attraction between metal cations in a lattice and a sea of delocalised electrons
-For every 1 cation 1 electron will be delocalised
why do metallic structures have a high melting point
-lattice structure
-strong attractions within lattice structure
-a lot of energy required to overcome the electrosatic force of attraction between cations and electrons
factors affecting melting point
-nuclear charge
-ionic radius
-attraction
hydrogen bonding
-soluble in water
-high melting and boiling point
what IMF forces are present in a NaCl lattice
permanent-dipole-permanent dipole –> polar
describe how the intermolecular forces arise in Cl2
-van der waal interaction arise due to uneven distribution in electron cloud
-results in instantaneous dipole
-the end of molecule will induce dipole in another molecule due to electrostatic attraction
Explain how the value of the bond angle in AlCl3 changes by the formation of the compound H3NAlCl3
Aluminium now surrounded by 4 bonding pairs
tetrahedral
109.5 degrees
which species had one or more bond angles of 90 degrees
ClF4-
permanent dipole-permanent dipole
The electron distribution in a covalent bond between elements with different electronegativities will be unsymmetrical. This produces a polar covalent bond, and may cause a molecule to have a permanent dipole.
why are positive ions smaller
greater p:e ratio
define covalent bond
shared pair of electrons between non-metal atoms
soluble vs insoluble
ionic = soluble
simple covalent, macromolecular, metallic = insoluble
square planar
90 degree bond angle
4 bond pair
2 lone pair
what is the angle/shape of a bond with 5 bond pairs and 3 lone pairs
linear (180)
no dipole =
no polarity
is a C-H bond polar or non-polar
non-polar
what helps salts separate from water
ion-dipole forces
hydrated ions seperate leaving ions by themseleves
e.g potassium iodide in water forms K+ and IOH
identifying a square planar
In square planar molecular geometry, a central atom is surrounded by constituent atoms, which form the corners of a square on the same plane. The geometry is prevalent for transition metal complexes with d8 configuration
bond angle in benzene
120 degrees
bond angle in cyclohexane
109.5
empircal formula of cyclohexane
CH2
type of bond is different to intermolecular force of attraction
e.g bond between nitrogen and hydrogen is a covalent bond
