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chemistry: organic > topic 2 - bonding and structure > Flashcards

topic 2 - bonding and structure Flashcards

1
Q

What are ions formed from?

A

Ions are formed when electrons are transferred from one metal atom to another non-metal atom, forming positively charged cations or negatively charged anions.

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2
Q

What do elements in the same group have in common regarding outer electrons?

A

Elements in the same group have the same number of outer electrons, so they have to lose or gain the same number to get the full outer shell, meaning they form ions with the same charges.

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3
Q

What is ionic bonding?

A

Ionic bonding is the strong electrostatic attraction between two oppositely charged ions. When oppositely charged ions form an ionic bond, an ionic compound is formed. The stronger the electrostatic attraction, the stronger the ionic bond and more energy needed to break it.

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4
Q

How does ionic charge affect the strength of an ionic bond?

A

The greater the charge on an ion, the stronger the ionic bond as the stronger electrostatic attraction, therefore the higher the melting/boiling point; ions with a high charge density form stronger bonds than ions with a low charge density.

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5
Q

How do ionic radii affect ionic bond strength?

A

The smaller the ions, which can pack closer together than larger ions, the stronger the ionic bond as the stronger electrostatic attraction due to smaller distance, therefore the higher melting/boiling point.

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6
Q

How do positive ions compare to their atoms?

A

Positive ions are smaller compared to their atoms as less electrons than the corresponding atom and the ratio of protons has increased so there is less repulsion between the remaining electrons, holding them more closely

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7
Q

How do negative ions compare to their atoms?

A

Negative ions are larger compared to their atoms as more electrons than the corresponding atoms but the same number protons so there is more repulsion between the electrons, making ion bigger

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8
Q

What does isoelectronic mean?

A

Isoelectronic is when ions have exactly the same number and arrangement of electrons, but the number of protons increases going through the series, increasing the attraction between the positive nucleus and the electrons, decreasing the ionic radius.

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9
Q

What are giant ionic lattice structures?

A

Ionic compounds form giant ionic lattice structures, which forms because each ion is electrostatically attracted in all directions to ions of the opposite charge.

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10
Q

What is a giant structure?

A

Giant structures are crystal structures in which all the atoms or ions are linked by a network of strong bonding extending throughout the crystal.

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11
Q

What is a lattice?

A

A lattice is a three-dimensional arrangement of atoms or ions in a crystal.

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12
Q

Do different ionic compounds have the same shaped structures?

A

Different ionic compounds have different shaped structures, but they are still giant lattices.

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13
Q

What do dot and cross diagrams illustrate in ionic bonding?

A

Dot and cross diagrams show the arrangement of electrons in an atom or ion and additionally which atom the electrons in a bond originally came from.

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14
Q

How does the theory of ionic bonding fit evidence from physical properties?

A

The theory of ionic bonding fits the evidence from physical properties such as high melting points, solubility, electrical conductivity, and malleability.

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15
Q

Why do ionic compounds have high melting points?

A

Ionic compounds have high melting points because ions are held together by strong electrostatic attraction (ionic bonds) which need a lot of energy to be overcome.

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16
Q

Are ionic compounds soluble in water?

A

Ionic compounds are soluble in water but not in non-polar solvents, supporting the idea that particles are charged.

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17
Q

What happens to ions in polar vs non-polar solvents?

A

Ions are pulled apart by polar molecules like water, but not by non-polar molecules.

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18
Q

Do ionic compounds conduct electricity in solid form?

A

Ionic compounds do not conduct electricity when they’re solid, but do when molten or dissolved, as ions are fixed in position in a solid but are free to move and carry a charge as a liquid or in a solution.

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19
Q

What happens to ionic compounds when shaped?

A

Ionic compounds can’t be shaped as ions of the same charge can’t be directly over each other if the layers are pulled, leading to strong repulsion and making ionic compounds brittle (break when they are stretched or hammered)

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20
Q

What does the migration of ions in electrolysis demonstrate?

A

The migration of ions, such as when a green solution of copper (II) chromate (VI) is electrolysed, supports the idea that particles are charged, cathode turns blue due to copper (II) and anode turns yellow due to chromate (VI) when current is passed through the solution

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21
Q

What are simple molecules formed from?

A

Simple molecules are formed when two or more non-metal atoms bond together and are held together by covalent bonds, but with weak forces of attraction between the molecules.

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22
Q

What is covalent bonding?

A

Covalent bonding is the strong electrostatic attraction between a shared pair of electrons and the positive nuclei of the atoms involved.

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23
Q

What do dot and cross diagrams illustrate in covalent bonding?

A

Dot and cross diagrams show how electrons behave in covalent bonds.

For covalent bonds, the number of outer electrons atoms have to lose/gain is the number of covalent bonds it forms with other atoms

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24
Q

What are hypervalent central atoms?

A

Have more than eight electrons in the outer shell, meaning they don’t follow the octet rule – commonly occur in third period elements or below because atoms can use d-orbitals to expand valence shell

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25
What are hypovalent central atoms?
Have fewer than eight electrons in their outer shell, resulting in an incomplete octet as don’t form all the bonds they can – typically found in electron-deficient elements which form stable compounds despite not having full octet
26
What is dative covalent bonding?
Dative covalent bonding is when one atom donates both electrons to a shared pair.
27
What must be balanced to maintain a covalent bond?
To maintain the covalent bond, there has to be a balance between the repulsive forces between the nuclei/bonding electrons respectively and the attractive forces between the nuclei and the shared electrons.
28
How are positive nuclei attracted in covalent molecules?
In covalent molecules, the positive nuclei are attracted to the area of electron density (shared electrons) between the two nuclei.
29
What is bond length?
Bond length is the distance between nuclei in a covalent bond, where attractive and repulsive forces balance each other.
30
How is bond length measured?
Bond length is measured by X-ray diffraction (for solids) or microwave spectroscopy (if gaseous).
31
How does electron shell/atomic radius affect bond length?
As the distance (radius) increases, the weaker attraction between the positive nucleus and the bonding electrons results in a longer bond.
32
What effect does shielding have on bond length?
Inner shells create a ‘barrier’ that reduces attraction between the positive nucleus and bonding electrons, leading to a longer bond.
33
How does the number of bonds between atoms affect bond length?
As the number of bonding electrons increases in a single covalent bond, the stronger the attraction between the positive nucleus and the bonding electrons, resulting in a shorter bond.
34
What is bond energy/enthalpy?
Bond energy/enthalpy is the energy required to break one mole of the bonds in a substance in the gaseous state.
35
What does molecular shape depend on?
The molecular shape depends on the number of electron pairs in the outer shell around the central atom and the type of electron pairs surrounding the central atom.
36
What does Electron-Pair Repulsion Theory state?
Electron-Pair Repulsion Theory states that a certain number of negatively charged electron pairs will repel each other to maximize separation and minimize repulsion.
37
How do lone pairs affect bond angles?
Lone pairs, which are electrons not involved in bonding, repel more than bonding pairs, causing the bond angle to decrease.
38
What is the effect of a lone pair in a trigonal pyramidal shape?
A lone pair causes the bond angle to decrease by 2.5º because the repulsion between the lone pair and bonding pairs is greater than bonding pair-bonding pair repulsion in the molecule.
39
What is the effect of a lone pair in a V-shaped molecule?
In a V-shaped molecule, the lone pair-lone pair repulsion is greater than the lone pair-bonding pair repulsion in trigonal pyramidal, further reducing the bond angle by an additional 2.5º.
40
How to explain shapes of molecules
1. State number of bonding pairs and lone pairs of electrons. 2. State that electron pairs repel and try to get as far apart as possible (or to a position of minimum repulsion.) 3. If there are no lone pairs state that the electron pairs repel equally 4. If there are lone pairs of electrons, then state that lone pairs repel more than bonding pairs. 5. State actual shape and bond angle
41
What is electronegativity?
Electronegativity is the tendency of an atom to attract a pair of electrons in a covalent bond, measured using the Pauling scale where a higher value indicates a more electronegative element.
42
How does electronegativity change across a period?
Electronegativity increases across a period due to increased nuclear attraction, with nuclear charge increasing and electron shell/atomic radius slightly decreasing.
43
How does electronegativity change down a group?
Electronegativity decreases down a group due to decreased nuclear attraction, as nuclear charge increases, shielding increases, and electron shell/atomic radius increases.
44
What characterizes a polar bond?
When the bond has different electronegativities, the bonding electrons are pulled towards the more electronegative atom, causing an uneven charge distribution and resulting in a polar bond.
45
What is a dipole in the context of electronegativity?
The difference in electronegativity between the two atoms causes a dipole which is caused by a shift in electron density in the bond
46
What is a dipole moment?
A dipole moment is a measure of the overall polarity of a molecule.
47
How does the difference in electronegativity affect bond polarity?
The greater the difference in electronegativity, the more polar the bond becomes, leading to a larger dipole moment.
48
What is formed if a molecule has a dipole?
Each atom has a partial charge, where one atom is slightly positive and the other slightly negative.
49
What characterizes a non-polar bond?
If both atoms have similar or identical electronegativities, the electrons sit roughly midway between the two nuclei, resulting in a non-polar bond.
50
What allows polar molecules to have a net dipole moment?
Polar molecules have polar bonds and an asymmetrical shape, allowing for a net dipole moment.
51
What doesn't allow non-polar molecules to have a net dipole moment?
Non-polar molecules may have polar bonds, but their symmetrical shape (all bonds identical and no lone pairs) cancels out any dipole moments, resulting in no overall polarity.
52
When can bonds between atoms be purely covalent?
Bonds between atoms of a single element, like diatomic gases, can be purely covalent because the electronegativity difference is zero, so bonding electrons are evenly arranged within the bond.
53
Are most compounds purely ionic?
Very few compounds are completely ionic due to oppositely charged ions; most have some degree of covalent character, meaning ionic and covalent bonding exist on a continuous scale at the extremes.
54
How does electronegativity predict bonding type?
Electronegativity can predict the type of bonding that will occur between two atoms; the greater the difference in electronegativity, the more ionic in character the bonding becomes. Correspond this electronegativity difference to the % ionic character in the Pauling scale to predict the type of bonding.
55
What is the experiment which can determine the polarity of molecules?
In this experiment, a charged rod (formed by rubbing a plastic rod) is brought close to a jet of liquid flowing from a burette. If the liquid is polar, the jet of liquid will be attracted to the electrostatic force of the rod. The dipoles in the polar molecules will all align and the negative ends δ- will be attracted to the positive rod (or vice versa). The stronger the dipole the more the deflection of the jet. Non-polar liquids will not be deflected and attracted to the charged rod
56
Can covalent bonding form giant structures?
Yes, covalent bonding can form great lattices as well as small molecules, where the giant structures have a huge network of covalently bonded atoms. The electrostatic attraction holding the atoms together in these structures are much stronger than the ones in simple covalent molecules.
57
What evidence do giant structures provide for covalent bonding?
The properties of giant structures provide evidence for covalent bonding, such as high melting points, insolubility in polar solvents, lack of electrical conductivity, and good thermal conductivity.
58
Why do giant structures have high melting points?
They have high melting points because lots of atoms are held together by many strong covalent bonds, which require a lot of energy to be overcome.
59
Are giant covalent structures soluble in polar solvents?
No, they are insoluble in polar solvents because strong covalent bonds mean atoms are more attracted to neighbors in the lattice than to solvent molecules, supporting the idea that they don’t contain ions.
60
Do giant covalent structures conduct electricity?
No, they do not conduct electricity as there are no charged ions or free electrons (all bonding electrons are held in localized covalent bonds) - except from graphite and graphene
61
Why are giant covalent structures good thermal conductors?
They are good thermal conductors since vibrations travel easily through the stiff lattices.
62
What makes the structure of giant covalent structures hard?
They are hard due to very strong covalent bonds throughout the lattice arrangement.
63
What is the structure of diamond?
In diamond, each carbon atom forms four covalent bonds with other carbon atoms. This forms a very rigid structure in a tetrahedral shape.
64
What is the structure of graphite?
In graphite, each carbon atom only forms three covalent bonds. This creates sheets of carbon atoms arranged in hexagons. There aren't any covalent bonds between the layers - they are only held together by weak intermolecular forces, so they are free to move over each other. This makes graphite soft and slippery.
65
Why can graphite conduct electricity?
In graphite, only three out of each carbon’s four outer shell electrons are used in bonds, so each carbon atom has one electron that's delocalized and can move. It does not conduct electricity from one layer to the next because the energy gap between layers is too large for easy electron transfer
66
What is the structure of graphene?
Graphene is a sheet of carbon atoms arranged in hexagons. It is basically a single layer of graphite. The sheet is just one atom thick, making it a two-dimensional compound. The network of covalent bonds makes graphene have very high tensile strength, so it can be added to composite materials to improve their strength without adding much weight.
67
Why can graphene conduct electricity?
Like graphite, graphene contains delocalized electrons, so it can conduct electricity through the whole structure.
68
What is metallic bonding?
Metallic bonding is the strong electrostatic attraction between the lattice of closely packed positive ions in a sea of delocalized electrons.
69
How is the overall lattice structure of metals formed?
The overall lattice structure is made up of layers of positive metal ions, separated by layers of electrons.
70
Why do metals have high melting points?
Metals have high melting points because lots of ions are held together by strong electrostatic attraction with delocalized electrons, which need a lot of energy to be overcome.
71
Are metals soluble?
Metals are insoluble except in liquid metals because of the strength of the metallic bond.
72
Do metals conduct electricity?
Yes, metals are good electrical conductors as delocalized electrons are free to move throughout the whole structure and can transfer charge through the metal.
73
How do impurities affect electrical conductivity in metals?
Impurities can dramatically reduce electrical conductivity by reducing the number of free electrons available to move and carry charge, as electrons transfer to the impurities and form anions.
74
Why are metals good thermal conductors?
Metals are good thermal conductors as delocalized electrons can transfer kinetic energy throughout the metal.
75
What is the malleability of metals?
Metals are malleable (can be shaped) because there are no bonds holding ions together and layers positive metal ions separated by layers of electrons, allowing layers of identical positive metal ions to slip/slide over each other without disrupting electrostatic attraction, the attractive forces in the lattice are the same whichever ions are adjacent
76
What is ductility in metals?
Metals are ductile (can be drawn into a wire) because there are no bonds holding ions together and layers positive metal ions separated by layers of electrons, allowing layers of identical positive metal ions to slip/slide over each other without disrupting electrostatic attraction, the attractive forces in the lattice are the same whichever ions are adjacent
77
How does nuclear charge influence the strength of metallic bonding?
The more protons, the stronger the bond
78
How does the number of delocalised electrons per atom influence the strength of metallic bonding?
The more electrons in the outer shell released to the sea of delocalised electrons, the stronger the bond
79
How does the electron shell/ionic radius influence the strength of metallic bonding?
The smaller the ionic radius, the stronger the bond * Decreases down a group due to shielding, increasing ionic radius and decreasing attraction * Increases along a period due to increasing nuclear number and no effect of shielding, decreasing ionic radius and increasing attraction
80
What are intermolecular forces?
Forces between molecules, much weaker than covalent, ionic, or metallic bonds.
81
What are London forces also known as?
Instantaneous dipole-induced dipole bonds.
82
Do London forces affect ionic substances?
No, they cause attraction in all atoms and molecules except ionic substances.
83
How are instantaneous dipoles formed?
Electrons in charge clouds always moving rapidly, so at any moment electrons in an atom more likely to be more to one side than the other causing instantaneous (temporary) dipole.
84
What effect does an instantaneous dipole have on neighboring atoms?
It induces another temporary dipole in the opposite direction on a neighboring atom, attracting them to each other. This continues with other neighbouring atoms.
85
Why do London forces constantly form and break?
Because electrons are constantly moving, dipoles are created and destroyed all the time, though keep changing the overall effect is attraction between atoms.
86
What is the effect of stronger London forces on melting and boiling points?
Stronger London forces result in higher melting and boiling points as more energy is needed to overcome them.
87
What two factors affect the strength of London forces?
1. Number of electrons (larger electron clouds form larger instantaneous dipoles, so stronger London forces). 2. Shape of the molecule (straight chains of alkanes have more molecular surface contact than branched alkanes, so stronger London forces).
88
Why do straight-chain alkanes have stronger London forces than branched ones?
Straight chains pack more closely together, allowing more molecular surface contact so more electrons to interact and form instantaneous dipoles for stronger London forces - longer the chain, stronger the London forces.
89
What is hydrogen bonding?
A strong intermolecular force occurring when hydrogen is covalently bonded to fluorine, nitrogen, or oxygen (NOF).
90
Why are substances with hydrogen bonding strong?
The large electronegativity difference between hydrogen and NOF causes strong electrostatic attraction between the positive partially charged hydrogen and lone pairs on NOF atoms in a molecule
91
What is the bond angle around hydrogen in hydrogen bonding?
180º, because two pairs of electrons around the H atom involved in a bond repel to maximize separation and minimize repulsion.
92
Why does ice float on water?
Ice has a lattice structure with maximum hydrogen bonds, wasting a lot of space as the length of hydrogen bonds > covalent bonds. As it melts, the lattice breaks down as some hydrogen bonds are broken, and water molecules fill the spaces, making ice less dense as there are more molecules in same space when melted - open hexagonal crystal lattice
93
Why do alcohols have higher boiling points compared to alkanes?
Alcohols form hydrogen bonds, which are stronger and require more energy to break than London forces in alkanes, meaning they have higher boiling points and more volatile.
94
Why does water have a higher boiling point than usual?
Water forms two hydrogen bonds per molecule due to oxygen's two lone pairs, making its bonding stronger and requiring more energy to break.
95
What are permanent dipole-permanent dipole forces?
Weak electrostatic forces between polar molecules due to partial charges and asymmetrical polar structures caused by a significant difference in the electronegativity between the atoms.
96
How do permanent dipole forces compare to London forces?
They are stronger and occur in addition to London forces, often resulting in higher boiling and melting points.
97
What causes the high boiling points of H2O, NH3, and HF?
Hydrogen bonding, in addition to London forces, requires more energy to break.
98
What causes the general increase in boiling points?
Increasing London forces due to the increasing number of electrons in the molecules.
99
What factors must occur for a substance to dissolve?
1. Bonds in the substance must break. 2. Bonds in the solvent must break. 3. New bonds must form between the substance and solvent.
100
Why do substances dissolve best in similar solvents?
The new bonds formed must be of similar or greater strength than the bonds broken, so substances usually dissolve best in solvents with similar intermolecular forces.
101
How do ionic substances dissolve in water?
Negative ions are attracted to the δ+ hydrogen atoms, and positive ions are attracted to the δ- oxygen atoms of water.
102
What happens during hydration of ions?
Ionic bonds in the lattice break, and new bonds form between ions and water molecules.
103
What determines the hydration enthalpy of an ion?
Higher charge density (e.g., smaller size or larger charge) increases hydration enthalpy by attracting water molecules more strongly.
104
Why don't some ionic substances dissolve in water?
The bonding between their ions is stronger than the bonds they would form with water molecules.
105
How do alcohols dissolve in water?
The polar -OH group forms hydrogen bonds between the lone pairs on the δ- oxygen atoms and the δ+ hydrogen atoms.
106
Why does the carbon chain length of alcohols affect solubility?
The carbon chain is non-polar, so longer chains reduce solubility as they are not attracted to water.
107
Why don't halogenalkanes dissolve in water?
Halogenalkanes contain polar bonds but their dipoles aren’t strong enough to form hydrogen bonds with water. The hydrogen bonding between water molecules is stronger than the bonds they would form with halogenalkanes, so halogenalkanes don’t dissolve.
108
What solvents can dissolve halogenalkanes?
Polar solvents that can form permanent dipole-permanent dipole bonds.
109
Why don't non-polar substances dissolve in water, and what substances do they dissolve in instead?
Non-polar substances form similar bonds with non-polar solvents. The hydrogen bonding between water molecules is stronger than the bonds they would form with non-polar substances, so non-polar substances don’t dissolve.
110
How can propanone dissolve both polar and non-polar substances?
Its CH3 groups form London forces with non-polar substances, and its C=O bond can hydrogen bond with water.

chemistry: organic (6 decks)

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