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Chemistry > Chemical Bonding > Flashcards

Chemical Bonding Flashcards

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1
Q

Structure of giant ionic lattice

A

Constituent ions held in fixed positions in an orderly arrangement,

attraction between oppositely charged ions is maximum and repulsion between similarly charged ions is minimum.

Bonds are non-directional, attracts oppositely charged ion in all directions without preferred orientation

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2
Q

Ionic bond definition and factors

A

Ionic bond is electrostatic attraction between cations and anions in ionic lattice

Greater magnitude of lattice energy, stronger the ionic bond

Favoured by higher charge (greater electrostatic attraction) and smaller radius (shorter inter-ionic distance between ions, resulting in greater attraction)

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3
Q

Physical properties of ionic compounds

A

High melting and boiling points (low volatility)
- Large amount of energy required to break strong ionic bonds between oppositely charged ions for melting/ boiling

Generally soluble in polar solvent but insoluble in non-polar solvent

Conducts electricity in molten/ aqueous state but not in solid state (ions can act as mobile charge carriers only if they are free to move)

Hard and brittle (strong attraction between planes becomes strong repulsion and ionic crystal lattice shatters)

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4
Q

Simple molecular lattice made up of…

A

Made up of molecules attracted to each other by weak intermolecular forces

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5
Q

Physical properties of simple molecular lattices

A

Relatively low melting points (attractive forces between molecules are weak)

Soluble in non-polar solvents (both solute and solvent have same type of intermolecular interaction)

Do not conduct electricity in solid or molten state (absence of mobile charge carriers)

Substance may conduct electricity if it ionises in the water (hydrogen chloride)

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6
Q

Giant metallic lattice and metallic bond

A

Composed of rigid lattice of positive ions surrounded by a sea of delocalised electrons

Electrostatic attraction between a lattice of positive ions and delocalised valence electrons that do not belong to any cation but to crystal lattice as a whole

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7
Q

Strength of metallic bonds and factors

A

Strong and non directional

  1. Number of valence electrons available (greater number of valence electrons, more delocalised electrons and greater electrostatic attraction between electrons and cations, bonds stronger)
  2. Charge of cations (higher charge of cations, more attractive, stronger bonds)
  3. Size of cations (smaller size, higher charge density, greater electrostatic attraction for delocalised electrons, stronger bonds)
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8
Q

Physical properties of metals

A
  1. High electrical conductivity (delocalised electrons function as charge carriers and flow towards positive terminal)
  2. Good thermal conductivity (electrons take in thermal energy and move faster and randomly, colliding w other electrons and passing energy to them)
  3. Malleable and ductile (layer of positive ions can glide over another easily due to delocalised electrons)
  4. High density (closely packed ions)
  5. High melting and boiling points (strong metallic bonds)
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9
Q

Covalent bond definition

A

Electrostatic attraction between shared pair of electrons and positively charged nuclei

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10
Q

Dative covalent bond definitions and conditions

A

Formed when shared pair of electrons provided by only ONE of bonding atoms

One atom must have lone pair of electrons for donation, while another atom must have a vacant, low-lying orbital (lowest possible energy level) to accept the pair of electrons

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11
Q

Guidelines to drawing dot-cross for dative bonds

A
  1. Determine valence electrons of each atom
  2. Identify central atom (less electronegative and more unpaired electrons) and side atom (more electronegative, fewer unpaired electrons other than H)
  3. Help side atom achieve octet configuration, then central atom if possible
  4. Show lone pairs of electrons
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12
Q

Guidelines to drawing dot-cross for charged species

A

Electrons generally lost from less electronegative atom for polyatomic cations

Electrons generally gained from more electronegative atoms for polyatomic anions

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13
Q

Why can elements in Period 3 accommodate more than 8 valence electrons?

A

Period 3 elements have vacant, low-lying orbitals such as 3d orbitals, which are in the same shell as 3s and 3p orbitals and have a slightly higher energy, so electrons can be promoted to 3d orbitals for covalent bond formation and expand octet.

Period 2 does not have vacant, low-lying orbitals as the empty orbital with the next lowest energy is 3s which is much higher in energy than 2s and 2p orbitals.

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14
Q

What causes deviations in bond angles?

A
  1. Presence of lone pairs
  2. Electronegativity
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15
Q

Why is lone pair-lone pair repulsion greater than bond pair-bond pair repulsion?

A

Lone pair is attracted by only one positive nucleus and hence is closer to central atom, compared to bond-pair electrons attracted by 2 nuclei

Since the repulsion would be greater if electron pairs are closer, lone pair would exert greater repulsion than a bond pair.

Bond angle would deviate greatly as number of lone pair increases

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16
Q

Electronegativity of central atom impact on bond angle

A

When central atom is more electronegative, it will attract shared electron-pair more and draw bond-pair closer to itself, hence bond-pair would be nearer to the nucleus and hence exert more repulsion , so bond angle would be larger.

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17
Q

What causes deviations in bond angles?

A
  1. Presence of lone pairs
  2. Electronegativity
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18
Q

What is a non-polar/ polar covalent bond

A

Non-polar when electron pair is equally shared between two nuclei due to same electronegativity.

Polar when 2 atoms of different electronegativities form a covalent bond, where the electron-pair is not equally shared and the shared electron-pair would be closer to one atom

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19
Q

Dipole moment, factors and overall dipole moment

A

Measures degree of polarity of bond, vectoral quantity with both magnitude and direction, where the arrow points towards more electronegative atom

Greater electronegativity difference means greater bond dipole moment and the bond being more polar

Overall dipole moment is vector sum of all bond dipole moments

20
Q

Polar molecules

A

Polar if overall dipole moment is not zero and made up of atoms of different electronegativities

Have distinct partially positive and partially negative region in structure, contains permanent dipole

21
Q

Behaviour of polar molecules in electric field

A

Orientate direction opposite to that of field to minimise electrostatic energy of molecules

Slight separation of charge, forming a delta negative side and a delta positive side, when negatively charged rod, sides would realign such that delta positive is pointing to the rod to minimise repulsion

22
Q

Intermolecular forces of attraction

A

Broken during melting and boiling of simple covalent molecules compounds

3 types: Instantaneous dipole-induced dipole forces, permanent dipole-permanent dipole forces and hydrogen bonds

23
Q

Instantaneous dipole-induced dipole interactions (where it exists, how it exists, strength)

A

Only type that exists between non-polar molecules, present between all particles

Instantaneous dipole caused by constant moving of electrons, leading to unsymmetrical electron density,
inducing dipole in neighbouring particle causing an attraction between them

Short-lived as electrons keep moving and dipoles vanish and reform, weak overall attraction

24
Q

Factors affecting strength of instantaneous dipole-induced dipole interactions

A

Number of electrons/ electrons cloud size
Surface area for molecular interaction

25
Q

Number of electrons

A

When no. of electrons increases, size and ease of polarisability of electron cloud increases, strength of id-id interactions increases

26
Q

Surface area

A

Stronger in molecules with greater surface area between molecules with same number of electrons

Straight chained hydrocarbons have greater surface area for intermolecular interactions, more id-id interactions

Branching increasing decreases surface area for intermolecular interaction, less id-id interactions

27
Q

Permanent dipole- permanent dipole interactions

A

Caused by electrostatic attraction between delta plus end of one molecule and delta negative end of other molecule, where these molecules are polar molecules that have permanent dipoles in structures

Molecules align such that partially positive end of one molecule is near partially negative end of other molecule

28
Q

pd-pd vs id-id

A

For molecules with similar no. of electrons
- Electron cloud size is similar, so strength of id-id interactions are similar
- The molecule which is polar can form both id-id interactions and stronger pd-pd interactions, while non-polar molecules form only id-id interactions

For molecules with drastically different no. of electrons
- Bigger molecule has greatest electron cloud size and so stronger id-id interactions

29
Q

Hydrogen bonding

A

Occurs between molecules containing a hydrogen atom covalently bonded to very small, highly electronegative atom (F, O, N) with one electron pair

Causes H atom to have high delta plus charge, forming a strong attraction with lone pair of electrons on adjacent molecule, forming a hydrogen bond

30
Q

Criteria for hydrogen bonding

A

Hydrogen atom covalently bonded to F,O, N
Lone pair of electrons on F, O, N atom in neighbouring molecule bearing delta minus which can attract delta plus charge on H atom

31
Q

Strength of bonds assuming number of electrons is the same

A

Hydrogen bonds > pd-pd interactions > id-id interactions

32
Q

When explaining boiling points…. ASSUMING SIMILAR NUMBER OF ELECTRONS

A

IF ONE MOLECULE IS NON-POLAR: This molecule is non-polar, and so the main forces of attraction between molecules are due to instantaneous dipole- induced dipole interactions. Since A is polar and B is non-polar….

Electron cloud sizes of these 2 molecules are very similar, so the strength of the id-id interactions are similar

Molecule A forms stronger hydrogen bonds/ pd-pd interactions between molecules while Molecule B forms weaker pd-pd interactions/ id-id interactions.

Hence, more energy is required to overcome the stronger interactions in Molecule A, and hence Molecule A would have a higher melting boiling point.

33
Q

How to explain boiling points difference in molecules of DIFFERENT NUMBER OF ELECTRONS?

A

FOR ID-ID INTERACTIONS vs ID-ID INTERACTIONS
1. Molecule A has a greater number of electrons,
2. the size and polarisability of the electron cloud would be greater,
3. the strength of the id-id interaction would also be greater
4. more energy is required to overcome the stronger interactions

FOR PD-PD INTERACTIONS vs PD-PD INTERACTIONS
1. Dipole moments increases, delta positive and delta negative would have a greater magnitude,
2. attraction between them would be stronger
3. pd-pd interactions would be stronger.

FOR different interactions vs different interactions (to explain how id-id is greater than pd-pd/ hydrogen bonding)
1. Strength of id-id interactions depends on number of electrons
2. If molecule A has many more electrons
3. instantaneous dipole-induced dipole interactions between molecule A is significantly stronger than the pd-pd interactions/ hydrogen bonding between molecule B

34
Q

2 factors affecting strength of bonds

A

Extensiveness of hydrogen bonding:
Depends on the average number of h-bonds per molecule (lone pairs on F,O or N) or the number of H atoms attached to the molecule, whichever is smaller

More average number of H-bonds means more hydrogen bonds that have to be broken during melting/ boiling so more energy is required to overcome more interactions

Polarity of bond:
More greater the difference in electronegativity, the more polar the bond is, the greater the dipole moment and hence the stronger the hydrogen bond, hence more energy is needed to overcome the bonds

35
Q

Why is ice less dense than water?

A

Each oxygen atom in ice is tetrahedrally bonded to four hydrogen atoms. 2 by covalent bonds and 2 by hydrogen bonds, enable water molecules in ice to form rigid, open 3D networks that creates an open structure, occupying a larger volume for same mass of liquid water

36
Q

Why is the molar mass of some carboxylic acids in vapour phase double of molar mass from molecular formula? Where else does this happen?

A

Such carboxylic acids exists as dimers, made up of 2 carboxylic acids bonded to each other by hydrogen bonds.

Carboxylic acids also exist as dimers in some non-polar solvents but forms hydrogen bonding with water molecules in water, and will not dimerise.

37
Q

Why is boiling point and solubility different in 2 isomers?

A

In the isomer of lower boiling point, there is formation of intramolecular hydrogen bonding, hence less sites are available for hydrogen bonding with other molecules. Since less INTERmolecular interactions need to be overcome, lower boiling point.

When added to H2O, less hydrogen bonds can be formed with H2O molecules due to presence of more intramolecular interactions, so it is less soluble.

38
Q

3 cases of dissolution occuring

A
  1. Simple molecules with same type of intermolecular forces mix well
  2. Ionic solids dissolving in water
  3. Chemical reaction occurs
39
Q

Why does simple molecules with same type of intermolecular forces mix well?

A

If interactions within solute (solute-solute interaction) and interactions within solvent (solvent-solvent interaction) is the same as the solute-solvent interaction, reaction is favourable.

Unfavourable if solute-solvent interaction is id-id interaction but solvent-solvent interaction/ solute-solute interaction is pd-pd/ hydrogen bonding which is stronger than id-id interaction.

Energy released in forming id-id interactions between solute and solvent cannot compensate for energy needed to overcome hydrogen bonding/ pd-pd interaction in solvent-solent interaction/ solute-solute interaction.

40
Q

Why do ionic solids tend to dissolve in water?

A

Large amount of energy released in formation of strong ion-dipole interactions can compensate for energy required to overcome strong ionic bonds in solid crystal lattice.

Some ionic compounds are insoluble in water as ionic bonds are very strong and required a lot of energy to overcome.

41
Q

When a chemical reaction occurs why does dissolution occur?

A

Solute concerned reacts with solvent and products of reaction form favourable interactions with solvents.

42
Q

Sigma bond and pi bond (when it is formed, electron density), when these bonds formed and strength

A

Sigma bond formed when 2 orbitals overlap head-on, electron density concentrated between nuclei of 2 bonding atoms, along nucleus axis.

Pi bond formed when 2 orbitals overlap collaterally (side-to-side), electron density above and below nuclear axis but with 0 density along axis.

Pi bonding takes place only when atoms undergo multiple bonding (double or triple), where one bond is sigma while the rest are pi bonds

Sigma bond stronger than pi bond because head-to-head orbital overlap in a sigma bond has a greater degree of overlap than side-to-side orbital overlap in pi bond.

43
Q

Definition of bond length and bond energy

A

Bond length is distance between nuclei of 2 bonded atoms (shorter the bond, the shorter the bond length)

Bond energy is average energy absorbed when one mole of bond is broken in the gaseous state

44
Q

Factors of strength of covalent bond

A
  1. Number of bonds between atoms
  2. Effectiveness of overlap
  3. Differences in electronegativities of bonding atoms
  4. Type of hybridisation of orbitals of bonding atoms
45
Q

Number of bonds between atoms

A

Increase in bonds increases number of shared electrons between 2 atoms (increased electrostatic attraction between bond-pairs and nuclei), increasing bond strength

Double bond is less than twice of single bond (double bond consists of sigma bond and pi bond, but pi bond weaker than sigma bond since orbital overlap less effective, and single bond only consists of sigma bond)

46
Q

Effectiveness of overlap

A

More effective orbital overlap means stronger bond

If valence orbital is larger and hence more diffuse, overlap of orbitals is less effective and bond energy decreases, thus bond would be weaker

47
Q

Differences in electronegativities

A

Greater difference in electronegativity means covalent bond is more polar and bond is stronger

Chemistry (12 decks)

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