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H2 Chemistry > Chemical bonding > Flashcards

Chemical bonding Flashcards

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1
Q
  • Metallic
A

BONDs
electrostatic forces of attraction between metal cations and the sea of delocalised electrons. Bonds are non directional

STRUCTURE
metal lattice comprising of layers of metal cations immersed in sea of delocalised electrons. (SODE) Each metal atom contributes its loosely bound electrons to form SODE

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2
Q

Physical properties of metals

A
  1. High MP/BP
  2. Good electrical conductors
  3. Thermal conductivity
  4. Malleable
  5. Soluble in other metals
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3
Q

Factors affecting strength of metallic bonds

A
  1. amount of electrons contributed by each metal atom to SODE (greater, stronger)Io
  2. Ionic radius (smaller, stronger)
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4
Q

Ionic

A

BONDs
efa between oppositely charged anions and cations in an ionic compound. ionic bonds are non directional. Each ion is attracted equally to several oppositely charged surrounding ions

STRUCTURE
involves complete transfer of electrons from an atom (forms cation) to another atom (forms anion)
Giant ionic crystal 3D lattice structure
oppositely charged ions held in fixed positions in an orderly manner in a regular structure. (FOR)

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5
Q

Factors affecting strength of ionic bonds

A

In other words, factors affecting magnitude of L.E.
|L.E| ∝ |q+ x q- / r+ + r- |
1. Ionic radius (Interionic distance of compound) shorter, greater
2. Charge of ions (Product of charges of anion and cation) greater, stronger

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6
Q

Physical properties of ionic solids

A
  1. High MP/BP
  2. Hard and brittle
  3. Different electrical conductivity in different physical states
    - in aq
    - as a solid
    - molten
  4. Soluble in water and other polar solvents (usually)
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7
Q

Covalent bonds

A

BONDs
efa of positively charged nuclei of each bonding atom for the shared pair of electrons/the efa between the electron density and the bonded nuclei. Sharing a pair of electrons between two atoms of similar electronegativity

Is formed as a result of maximal overlap of valence atomic orbitals cont. one electron each. Maximal overlap ensures that the electron density is concentrated between the nuclei and can hold the atoms against the mutual repulsion of the nuclei. Bonds are localised and directional as electron pair is confined between nuclei of two bonding atoms

Structure
Simple covalent structure
Giant covalent compounds/structures

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8
Q

Dative covalent bond

A

When both electrons come from only one of the atoms
When a filled valence orbital of an atom overlaps with a vacant valence orbital of another atom. An atom donates a lone pair of electrons to another atom which has an empty low lying orbital to accommodate the electrons.

denoted by “ —–>”

examples AlCl3 , NH4 ion

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9
Q

Types of covalent bond

A
  1. Sigma σ
    the collinear overlap of two atomic orbitals
    there can only be one sigma bond between two atoms
  2. pi π
    the collateral overlap of two atomic p orbitals
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10
Q

π vs σ strength

A

Sigma is stronger as there is greater degree of overlap of orbitals than in pi bonds

a pi bond is formed after a sigma bond is formed. so pi bonds are only present in multiple bonds (double bonds/ triple bonds)

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11
Q

Bond length

A

the distance between the nuclei of the two bonding atoms in a covalent bond
a balance between
1. the maximum attraction between the nuclei for the shared electron density
2. the minimum repulsion between two positive nuclei and between electron clouds

Stronger the covalent bond shorter the bond length

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12
Q

Bond energy

A

can be used to infer degree of orbital overlap between two bonding pair of atoms and hence the strength of covalent bond.
The energy required to break one mole of covalent bonds between atoms in a gaseous molecule

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13
Q

Factors affecting strength of covalent bonds

A

BEBT

  1. Bond order
    - the number of covalent bonds formed between two atoms (double bonds-2/ triple bonds-3)
    - higher the bond order greater the no.of orbitals overlapped. increased electron density bet.bonding atoms greater att. bet. bonding nuclei and shared electrons. stronger covalent bond
  2. Effectiveness of orbital overlap
    - more effective the orbital overlap, stronger the bond
    - large orbitals are more diffuse. hence when large orbitals overlap with each other there is less effective orbital overlap and lower percentage of electron density between the two nuclei. hence bond weaker
  3. Bond polarities
    - Presence of partial charges increase the attraction between bonding atoms on top of existing cov. bond. The more electronegative the atom, the greater the partial charges that arise
  4. *type of hybridisation
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14
Q

Physical properties of covalent cmpds

A

Simple molecular (discrete molecules)

  1. Low MP/BP
  2. Soluble in non polar organic solvents usually
  3. non electrical conductors

Giant covalent

  1. Very high MP/BP
  2. Non electrical conductors (except graphite)
  3. Hard
  4. Insoluble in all solvents
  5. Slippery/lubricating property (Graphite)
  6. Electrical conductor (Graphite)
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15
Q

Giant covalent

A

Diamond/ Silicon dioxide
- Rigid 3D tetrahedral structure. Each C atom bonded to 4 other C/ Each Si bonded to 4 O
by strong covalent bonds throughout lattice
Graphite
-Network of planar hexagonal ring layers
- C bonded to 3 other C by covalent bonds
- Between each layers weak intermolecular forces

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16
Q

Intermediate bond types

A
  1. Pure ionic bond
    - ions exist as discrete point charges with no electron density bet.them
    - does not occur in reality in ionic cmpds
  2. Polarised ionic bond
    - cations attracts and distorts electron cloud of anion
    - partial sharing of electrons as electron density drawn into region bet.2 nuclei
    -occurs in ionic cmpds
    3.Polar covalent bond
    -Electron density not symmetrically distributed in a bond bet. diff atoms
    - more electronegative atoms has a greater share of the shared electron density
    - there is permanent separation of partial charges and compds exist as polar molecules
  3. Pure covalent bond
    - Electron density symmetrically distributed in a bond bet. identical atoms
    like Br2
17
Q

Factors affecting polarisation

A
  1. Charge to size ratio of the cation/ Charge density
  2. Size of the anion

greater the polarisation greater the covalent character in the cmpd

18
Q

Molecular geometry and polarity

A

refer to chart
VSEPR theory
the geometry of a covalent compd affects its polarity and its physical properties

19
Q

Deviation of bond angle predicted by VSEPR theory

A

due to
- Different electronegativity of central atoms given same terminal atoms
as electronegativity of the central atom increases electron density in the bond pairs is drawn closer to the central atom. Increased electron density around the central atom results in increasing bond pair-bond pair repulsion. Hence bond angle increases

-Different electronegativity of terminal atoms given same central atoms
electron density of bond pairs drawn to the more electronegative terminal atoms away from central. Lesser electron density around central atom hence lesser bond pair bond pair repulsion hence bond angle decreases

20
Q

Polar and Non polar molecules

A

greater the difference in electronegativity the greater the ionic character in covalent bond
polar : there is a difference in polarity and partial charges arise
individual bond dipoles do not cancel out each other giving rise to net dipole moment
non polar : no partial charges arise due to negligible difference in electronegativity
individual bond dipoles cancel out each other

21
Q

How to determine the polarity of a molecule

A
  1. Polarity of bonds in the molecule

2. Shape/Geometry of molecule

22
Q

instantaneous dipole- induced dipole

A

interaction between non polar molecules and noble gases

As electrons are in constant motion at some instant, there is a temporary shift of electrons to one side of the atom and results in an instantaneous dipole
the instantaneous dipole induces a similar dipole on an adjacent atom an induced dipole is formed
this repeats
dipoles are temporary but net attraction they produce is permanent

23
Q

Factors affecting strength of id-id

A
  1. Size of electron cloud

2. Surface area in contact between molecules

24
Q

Permanent dipole-permanent dipole

A

interactions between polar molecules

stronger than id-id

25
Q

Hydrogen bonding

A

efa between protonic H atom in H-F / H-O/ H-N bond and a lone pair on an electronegative atom F,O,N in a neighbouring molecule

When H is bonded to a highly electronegative atom, the highly electronegative atom attracts bonding electrons towards itself leaving H with a very small share of the electron pair. H acquires a large partial positive charge and electronegative atom a large partial negative charge. H behaves like a bare proton as a result

26
Q

Conditions required for H-bonds

A
  1. Protonic H in H-F/H-O/H-N

2. Lone pair(s) of electrons on an electronegative F,O,N atom in neighbouring molecule

27
Q

Factors affecting strength of hydrogen bonds

A
  1. Extensiveness of hydrogen bonding (greater, stronger)
    determined by average no.of H-bonds formed per molecule
    which can be determined by
    -counting total no.of protonic H per molecule
    -count total no.of lone pairs on F,O,N
    and taking the lower value of the two
  2. Polarity of H-Y bond (more electronegative Y, stronger)
28
Q

Boiling melting point of cmpds

A

SSCLC

can also be determined by the electrons cloud size of species when considering strength of id-id vs pd-pd vs H bond

29
Q

Solubility of compounds in solvents

A

3 types of interactions involved in determining solubility of a solute in a solvent

  1. solute-solute interaction
  2. solvent-solvent interaction
  3. solute-solvent interaction

PSSSI

30
Q

Solubility in ionic cmpds

A

ion dipole interactions formed in polar solvents
for eg in water, ion-dipole between oppositely charged ions and water molecules
ion dipole overcomes ionic bonds ionic lattice breaks down

acid disassociates in water. disassociated ions form ion dipole w water
sufficient to overcome H-bond
between water and covalent bond bet. acid molecules

31
Q

Structure and properties of ice

A

Ice is less dense than water which is anomalous

why?

32
Q

Dimerisation

A

Mr of molecule doubles

of ethanoic acid
-dimer formed due to H-bonds between two molecules

dimer not formed in (aq) state why?

AlCl3—-> Al2Cl6
-via dative bonding (describe the process)
NO2—> N2O4
-via covalent bond ( describe)

33
Q

Intramolecular H-bonds

A

2-nitrophenol vs 4-nitrophenol
are isomers

2-nitrophenol lower BP than 4-nitrophenol
due to NO2 and OH groups, 2 nitrophenol forms intramolecular H bonds whereas 4 nitrophenol forms only intermolecular hydrogen bonding
less sites available for intermolecular H bonding in 2 nitrophenol
more energy required to overcome intermolecular H bonding in 4 nitrophenol hence high BP

H2 Chemistry (22 decks)

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