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Chemistry > TOPIC 2: BONDING & STRUCTURE > Flashcards

TOPIC 2: BONDING & STRUCTURE Flashcards

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1
Q

Cation

A

A positively charged ion

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2
Q

Anion

A

A negatively charged ion

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3
Q

ionic Bonding

A

Strong electrostatic attraction between oppositely charged ions

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4
Q

Two factors that affect the strength of an ionic bond

A
  1. Ionic charge (greater the ionic charge the greater the strength of the ionic bond)- so higher m.p and b.p
  2. Ionic Radii (smaller ions can pack closer together than larger ions)- so have greater m.p and b.p.
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5
Q

High charge density

A

Large charge spread over smaller area (strong ionic bonding)

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6
Q

Properties of Ionic compounds

A
  1. High melting points due to strong electrostatic attraction between ions
  2. Soluble in water and not soluble in non-polar solvents because ions are charged
  3. Do not conduct electricity when solid as ions in a solid are fixed in place only conduct electricity when molten or dissolved in water
  4. Cant be shaped due to repulsion of ions so are very brittle
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7
Q

Covalent bond

A

the strong electrostatic attraction between the two positive nuclei and the shared electrons in the bond

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8
Q

What is the bond length

A
  1. The bond length is the distance between nuclei where the repulsion and attractive each other
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9
Q

Describe the relationship between electrons and bond length

A
  1. The more electrons in the bond (the higher the electron density)
  2. The higher the bond enthalpy
  3. The shorter the bond length
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10
Q

Dative covalent bond

A

A shared pair of electrons where both electrons come from the same atom

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11
Q

Properties of Giant Covalent structures

A
  1. High melting points-due to strong covalent bonds
  2. Hard-due to strong covalent bonds
  3. Good thermal conductors-vibrations travel easily through stiff lattices
  4. Insoluble-more attracted to nearby atoms in lattice than with solvents
  5. Cant conduct electricity (except from graphite) as there are no charged ions or free electrons.
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12
Q

Metallic bonding

A

The positive metal ions are electrostatically attracted to the delocalised negative electrons

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13
Q

Properties of metals

A
  1. High melting points,the more electrons there are the stronger the bonding
  2. Malleable and ductile, layers of metal ions can slide over each other as there are no specific bonds holding ions together
  3. Good thermal conductors as the delocalised electrons can pass Kinetic energy to each other
  4. can conduct electricity due to the sea of delocalised electrons
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14
Q

Three types of intermolecular forces

A
  1. .London forces
  2. permanent dipole-dipole
  3. Hydrogen bonding
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15
Q

Factors affecting strength of London forces

A
  1. Larger molecules have larger electron charge clouds-the stronger the London forces
  2. The more electrons the more temporary dipoles
  3. Greater surface area-the bigger the exposed electron clouds the stronger the London forces
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16
Q

What bonding is found in Alkanes

A

Covalent bonding ,London forces

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17
Q

Difference in strength of london forces in linear alkanes and branched alkanes

A
  1. Linear alkanes can pack closer together and the surface contact is large
  2. Branched alkanes cant pack tightly
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18
Q

Which molecules have permanent dipole-dipole bonds

A

Polar molecules- the delta positive and delta negative charge on the atoms cause weak electrostatic forces between them (permanent dipole-dipole)

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19
Q

Electronegativity

A

The ability of an atom to attract the bonding electrons in a covalent bond

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20
Q

ionic character

A

the greater the electronegativity difference the greater the ionic character

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21
Q

Covalent character

A

The smaller the difference in electronegtaitivities the greater the covalent character

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22
Q

What affects polarising power in cations

A

The smaller the radius the greater the polarizing power

23
Q

What affects polarisation in anions

A

The lower the charge density the more polarised the anion

24
Q

Which elements hydrogen bond

A
  1. Fluorine
  2. Nitrogen
  3. Oxygen
  4. OH- and -NH (alcohols and amine groups)
25
Q

What do ionic compounds form

A

Giant ionic lattices where each ion is electrostatically attracted in all directions to ions of the opposite charge

26
Q

Describe what the migrations of ions experiment is and what it shows

A
  1. A green solution of copper (III) chromate (VI) on a piece of wet filter paper, the filter paper turns blue at the cathode (the negative electrode) and yellow at the anode (positive electrode)
  2. Copper (III) ions are blue whereas chromate (VI) ions are yellow
  3. When you pass a current through the solution the positive ions move to the cathode and the negative ions move to the anode
27
Q

Give an example of a compound that dative covalent bonds and what does it form

A

NH3 - ammonia can dative covalent bond to form NH4+

NH3 + H+ > NH4+

28
Q

Why can graphite conduct electricity

A

Carbon atoms in graphite form sheets which each carbon atoms shares three of its outer shell electrons with three other carbon atoms. This leaves the fourth outer electron free making graphite a conductor

29
Q

Describe the structure and the properties of graphite

A
  1. One sheet of carbon atoms and is one atom thick

2. It can conduct electricity due to the delocalised electrons free to move

30
Q

Describe the trend of electronegativity in the periodic table

A

Elements with a high nuculear charge and small radius are electronegative - so the electronegativity increases across periods and up the group

31
Q

How does a polar bond come about

A

When two atoms with different electronegativities bond- the electrons will be pulled towards the more electronegative element causing the electons to be spread unevenly and each atom will have a slight charge- the bond will be polar

32
Q

What is a purely covalent atom

A

Where the electronegativity between atoms is zero

33
Q

How can a polar bond not make polar molecules

A

A molecule may have several polar bonds that if they are in opposite directions they will cancel each other out making a non-polar molecule overall

34
Q

What are london forces also known as

A

instantaneous dipole-dipole bonds

35
Q

How is an instantaneous dipole bond formed

A
  1. Electrons in charge clouds are always moving quickly at any moment the electrons in an atom are more likely to be in one side then the other causing the atom to have a temporary dipole
  2. This dipole can induce another temporary dipole in another atom causing them to be attracted to one another
36
Q

What force is responsible for holding iodine molecules in a lattice

A

London forces hold together the molecules of iodine atoms the iodine atoms themselves however are held together by strong covalent bonds in pairs

37
Q

Relationship between carbon chains and london forces

A

The longer the carbon chain the stronger the London Forces as there are more electrons and a larger surface contact

38
Q

What are the strongest type of Intermolecular forces

A

Hydrogen Bonding

39
Q

Describe why the boiling point between HCL to HI increases

A

From HCL to HI although the permanent dipole-dipole interactions decreases the number of electrons increases so the strength of the London forces also increase. This effect overrides the decrease in the strength of the permanent dipole-permanent dipole interactions and B.P increases

40
Q

Use hydrogen bonding to explain why ice floats on water

A
  1. In ice the water molecules are arranged so that there is the maximum number of hydrogen bonds

2, As the ice melts some of the hydrogen bonds are broken and the lattice breaks down filling the spaces

  1. This means ice is less dense than water so it floats
41
Q

Why are alcohols less volatile than Alkanes

A

Alcohols can hydrogen bond as well as having London forces. Hydrogen bonds are the strongest inter-molecular force so require more energy to break

42
Q

What is meant by volatile

A

Can evaporate easily

43
Q

Why does the boiling point of the Group 6 hydrides between H2S to H2Te increase

A

There is an increase in the strength of london forces between H2S to H2Te which overrides the effect of the decrease in permanant dipole-dipole forces

44
Q

What 3 things need to happen for a substance to dissolve in water

A
  1. Bonds in the substance have to break
  2. Bonds in the solvent have to break
  3. AND new bonds have to be formed between the substance and the solvent
45
Q

Give an example of a non-polar solvent

A

Hexane

46
Q

Name a polar solvent that cant form hydrogen bonds and state the bonds it forms

A

Propanaone = It can only from London forces and permanent dipole-permanent dipole bonds

47
Q

Describe the process of hydration

A
  1. Water is a polar solvent
  2. When an ionic substance is mixed with water the ions in the ionic substance are attracted to the oppositely charged ends of the water molecules
  3. The ions are pulled away from the ionic lattice by the water molecules which surround the ions
48
Q

Describe the relationship between the carbon chain of the alcohol and solubility

A

The longer the chain - the more carbon atoms there are- the less soluble the alcohol will be

49
Q

Why do halogenoalkanes not dissolve in water

A
  1. Halogenoalkanes contain polar bonds but their dipoles are not strong enough to form hydrogen bonds with water
  2. The hydrogen bonding between molecules of water is stronger than the bond that would be formed with halogenoalkanes so the halogenoalkanes will not dissolve
  3. Halogenoalkanes can form permanant dipole- permanent dipole bonds so will dissolve in polar solvents that also form permanant dipole- permanent dipole bonds (HEXANE)
50
Q

Key thing to remember above dissolving

A
  1. Usually a substance will only dissolve if the dtrength of the new bonds formed is about the same as or greater than the bonds that are broken
  2. Like dissolves like - Non polar substances will dissolve in non polar solvents same with polar
51
Q 
Give=  IONIC BONDING 
Examples
M.P and B.P 
State at room temperature 
Does it conduct electricity 
Does liquid conduct electricity 
Soluble in water
A

Examples= NaCl, MgCl2

M.P and B.P = High

State at room temperature = Solid

Does it conduct electricity = No

Does liquid conduct electricity = yes (IONS FREE TO MOVE)

Soluble in water= Yes

52
Q 
Give=  SIMPLE COVALENT (MOLECULAR)
Examples
M.P and B.P 
State at room temperature 
Does it conduct electricity 
Does liquid conduct electricity 
Soluble in water
A

Examples= CO2, I2, H2O

M.P and B.P = Low ( intermolecular force broken not covalent bonds)

State at room temperature = Usually liquid or gas (I2 =Solid)

Does it conduct electricity = No

Does liquid conduct electricity = No

Soluble in water = Depends if it can form hydrogen bonds

53
Q 
Give=  GIANT COVALENT 
Examples
M.P and B.P 
State at room temperature 
Does it conduct electricity 
Does liquid conduct electricity 
Soluble in water
A

Examples= Diamond, Graphite, Silicon dioxide

M.P and B.P = High

State at room temperature = Solid

Does it conduct electricity = No except graphite

Does liquid conduct electricity = No they sublime they do not melt

Soluble in water = No

54
Q 
Give= METALLIC 
Examples
M.P and B.P 
State at room temperature 
Does it conduct electricity 
Does liquid conduct electricity 
Soluble in water
A

Examples= Fe, Mg, Al

M.P and B.P = High

State at room temperature = Solid

Does it conduct electricity = YES

Does liquid conduct electricity =YES

Soluble in water = No

Chemistry (20 decks)

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