EL - Bonding and structure *01 *02 Flashcards Preview

A level Chem OCR B > EL - Bonding and structure *01 *02 > Flashcards

Flashcards in EL - Bonding and structure *01 *02 Deck (29)
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1
Q

what is ionic bonding?

A

when ions are stuck together by electrostatic attractions

ions are formed when electrons are transferred from one atom to another

overall charge zero

2
Q

what are electrostatic attractions?

A

the forces that hold positive and negative ions together

- very strong

3
Q

what is a giant ionic lattice

A

ionic crystals are giant lattices of ions

giant because made of the same unit over and over again

within the lattice, the ions with different charges attract each other and the ions with the same charge repel each other. the ions arrange themselves to maximise attractions and minimise repulsions

4
Q

examples of a giant ionic lattice?

A

Sodium chloride

Na+ Cl-

5
Q

Behaviour of ionic compounds

A
  1. conduct electricity when molten or dissolves - the ions are free to move so charge can move
  2. high melting points - giant ionuc lattices held together by strong electrostatic forces, it takes lots of energy to overcome these forces so melting point very high.
  3. often soluble in water - water molecules are polar, the water molecules pull the ions away from the lattice and cause it to dissolve
6
Q

what is covalent bonding?

A

when atoms share electrons so they both have a full outer shell of electrons

both the +ve nuclei are attracted electrostatically to the shared electrons

7
Q

what are simple covalent molecules?

A

substances made up of small molecules

8
Q

properties of simple covalent molecules?

A
  1. fairly low melting point (no giant structure that needs to be broken down)
    - don’t need to overcome covalent bonds that hold atoms together only the electrostatic forces between the molecules (these are weak)
  2. don’t conduct electricity - no charge carriers
  3. usually insoluble in water (very slightly) - polar water molecules more attracted to each other than the molecular substance
9
Q

what is dative covalent bonding?

A

when one atom donates both electrons to a bond

10
Q

covalent bonding: exceptions to full outer rule

A

BF3 (B 6 electrons in outer shell, F 8 electrons in outer shell)

SF6 (S 12 electrons in outer shell, F 8 electrons)

11
Q

what are giant covalent structures?

A

these structures have a huge network of covalently bonded atoms

the electrostatic forces holding the atoms together in these structures are much stronger than simple covalent molecules

12
Q

examples of giant covalent structures

A

carbon and sillicon

13
Q

giant covalent structures: carbon and silicon

A

each atom is bonded to its 4 neighbours in a tetrahedral arrangement

14
Q

giant covalent structures: silicon dioxide (SiO2)

A

each atom bonded to 4 neighbouring atoms with oxygen atoms between each silicon atom

15
Q

properties of giant covalent structures

A
  1. very high melting points - need to break lots of very strong bonds before the substance melts which takes a lot of energy
  2. extremely hard - very strong bonds all through lattice arrangement
  3. good thermal conductors - vibrations travel easily through lattice arrangement
  4. won’t dissolve - covalent bonds mean atoms are more attracted to their neighbours in the lattice than to solvent molecules (all insoluble in polar solvents shows they don’t contain ions)
  5. cant conduct electricity - no charged ions or free (graphite can)
16
Q

what is metallic bonding?

A

the electrons in the outermost shell of the metal atoms are delocalised (free to move)

this leaves a +ve metal ion

the positive metal ion are attracted to the delocalised -ve electrons

they form a lattice of closely packed +ve ions in a sea of delocalised electrons - this is metallic bonding

so metals exists as GIANT METALLIC STRUCTURES

17
Q

properties of metals: melting point

A
  1. melting points - generally high because of the strong metallic bonding. the number of delocalised electrons per atom affects the melting point.
    - the more electrons the stronger the bonding will be so the higher the melting point
    eg Mg2+ higher than Na+ as has two delocalised electrons per atom
    - size of the metal ion and the lattice structure also affects the melting point.
18
Q

properties of metals: ductile?

A

yes

metals can be shapes and are ductile as there are no bonds holding specific ions together, so metal ions can slide over each other when the structure is pulled

19
Q

properties of metals: thermal conductors?

A

good thermal conductors

delocalised electrons can pass kinetic energy to eachother

20
Q

properties of metals: electrical conductors?

A

good electrical conductors

delocalised electrons are free to move and can carry a charge

any impurities can dramatically reduce electrical conductivity by reducing the number of electrons that are free to move and carry charge –> the electrons transfer to the impurities and form anions.

21
Q

properties of metals: soluble?

A

insoluble

except in liquid metals because of the strength of the metallic bonds

22
Q

what does molecular shape depend on?

A

electron repulsion

electron pairs repel each other as much as possible

23
Q

Linear molecules

A

2 areas of electron density
both bonding pairs
bond angle 180

24
Q

Trigonal planar molecules

A

3 areas of electron density
all bonding pairs
bond angle 120

25
Q

Bent molecules

A

3 areas of electron density
2 bonding pairs
1 lone pair
bond angle 120

26
Q

Tetrahedral molecules

A

4 areas of electron density

all bonding pairs = 109.5

3 bonding pairs = 107

2 bonding pairs = 104.5

minus 2.5 for each lone pair

27
Q

trigonal bipyramidal molecules

A

5 areas of electron density
all bonding pairs

120 and 90

28
Q

octahedral

A

6 areas of electron density
all bonding pairs
bond angle = 90

29
Q

structure of compounds that have a sodium chloride type lattice

A

ionic bonding is the overall attraction in a lattice and is made up of attraction between ions of different charge and repulsion between ions of the same charge

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