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Chemistry > Bonding > Flashcards

Bonding Flashcards

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1
Q

What is ionic bonding?

A

The strong electrostatic force of attraction between oppositely charged ions formed by electron transfer

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2
Q

How are cations formed?

A

Metals lose electrons from their valence shell forming positively charged cations

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3
Q

How are anions formed?

A

Non-metal atoms gain electrons forming negatively charged anions

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4
Q

When is the ionic bonding stronger and when are the melting points higher?

A

When the ions are smaller and/or have higher charges
e.g. MgO has higher m.p. than NaCl as Mg is 2+ and Na is +

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5
Q

Why are positive ions smaller compared to their atoms?

A
  • It has one less shell of electrons - The ratio of protons to electrons has increased
  • So there is a greater net force on the remaining electrons holding them more closely
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6
Q

Why are negative ions from groups 5-7 larger than their corresponding atoms?

A
  • The negative ions have more electrons than the atom
  • But it has the same number of protons
  • So the pull of the nucleus is shared over more electrons and the attraction per electron is less, making the ion bigger
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7
Q

Which predictable patterns do ionic radii show?

A
  • Ionic radii increase with increasing negative charge
  • Ionic radii decrease with increasing positive charge
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8
Q

Give an example of the patterns of ionic radii

A
  • N3-, O2-, F- and Na+, Mg2+, Al3+ all have the same electronic structure
  • There are increasing numbers of protons from N to F and then Na to Al but the same number of electrons
  • The effective nuclear attraction therefore increases and ions get smaller
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9
Q

What is the trend of ionic radii in a group?

A

The size increases down the group. As one goes down the group, the ions have more shells of electrons so distance increases

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10
Q

What kind of structure do ionic compounds form?

A

Giant ionic lattice (crystal structures)

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11
Q

What is the attraction like when ionic compounds are formed?

A

The attraction between the ions happens in all directions
Overall the lattice is electrically neutral as the positive charges cancel out the negative charges

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12
Q

What does the type of ionic lattice formed depend on?

A

The size of the positive ions and negative ions which are arranged in an alternating fashion
e.g. ionic lattice of MgO and NaCl are cubic

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13
Q

What state are most ionic compounds in at room temp?

A

Solid

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14
Q

Why are most ionic compounds solid at room temp?

A

There is not enough energy to overcome the strong electrostatic forces of attraction between the oppositely charged ions
(So ionic compounds have high m.p. and b.p.)

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15
Q

When are melting and boiling points also higher in ionic lattices?

A

They are higher for lattices that contain ions with a greater ionic charge (there is a stronger attraction between the ions)

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16
Q

What must there be for electrical current to flow?

A

Present, freely moving, charged particles such as electrons or ions

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17
Q

What will many ionic compounds dissolve in?

A

Polar solvents e.g. water

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18
Q

What 2 main factors is solubility dependent on?

A
  • Breaking down the ionic lattice
  • The polar molecules attracting and surrounding the ions
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19
Q

How do polar molecules affect ionic lattices?

A

They can break down and disrupt the ionic lattice and surround each ion in solution
- The + end of the polar molecule can surround the negative anion
- The - end of the polar molecule can surround the positive cation

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20
Q

What does the solubility of an ionic compound depend on?

A

The relative strength of the electrostatic forces of attraction within the ionic lattice and the attractions between the ions and the polar molecules

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21
Q

What is the connection between ionic charge and solubility of a compound?

A

In general, the greater the ionic charge the less soluble an ionic compound is
(there are many exceptions though)

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22
Q

What gives evidence for the existence of ions?

A

The behaviour of ionic substances during electrolysis

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23
Q

Why does electrolysis give evidence for the existence of ions?

A
  • Positive ions in solution are attracted to the negative electrode
  • Negative ions in solution are attracted to the positive electrode
24
Q

What is a covalent bond?

A

A covalent bond involves the electrostatic attraction between nuclei of 2 atoms and the bonding electrons of their outer shells

25
Q

What are lone pairs?

A

Non-bonded pairs

26
Q

What is dative covalent bonding?

A

Some molecules have a lone pair of electrons that can be donated to form a bond with an electron deficient atom

27
Q

What is an electron deficient atom?

A

An atom that has an unfilled outer orbital

28
Q

Are both electrons from the same atom in dative covalent bonding?

A

Yes

29
Q

What is dative covalent bonding also known as?

A

Coordinate bonding

30
Q

What happens in an ammonium ion?

A
  • The hydrogen ion H+ has space for 2 electrons
  • The nitrogen atom in ammonia has a lone pair of electrons which it can donate to the hydrogen ion to form a dative covalent bond
31
Q

What does ammonium chloride exist as at high temperatures?

A
  • As a monomer (AlCl3)
  • The molecule is electron deficient and needs 2 electrons to complete the aluminium atom’s outer shell
32
Q

What happens to aluminium chloride at lower temperatures?

A
  • The 2 molecules of AlCl3 join together to form a dimer (Al2Cl6)
  • The molecules combine because lone pairs of electrons on 2 of the chlorine atoms form 2 coordinate bonds with the aluminium atoms
33
Q

What is the bond energy?

A

The energy required to break one mole of a particular covalent bond in the gaseous states (its units are kjmol^-1)

34
Q

What does a larger bond energy mean?

A

The stronger the covalent bond

35
Q

What is bond length?

A

The internuclear distance of 2 covalently bonded atoms (the distance from the nucleus of 1 atom to another atom which forms the covalent bond)

36
Q

What does a greater force of attraction between the electrons and nuclei mean?

A
  • The more the atoms are pulled closer to each other
  • This decreases the bond length of a molecule and increases the strength of the covalent bond
37
Q

Which are the shortest and strongest covalent bonds?

A

Triple bonds

38
Q

Why are triple bonds the shortest and strongest covalent bonds?

A
  • Due to the large electron density between the nuclei of the 2 atoms
  • This increases the forces of attraction between the electrons and nuclei of the atoms
  • As a result of this, the atoms are pulled closer together causing a shorter bond length
  • The increased forces of attraction also means the covalent bond is stronger
39
Q

What is the theory for valence electrons?

A

The valence shell electron pair repulsion theory (VSEPR)

40
Q

What is VSEPR?

A

It predicts the shape and bond angles of molecules

41
Q

What happens because electrons are negatively charged?

A

They will repel other electrons when close to each other

42
Q

What happens in a molecule with bonded pairs of electrons?

A

The bonding pairs of electrons will repel other electrons around the central atom forcing the molecule to adopt a shape in which these repulsive forces are minimised

43
Q

When determining the shape and bond angles of a molecule, what VSEPR rules need to be followed?

A
  • Valence shell electrons are found in the outer shell
  • Electron pairs repel each other as they have the same charge
  • Lone pair electrons repel each other more than bonded pairs
  • Repulsion between multiple and single bonds is treated the same as repulsion between single bonds
  • Repulsion between pairs of double bonds are greater
  • The most stable shape is adopted to minimise the repulsion forces
44
Q

How do lone pairs of electrons affect the shape and bond angles?

A
  • They have a more concentrated electron charge cloud than bonding pairs of electrons
  • The cloud charges are wider and closer to the central atom’s nucleus
  • The order of repulsion is lone pair-lone pair >lone pair-bond pair>bond pair-bond pair
45
Q

How many degrees is in a linear shape?

A

180 e.g. CO2

46
Q

How many degrees is in a trigonal planar?

A
  1. e.g. BF3
47
Q

How many degrees is in a non-linear?

A

104.5 e.g. H2O

48
Q

How many degrees is in a trigonal pyramidal?

A

107 e.g. NH3

49
Q

How many degrees is in a tetrahedral?

A

109.5 e.g. CH4

50
Q

How many degrees is in a triganol bipyramidal?

A

90 and 120 e.g. PF5

51
Q

How many degrees is in an octahedral?

A

90 e.g. SF6

52
Q

How are metal atoms arranged?

A

They are tightly packed together in a lattice structure
They are often packed in hexagonal layers or in a cubic arrangement

53
Q

What happens to the electrons when the metal atoms are in lattice structures?

A
  • The electrons in their outer shells are free to move throughout the structure
  • They are called delocalised electrons and they are not bound to their atom
54
Q

What happens when the electrons are delocalised?

A

The metal atoms become positively charged ions

55
Q

How is the neatly arranged lattice in a metal kept in place?

A

The positive charges repel each other

56
Q

What kind of forces are there in a metal lattice?

A

There are very strong forces between the positive metal centres and the ‘sea’ of delocalised electrons

Chemistry (7 decks)

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