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Chemistry > Bonding and Structure > Flashcards

Bonding and Structure Flashcards

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1
Q

Define

A chemical bond

A

An electrostatic force of attraction between oppositely charged particles

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2
Q

Define

Ionic bonding

A

The mutual electrostatic attraction between positive and negative ions

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3
Q

What are the physical properties of ionic compounds?

Categories: State at rtp, melting/boiling point, electrical conductivity, solubility, hardness

A
  1. Solid at r.t.p.
  2. High melting and boiling point
  3. Only conducts electricity in molten or aquaeous states
  4. Most are soluble in water, all insoluble in organic solvents
  5. Hard but brittle
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4
Q

Why do ionic compounds have high melting/boiling points and are solid at rtp?

A
  • Giant ionic structure
  • A lot of energy required to overcome the strong ionic bonds between oppositely charged ions
    - The higher the charge of the ions, the stronger the ionic bonds
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5
Q

Why do ionic compounds only conduct electricity in the molten or aquaeous states?

A
  • When solid, the ions are held in fixed positions by strong ionic bonds in giant ionic lattice structure
  • Ions cannot move freely to conduct electricity
  • Giant ionic structure collapses as ionic compound melts/dissolves in water
  • Ions now can move freely to act as charge carriers to conduct electricity
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6
Q

Why are ionic compounds brittle? for info only

A
  • When enough force is applied, ions shift and approach ions of same charge
  • Repulsive forces between same charge become larger than attractive forces
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7
Q

Define

Covalent Bonding

A

The electrostatic force of attraction between the nucleus and the shared pair(s) of electrons

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8
Q

Define

Simple molecular substance

A

The atoms within the molecule are joined by strong covalent bonds but the discrete molecules are held together by weak intermolecular forces of attraction

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9
Q

What are the physical properties of simple molecular substances?

Categories: State at rtp, melting/boiling points, electrical conductivity, and solubility

A
  1. Usually liquids or gases
  2. Low melting/boiling points
  3. Do not conduct electricity in all states
  4. Usually insoluble in water but soluble in organic solvents
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10
Q

Why are most simple molecular substances liquid or gases at rtp/why do they have low melting/boiling points?

A
  • During change in state, only weak intermolecular forces of attraction are overcome
  • Little energy is required to break weak intermolecular forces of attraction

Note: The greater the molecular mass, the stronger the intermolecular forces of attraction

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11
Q

Why do simple molecular substances not conduct electricity in all states?

A
  • They exist as neutral molecules
  • They have no mobile charged particles to conduct electricity
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12
Q

Define

Giant molecular substance

A

A substances consisting of an extensive network of atoms that are joined to one another by strong covalent bonds in a giant molecular structure

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13
Q

Describe the structure of diamond

A

Each carbon atom is bonded by strong single covalent bonds to 4 other carbon atoms in a tetrahedral arrangement, which is repeated over the whole structure

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14
Q

What are the properties of diamond and why?

Categories: hardness, melting/boiling points, electricical conductivity, solubility

A
  1. Very hard: extensive network of strong covalent bonds between atoms that requires a lot of force to distort the rigid structure
  2. Very high melting and boiling points: much energy needed to overcome the extensive network of strong covalent bonds between atoms
  3. Non-conductor or electricity: each carbon atom is bonded to 4 other carbon atoms. No mobile electrons to conduct electricity as all valence electrons are involved in bonding
  4. Insoluble in water and organic solvents
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15
Q

Describe the structure of graphite

A

Consists of hexagonal layers of carbon atoms stacked parallel to each other. Within the layer, every carbon atom is bonded by strong covalent bonds to 3 carbon atoms, forming hexagonal rings. Between layers, molecules are held together by weak intermolecular forces of attraction

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16
Q

What are the properties of graphite and why?

Categories: hardness, melting/boiling points, electricical conductivity, solubility

A
  1. Slippery and relatively soft: Weak intermolecular forces of attration between layers of atoms, thus layers can slide past one another when sufficient/little force is applied
  2. Very high melting and boiling points: Much energy needed to overcome the extensive network of strong covalent bonds between atoms
  3. Good conductor of electricity: Each carbon atom is bonded to 3 other carbon atoms, hence the unbonded valence electrons can move to conduct electricity
17
Q

Describe the structure of silicon dioxide

A

Each silicon atom is covalently bonded to 4 oxygen atoms. Each oxygen atom is covalently bonded to 2 silicon atoms. This pattern is repeated in all directions, forming a three-dimensional giant molecule

18
Q

What are the properties of silicon dioxide and why?

Categories: hardness, melting/boiling points, electricical conductivity, solubility

A
  1. Hard: Extensive network of strong covalent bonds between silicon and oxygen atoms that requires a large amount of force to distort the structure
  2. High melting and boiling points: Much energy needed to overcome the extensive network of strong covalent bonds between atoms
  3. Non-conductor of electricity: Each silicon atom is bonded to 4 other oxygen atoms. No mobile elctrons to conduct electricity as all valence electrons are involved in bonding
19
Q

What are allotropes?

A

Different forms of the same element/compound

20
Q

Define

Metallic bonding

A

Metallic bonding is the elctrostatic force of attraction between the positive metal ions and the ‘sea’ of mobile delocalised ions

21
Q

How does a metal lattice structure form?

A

The atoms “lose” their valence electrons and become positively charged. Thus the valence electrons of each atom are delocalised and moving freely throughout the lattice and are only loosely held by the nucleus

22
Q

What are the physical properties of metals and why?

Categories: State at rtp, melting and boiling point, electrical conductivity, solubility, malleability, heat conductivity

A
  1. Solid at rtp (except for mercury): A lot of energy is required to break the strong metallic bonds between positive metal ions and the ‘sea’ of mobile delocalised electrons
  2. Relatively high melting and boiling points (except group 1 metals; these are lower)
  3. Conduct electricity in solid/molten states: ‘Sea’ of mobile delocalised electrons make good electrical conductors. Electrons can move from the negative terminal to the positive terminal of the elctrical circuit
  4. Insoluble in water and organic solvents
  5. Malleable: If sufficient force is applied, a layer of atoms can slide over one another without disturbing the metallic bonds
  6. Good conductor of heat: When a metal is heated, the delocalised electrons move and spread heat to the other atoms
23
Q

Define

Alloys

A

A homogeneous mixture of a metal with other elements

24
Q

Why are alloys stronger and harder than pure metals?

A

Have different atomic radii. Disrupts the orderly arrangement of the layer of atoms within the metal lattice, hence it is more difficult for the layers to slide over one another when force is applied.

25
Q

What are physical properties of alloys?

A
  1. Harder than pure metals
  2. Improved appearance
  3. Improved resistance to corrosion
  4. Lower melting points than pure metals
26
Q

What are the trends in electronegativity?

A
  1. Metals generally have low electronegativity values, while non-metals have high electronegativity values
  2. Generally increase from left to right across the period
  3. Generally decreases from top to bottom down the group
27
Q

What is a polar bond?

A

A covalent bond between 2 atoms when the electrons forming the bond are unequally distributed, where one atom is more electronegative than the other.

This causes the molecule to have a slight dipole moment where one end is slightly negative and the other slightly positive. Dipoles are represented by arrows pointing towards delta minus, with a line perpendicular on the opposite side.

28
Q

What is the valence shell electron pair repulsion (VSEPR) theory?

A
  • Each pair of valence electrons around a central atom is located as far away from another pair as possible to minimise repulsion, maximising angles between them
  • Gives rise to a three-dimensional shape
  • Single bonds, double bonds and triple bonds can all be classified as a ‘pair’ of electrons
29
Q

What is the shape for 2 bond pairs, 0 lone pairs?

A

Linear

30
Q

What is the shape for 3 bond pairs, 0 lone pairs?

A

Trigonal planar

31
Q

What is the shape for 2 bond pairs, 1 lone pair?

A

Bent

32
Q

What is the shape for 4 bond pairs, 0 lone pairs?

A

Tetrahedral

33
Q

What is the shape for 3 bond pairs, 1 lone pair?

A

Trigonal pyramidal

34
Q

What is the shape for 2 bond pairs, 2 lone pairs?

A

Bent

35
Q

When is a molecule non-polar?

A

When the individual dipoles cancel out to no net dipole

36
Q

What is hydrogen bonding?

A

When a hydrogen atom is bonded to fluorine, oxygen or nitrogen, which are extremely electronegative atoms, it results in a very polar bond
As a hydrogen atom has no inner shell electrons, the nucleus is exceptionally bare and attractive to any lone pair of electrons on another electronegative atom, forming a hydrogen bond

Although it is weaker than ionic/metallic/covalent bonds, it is stronger than weak intermolecular forces of attraction

37
Q

What is dative bonding?

A

A bond that is formed by the sharing of a pair of electrons both of which are provided or donated by the same atom. An arrow is used to denote a dative covalent bond

Lone pairs are essential in the forming of dative bonds

Chemistry (10 decks)

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