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PHYSICAL CHEMISTRY 3.1 > 3.1.3 - bonding > Flashcards

3.1.3 - bonding Flashcards

1
Q

Define electronegativity

A

The ability of an atom to attract electron density in a covalent bond

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2
Q

State intermolecular forces in order of strongest to weakest

A
  1. Hydrogen bonds
  2. Dipole-Dipole forces
  3. Van der Waals forces
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3
Q

Describe how a hydrogen bond forms

A
  • between H atom and a Nitrogen, Fluorine or Oxygen atoms lone pair
  • sandwich of the H atom must be linear, due to electrostatic repulsion
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4
Q

How does hydrogen bonding effect sold structures

A
  • ice is less dense than water
  • liquid, H bonds constantly broken and remade due to constant movement
  • when cooled to ice, molecules slow
  • arrange into ordered structure, allows H bonds to form in a linear structure
  • molecules held further apart in ice
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5
Q

Describe how dipole dipole forces form

A
  • between molecules with a permanent dipole
  • δ+ and δ- regions attract each other
  • dipoles align due to electrostatic repulsion
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6
Q

Describe how Van der Waals forces form

A

A molecules instantaneous dipole induces a dipole on another molecule

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7
Q

Describe how an instantaneous dipole occurs

A
  • due to random electron movement around a stationary nucleus
  • one side of an atom can become δ- (due to e’s)
  • the other side is therefore δ+
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8
Q

Describe why boiling points increase down a group

A
  • the Mr of an atom increases, meaning the number of electrons increases
  • this means greater induced dipoles
  • therefore, VDW’s between molecules is stronger, which require more energy to break
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9
Q

Name the 4 types of crystal structure

A
  • ionic
  • metallic
  • macromolecular
  • molecular
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10
Q

Describe what ionic bonding is

A
  • electrostatic attraction between positively charged ions and negatively charged ions
  • electrons transferred between metals and non-metals
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11
Q

Explain properties of ionic compounds

A
  • high melting and boiling point, due to strong electrostatic forces
  • can only conduct electricity when molten or aqueous, as ions are free to move and carry a charge
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12
Q

Describe metallic bonding

A

Attraction between a lattice of positive ions and their delocalised outer shell electrons

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13
Q

How is the strength of an ionic compound determined

A
  • based on charge density
  • greatest charges for the smallest sized ions result in higher strengths
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14
Q

What is charge density

A

= charge/size
- charge depends on the group in periodic table
- size of the ion increases down a group

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15
Q

Explain the properties of metallic structures

A
  • do not dissolve, as they often react with water
  • conduct electricity in any form, as there is a sea of delocalised electrons which can move and carry a charge
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16
Q

What determines a metallic structures strength

A
  • charge density
  • the higher the charge for smaller metal ions will result in a greater attraction between the cation and the delocalised electrons
17
Q

Describe how molecular substances bond

A
  • “2 non-metals sharing pair(s) of electrons
  • atoms within the molecule are held together by covalent bonds
  • individual molecules are held together by weak intermolecular forces
18
Q

Explain the properties of molecular structures

A
  • low boiling + melting point, due to the weak intermolecular forces
  • cannot conduct electricity, due to no delocalised electrons
19
Q

Describe a macromolecular substances structure

A
  • thousands of atoms in a lattice structure
  • held together by covalent bonds
20
Q

Explain the properties of a macromolecular substance

A
  • high melting + boiling point, due to strong covalent bonds that must be broken
  • graphite and graphene can conduct electricity , due to delocalised electrons
  • others can’t conduct electricity
21
Q

Outline the “exceptions to the octet rule” within covalent bonding

A
  • some elements may end up having more than 8 electrons in their outer shell once covalently bonded
  • some elements with few electrons may have less than 8 electrons in their outer shell once covalently bonded within a compound
22
Q

Why do some elements have more than 8 electrons in their outer shell once they are in a covalent compound

A
  • the d sub shell is close in energy to other sub shells
  • this allows electrons within it to move between sub shells
23
Q

What is a dative covalent bond

A
  • when the shared pair of electrons comes from one atom only
24
Q

Describe the VSEPER theory

A
  • Valence shell electron pair repulsion theory
  • predicts the shape of a molecule based on the no. of electron pairs surrounding the central atom
  • lone pairs and bonding pairs affect the molecules bond angle / shape
25
Q

Describe how lone pairs and bonding pairs of electrons experience repulsion

A

HIGHEST REPULSION = lone pair - lone pair
lone pair - bonding pair
LOWEST REPULSION = bonding pair - bonding pair

26
Q

Describe how lone pairs affect a molecules bond angle

A
  • lone pairs repel from each other the most
  • this means they push bonding pairs closer together
  • the more lone pairs, the smaller the bond angle
27
Q

Describe the trends related to electronegativity

A
  • across the periodic table = increases
  • down the groups = decreases
  • Fluorine = most electronegative
28
Q

What makes a covalent bond polar

A
  • if the atoms have a difference in electronegativity
  • earning telectrons would be closer to the δ- element
29
Q

What makes an overall molecule polar

A
  • if it has an overall δ+ side and overall δ- side
  • meaning it will have an overall permanent dipole
30
Q

What is the name and bond angle of a molecule with
- 3 lone pairs
- 3 bonding pairs

A
  • T shaped
  • 86°
31
Q

What is the name and bond angle of a molecule with
- 0 lone pairs
- 6 bonding pairs

A
  • octahedral
  • 90°
32
Q

What is the name and bond angle of a molecule with
- 0 lone pairs
- 5 bonding pairs

A
  • trigonal bipyramidal
  • 90° and 120°
33
Q

What is the name and bond angle of a molecule with
- 1 lone pair
- 4 bonding pairs

A
  • see saw shape
  • 88° and 118°
34
Q

What is the name and bond angle of a molecule with
- 2 lone pairs
- 3 bonding pairs

A
  • t shaped
  • 86°

PHYSICAL CHEMISTRY 3.1 (4 decks)

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