Topic 4 - Chemical bonding Flashcards

1
Q

How are ions formed?

A
  • when one or more electrons are transferred from one atom to another
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2
Q

What is an ionic bond?

A
  • the electrostatic attraction experienced between the electric charges of a cation and an anion
  • build up into a strong lattice
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3
Q

What is oxidation?

A
  • loss of electrons

- gain of oxygen

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4
Q

What is reduction?

A
  • gain of electrons

- loss of oxygen

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5
Q

Between what are ionic compounds generally formed by?

A
  • metals and non-metals
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6
Q

What is the octet rule?

A
  • elements tend to lose electrons (oxidation), gain electrons (reduction) or share electrons to acquire a noble gas core electron configuration
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7
Q

What is volatility?

A
  • the tendency of a substance to vaporise
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8
Q

How are the boiling and melting points of ionic compounds and why?

A
  • high
  • strong electrostatic attractions between ions
  • large input of energy needed to break apart the forces
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9
Q

How is the volatility of ionic compounds and why?

A
  • low

- electrostatic forces of attraction are very strong

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10
Q

How is the electrical conductivity of ionic compounds and why?

A
  • good electrical conductor when molten
  • ions cannot move in a lattice structure (do not conduct)
  • ions are free to move in a molten state (conduct?
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11
Q

How is the solubility of ionic compounds and why?

A
  • dissolve in polar solvents

- do not dissolve in non-polar solvents

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12
Q

How are covalent bonds formed?

A
  • an electrostatic attraction between the shared pair of electrons and the positively shared nuclei
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13
Q

What kind of region is a covalent bond?

A
  • relatively high electron density between nuclei that arises at least partly from the sharing of electrons and gives rise to an attractive force and characteristic internuclear distance
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14
Q

Between what are covalent compounds generally formed by?

A
  • non-metals
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15
Q

What is the Lewis electron dot structure?

A
  • simple method of representing the valence electrons of an element
  • each element is surrounded by a number of dots/crosses that represent the valence electrons
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16
Q

How are the boiling and melting points of covalent compounds?

A
  • low
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17
Q

How is the volatility of covalent compounds?

A
  • can be
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18
Q

How is the electrical conductivity of covalent compounds and why?

A
  • do not conduct

- there are no ions to carry the charge

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19
Q

How is the solubility of covalent compounds?

A
  • typically insoluble
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20
Q

How is a polar covalent bond formed?

A
  • when one has a greater attraction - one atom has a partial negative charge and the other a partial positive charge
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21
Q

What is a dipole moment?

A
  • vectorial representation of the separation of charge
22
Q

What is a pure covalent bond?

A
  • when the two atoms involved are identical
23
Q

What is electronegativity defined as?

A
  • the relative attraction that an atom of an element has for the shared pair of electrons in a covalent bond
24
Q

What is the trend of electronegativity on the periodic table?

A
  • increases across a period

- decreases down a group

25
Q

What is the valence shell electron pair repulsion theory?

A
  • since electrons are negatively charged subatomic particles, pairs of electrons repel one another to be as far apart as possible in space
26
Q

What are delocalised electrons?

A
  • shared by more than two atoms in a molecule of ion as opposed to being localised between a pair of atoms
27
Q

What is molecular polarity?

A
  • whether the molecule itself is polar or non-polar

- distinct from the polarity of individual bonds - a non-polar molecule may have polar bonds

28
Q

What are allotropes?

A
  • different structural modifications of the same element

- vary in both physical and chemical properties

29
Q

What are covalent network solids?

A
  • atoms are held together by covalent bonds in a giant 3D lattice structure
30
Q

What is graphite?

A
  • layers of hexagonal rings consisting of carbon atoms
  • connected by weak intermolecular forces of attraction called London forces
  • each carbon atom adopts a trigonal planar geometry (120°)
  • strong covalent bonds, but weak London forced between layers - meaning layers can slide over eachother
31
Q

What are the properties of covalent network solids?

A
  • high melting point
  • poor electrical conductors (except graphite and graphene)
  • insoluble in common solvents
  • generally hard, but layers can slide over eachother
32
Q

What is diamond?

A
  • each carbon is bonded to 4 other carbons

- one of the hardest substances due to the structure

33
Q

What is graphene?

A
  • one of the thinnest and strongest of known materials
  • first 2D crystal discovered
  • densely packed carbon atoms in honeycomb crystalline lattice
34
Q

What is C60, fullerene?

A
  • truncated icosahedral cage - football shape (spherically symmetrical)
  • each carbon forms 3 covalent bonds
  • known as ‘buckminsterfullerene’
  • not a covalent network solid
35
Q

What is silicon dioxide (SiO2 - quartz)?

A
  • arrays of SiO4 tetrahedral arranged in a lattice

- round in its amorphous form as sand

36
Q

What is coordinate covalent bonding?

A
  • covalent bond when the shared pair of electrons originates from only one of the atoms (donates the pair)
37
Q

What are intramolecular forces of attraction?

A
  • hold atoms together within molecules, resulting in covalent bonds
  • affect molecular geometry, physical properties and reactivities of compounds
38
Q

What are intermolecular forces of attraction?

A
  • interactions between molecules within a compound

- largely responsible for the bulk properties of matter (e.g. physical properties such as melting and boiling point)

39
Q

What are the 3 main forces of intermolecular forces of attraction? - all van der Waals forces

A
  • London forces (or dispersion forces)
  • dipole-dipole forces
  • hydrogen bonding
40
Q

What are London forces?

A
  • exist in all molecules
41
Q

What is polarisability?

A
  • the ease of distortion of the electron cloud of a molecular entity by an electric field
42
Q

What is an orbital?

A
  • region of space where there is a high probability of finding electrons
43
Q

What 3 factors affect the magnitude of London forces?

A

1) number of electrons
2) size (volume) of electron cloud
3) shapes of molecules

44
Q

What are dipole-dipole forces?

A
  • exist in all polar molecules with a permanent dipole moment
45
Q

What is Hydrogen bonding?

A
  • an attractive interaction between a hydrogen atom from a molecular fragment, X - H, in which X is more electronegative than H, an an atom or group of atoms in the same or different molecule, in which there is evidence of bond formation
46
Q

What are the strength of the intermolecular forces?

A

1) Hydrogen bonds
2) Dipole-dipole forces
3) London forces

47
Q

What is a metallic bond?

A
  • the electrostatic attraction between a lattice of positive ions and delocalised electrons
  • giant lattice structure
48
Q

What are alloys?

A
  • metallic material, homogenous or a macroscopic scale, consisting of two or more elements so combined that they cannot be readily separated by mechanical means
  • have enhanced properties (strength, hardness, durability)
49
Q

What is ductility?

A
  • mechanical property that allows a metal to deform under tensile stress (able to be pulled into a wire)
50
Q

What is malleability?

A
  • the ability of a solid to be pounded or hammered into a sheet or other shape without breaking