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IB Chem HL > Chapter 4 SL: Bonding > Flashcards

Chapter 4 SL: Bonding Flashcards

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1
Q

What is the octet rule?

A

Atoms bond together in order to achieve a full valence shell, containing 8 electrons/

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2
Q

What are exceptions to the octet rule?

A

Hydrogen and Helium - Period 1 elements, therefore only have one energy level, containing 2 electrons.
Boron (6), Beryllium (4) are stable with less than 8 electrons (incomplete octet)
Period 3 elements such as Sulfur and Phosphorus can have expanded octets.

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3
Q

What is electronegativity?

A

A measure of the attraction of an atom for a bonding pair of electrons.

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4
Q

What is the trend in electronegativity on the periodic table?

A

Increases across a period, due to increasing nuclear charge.
Decreases down a group, due to increasing atomic radius.

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5
Q

What is the difference in electronegativity for non-polar covalent, polar covalent and ionic bonding?

A

0-0.4: non-polar covalent
0.5-1.7: polar covalent
> 1.8: Ionic

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6
Q

What defines a polar covalent molecule?

A

The difference in electronegativity will be between 0.5 & 1.7, resulting in one element having greater electrostatic forces of attraction with the shared pairs of electrons, causing it to have a partial negative charge.

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7
Q

What are positive ions called?

A

Cations

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8
Q

What are negative ions called?

A

Anions

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9
Q

What is ionic bonding?

A

An ionic bond is the electrostatic attraction between oppositely-charged ions.

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10
Q

How are ionic compounds formed and what are their properties?

A

Ionic compounds are formed by ions held in a lattice structure due to strong forces of electrostatic attraction between oppositely charged ions.
They have high melting and boiling points, and only conduct electricity when molten/dissolved in water, as the ions are free to move.

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11
Q

Describe the solubility of ionic compounds?

A

Ionic compounds are soluble in polar solvents such as water, as the ions are separated from their lattice structure by polar water molecules and then surrounded by water molecules (hydration) as the negative dipole of the water molecules is attracted to the positive one of sodium.

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12
Q

What is the effect of ionic charge on melting point?

A

The greater the charge on the ion, the stronger the electrostatic attraction between oppositely charged ions and the higher the melting point.

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13
Q

What is the effect of ionic radius on melting point?

A

The greater the ionic radius of the ion, the weaker the electrostatic attraction and the lower the melting points.

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14
Q

What are polyatomic ions?

A

Molecular ions that consist of two or more atoms bonded together with covalent bonds.

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15
Q

What bonding occurs between polyatomic ions within a compound?

A

Ionic bonding

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16
Q

What is Covalent Bonding?

A

Electrostatic forces of attraction between a positively charged nucleus and shared pair of bonding electrons.

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17
Q

What is the trend in the increase of covalent bonds?

A

Increased bond strength and decreased bond length

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18
Q

What do polar covalent bonds consist of?

A

A dipole which can be represented by a partial negative and positive charge and also with an arrow pointing to the more electronegative atom due to unequal sharing of electrons.

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19
Q

What does the polarity of a molecule depend on?

A

The presence of polar bonds and the molecular geometry
If the molecular polar bonds cancel each other out, it has no net dipole moment.

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20
Q

What are the trends in polarity of tetrahedral molecules?

A

Tetrahedral molecules with the same type of atom bonded to the central atom are usually non-polar.
When different atoms are bonded to the central atom, it is usually polar.

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21
Q

What are the trends in polarity of trigonal planar molecules?

A

Trigonal planar molecules with the same type of atom bonded to the central atom are usually non-polar.

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22
Q

What are the trends in polarity of trigonal pyramidal molecules?

A

Usually polar, if containing polar bonds.

23
Q

What are the trends in polarity of bent molecules?

A

Usually polar if contain polar bonds.

24
Q

What are the trends in polarity of linear molecules?

A

Linear molecules with the same type of atom bonded to the central atom are usually non-polar.
With different atoms bonded to the central atom, are polar.

25
Q

What is a coordinate covalent bond?

A

When one atom contributes both bonding electrons to the bond.

26
Q

What is the difference between giant covalent structures and molecular covalent compounds?

A

Giant covalent compounds have high melting and boiling points due to no intermolecular forces, whereas molecular compounds have low melting and boiling points due to weak intermolecular forces.

27
Q

What is the trend in solubility of polar covalent molecular compounds?

A

Polar molecules are soluble in polar solvents whereas non-polar molecules are soluble in non-polar solvents

28
Q

How to determine the number of resonance structures?

A

Equal to the number of lewis structures for a compound

29
Q

What would the actual structure of a molecule with multiple resonance structures be?

A

The Resonance Hybrid structure where the bond lengths and strengths are identical and intermediate in length and strength between a single double bond.
Resonance structures have delocalized electrons which are shared over the two nuclei.

30
Q

What is VSEPR Theory and its rules?

A

Valence shell electron pair repulsion theory is used to predict the molecular geometry of a compound where electron pairs repel each other and spread out as far as possible.
The greatest repulsion occurs between lone pairs of electrons whereas the least repulsion occurs between bonding pairs of electrons.

31
Q

What are electron domains?

A

Bonds/lone pairs of electrons around an atom in a molecule.

32
Q

What are the properties of the tetrahedral shape?

A

4 electron domains + Bond angle of 109.5

33
Q

What are the properties of the trigonal pyramidal shape?

A

4 electron domains, 1 lone pair and bond angle of 107.5

34
Q

What are the properties of the bent shape?

A

4 electron domains, 2 lone pairs and bond angle of 104.5

35
Q

What are the properties of the trigonal planar shape?

A

3 electron domains + Bond angle of 120

36
Q

What are the properties of the linear shape?

A

2 electron domains + bond angle of 180

37
Q

What are allotropes?

A

Different forms of the same element in the same physical state.

38
Q

Describe Graphite

A

Forms layers, held by weak intermolecular forces - therefore can slide over each other.
Each carbon atom is bonded to 3 other carbons.
Bond geometry is trigonal planar(120)
Good conductor of electricity due to delocalized electrons.
Graphene is a single layer

39
Q

Describe Diamond

A

Giant covalent structure with high melting + boiling points with each carbon bonded to 4 other crayon atoms.
The bond angle is 109.5 with a tetrahedral geometry.

40
Q

Describe Fullerene C60

A

12 pentagons and 20 hexagons
Each carbon atom is bonded to 3 other carbons
Bond angle is 120, trigonal planar
Poor conductor of electricity
Molecules contain London dispersion forces between each other.

41
Q

What are London Dispersion Forces?

A

The movement of electrons within an atom/molecules where the constant motion of electrons within an atom can cause a temporary/instantaneous dipole, which induces a dipole in another molecule allowing for attraction.

42
Q

What is the trend in molar mass and London dispersion forces?

A

As molar mass increases, strength of the London dispersion forces also increase - resulting in an increased boiling point.

43
Q

What are Dipole-Dipole Forces?

A

Occur between polar molecules, where the partial negative positive charge on one molecule and the partial negative charge on another attract.

44
Q

What is Hydrogen Bonding?

A

When a hydrogen atom is bonded to either a nitrogen, fluorine or oxygen atom and is the attraction between the partial positive charge on the hydrogen atom and the lone pair of electrons on the other atom.
NOF element must interact with hydrogen bonded to another NOF element.

45
Q

What are Ion-dipole forces?

A

Occur between ions in aqueous solutions and water molecules. (Hydration shell)

46
Q

Why are polar substances and non-polar substances soluble in their respective solvents?

A

Non-polar substances are soluble in non-polar solvents due to London dispersion forces which occur.
Polar substances are soluble in polar solvents due to hydrogen bonding with water molecules.

47
Q

Why are benzene and fullerenes C60 not good conductors of electricity?

A

While they have delocalized electrons, these are only free to move within the molecule and not across multiple molecules.

48
Q

Why are metallic substances good conductors?

A

As a metallic bond is defined as the electrostatic attraction between the lattice of positive metal ions and sea of delocalized electrons(non-directional bonding), which are free to move and conduct electricity.

49
Q

What is the trend between ionic radius and melting point of a metal?

A

The smaller the ionic radius, the greater the charge and the higher the melting point.

50
Q

What is the difference between substitutional alloys and interstitial alloy?

A

Substitutional alloy: atoms of one metal are substituted by atoms of another.
Interstitial alloy: A different metal occupies interstitial spaces in the lattice structure.

51
Q

How are alloys different from the original metals they are made from?

A

They are less malleable (harder) and have greater tensile strength as the added metal atoms distort the lattice structure, making it more difficult for the layers to slide over each other.

52
Q

Explain why the hybrides of Group 16 elements (H20, H2S, H2Se, H2Te) are polar molecules-

A

As Group 16 elements are the most electronegative, thus will have polar bonds with hydrogen itself due to the differences in electronegativity, thus leading to an uneven distribution of charge.

53
Q

Explain the increase in boiling point from H2S to H2Te:

A

As polar molecules, they will contain London dispersion molecules as well as permanent dipole-dipole interactions and thus, the increase in electrons down the group will result in stronger intermolecular forces between the molecules, thus leading to higher boiling points.

IB Chem HL (5 decks)

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