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Chemistry > Covalent Bonding > Flashcards

Covalent Bonding Flashcards

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1
Q

what are properties of non-metal compounds?

A

Low boiling temperatures (often gases and liquids at room temperatures): bonding is often weak.
Soft in solid state: weak bonds.
Do not conduct electricity in any state: do not contain moving charged particles.
Many non-metal elements are composed of molecules.

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2
Q

why do they have low boiling temperatures?

A

bonding is often weak.

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3
Q

why are they soft when solid?

A

bonding is often weak

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4
Q

why do they not conduct electricity?

A

do not contain moving charged particles.

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5
Q

most non-metals are made of molecules. what are molecules?

A

discrete groups of atoms of known formula

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6
Q

what are bonds within?

A

intramolecular

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7
Q

what are bonds between molecules?

A

intermolecular

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8
Q

what does melting and boiling temperatures depend on?

A

the bonding between molecules

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9
Q

what is covalent binding?

A

Non-metals chemically combine.

Atoms share electrons- shared electrons act as glue between atoms.

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10
Q

how do atoms obtain outer shells? what rule do they follow?

A

Obtain stable outer shell by sharing electrons.

Octet rule: like to have eight electrons to be stable.

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11
Q

what are single covalent bonds?

A

Two shared electrons spend most time between the two nuclei and are said to be localised.
Force of attraction between one pair of electrons is a single covalent bond.
Hydrogen is an example of a diatomic molecule.

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12
Q

what are bonding electrons?

A

electrons that are shared

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13
Q

what are non-bonding electrons?

A

electrons that are not shared, they are called lone pairs

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14
Q

what are double covalent bonds?

A

two pairs shared

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15
Q

what are triple covalent bonds

A

three pairs shared

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16
Q

what is the electron dot diagram best for? limitation?

A

Determining the formula of the molecule and the types of bonds.
Does not show the relative size of atoms or the shape of the molecule.

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17
Q

what is the valence model best for? limitation?

A

Simplifying the electron dot.

Does not show the relative size of atoms of shape of the molecule.

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18
Q

what is the ball and stick model best for? limitation?

A

Displaying the molecule shape.

Shows the shape but not the relative size of atoms.

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19
Q

what is the spaced filled model best for? limitation?

A

Showing the relative size and position of the atoms in the molecule.
Shows the relative size and position of the atoms but not the bond angles of types of bonds.

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20
Q

how are electron pairs around an atom arranged?

A

Electron pairs repel and must be as far apart as possible.

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21
Q

what determines the shape of a molecule?

A

lone pairs

22
Q

how many single bonds; lone pairs for tetrahedral?

A

4;0

23
Q

how many sing bonds; lone pairs for pyramidal

A

3;1

24
Q

how many single bonds; lone pairs for v-shaped?

A

2;2

25
Q

how many single bonds; lone pairs for linear?

A

1;3

26
Q

why do non-metals come together? when are electrons shared?

A

because of an attraction between the positive nucleus of one and the negative outer shell of another.
When they come close enough to repel, the orbitals of the outer shell are overlapping and the electrons are shared.

27
Q

how strong are intramolecular forces?

A

very and hard to break

28
Q

how strong are intermolecular forces? what does this result in?

A

very weak in comparison (intramolecular force). So many covalent compounds are gases or liquids at room temperature.

29
Q

what are the three forces holding molecules together?

A

dipole-dipole forces
Hydrogen bonding
Dispersion forces

30
Q

who do molecules act like they are charged? what is this called?

A

When two different non-metal atoms form a covalent bond, one atom usually attracts bonding electrons more strongly than the other.
This atom has greater pull and therefore greater electronegativity.
The electronegativity of an element is a measure of the relative attraction that the element has for the electrons in the bonds.
It is often referred to as electron pulling power.

31
Q

what are the trends in electronegativity?

A

Increases from left to right and decreases down a group.
Non-metals tend to have greater electronegativity than metals because they want to gain electrons.
Noble gases have undefined electronegativities because they have full outer shells and don’t need to attract electrons.

32
Q

how is a polar bond formed?

A

The bonding electrons are shared unequally and move closer to the more electronegative atom.
More electronegative looks like it has a partially negative pole.
Less electronegative- partially positive pole.
A bond dipole develops which is a polar bond.
A polar bond occurs when one atoms is able to pull electrons to it more easily than the other.

33
Q

when does a non-polar bond occur?

A

when atoms have equal pull

34
Q

what electonegativities are non-polar?

A

Difference is less than 0.5- non-polar covalent

35
Q

what are the electronegativities of polar covalent?

A

Between 0.5 and 1.6- polar covalent

36
Q

what is the electronegativities of Ionic?

A

greater than 2.0

37
Q

between 1.6 and 2.0, what happens?

A

a metal- ionic, without a metal- polar covalent

38
Q

what do polar molecules contain?

A 
contains dipoles (polar bonds).
Arrangement is asymmetrical.
39
Q

what do non-polar molecules contain?

A

does not contain dipoles (polar bonds).

Is symmetrical.

40
Q

when do dipole-dipole forces occur? how strong are they? how is an intermolecular force shown?

A

Occur between polar molecules where the negative pole on one molecule is attracted to the positive pole on the other.
Relatively strong forces of attraction (weak compared to covalent bonds).
Greater the dipole, stronger the attraction, stronger the intermolecular bonding and higher the melting and boiling point.
Intermolecular force is how as a dotted line.

41
Q

what is hydrogen bonding? what does it occur between? what are its properties?

A 
Stronger form of dipole-dipole. 
Small and highly electronegative atoms (oxygen, nitrogen fluorine etc.) bond directly with hydrogen.
A large dipole is set up.
The strongest force of attraction.
Higher melting temperatures.
42
Q

why does ice float?

A

Hydrogen is the reason why ice floats.
Hydrogen bonds between water form crystal lattices in which the molecules are spaced further apart than in liquid water.
Greater spacing makes the ice less dense then the liquid water and so it floats on water.

43
Q

what do dispersion forces explain?

A

Explain the existence of intermolecular forces in non-polar molecules.
We know that they have intermolecular forces because they form liquids and solids and without them they would not stay together (just be gases).

44
Q

what are the properties of dispersion forces?

A

Weakest of the forces.

Operate in all covalent molecules.

45
Q

what causes dispersion forces?

A

Constant movement of electrons within atoms results in an instantaneous dipole.
These temporary dipoles attract each other but because they are not permanent they are weak.
Strength depends on the number of electrons in the molecule and the shape of the molecule.

46
Q

how do dispersion forces become stronger?

A

When they increase in size, the dispersion forces increase as does the boiling temperature.
Strength of dispersion forces of similar size depends on the shape of the molecule. eg. Longer molecules can form more interactions with other molecules meaning that the dispersion forces are stronger and the boiling temperature is higher.

47
Q

what is an example of a covalent network lattice? and what is its and structure?

A

Hardest known substance.
Composed only of carbon.
Each carbon is bonded to four other carbons (tetrahedral).

48
Q

what are the properties of diamonds?

A

Hard since strong covalent bonds are continuous throughout the lattice.
Require extremely high temperatures sublime (solid to gas).
Does not conduct electricity because it has no freely moving charged particles.
Chemically inert, insoluble in water and most other solvents.

49
Q

what are other covalent network lattices?

A

Other covalent network lattices are silicon, silicon carbide and silicon dioxide.

50
Q

what is an example of a covalent layer lattice? and what is its structure?

A

graphite. Composed entirely of carbon atoms.
Each carbon is bonded to 3 others.
Forms layers of hexagonal rings with strong covalent bonds in 2D.
Extra valence electrons are delocalised and are free to move throughout the layer.
Layers are stacked and held by weak dispersion forces.

51
Q

what are properties of graphite?

A

black, opaque, solid, soft, flaky and feels slippery as weak dispersion forces allow layers to slide over each other.
High melting point- strong covalent bonds within layers.
Good conductor of electricity- delocalised electrons are free to move.
Lustrous- delocalised electrons reflect light.

52
Q

what are diamond and graphite?

A

Diamond and graphite are the most common allotropes of carbon- each is composed entirely of the same elect but has very different structures and properties.

Chemistry (28 decks)

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