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bonding Flashcards

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1
Q

what do bonds always involve

A

the bonds between atoms always involve their outer electrons

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2
Q

why do chemical bonds form

A

noble gases have full outer main levels of electrons and are very unreactive

When atoms bond together they share or transfer electrons to achieve a more stable electron arrangement, often a full outer main level of electrons, like the noble gases

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3
Q

what are the three types of strong chemical bonds

A

there are three types of strong chemical bonds:

  1. ionic
  2. covalent
  3. metallic
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4
Q

what is the easiest way for metals to gain an electron structure of a noble gas

A

metals have 1, 2, 3 electrons in their outer main levels, so the easiest way for them to attain the electron structure of noble gases to lose their outer electron

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5
Q

what is the easiest way for non-metals to gain an electron structure of a noble gas

A

non-metals have spaces in their outer main levels so that the easiest way for them to attain the electron structure of a noble gas is to gain their electrons on their outer shell

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6
Q

when does ionic bonding occur

A

ionic bonding occurs between metals and non - metals

Electrons are transferred from metal atoms to non - metals

This causes the formation of positive and negative ion

The two ions are attracted to each other and to other oppositely charged ions in the compound by electrostatic forces of attraction

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7
Q

what is an example of ionic bonding

A

sodium chloride has ionic bonding

The sodium, Na, has 11 electrons (and 11 protons)
The electron arrangement is 1s2, 2s2, 2p6, 3s1

chlorine has 17 electrons (and 17 protons). The electron arrangement is 1s2, 2s2,2p6,3p5

An electron is transferred. The single outer electron of the sodium atom moves into the outer main level of the chlorine atom ( the 3s1 electron from the sodium atom to the 3p orbital on a chlorine atom)

Now both sodium and chlorine have a noble gas electron arrangement - sodium has the neon noble gas arrangement whereas chlorine has the argon noble gas arrangement

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8
Q

what are ions

A

the two charged particles that result from the transfer of an electron are called ions

e.g. the sodium ion is positively charged because it has lost a negative electron

the chloride ion is negatively charged because it has gained a negative electron

the two ions are attracted to the oppositely charged ion in the sodium chloride compound by electrostatic forces of attraction
This attraction extends throughout the compound

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9
Q

what is ionic bonding the result of

A

ionic bonding is the result of electrostatic forces of attraction between oppositely charged ions

This attraction extends throughout the compound

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10
Q

what do ionic compounds always exist as

A

a lattice

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11
Q

what are the properties of ionically bonded compounds

A
  1. ionic compounds are always solids at room temperature
    - They have giant structures and therefore high melting temperatures. This is because in order to melt an ionic compound energy must be supplied to break up the lattice of ions (break electrostatic forces of attraction)
  2. ionic compounds conduct electricity when molten or dissolved in water (aqueous) but not when solid.
    - This is because the ions that carry the current are free to move in the liquid state but are not free in the solid-state
  3. ionic compounds are brittle and shatter easily when given a sharp blow. This is because they form a lattice of alternating positive and negative ions
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12
Q

when do covalent bonds occur

A

non - metal atoms need to receive electrons to fill the spaces in their outer shells

a covalent bond forms between a pair of non - metal atoms
The atom share some of their outer electrons so that each atom has a stable gas arrangement

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13
Q

what is a covalent bond

A

a covalent bond is a shared pair of electrons

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14
Q

what is a molecule

A

a small group of covalently bonded atoms is called a molecule

they are three dimensional and they come in many different shapes

e.g. chlorine exit as a gas that is made up of molecules Cl2

two chlorine atoms make a chlorine molecule

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15
Q

how does a chlorine molecule form

A

the two chlorine atoms share one pair of electrons

each atom now has a stable noble gas arrangement
The formula is Cl2

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16
Q

why are molecules neutral

A

molecules are neutral because no electrons have been transferred from one atom to another

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17
Q

how do you represent one pair of shared electrons

A

you can represent one pair of shared electrons in a covalent bond by a line e.g. Cl - Cl

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18
Q

how do sharing electrons hold atoms together

A

atoms with covalent bonds are shared together by the electrostatic attraction between the nuclei and the shared electrons

This takes place within the molecule.

The simplest example is hydrogen. The hydrogen molecule consists of two protons held together by a pair of electrons
The forces within this molecule
( repulsion and attraction) are balanced when the nuclei are a particular distance apart

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19
Q

what are double covalent bonds

A

in a double bond, four electrons are shared

e.g. the two atoms in an oxygen molecule share two pairs of electrons so that the oxygen atoms have a double bond between them

You can represent the two pairs of shared electrons in a covalent bond by a double line O=O

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20
Q

what are the properties of substances that are covalently bonded together (have a molecular structure)

A
  1. substances composed of molecules are gases, liquids or solids with low melting temperatures.
    - This is because the strong covalent bonds are only between the atoms
  2. There is only weak attraction between the molecules so the molecules do not need energy to move apart from each other ( low melting point)
  3. They are poor conductors of electricity because the molecules are neutral overall.
    This means that there are no charged particles to carry the current
  4. If they dissolve in water, and remain as molecules, the solutions do not conduct electricity.
    Again, this is because there are no charged particles
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21
Q

what is co - ordinate bonding

A

single covalent bonds consist of a pair of electron shared between two atoms

In most covalent bonds each atom provided one of the electrons

But, in some bonds, one atom provides both the electrons. This is called co - ordinated bonding
It is also called active covalent bonding

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22
Q

what is involved in a dative bond

A

In a co - ordinate or dative covalent bond:

  1. the atom that accepts the electron pair is an atom that does not have a filled outer main level of electrons -the atom is electron deficient
  2. the atom that is donating the electrons has a pair of electrons that is not used in a bond, called a lone pair
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23
Q

what are dative bonds represented by

A

by an arrow

The arrow points towards the atom that is accepting the electron pair

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24
Q

what is the length and strength of coordinate bonds

A

coordinate bonds have exactly the same strength and length as ordinary covalent bonds between the same pair of atoms

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25
Q

what is the strength of covalent bonds

A

double and triple bonds are stronger than single bonds but they are shorter than single bonds

more bonds =higher bond strengths
fewer bonds = smaller bond strength

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26
Q

what are metals

A

metals are shiny elements made up of atoms that can easily lose up to three outer electrons, leaving positive metal ions

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27
Q

what is metallic bonding

A

the atoms in a metal element cannot transfer electrons ( as happens in ionic bonding) unless there is a non -metal atom present to receive them

In a metal element, the outlet main levels of atoms merge
- The outer electrons are no longer associated with any particular atom.
A simple positive picture of metallic bonding is that metals consist of a lattice of positive ions existing in a “sea” of outer electrons

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28
Q

what are delocalised electrons

A

delocalised electrons are the electrons that a free in the lattice of positive metal ions

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29
Q

what are the forces within metallic bonding

A

the positive ions tend to repel one another and this is balanced by the electrostatic forces of these positive ions and the negatively charged “sea”of delocalised electrons

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30
Q

what do the number of delocalised electrons depend on

A

the number of delocalised electrons depends on how many electrons have been lost by each metal atom

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31
Q

why do metals have giant structures

A

the metallic bonding spreads throughout so metals have giant structures

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32
Q

what are the properties of metals

A
  1. metals are good conductors of electricity
  2. metals are also good conductors of heat
  3. metals tend to be strong
  4. metals are malleable and ductile
  5. metals have high melting points
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33
Q

what does the strength of metals depend on

A
  1. the charge on the ion
    - the greater the charge on the ion, the greater the number of delocalised electrons and the stronger the electrostatic attraction between the positive ions and the electrons
  2. the size of ion
    - the smaller the ion, the closer the electrons are to the positive nucleus and the stronger the bond
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34
Q

why are metals a good conductor of electricity

A
  1. delocalised electrons that can move throughout the structure explains why metals are good conductors of electricity
    - an electron from the negative terminal of the supply joins the electron sea at one end of a metal wire while at the same time a different electron leaves the wire at the positive terminal
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35
Q

why are metals good conductors of heat

A
  1. metals are also good conductors of heat
    - they have a high thermal conductivities. The sea of electrons is partly responsible for this property, with energy also spread by increasingly vigorous vibrations of the closely packed ions
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36
Q

why are metals strong

A
  1. metals tend to be strong
    - the delocalised electrons also explain this. These extend throughout the solid so there are no individual bonds to break
37
Q

why are metals malleable and ductile

A
  1. metals are malleable and ductile

metals are malleable ( they can be beaten into shape) and ductile (they can be pulled into thin wires)
After a small distortion, each metal ion is still in exactly the same environment as before so thee new shape is retained - different with the brittleness of ionic compounds

38
Q

why do metals have a high melting and boiling points

A
  1. metals have high melting points

metals generally have high melting and boiling points because they have giant structures.
There is a strong attraction between metal ions and the delocalised sea of electrons.
This makes them difficult to separate

39
Q

what is the electron pair repulsion

A

electrons in molecules exists in pairs in volumes of spaces called orbitals

You can predict the shape of a simple covalent molecule
e.g. one consisting of a central atom surrounding by a number of atoms, by using the ideas that:

  • each pair of electrons around an atom will repel all other electron pairs
  • the pairs of electrons will therefore take up positions as far apart to minimise repulsion

This is called the electron repulsion theory

40
Q

what are the two types of electron pairs

A

electron pair may be a shared pair or a lone pair

41
Q

what does the shape of a sim0ple molecule depend on

A

the shape of a simple molecule depends on the number of pairs of electrons that surround the central atom

To work out the shape of any molecule you first need to draw a dot and cross diagram to find the number of pairs of electrons

42
Q

what is the shape of a molecule when there is two pairs of electrons

A

if there are two pairs of electrons around the atom, the molecule will be linear

The furthest away from each other the two pairs can get is 180° part

e.g. beryllium chloride for example

Cl- Be-Cl

43
Q

what is the shape of a molecule when there are three pairs of electrons

A

if there are three pairs of electrons around the central atom, they will be 120° apart.

The molecule is planar (flat) and is called trigonal planar

44
Q

what is the shape of a molecule when there are four pairs of electrons

A

If there are four pairs of electrons, they are furthest apart when they are arranged so that they point to the four corners of a tetrahedron ]

This shape, with one atom position at the centre is called tetrahedral

The angles that the bonds are a is 109.5°.
It is a 3-D shape not planar so thee sim of the angles can be more than 360°

This is better than a square planar because bonds are further apart

45
Q

what is the shape of a molecule when there are five pairs of electrons

A

If there are five pairs of electrons, the shape usually adopted is that of a trigonal bipyramid

1 angle is 90° and the rest are 120°

46
Q

what is the shape of a molecule when there are six pairs of electrons

A

If there are six pairs of electrons, the shape adopted is octahedral, with bond angle at 90°

Remember that an octahedral has eight faces but six points

47
Q

do the overall charge affect the shape of a molecule

A

no

48
Q

what do the wedges and dashes represent

A

in three - dimensional representaions of molecules a wedge is used to represent a bond coming our of the paper

and a dashed line represents a one going into a paper away form the reader

49
Q

what is a lone pair

A

lone pairs is a pair of electrons that are unshared in a molecule

Lone pairs can affect the shape of molecules

50
Q

what are the rules for working out the shape of a molecule

A
  1. central atom
  2. group (this tells us the number of outer electrons
  3. charge - if it has lost or gained an electron
  4. bonds - number of bonds on the molecule
  5. add up the total of step 2, 3, 4
  6. divide by to to work out the number of electron pairs
  7. draw out the structure
  8. look at steps 6 and 4 to work out the lone pairs ) bonds + lone pairs = total electron pairs)
  9. the shape ( the shape does not include the lone pairs)
  10. work out the bond angles
51
Q

what does the forces that hold the atoms together depend on

A

the attraction between positive charges and negative charges

e.g.
In ionic bonding there is complete transfer of electrons from one atom to another

in covalent bonds, the electrons shared by atoms will not be evenly spread if one of the atoms is better at attracting electrons than the other

52
Q

what is electonegativity

A

electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons in a covalent bond

53
Q

what does the term electron density mean

A

when chemists consider the electrons as charge clouds the term electron density is often used to describe the way the negative charge is distributed in a molecule

54
Q

what are the four most electronegative atoms

A

nitrogen =3.0

oxygen = 3.5

fluorine = 4.0

chlorine = 3.0

55
Q

why do the noble gases not electronegative

A

because, in general, they do not form bonds (covalent bonds)

56
Q

what does electronegativity depend on

A
  1. the nuclear charge
  2. the distance between the nucleus and the outer shell electrons
  3. the shielding of the nuclear charge by electrons in inner shells
57
Q

what are the trends of electronegativity going down a group

A

going down a group, the electronegativity decreases

This is because there is more shells and shielding of the nucleus by electrons in inner shells

58
Q

what are the trends of electronegativity going along a period

A

going across a perios in the Periodic Table,the electronegatibvity increases

This is because the nuclear charge increases while the number of inner main levels remain the same and the atoms become smaller

59
Q

what is polarity

A

polarity is the unequal sharing of the electrons between atoms that are bonded together covalently

It is a property of the bond

60
Q

how is the covalent bond when both of the atoms are the same

A

when both atoms are the same, e.g. in flourine F2, the electrons in the bond must be shared equally between the atoms

This is because both atoms have exactly the same electronegativity and the bond is completely non - polar
If you think of the electrons as being in a cloud of charge, then the clouds is uniformly spread between the two atoms

61
Q

how is the covalent bond when there is two atoms that are different in electronegativity

A

in a covalent bond between two atoms of different electronegativity, the electrons in the bond will not be shared equally between the atoms
e.g. the molecule hydrogen fluoride HF

hydrogen has an electronegativity of 2.1 and fluorine of 4.0
This means that the electrons in the covalent bond will be attracted more by the fluorine than the hydrogen

The electron cloud is therefore distorted towards the fluorine

The fluorine end of the molecule is therefore relatively negative and the hydrogen end relatively positive, that is, electron deficient

covalent bonds like this are said to be polar - the greater the electronegativity difference the more polar the covalent bond

62
Q

what kind of properties could you say HF has

A

although HF is covalent, it has some ionic characteristics - it is going some way toward the separation of the atoms into charge ions

It is also possible to have ionic bond with some covalent character

63
Q

what are intermolecular forces

A

simple covalent molecules are attracted to one another by weak forces called intermolecular forces

These forces are between molecules

If the intermolecular forces are strong enough then molecules are held closely enough to be liquids or even solids

64
Q

what are the three intermolecular forces

A

van der waals forces weakest

dipole dipole forces

hydrogen forces
strongest

65
Q

when do dipole dipole forces occur

A

dipole forces act between molecules that have permanent dipoles ( occur when a molecule has a polar bond)

Two molecules which both have dipoles will attract one another

e.g. in the hydrogen chloride molecule; chlorine is more electonegative than hydrogen

so the electrons are pulled towards the chlorine atom rather than hydrogen
The molecule therefore has a dipole and, is written H +δ - CL-

66
Q

why do molecules with dipoles sometimes flip

A

whatever their starting positions, the molecules with dipoles will “flip” to give an arrangement where the two molecules attract

67
Q

what does the dipole dipole forces depend on

A

it depends on the shape of the molecule

so if the shape is symmetrical, dipoles cancel each other out

68
Q

what are Van Der Waal forces

A

all atoms and molecules are made up of positive and negative charges even though they are neutral overall

These charges produce very weak electrostatic attraction between all atoms and molecules

These are called Van Der Waals forces

69
Q

how do Van Der Waal forces work

A

imagine a helium atom

It has two positive charges on its nucleus and two negatively charged electrons

The atom as a whole is neutral but at any moment in time the electrons could be anywhere
This means that the distribution of charge is changing at every instant
Any of the arrangements mean that the atom has a dipole at that moment
An instant later, the dipole may be in a different direction

This dipole then affects the electron distribution in nearby atoms so that they are attracted to the original helium atom for that instant

The original atom had induced dipoles in the nearby atoms
- as the election distribution changes in the helium atom, it will induce new dipoles in the atoms around it, which will be attracted to the original one

70
Q

how long is the dipole last in the atom

A

any particular dipole will last be instant and temporary

71
Q

van der waal forces…

A

act between atoms or molecules at all times

they’re in addition to any intermolecular forces

the dipole caused by the changing position of the electrons cloud so the more electrons there are the larger the instantaneous dipole will be

72
Q

why do noble gases and hydrocarbons boiling points increase as the as it gets larger/ the atomic numbers get larger

A

The size of the Van Der Waals forces increases with the number of electrons present

This means that atoms or molecules with larger atomic/ molecular masses produce stronger Van Der Waals forces than atoms or molecules with small atomic molecular masses

73
Q

what is hydrogen bonding

A

it is a special type of intermoleculer forces with some characteristics of dipole dipole attraction and some of a covalent bond

74
Q

what does a hydrogen bond consist of

A

it consists of a hydrogen atom “sandwiched” between two very electronegative atoms

75
Q

what are the conditions that must be met in order for a hydrogen bond to occur

A

a hydrogen atom that is bonded to a very electronegative atom
- This will produce a strong partial positive charge on the hydrogen atom

a very electronegative atom with a lone pair of electrons
These will be attracted to the partially charged hydrogen atom in another molecule and forms the bond (hydrogen)

only atoms that are electronegative enough can form hydrogen bonds are N,O,F
e.g. NH3 form hydrogen bonds with O2

76
Q

why are hydrogen bonds more stronger than dipole-dipole forces

A

it is stronger for two reasons:
consider water for example

  1. in water the hydrogen atoms are highly elctron deficient
    This is because the oxygen is very electronegative and attracts the shared electrons towards it
    The hydrogen atoms in water are positively charged and very small. These exposed protons have a very strong eclectic field around them because of their small size
  2. the oxygen atom in water have lone pairs of electrons
    the lone pair of electrons on the oxygen atom of another water molecule is strongly attracted to the electron-deficient hydrogen atom - this strong intermolecular force is called a hydrogen bond
77
Q

what are hydrogen bonds represented by

A

they are represented by: —

78
Q

why is the shape of a molecule with hydrogen bonds always linear

A

take H2O with NH3 for example

the pair of electrons in the N-H covalent bond repels those in the hydrogen bond between nitrogen and hydrogen

This linearity is always the case with hydrogen bonds -

79
Q

what is the effect of hydrogen bonding on the boiling point of the hydrides in different groups

A

the effect of hydrogen bonding between molecules can be seen if you look at the boiling points of hydrides of elements of group 4,5,6,7, against the period number

The noble gases show a gradual increase in boiling points because the only forces between the storms are Van der Waals forces and these increase with the number of electrons

the boiling points of water H20, hydrogen fluoride HF and ammonia NH3, are all higher than those of the hydrides of the other elements in their group where you would expect to lower as they only have Van der Waals forces operating.
This is because hydrogen bonding is present in each of these compounds making them harder to separate

80
Q

what is the importance of hydrogen bonding

A

although hydrogen bonds are only 10% if the strength of covalent bonds, their affect can be significant especially when there are a lot of them

  • the very fact that they are weaker than covalent bonds and can break or make under conditions where covalent bonds are unaffected is very significant - e.g. water forming ice
81
Q

what happens when water is in its liquid state

A

when water is in its liquid state, the hydrogen bonds break and reform easily as the molecules are moving about

82
Q

what happens when water freezes

A

when water freezes, the water molecules are no longer free to move about and the hydrogen bonds hold the molecules in fixed positions

This results in a three - dimensional structure resembling the structure of diamond

83
Q

what must water molecules do in order to fit into the diamond structure when it freezes

A

in order to fit into this structure, the molecules are slightly less closely packed than in liquid water

This means that ice is less dense than water and forms on top of ponds rather than at the bottom

This insulated the pond and enables fish to survive through the winter - this feature must have helped life to continue in the relative warmth of the water under the ice during the Ice Ages

84
Q

simple covalent compounds

A

Compounds that are made up of lots of individual molecules are called simple covalent compounds

The atoms in the molecules are held together by a strong covalent bond, but the molecules within the simple covalent are geld together by intermolecular forces

-low melting points and electrical insulators

85
Q

giant covalent structures

A

sometimes called macromolecules

Carbon atoms can form this type of structure because they can each form four, strong covalent bonds

There are two types of ain’t covalent carbon structure you need to know about:

  • graphite
  • diamond
86
Q

graphite

A

the carbon atoms in graphite are arranged in sheets of flat hexagons covalently bonded with three bonds

The fourth outer electron of each carbon atom is delocalised
The sheets of hexagons are bonded together by weak van der Waals forces

87
Q

what are the properties of graphite

A

the weak bonds between the layers in graphite are easily broken so the sheets can slide over each other - graphite feels slippery and can be used as a lubricant and in pencils

the delocalised electrons in graphite are free to move also along the sheets so an electric current can flow

the layers are quite far apart compared to the length of the covalent bonds, so graphite has a low density and is used to make strong lightweight sports equipment

because of the strong covalent bonds in the hexagon sheet, graphite has a very high melting point (it sublimes at over 3900K)

graphite is insoluble in any solvent
the covalent bonds in the sheets are too difficult to break

88
Q

diamond

A

diamond is also made up of carbon atoms
each carbon atom is covalently bonded to four other atoms

The atoms arrange themselves in a tetrahedral shape - it is a crystal lattice structure

89
Q

what are qualities of diamond

A

because of its strong covalent bonds

diamond has a high melting point - it sublimes at over 3800K

diamond is extremely hard - it is used in diamond tripped drills AND SAWS

VIBRATIONS TRAVEL EASILY THROUGH THE STIFF LATTICE SO IT IS A GOOD THERMAL CONDUCTOR

IT CANT CONDUCT ELECTRICITY 0 ALL THE OUTEWE ELECTRONS ARE HELD IN LOCALUISED BONDS

LIKE GRAPHITE, DIAMOND WON’T DISSOLVE IN ANY SOLVENT

chemistry a level (24 decks)

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