Unit 3.1.3 - Bonding Flashcards
What happens during the formation of an ionic bond?
Electrons are transferred from on atom to another so that they have a full outer shell and are more stable. This forms two oppositely charged ions which are then strongly attracted to each other and this electrostatic attraction holds the two ions together forming an ionic bond
What structure do atoms that have formed ionic bonds form?
Ionic lattices
What happens during the formation of a covalent?
Two atoms share electrons so that they have both got a full outer shell, both nuclei are then electrostatically attracted to the shared electrons
Draw the structure of sodium chloride?
See flash 13
What is a dative covalent bond?
When one atom donates both of the electrons to form the covalent bond
How can you show a dative covalent bond on a diagram?
An arrow pointing away from the donor atom
What are electrons referred to and why?
Charge clouds as they are in a constant state of motion
What bonds do metals form?
Metallic bonds
Describe what happens why a metallic bond forms?
In metals the outermost electrons are delocalised leaving a positive metal ion. The positive metal ions are strongly attracted to the delocalised electrons and form a lattice of closely packed ions
Draw the structure of magnesium?
See flash card 14
What does the term electronegativity mean?
The ability of an atom to attract electrons in a covalent bond
What is the highest and lowest electronegativity can be?
Lowest - 0.7
Highest - 4
What can you use electronegativity to predict?
Whether a bond is going to be ionic, metallic or covalent
How close do the two electronegativities have to be to form a non polar covalent bond?
Less than 0.5
What is meant by a non polar covalent bond?
Both nuclei are able to attract the electrons equally
How close do the two electronegativities have to be to form a polar covalent bond?
Between 0.5 and 2.1
What is meant by a polar covalent bond?
One atom in the covalent bond can attract the electrons more strongly and so the electrons are positioned closer to that atom making the bond polar
In a polar covalent bond what does the difference in electronegativities form?
A dipole to form
What is a dipole?
It is the difference in charge between two atoms caused by a shift in electron density
How far apart do the electronegativities have to be to form an ionic bond?
More than 2.1
Why does a difference greater than 2.1 mean the bond formed is ionic?
The difference is so large that the sharing of electrons is so uneven that one atom basically has both electrons, at this point the electrons are no longer shared but instead they are transferred from one atom to another and so the bond is ionic
What electronegativities mean the bond is metallic?
Less than 1.6
Why does having an electronegativity of less than 1.6 mean the bond is metallic?
The atoms don’t have the ability to attract the outermost electrons and so the electrons become delocalised and so forming the metallic bonds
What are the three types of intermolecular forces?
Induced diploe - diploe, permanent dipole - dipole and hydrogen bonding
How is a temporary dipole formed?
As electrons are in a constant state of motion and exist as charge clouds it is likely at any given time the electrons will not be symmetrical and the electrons will be closer to one atom than the other, when this happens it forms a temporary dipole
What happens when temporary dipoles interact with surrounding atoms ?
If a temporary dipole comes close to another atom, the negative part of the dipole would repel the electrons or the positive part would attract the electrons. This creates an induced dipole. There is then electrostatic attraction between the two atoms creating and induced dipole - dipole
Why are induced dipole - diploes constantly being created and destroyed?
The electrons are constantly moving and so the tempera dipoles are constantly changing therefore changing the induced dipole - dipoles
What two things increase the strength of induced dipole - dipole and why?
- ) the more electrons because there is a greater chance of temporary dipoles being formed and they are often bigger
- ) larger surface area because the atoms will have more contact with adjacent atoms and more induced dipoles will be created
How are permanent dipole-dipoles created?
In polar covalent bonds there is always a dipole present so there will always be weak electrostatic forces of attraction between the positive and negative ends of the atoms, creating permanent dipole - dipoles
What is the strongest type of intermolecular force?
Hydrogen bonding
What does hydrogen have to be bonded to to form hydrogen bonds?
To fluorine, nitrogen and oxygen
What do hydrogen bonds only form when hydrogen is bonded to fluorine, nitrogen or oxygen
Because those are the elements which have a large enough electronegativity to attract the electrons away from the hydrogen and make the bond polar
What happens when a hydrogen bond forms?
As the bond between hydrogen and either fluorine, nitrogen and oxygen is so polarised and because hydrogen is so small it has a high charge density. This means its able to form weak bonds with lone pairs of electrons
Draw the hydrogen bonds that form between two water molecules?
See flash card 15
Why does ice have a lower density than water?
The hydrogen bonds in ice are relatively long in length compared to in water which means the water molecules in ice are packed less tightly and are further away reducing its density
Describe how particles act in a solid?
Particles vibrate about a fixed position and can’t move around freely
Describe how particles act in a liquid?
Particles move around freely and randomly however they are still quite close together
Describe how particles act in a gas?
Particles move in a rapid and random motion and the spaces between the molecules become a lot larger
Describe what happens when a solid is heated to a liquid?
If a solid is heated the kinetic energy of the particles increase and vibrate more, as they vibrate more the bonds between the particles are weakened and some are even broken and so space starts to appear between particles and the solid becomes a liquid
Describe what happens when a liquid is heated into a gas?
If a liquid is heated the kinetic energy of the particles increase and vibrate more, as they vibrate more the energy becomes great enough to break nay intermolecular forces and the liquid becomes a gas
What are the four types of “crystals” ?
Ionic lattice, metallic, simple molecular and giant covalent
When do ionic lattices conduct electricity and why?
They conduct electricity when molten or dissolved because the ions are free to move and carry the current
Do ionic lattices have a high or low melting and boiling point?
High
Why do ionic lattices have a high melting and boiling point?
There are strong electrostatic forces of attraction between all the oppositely charged ions which take a lot of energy to overcome
Do ionic lattices dissolve in water?
They tend to
Why do ionic lattices tend to dissolve in water?
The water molecule is polar and so can pull the positive ions away from the lattice and cause it to dissolve
Do metallic structures conduct electricity?
Yes
Why do metallic structures conduct electricity?
Their electrons are delocalised and are free to move and carry the current
Do metallic structures or ionic lattices have higher melting and boiling points?
Ionic lattices
Where do metallic structures have a relatively high melting and boiling point?
There is electrostatic forces of attraction between the positive metal ion and the negative delocalised electrons
Which metallic structures will have the highest melting and boiling point?
The ones with the most delocalised electrons because then the metallic bonds will be stronger
Why are metals malleable?
There are no specific bonds holding the positive ions together so they are free to move and can slide over each other making metals malleable
What are simple molecular structures?
Structures where there are strong covalent bonds within molecules but weak forces of attraction between the molecules
Do simple molecular structures conduct electricity and why?
No as there are no free ions or delocalised electrons
Do simple molecular structures have high or low melting and boiling points?
Low
Why do simple molecular structures have low melting and boiling points?
The weak intermolecular forces between the molecules are easy to overcome and don’t require a lot of energy to do so
Are simple molecular structures soluble in water and why?
Some are depending on how polar the molecule is
What is an example of a simple molecular structure?
Iodine - I2
Draw the structure of the simple molecular structure of iodine?
See flash card 16
What are giant covalent structures?
When each atom is covalently bonded to other atoms forming a network of strong covalently bonded atom
Name two giant covalent structures?
Graphite and diamond
How are the carbon atoms bonded and in a graphite?
Each carbon atom forms three covalent bonds with other carbon atoms leaving one delocalised electron per atom
How are the carbon atoms arranged in graphite?
The are arranged in sheets of flat hexagons
Can graphite or diamond conduct electricity?
Graphite
Why can graphite conduct electricity?
It has the delocalised electrons which are free to move and carry the current
Does graphite have a higher or lower density than diamond?
Lower
Why does graphite have a lower density than diamond?
There is a relatively large distance between the layers compared to the length of a covalent bond
Why do diamond and graphite have high melting and boiling points?
Because of the strong covalent bonds which are hard to overcome
What property of graphite makes it good for the use in pencils?
The layers are only bonded together by weak intermolecular forces and so the layers are free to slide over each other so it can easily be rubbed off onto a piece of paper
How are the carbon atoms bonded and arranged in diamond?
Each carbon atoms forms four strong covalent bonds to other carbon atoms, it forms a tetrahedral shape
What property of diamond means it’s good for use in drill heads?
The four strong covalent bonds means it is very strong and so be used as a drill
What is a charge cloud?
A place where you have a large chance of finding an electron pair
What does the valance shell electron pair repulsion theory say?
All pairs of electrons will arrange themselves as far apart in space as is possible
How does the repulsion between lone pairs and bonding pairs go?
lone pair/lone pair > lone pair/bonding pair > bonding pair/bonding pair
Between lone pairs and bonding pairs which electrons repel the most?
Lone pairs
