Bonding Flashcards
When does an ion from?
When electrons are transferred between elements with a large difference in electronegativity
What forms when an elements transfer electrons?
A regular ionic lattics
How is the regular ionic lattice held together?
By the strong electrostatic attractions between the alternating cations and anions (the ionic bond)
How is the regular ionic lattice arranged?
In alternating cations and anions ionically bonded together
What is an ionic bond?
The strong electrostatic attractions formed between a cation and an anion
What are the properties of an ionic crystal?
- Very high melting points- Brittle- Electrical insulators when solid- Electrical conductors when molten/dissolved- Generally dissolve in H2O
Why do ionic crystals have very high melting points?
There are strong electrostatic attractions between oppositely ions which take a large amount of energy to break
Why are ionic crystals generally dissolvable in H2O?
Water is very polar and is able to disrupt electrostatic attractions between oppositely charged ions and break them apart
Why are ionic crystals electrical insulators when solid?
Ions are held in a fixed position so cannot carry a charge
Why are ionic crystals electrical conductors when molten/dissolved?
Ions are no longer held in fixed positions, they are able to move and carry a charge
Why are ionic crystals brittle?
When ions are moved/hit they are moved from there arrangement of alternating cations and anions so they repel each other and the lattice breaks
What does a covalent bond form between?
Two elements with high electronegativity values (non-metals)
What is a covalent bond?
A shared pair of electrons with opposite spins, one electron is donated by each atom
What are the two types of covalent bond?
Simple molecular and macromolecular
Give examples of simple molecular
Methane, water and diatomic elements
Give examples of macromolecular
Diamond and Graphite
What is the intention of a covalent bond?
For both atoms to obtain full orbitals
What happens when a covalent bond is formed?
A region with high electron density forms (highly negative) which causes very strong attractions between electrons and the positive nucleus
What is a double covalent bond?
2 pairs of shared electrons
What is a triple covalent bond?
3 pairs of shared electrons
What is a co-ordinate bond?
A covalent bond formed when both donated electrons are from the same atom
How is a covalent bond formed?
A lone pair is donates its electrons to an electron deficient ions
What happens once a co-ordinate bond is formed?
It behaves the same way as a normal covalent bond
What bonds hold H2O together?
Covalent bonds
What are the IMFs between water molecules?
Hydrogen bonds
Why do hydrogen bonds form?
Because oxygen is delta negative and hydrogen is delta positive, hydrogen bonds are the attractions between the hydrogen of one molecule and the oxygen of another
At 0 to 100 degrees celcius how do hydrogen bonds hold water molecules?
Close to each other but allowing them to move freely (liquid)
How do hydrogen bonds hold ice molecules?
Below 0 degrees molecules have less energy so hydrogen bonds fix molecules in position
What is the structure of ice?
A 3D hexagonal crystal structure
Why does ice float?
The spaces created between the H2Os cause it to expand and become less dense
Why does ice have a relatively high melting point?
The strong hydrogen bonds between molecules take a lot of energy to break
What is iodine?
A diatomic, covalently bonded molecule
What forces are between I2 molecules?
Weak induced dipole forces (Van Der Waals) which give it its crystal structure
What is iodine at room temperature?
A grey solid
What happens when you heat iodine?
It sublimes to a purple gas
Why does iodine have a low melting/boiling point?
The weak Van Der Waals forces between I2 molecules are easily broken but the individual I2 molecules remain intact
Is iodine soluble?
It is slightly soluble but I2 is non-polar
What are the two allotropes of carbon?
Diamond and graphite
How are carbon atoms bonded in diamond?
Each carbon atom is covalently bonded to 4 other carbon atoms
What is the arrangement of diamond?
Tetrahedral
What is the bond angle of diamond?
109.5
What is the shape of diamond?
A 3D lattice of solid carbon
Why is diamond hard?
Because of the strong covalent bonds between carbons
Why does diamond have a very high melting point?
Because the strong covalent bonds require large amounts of energy to break
Why is diamond an electrical insulator?
All electrons are involved in bonding so none are delocalised
Why is diamond insoluble?
Strong covalent bonds between carbon
What is the carbon arrangement in graphite?
Each carbon atom forms 3 single covalent bonds with 3 other carbons
What happens to the 4th carbon electron?
It is delocalised
What is the arrangement of graphite?
Trigonal planar
What is the bond angle around graphite?
120
How is graphite arranged?
In a 2D hexagonal structure built up in layers
Why is graphite soft?
The layers of graphite are held together with weak van der waals forces which are easy to overcome, therefore the layers of graphite can easily slide over each other
Why does graphite have a very high melting point?
The very strong covalent bonds between carbon atoms require large amounts of energy to overcome
Why is graphite an electrical conductor?
Delocalised electrons are able to carry a charge
Why is graphite insoluble?
Strong covalent bonds between carbon atoms
When do metallic crystal structures occur?
In pure metals or alloys
What are alloys?
Mixtures of metals
What is a metallic crystal structure?
A regular lattice of cations, surrounded by a sea of delocalised electrons
What is the cation charge of a group 1 metal and why?
1+ because it gives up 1 electron
What is the cation charge of a group 2 metal and why?
2+ because it gives up 2 electrons
What is the cation charge of a group 3 metal and why?
3+ because it gives up 3 electrons
What does the sea of delocalised electrons form?
non-directional electrostatic attractions, so electrons can move around and be attracted to any cation
Why do metallic crystal structures have high melting points?
Strong electrostatic attractions require large amounts of energy to overcome
What happens to the melting points of metals across a period?
They increase because the charge on the cation increases
What happens to the melting points of metals down a group?
They decrease because of shielding
Why can metals conduct electricity?
The delocalised sea of electrons can carry a charge
Why can metals conduct heat?
The delocalised sea of electrons quickly transfers energy
Why are metals malleable/ductile?
The sea of delocalised electrons is able to move with the ions as they move which maintains the non-directional electrostatic attractions and therefore the shape
What are the electron pairs in linear?
2 Bonded pairs and 0 lone pairs
What are the electron pairs in bent?
2 bonded pairs and 2 lone pairs
What are the electron pairs in trigonal planar?
3 bonded pairs and 0 lone pairs
What are the electron pairs in trigonal pyramidal?
3 bonded pairs and 1 lone pair
What are the electron pairs in tetrahedral?
4 bonded pairs and 0 lone pairs
What are the electron pairs in trigonal bypyramidal?
5 bonded pairs and 0 lone pairs
What are the electron pairs in octahedral?
6 bonded pairs and 0 lone pairs
What are the electron pairs in square planar?
4 bonded pairs and 2 lone pairs
What is the bond angle in linear?
180
What is the bond angle in bent?
104.5
What is the bond angle in trigonal planar?
120
What is the bond angle in trigonal pyramidal?
107
What is the bond angle in tetrahedral?
109.5
What is the bond angle in trigonal bipyramidal?
90 in the plane and 120 around the equator
What is the bond angle in octahedral?
90
What is the bond angle in square planar?
90
What are the steps for finding the shape of an unknown molecule?
1 - Find the formula2 - Identify the central atom3 - Add up valence electrons4 - Draw molecule5 - Add all bonding electrons6 - Add all satellite electrons7 - Any remaining electrons are lone pairs on the central atom
What is electronegativity?
The power of an atom to attract a bonding pair of electrons
What are the elements with the highest electronegativity?
N, O and F
What does it mean to have low electronegativity?
Low effective charge on the nucleus and high sheilding
What does it mean to have high electronegativity?
High effective charge on the nucleus and low sheilding
What is the impact of electronegativity on a covalent bond?
A difference in electronegativity causes pairs of electrons in a bond to be shared unequally
How does electronegativity explain an ionic bond?
Difference in electronegativity so big that electrons are transferred
Explain the covalent bond of a diatomic element
The electronegativity will be the same for both elements (same element) so the electrons are shard equally, there will therefore be no dipole and the molecule will be non polar
Explain the covalent bonds of a molecule with unequal electronegativity?
The element with the greater electronegativity will draw the bonded pair of electrons towards it and a dipole will form and it will be a polar molecule
In which molecules will hydrogen bonds form?
H-F, H-O and H-N because the difference in electronegativity is so big
What is an induced dipole known as?
Instantaneous dipole, van der waals forces, london forces and dispersion
What molecules do induced dipole occur between?
All molecules
How strong is an induced dipole compared to other IMFs?
It is the weakest
Why do induced dipoles happen?
The pair of shared electrons between a molecule can move around both atoms so in one instant may be found on one atom and not the other inducing a brief dipole. This induced dipole will induce a dipole on neighbouring molecules because of repulsion and in this instant the opposite poles will attract
What are examples of molecules with induced dipoles?
- Monatomic elements (cannot be polar)- Diatomic elements (atoms have the same electronegativity)- Large non polar molecules (symmetrical)
Why do IMFs increase with increasing Mr?
There are more electrons involved so the size of the induced dipole increases
Why do IMFs explain the increase of melting and boiling points as Mr increases?
Greater energy is needed to overcome the induced dipole forces
What molecules have permanent dipole forces?
Polar molecules
What is the strength of the permanent dipole forces relative to the other IMFs?
Stronger than induced dipole forces but weaker than H-Bonds
What do permanent dipoles do to the melting and boiling points?
They increase them as it requires a lot of energy to overcome a permanent dipole
What happens to the effect of a permanent dipole as the Mr increases?
It increases because more electrons will be involved so the effective charges on the atoms will be greater and the strength of the dipole-dipole forces will increase
How is a permanent dipole formed?
The atom in a molecule that is more electronegative (greater effective charge on the nucleus and less shielding) will have the electrons present on it most of the time therefore leaving the other atom electron deficient. This is the permanent dipole. The more electronegative atom will be delta negative and the electron deficient atom will be delta positive
How are dipole-dipole forces formed?
When two polar molecules are near each other the deltya positive end of one will be attracted to the delta negative of the other and this attraction is known as a dipole-dipole forces. Whilst these forces are present in induced dipoles they are only present for and instant whereas they are permanent in a permanent dipole
What is a hydrogen bond?
A very strong dipole-dipole interaction that can only happen between molecules that have a H DIRECTLY bonded to an O, N or F
How strong are H bonds relative to other IMFs?
Very strong because the difference in electronegativity is huge so the dipole-dipole forces between the two molecules are significantly stronger than any other IMF
What will molecules that are hydrogen bonded together have?
Very high melting and boiling points because the amount of energy needed to over come the H-bonds is huge
What organic molecules are capable of H-bonding?
Alcohols, amines and carboxylic acids
