Topic 2-Bonding Flashcards
What is metallic bonding and describe features of metals?
Electrostatic attraction between positive ions and a sea of delocalised electrons.
Metals are malleable and ductile
What does the strength of metallic bonding depend on and the effect on melting and boiling point?
Metallic bonds depend upon the amount of protons
The more protons the stronger the metallic bond as greater nuclear charge pulls in valence electrons
This increases boiling and melting point as more energy required to overcome metallic bonds
What is Ionic bonding and explain some properties?
Bond between positive and negative ions held together by electrostatic forces of attraction
Involves transfer of electrons
High Melting point
Soluble in water as they are charged
Does not conduct electricity in solids
Cannot be shaped
Brittle-As repulsion between same charged ions are strong
What is covalent bonding?
Electrostatic attraction between positive nucleus and negative electrons
It forms between 2 non metals
Involves sharing of electrons
What evidence is there for the existence of ions?
Migration of ions on wet filter paper-electrolysis of copper chromate
Electron Density Maps
Why does Ionic bonding have high melting and boiling points?
Strong electrostatic forces of attraction between oppositely charged ions so more energy is required to break forces
Why can Ionic compounds conduct electricity in solution but not in solids?
In solutions,ions are free to move and carry charge so it can conduct electricity
In solids,ions cannot move
Explain the properties of Diamonds?
High Melting Point- as it has strong covalent binds so lots of energy is required to overcome these bonds
High strength as each carbon is joined to 4 others so has a coordination no. of 4,strong delocalised electrons
Cannot conduct electricity
Explain the bonding,structure and properties of graphite?
High Melting Point-Has lots of strong covalent bonds so lots of energy required to break bonds
Each Carbon bonded to 3 others
Strength- Low strength as it has weak intermolecular forces of attraction so layers can slide over each other
Can conduct electricity as it has delocalised electrons
How does Ionic charges and Ionic Radii affect Ionic bonding?
The Greater the charge of the ion,the stronger the Ionic bond and so a higher melting and boiling point
The smaller the Ionic radii the greater the Ionic bonding as electrostatic attraction is greater when Ionic radii is small so it is stronger and has a higher melting and boiling point
Explain how Ionic radius changes down the group?
Ionic Radius increases down the group as atomic number is greater so there is more electron shell
What is a dative covalent bond?
This is where one atom donates both electrons to a bond for example carbon monoxide
Contributes to donate both electrons to form a covalent bond
Explain the properties of giant covalent bonds?
Strong covalent bonds and strong electrostatic forces of attraction allow:
Very High Melting points
Extremely hard-strong bonds in the regular lattice,so atoms cannot slide past each other
Good thermal conductors
Insoluble-As atoms are more attracted to neighbours than to solvent molecules
Cannot conduct electricity
Explain the angle size difference between lone pairs and electron pairs?
Explain the effect of electron repulsion on angle size?
As you know,pairs of electrons will always repel so stronger repulsion means greater angle difference
Lone pairs have stronger repulsion so they have greater angle size
What is the Octet rule and what elements are exemptions and why?
Tendency of electrons to have 8 electrons in the outer shell
Elements in the 3rd row or below don’t need to follow the Octet rule as they can have more electrons as they can promote some electrons in a 3d subshell
They can have upto 18
What are hypervalent compounds?
Compounds that do not follow the Octet rule and can have more than 8 electrons in a subshell
What is a sigma bond?
Is the overlap of a covalent bond which passes the internucleaur axis
Single bonds are sigma
What is a pi bond?
Pi bonds are a bond between 2 covalent bonds where it passes the internucleur axis
Double bonds have 1 sigma and 1 pi bond
Triple bonds have 1 sigma and 2 pi bonds
What is a molecule?
An uncharged group of 2 or more atoms stuck together
What is a double bond?
Its where 2 pairs of electrons are shared between 2 elements
Explain how the length of a covalent bond is dependant on the relative atomic mass?
Greater relative atomic mass means that there is more electrons and greater nuclei distance so that means the length of the covalent bond is greater.
Explain how the proton number affects the length of a covalent bond?
The Greater the proton number,the greater the attraction between positive nuclei and outer electrons so this means atomic radius is smaller so length of covalent bond is smaller
How are dative bonds represented?
They are represented by 2 dots or 2 crosses or as an arrow
What is needed for a dative bond to form?
An element/atom needs a lone pair of electrons to form a full outer shell
It requires an acceptor and a donor
What is the Valence Shell Electron pair repulsion theory and its purpose?
This is a theory used to predict the geometry of molecules based on minimising electron repulsion
How is the shape of a molecule determined?
It is determined by the electron pairs surrounding the central atom
This is based on the fact that pairs of electrons repel other pairs of electrons
This means electron pairs move as far as possible creating bigger bond angles
What angle does lone pairs decrease bond angle by and why?
Each lone pair decreases bond angle by 2.5 degrees and this is because they create repulsion
A lone pair also counts as a region
What is the bond angle for tetrahedron?
It’s 109.5
Describe the geometry of water,shape and bond angles
Water is a tetrahedron with a bent shape as it has 4 electron density regions(2 bonding pairs and 2 lone pairs)
It has a bond angle of 104.5 and 109.5-2.5-2.5 is 104.5
Explain variations in melting temperature across period 3 in terms of structure and bonding?
Na,Mg,Al have metallic bonding,number of protons increase,radius decreases so metallic bond strength increases
Si is a giant covalent molecule so lots of energy required to break covalent bonds
Phosphorus is a simple molecular so it has low melting pointe as it has weak intermolecular forces
What is electronegativity?
The power/ability of an element to attract the shared pair of electrons in a covalent bond
Explain how electronegativity changes down a group?
Electronegativity decreases down the group as shielding increases which decreases the effective nucleur charge so the element is less likely to attract electrons as positive nuclear charge is lowered by shielding
Explain how electronegativity changes across a period?
Across a period,electronegativity increases as proton no increases so effective nucleur charge increases as atomic radius gets smaller
What is the Pauling Electronegativity of non polar,polar and Ionic compounds?
Non polar-0 to 0.5
Polar-0.5 to 1.7
Ionic-Greater than 2 and smaller than 4(4 is max and fluorine has EN of 4 )
What does electronegativity show in a compound?
In a compound such as HCL the element with a greater EN will have a greater share of the shared electron pair so its slightly more negative whereas the other is positive
Cl has a greater EN so its delta negative
Explain how lone pairs affect electronegativity?
Molecules with one or more lone pairs on the central atom are always polar as it breaks the symmetry
What are intermolecular forces and the 3 examples?
Intermolecular forces are forces between molecules and are weaker than Ionic and covalent
London forces(instantaneous dipole dipole bonds)
Permanent dipole dipole forces
Hydrogen bonding(strongest type)
What are London forces?
They are fluctuations in electrical distribution within atoms and molecules
They can induce another temporary dipoles forming weak london forces
They are instantaneous dipole forces
Explain how to increase strength of london forces?
Larger molecules(such as down the group) has larger electron clouds so stronger london forces
Increase SA increases strength of london forces
Greater electrons increase the strength
What are permanent dipole dipole forces and what compounds have these?
Polar compounds have permanent dipole dipole forces as they have some sort of electronegativity
Explain the strength of forces/bonding of london,hydrogen,dipole,covalent
London-weakest
Dipole dipole
Hydrogen-very strong
Covalent-strongest
What is hydrogen bonding and what elements can it occur with?
Hydrogen bonding is the electrostatic attraction between negative oxygen and positive hydrogen
They only occur in OH,FH,NH bonds
Why can hydrogen bonding only occur with elements:fluorine,oxygen and nitrogen?
These are the most electronegative elements so they draw the binding electrons away
Lone pairs make the bond polarised
Factors affecting bond length and explain them?
Atomic radius-greater atom means more electrons shells so more shielding which reduces attraction resulting in longer bond length
Greater attraction means shorter bind length
Explain why fluorine is more electronegative than bromine?
Less shielding,can form hydrogen bonds so more polar
Explain the relationship with solubility and bonding?
For a substance to dissolve in another:
Bonds in the substance has to break
Bonds in the solvent have to break
New Bonds have to form between substance and solvent
Define electron affinity?
The first electron affinity (EA1) is the enthalpy change when 1 mole of electrons is added to 1 mole of gaseous atoms, to form 1 mole of gaseous ions each with a single negative charge under standard conditions
First electrons affinity is exothermic,explain why 2nd and 3rd are endothermic?
The second and third electron affinities are endothermic, as energy is absorbed
This is because the incoming electron is added to an already negative ion
Energy is required to overcome the repulsive forces between the incoming electron and negative ion
Since these are endothermic processes, the values will be positive
Explain what characteristics lead to a shorter bond?
The Greater the electron density between atoms the stronger the attractive force,so atoms are pulled in further towards each other leading to a shorter bond
