C5. Electrons, Bonding and Structure

what is an orbital?

a region around the nucleus that can accommodate up to two electrons with opposite spins

what is the term given to the specific energy levels surrounding the nucleus?

shells

how does the energy in shells that are further from the nucleus compare to those closer?

higher

what indicates the relative distance from the nucleus of a shell?

principal quantum number

what are shells divided into and what are they labelled?

sub shells, s,p,d,f

where are electrons located within subshells

orbitals

how many orbitals can an s sub shell hold?

1

how many orbitals can a p sub shell hold?

3

how many orbitals can a d sub shell hold?

5

how many orbitals can a f sub shell hold?

7

maximum number of electrons a s subshell can hold?

2

maximum number of electrons a p subshell can hold?

6

maximum number of electrons a d subshell can hold?

10

maximum number of electrons a f subshell can hold?

14

which sub shells does shell 1 contain

1s

which sub shells does shell 2 contain

2s,2p

which sub shells does shell 3 contain

3s, 3p, 3d

which sub shells does shell 4 contain

4s, 4p, 4d, 4f

total number of electrons shell 1 can hold

2

total number of electrons shell 2 can hold

8

total number of electrons shell 3 can hold

18

total number of electrons shell 4 can hold

32

true or false : orbitals within the same subshell are or different energy

false - they are of equal energy

shape of s orbital

spherical

shape of p orbital

dumbell shape

how are the three p orbitals oriented in relation to one another

at right angles

why do atoms lose/gain electrons?

to form ions with full outer shells

metals lose electrons to become ___

positive ions/cations

non-metals gain electrons to become ___

negative ions/ anions

why can transition elements form multiple ions with different charges?

they have partially filled d-subshells

when transition elements ungergo ionisation are the electrons in 4s or 3d lost first?

4s

what allows for successive ionisations in many transition elements?

similar energies of the 3d and 4s subshells

what is the result of the successive ionisations in many transition elements?

formation of ions with varying charges

what is a compound ion?

consist of atoms from two or more elements chemically bonded together

examples of compound ions

nitrate, carbonate, sulfate, hydroxide and ammonium

what do ionic compound formulas indicate?

the ions present and their ratios

what must balance in an ionic compound?

total positive and negative charges

when does ionic bonding occur?

between oppositely charged ions

what is an ionic bond?

the electrostatic force of attraction between oppositely charged ions - usually a metal and non-metal

structure of ionic compounds?

have a giant lattice structure where positive and negative ions pack together

explain electrostatic attractions of ions in a giant lattice structure

each ion is electrostatically attracted to ions of the opposite charge in all directions

properties of ionic compounds

high melting and boiling points, conduct electricity when molten or in solution, do not conduct electricity as solids, dissolve in water

why do ionic compounds have high m.p and b.p?

strong electrostatic attractions between oppositely charged ions in the giant lattice must be overcome for the lattice to break apart - requiring a lot of energy

why can ionic compounds conduct electricity when molten or in solution?

ions can move freely and carry electric charge through the liquid

why can’t ionic compounds conduct electricity as solids?

in the solid lattice structure the ions are firmly locked in place so are unable to move to carry electric charge

why can ionic compounds dissolve in water?

polar water molecules attract the charged ions in the lattice via ion-dipole forces, pulling them away from the lattice and dissolving the structure

what is covalent bonding?

the strong electrostatic attraction formed between a shared pair of electrons and the nuclei of the bonded atoms

what does covalent bonding create?

a stable molecule

what is a stable molecule?

a group of two or more atoms held together by covalent bonds

what does the strength of a covalent bond depend on?

how much energy is needed to break the bond

how is bond strength measured?

using average bond enthalpy

what unit is used to measure average bond enthalpy?

kJmol^-1

the higher the average bond enthalpy value ___

the stronger the covalent bond

what does the number of covalent bonds an atom forms depend on?

how many electrons it needs to fill its outer shell

true or false atoms can only share one pair of electrons to fill their outer shell?

false they can share multiple electron pairs

what is another term of dative bonding?

coordinate bonding

what is dative covalent bonding?

when both shared electrons come from just one of the bonding atoms rather than one electron coming from each atom

what is needed for a dative covalent bond to form between two atoms?

one atom must have a lone pair of electrons to donate, the other atom must be electron deficient

when does it mean for an atom to be electron deficient?

have an incomplete electron shell

how is dative covalent bonding represented?

by an arrow showing the direction of electron donation from the atom with the lone pair to the electron deficient atom

what do metals exist as?

giant lattice structures made of positively charged metal cations and delocalised electrons

what do the outer electrons of metal atoms leave to become and what do they result in?

delocalised electrons, positively charged metal cations

what is metallic bonding?

the electrostatic attraction between positively charged metal ions and negatively charged delocalised electrons

are metallic bonds strong?

yes

what is the strength of metallic bonds influenced by?

number of delocalised electrons per atom, charge of metal cation and radius of the metal cation

metals with higher numbers of delocalised electrons per atom form ____ metallic bonds

stronger

why does having more delocalised electrons increase bond strength?

stronger electrostatic attractions between electrons and metal cations

does a higher or lower cation charge give stronger electrostatic attractions between cation and delocalised electrons?

higher

do smaller or larger metal cations have a higher charge density?

smaller

why does having a higher charge density give stronger metallic bonds?

allows them to hold delocalised electrons closer to the nucleus, enhancing electrostatic attraction between cations and electrons

properties of metals

high melting and boiling points, good conductors of electricity and heat, malleable and ductile, insoluble

why do metals have high m.p and b.p?

strong electrostatic forces of attraction between positively charged metal cations and the sea of delocalised electrons must be overcome for the lattice to break apart - requiring lots of energy

why are metals good conductors of heat and electricity?

the delocalised electrons can flow freely through the lattice to transfer charge and heat energy

why are metals malleable and ductile?

layers of cation lattice can slide over one another when the metal is distorted because there are no bonds locking individual cations together

why are metal insoluble?

strength of metallic bonding prevents water or any other solvent molecules pulling the cations away from the lattice structure and dissolving the metal

what is a giant covalent structure?

extensive interconnecting networks of covalently bonded atoms

what is an allotrope?

different structural forms of an element in the same state

allotropes of carbon with giant lattice structure

diamond, graphite and graphene

structure and bonding of carbon

each carbon atom forms 4 very strong covalent bonds with others in a tetrahedral arrangement

properties of diamond

extremely hard, very high melting point, good thermal conductor, electrical insulator, insoluble

why is diamond extremely hard?

extensive network of strong covalent bonds not easily broken

why does diamond have a very high melting point?

huge amount of energy needed to break enough bonds to melt it

why is diamond a good thermal conductor?

strong interatomic bonds transmit heat through vibrations

why is diamond an electrical insulator?

all outer electrons are tied up in localised bonds so no free electrons to carry charge

why is diamond insoluble?

covalent bonds are too strong to be broken by solvation

bonding and structure of silicon giant covalent structure

each silicon atom bonds to 4 strong covalent bonds in a tetrahedral arrangement

properties of silicon giant covalent structure

high melting point, very hard, insoluble

structure of graphite?

each carbon atom forms 3 strong covalent bonds in a planar hexagonal pattern so each carbon contributes 1 delocalised electron

arrangement of graphite

multiple stacked layers of hexagonal carbon arrays with weak intermolecular forces between layers

properties of graphite

soft and slipppery, conducts electricity along layers, lower density than diamond, high sublimation temperature but lower melting point than diamond

why is graphite soft and slippery?

weak intermolecular forces let sheets slide over each other

why can graphite conduct electricity along layers?

delocalised electrons move through the 2D lattice carrying electrical charge

why does graphite have a lower density than diamond?

weak intermolecular forces lead to increased separation between layers

why does graphite have a high sublimation temperature but lower melting point than diamond?

covalent bonds within each layer are very strong but the weaker intermolecular forces between layers means graphite melts at a lower temperature

structure of graphene

consists of a single layer of carbon atoms interconnected through strong planar covalent bonds in a hexagonal pattern, each carbon contributes 1 delocalised electron

how thick is graphene in comparison to graphite?

1 atom thick slice of graphite

properties of graphene

excellent electrical and thermal conductivity, very strong, transparent and extremely lightweight

why is graphene an excellent electrical and thermal conductor?

delocalised electrons move through the 2D lattice transporting heat and charge

why is graphene very strong?

extensive network of covalent bonds not easily broken

why is graphene transparent and extremely lightweight?

single layer of atoms light and thin enough to trnamit visible light