ES 1/ 11.3a- Halogens

What do halide crystalline salts look like?

Look white when solid but clear in solution

Which group are the halogens in?

Group 7

How many electrons are in the outer shell of all the halogen atoms?

Seven

What sort of molecules do the halogens usually form?

Diatomic- simple covalent molecules

What forms are the halogens found in naturally?

Not found naturally in elemental form usually in compounds such as metal halides

What is their relative reactivity compared to other elements?

Most reactive non-metal group

What is their ion charge?

1-

What is the difference between halide and halogen?

A halogen is an atom, a halide ion an ion- not interchangeable

What is the electronic configuration of the outershell of fluorine?

2s^2 2p^5

What is the physical appearance of fluorine at RTP?

Pale yellow gas

What is the relative reactivity of fluorine?

Most reactive halogen/ most reactive element- explosions occur when fluorine gas reacts and it can even react with krypton, xenon and radon- the noble gases

Why is fluorine so difficult to store?

Because it is able to react with steel and glass

What form can fluorine not be found in?

As a pure element

What is the physical appearance of chlorine at RTP?

pale green gas

What is the electronic configuration of chlorine?

3s^2 3p^5

What is the molecular formula of chlorine?

Cl2

What are the melting and boiling points of chlorine?

Melting point- 172K
Boiling point- 239 K

What is the solubility of chlorine in water?

Slightly (less than bromine, more than astatine)

What is the electronic configuration of the outer shell of bromine?

4s^2 4p^5

What is the physical appearance of bromine at RTP?

liquid- dark red-brown and very volatile

What is the solubility of bromine in water?

Slightly more soluble in water than chlorine

What is the electronic configuration of the outer shell of electrons in iodine?

5s^2 5p^5

What are the melting and boiling points of iodine?

Melting point- 387K
Boiling point- 457 K

What is the physical appearance of iodine at RTP?

A shiny grey/ clack solid

What happens to iodine when it is gently heated?

Sublimes to give a purple vapour on heating- v. low temperature is required

What is the approximate solubility of iodine in water?

Very low (lower than bromine and chlorine)

When can astatine be found?

It is radioactive and is found in the radioactive decay series of uranium and thorium

What is the predicted physical appearance of astatine at RTP?

Nearly black solid

What can be predicted would happen to astatine when it is heated?

It would form a dark purple vapour

Describe the electronic configuration of the halogens?

7 electrons in their outer shell, highest energy electron in the p-subshell, the outer p-subshell contains 5 electrons

Which block of the periodic table are the halogens in?

p-block

What is the electron configuration of the halogens in relation to their nearest noble gas?

The halogen atoms have one less electron than their nearest noble gas

What bonding form are all of the halogens found in?

Diatomic molecules- a simple covalent molecule, a single covalent bond between the two halogen atoms, each halogen atom has a full outer shell of electrons (8)

How do halogen atoms achieve stability in a compound?

By filling up their outer shell to 8 electrons- adding another electron

What are the intermolecular forces/ bonds between diatomic halogen molecules?

van der Waals dispersion forces

What two types of bonds can halogens form?

1) Ionic- ionic compounds (with a halogen and metal atom(s))- gaining of an electron from a metal atom forming a halide ion with then ending "ide"- ion

2) Covalent- sharing an electron from another non-metal atom in a covalently bonded compound- "ine" ending- still an atom

What is the trend in melting and boiling points?

Melting and boiling points increase going down the group. Start of the group they are found as gases, bottom found as solids.

Explain in 6 steps the reason for the trend in melting and boiling point

1) Halogens are diatomic molecules

2) Intermolecular bonds are van der Waals dispersion forces which are holding the molecules together (these forces are already weak as they are formed from only temporary dipoles which change as the electrons keep moving)

3) Down the group the number of electrons increases as there is one more shell for each period down the group

4) More electrons can move around and set up temporary dipoles- creates the van der Waals dispersion forces. As there are more electrons the uneven distribution is larger in charge so there are stronger dipoles

5) Stronger intermolecular attractions with larger atoms (further down group)

6) More energy must be supplied (heat energy) to turn them into liquid/ gas so the melting point and boiling point increases

What is the trend in volatility with the halogens?

Down the groupthe halogens become less volatile

What is volatility?

A measure of how easy it is to vapourise something and turn it from a liquid to a gas.

Explain the decrease in volatility down the group

Further down the group the atoms are larger/ larger relative atomic mass so they have stronger van der Waals dispersion forces which means they need higher temperatures to evapourate to a gas

What is the trend in atomic radius?

The atomic radius increases down the group

What two factors affect atomic radius of an atom?

1) number of layers of electrons around the nucleus- the number of electron shells

2) the pull the outer electrons feel from the nucleus

Explain the increase in atomic radius of the halogens down the group?

1) All the halogen outer electrons feel a net pull of 7+ from the nucleus - the positive charge ofthe nucleus cut down by the negativeness of the inner electrons. And the outer electron shell has a 7- charge in all the halogens. So this factor does not affect the change atomic radius as it is the same the whole way down the group.

2) Number of inner electron shells: only factor that affects size. More layers/ shells means more space, this is further increased as the electrons repel each other.

These two factors cause the atomic radius to increase down the group.

What is electronegativity?

A measure of the tendecyof an atom to attract a bonding pair of electrons (measured on the Pauling Scale)

What is the trend in electronegativity down group 7?

Electronegativity decreases down the group- atoms become less good at attracting bonding pairs of electrons

Which element is the most electrongeative in group 7/ in the periodic table?

Fluorine- 4.0

What does it mean to have high electrongeativity?

It means that the atom fills its electron shells more easily because the atom is good at attracting bonding pairs of electrons

What are the two reasons for the decreasing electronegativity of the halogens down the group?

1) Bonding pairs of electrons feel the same 7+ net pull to all of the halogens

2)Larger atomic radius because of more shells means the bonding pair is further from the nucleus so there is a a weaker electrostatic force of attraction between the positive nucleus and the negative bonding pair of electrons meaning the atom is lessable toa ttract these electrons so less electronegative

What is the trend in the reactivity of the halogens?

The halogens are generally very reactive elements

The reactivity of the halogens decreases down the group

How do the halogens react?

They remove an electron from the outershell of another atom to complete their own

Describe some of the properties of the elements at the top of the group

Most reactive

Strongest oxidising agents

More electronegative

Explain why the reactivity of the halogens is greater at the top of the group than at the bottom?

Smaller halogen atoms (at the top fothe group) have a stronger positive attraction/ electronstatic force of attraction between the protons in the nucleus and the negative outermost electron that is being added to the outer electron shell to make a full shell.

So a smaller halogen is more able/ more readily able to attract an outer electron from another atom in order to react- becomes a nagative halide ion more easily making it more reactive.

What three factors increase the strength of the electrostatic force of attraction?

1) smaller atomic radi- smaller distance from the nucleus to the outermost electron

2) more electronegative

3) less electron sheliding

Why does the trend in reactivity decrease down the group in a regular way?

Because each sucessive member has one more electron shell- fairly regular increase in atomic radius

What sort of agents can the more reactive halogens also be classed as?

Stronger oxidising agents (all halogens ae oxidising agents) because they remove electrons from other elements.

How do you calculate the core charge?

Atomic number minus the number of electrons not in the outer shell

Which two factors affect the reactivity of an element?

1) Distance/ atomic radi- nucleus tothe outer electron shell where the next electron is being added

2) Electron sheilding- reduce the strength of the attraction from the nucleus

Both of these factors increase down the group leading to the reduced ractivity

What is the solubility of fluorine in water and why is it the exception?

Fluorine cannot be considered to be soluble in water because it reacts with the water instead- forms hydrogen fluoride gas or a solution of hydrofluoric acid and a mixture of O2 and ozone which is not soluble

Describe the solubility of the other halides (not fluorine) in water, is there a pattern?

The other halides all dissolve in water but only a little and there is no pattern to their solubility in water

What are the colours of chlorine, bromide and iodine when dissolved in water?

Chlorine solution in water- pale green (small amount of HCl is formed)

Bromine solution in water- yellow to dark orange-red depending on the concentration

Iodine solution in water- pale brown

Only a very tiny amount of acid is formed when iodine and bromine dissolve in water

What is the relative solubility of chlorine, bromine and iodine in water?

Bromine is the most soluble, then chlorine then iodine

Explain why halogens are not very soluble in water

Halogens have covalent/ non-polar structures (diatomic- same molecule/ atom so they have the same electronegativity so no poles)- repelled by polar water molecules as they cannot form hydrogen bonds with the water molecules.

What substances are halogens more soluble in?

Organic solvents (such as hexane or cyclohexane)

Where does the organic solvent layer form in a test-tube and why?

It forms as a layer on top of the aqueous solution because it is less dense

What colours can be seen when halogens are dissolved in organic solvents and how is this helpful?

Much more distinct colours which makes it easier to see which halogen is present (when dissolved in water iodine and bromine look very similar)

Chlorine- pale green

Bromine- red-brown

Iodine- violet/ purple

Why do halogens dissolve more easily in organic solvents?

Because organic solvents and halogens both contain non-polar molecules which are attracted to each other by the van der Waals dispersion forces (cannot form these with water molecules as water molecules are polar molecules). Attraction broken between the hexane molecules and between the halogen molecules is similar to the attrations made when the two substances mix.

What is the colour of chlorine, bromine and iodine dissolved in organic solvents?

Chlorine: pale green solution
Bromine: Red/ Brown solution
Iodine: Purple/ Violet
Much more clear distinction between bromine and iodine- prevents confusion

How would you carry out an investigation to see the reaction between halogen atoms/ molecules and halide ions of a lower reactivity?

One halogen solution (X2 solution) containing the halogen molecules is added to a solution of a halide compound containing the 1- halide ions

How could an ionic compound with a halogen provide the 1- halide ions to a displacement reaction?

If an ionic compound the ionic lattice breaks down forming/ releasing the 1- halide ion

What happens when a solution of a more reactive halogen is added to a solution containing ions/ a compound of a less reative halogen?

The more reactive halogen displaces the less reactive halogen from its solution

What happens to each atom of the less reactive halogen?

Loses an electron, is oxidised- it is the reducing agent

What happens to each atom of the more reactive halogen?

Gains an electron, is reduced- it is the oxidising agent

Describe what happens in a displacement reaction?

The more reactive halogen displaces/pushes out the less reactive halogen from its compounds/ aqueous solutions of ions

What type of reaction is a displacement reaction?

A redox reaction- oxidation and reduction occur at the same time

What does a half equation show?

What is happening in a redox reaction- show the movement of electrons:

One of the half equation species gains electrons- it is reduced so the more reactive halogen atom becomes a halide ion

One of the half equation species loses electrons- it is oxidised, less reactive halide ions forms a halogen atom

Where would the electrons be in a half equations if it was reduction/ oxidation?

Reduction- gaining electrons, they would be a reactants (on the left side)
Oxidation- losing electrons, they would be a product (on the right side)

What halide ions does Cl2 oxidise?

Br- and I- ions