General Trends in Group 7

Question 1

what is the name of the group 7 elements

Answer 1

halogens

Question 2

why are the elements at the top and bottom (fluorine and astatine) usually ignored when it comes to trends

Answer 2

• fluorine sometimes behaves different from the following three
• astatine only exists as radioactive isotopes

Question 3

what are the states of fluorine, chlorine, bromine, iodine and astatine at room temp

Answer 3

• fluorine = gas
• chlorine = gas
• bromine = liquid
• iodine = solid
• astatine = solid

Question 4

what is the trend in boiling and melting points down the group

Answer 4

they increase

Question 5

what is the trend in electronegativity down the group

Answer 5

it decreases

Question 6

what is determining the boiling and melting temps of the halogens

Answer 6

• they all exist as diatomic molecules
• so the temps depend on the intermolecular forces of attraction between their relative molecules
• aka london forces

Question 7

how do instantaneous dipoles arise (again)

Answer 7

• in the diatomic molecule the pair of electrons in the covalent bond are shared equally
• but as positive charges of the protons in each nuclei are in fixed positions
• but the electron density in a halogen molecule continuously fluctuates
• sometimes the centres of the positive and negative charge dont coincide
• this forms a temporary / instantaneous dipole

Question 8

how is an induced dipole then formed

Answer 8

• with the ends of the now polar molecule being partially positively and negatively charged
• one side being close to the side of a non-polar molecule will give that side the opposite charge of it
• resulting in the other side of this new molecule having the opposite charge of that
• this forms the induced dipole

Question 9

what is the result of the interaction between the instantaneous and induced dipoles

Answer 9

• the oppositely charged ends attract forming a force of attraction
• this is called instantaneous-induced dipole attraction (/interaction)
• this is basically what london forces are

Question 10

how would these weak london forces increase

Answer 10

if the number of electrons and the size of the electron clouds increases

Question 11

therefore why does the boiling and melting temp of the halogens increase down the group

Answer 11

• because they have more london forces as you go down the group
• as the electrons in each diatomic molecule increase down the group

Question 12

what is the change of state equation for when bromine gives off a vopor

Answer 12

Br2(l) = Br2(g)

Question 13

what is unique about how iodine changes when it heated

Answer 13

• it changes state from a solid straight to a vapor, skipping the liquid state
• this is called sublimation

Question 14

what is the equation for this change of state of iodine

Answer 14

I2(s) = I2(g)

Question 15

what is electronegativity

Answer 15

the ability of an atom to attract the pair of electrons in a covalent bond

Question 16

what scale is used to measure the magnitude of electronegativity

Answer 16

• a scale devised by linus pauling

- ranging from 0 to 4

Question 17

what are the three factors the electronegativity of an atom depends on

Answer 17

• it nuclear charge
• distance between nucleus and bonding pair of electrons
• the shielding effect of electron in inner energy levels

Question 18

what does an increase in nuclear charge do to the electronegativity of an atom and why

Answer 18

• it increases it

- stronger positive charge means stronger forces of attraction between it and the electrons

Question 19

what does an increase in the distance between the nucleus and bonding pair of electrons do to the electronegativity of an atom and why

Answer 19

• it decreases it

- longer distances mean weaker electrostatic forces of attraction

Question 20

what does an increase in the shielding effect of electrons in inner energy levels do to the electronegativity of an atom and why

Answer 20

• it decreases it
• because there is more repulsion against the incoming bonding pairs of electrons attracted to the nucleus
• there is also a high chance the atomic radius has increases
• meaning increased distances between the nucleus and the bonding pair

Question 21

what element has the highest electronegativity and what group has the highest electronegativities

Answer 21

• fluorine

- group 7 halogens

Question 22

what is special about fluorines very high electronegativity when it comes to reactions with other elements

Answer 22

• it is basically always the oxidising agent
• even with oxygen
• oxygen would gain a positive charge if it reacted with fluorine