periodicity

Question 1

alkali metals - mp/bp, density, hardness, conductivity

Answer 1

• mp/bp: decrease as you descend the group because the distance of the delocalised electrons to the nucleus increases, so metallic bond strength decreases
• density: generally increases as you descend the group due to the increasing masses of the nuclei
• hardness: become softer as you descend the group due to the decreasing strength of metallic bonding
• conductivity: good conductors of heat and electricity due to the presence of delocalised electrons

Question 2

alkali metals reactivity

Answer 2

• very reactive as they only have to lose one electron to become stable
• the elements have to be stored in oil to prevent them from reacting with oxygen and water in the air
• when exposed to the air, the shiny metals will quickly react with oxygen and tarnish, forming metal oxide
• descending group 1, the elements become more reactive because less energy is required to remove the electron

Question 3

alkali metals reaction with water

Answer 3

lithium: reacts slowly, floats, gradually dissolves, lithium hydroxide formed, H2 given off which burns with a red flame when ignited
sodium: reacts more quickly, quickly dissolves, sodium hydroxide formed, H2 given off which burns with a yellow-orange flame when ignited
potassium: reacts vigorously, very quickly dissolves, potassium hydroxide formed, H2 given off which burns with a lilac flame when ignited

Question 4

metal hydroxide pH

Answer 4

• high pH as it is alkaline

- turns universal indicator blue/purple

Question 5

halogens - mp/bp, conduction

Answer 5

• mp/bp increase as you descend the group because there are more electrons so the LDFs are stronger
• poor conductors of heat and electricity

Question 6

halogens reactivity

Answer 6

• highly reactive as they only need 1 more electron
• reactivity decreases as you descend the group because the atoms get larger, so the incoming electron joins a shell that is further from the nucleus -> has a weaker force of attraction to the nucleus

Question 7

noble gases - colour, density, mp/bp

Answer 7

• all colourless at room temp and pressure
• very low mp/bp which increase as you descend the group due to more electrons -> stronger LDFs
• density increases as you descend the group due to increasing mass of atoms

Question 8

noble gases reactivity

Answer 8

• very un-reactive because they have a full outer electron shell
• therefore, they exist as single atoms (monatomic)
• described as being inert (chemically inactive)
• some compounds of noble gases at the bottom of the group have been made, e.g. XeF4, KrF2 but only with the most reactive of the non-metal elements

Question 9

general formula for metal reacting with water

Answer 9

1. metal + water -> metal hydroxide + hydrogen