C3 Flashcards
Who was Newlands?
A chemist who noticed every 8th element had similar properties and created Newlands octaves
Why was Newlands work criticised?
- his groups contained elements that didn’t have similar properties
- he mixed up metals and non-metals
- he didn’t leave gaps for undiscovered elements
What did Mendeleev do?
arranged the elements in order of atomic mass (like Newlands) but left gaps so that elements with similar properties were in the same vertical column. He also predicted properties of undiscovered elements
elements in the same group have the same…
number of electrons on their outer shell
if the electron is far from the nucleus the force of attraction is…
weak, especially if the electron is shielded by other elctrons
the combination of increased shielding and distance means that…
an electron in a higher energy level is more easily lost as there’s less attraction from the nucleus.
This is why group 1 is more reactive as you go down the group
what are the properties of alkali metals (group 1 metals)?
low density and 1 outer electron
As you go down group 1:
- become more reactive
- lower melting and boiling points
What happens when group 1 metals form ionic compounds with non-metals?
produces white compounds that dissolve to form a colourless solution
What happens when group 1 metals react with water?
produce hydrogen gas, they float and fizz alot
What are the first 3 group 1 metals?
lithium, sodium, potassium
what are the properties of the halogens (group 7)?
non-metals with coloured vapours
Describe fluorine
very reactive, poisonous yellow gas
Describe chlorine
fairly reactive, poisonous dense green gas
Describe Bromine
dense, poisonous red-brown volatile liquid
Describe Iodine
dark grey solid or purple vapour
What happens as you go down group 7?
- less reactive
- higher melting point
- higher boiling point
What happens when halogens bond with metals?
they form 1- ions called halides
What are the properties of transition metals?
- good conductor of heat + elctricty
- very dense, strong and shiny (more than group 1 metals)
- less reactive than group 1 metals
- much higher melting points than group 1 metals
What is the reactivity of an element?
how easily its atoms lose or gain electrons
What is soft water?
it easily lathers with soap and contains dissolved sodium ions
What is hard water?
contains dissolved magnesium and calcium ions and produces scum and scale when ions react with soap or when the water is heated
What is scum?
formed when the calcium ions in hard water displace the sodium stearate to form calcium stearate
What is scale?
a thermal insulator and is formed when hard water is heated. it collects in pipes, boilers and kettles.
How is hard water formed?
when rainwater flows over rocks and calcium ions and magnesium ions dissolve into the water
Positives of hard water?
- good for teeth and bones
- helps prevent heart disease
Positives of soft water?
- fewer products are used up
- cheaper bills
Negatives of hard water?
- reduces efficiency of heating elements
- clogs pipes and costs money for plumbing
Negatives of soft water?
- contains alt which is bad for your heart
What is temporarily hard water?
caused by dissolved calcium hydrogen carbonate the hardness can be easily removed with heating. Calcium hydrogen carbonate thermally decomposes to form calcium carbonate, water and carbon dioxide
What is titration (water)?
it can be carried out to compare the hardness of water samples e.g. you can measure the amount of lather produced from water when soap is added
Explain how you can soften water using a ion exchange column
the column contains lots of sodium ions held in a resin which exchange for the calcium ions when water is run through it to make the water soft
Explain how you can soften water using sodium carbonate
the calcium ions in the water are displaced by the sodium leaving sodium ions in the water
What is the first stage of water treatment?
after the water leaves the reservoir it goes through screens to remove large objects
What is the second stage of water treatment? (settlement)
it is piped into the settlement tanks where soil and sand is removed
What is the Third stage of water treatment? (clumping)
aluminium sulphate and lime are added which causes small particles to clump together and sink
What is the fourth stage of water treatment? (sand)
The water i passed through a sand filter to remove any insoluble particles
What is the fifth stage of water treatment? (bacteria)
chlorine is added to kill bacteria
What is the sixth stage of water treatment? (pH)
The pH is checked so that is is neutral. water is then pumped to homes or stored in large tanks
What are the positives of water fluoridation?
- reduction in teeth cavities
- kills bacteria which causes heart disease
What are the negatives of water fluoridation?
- could cause learning disabilties
- causes fluorosis which can link to cancer
Why is water not totally pure?
because distillation is needed which is expensive