Chemistry Topic 1 Flashcards
(25 cards)
What is a compound?
2 or more elements chemically combined in fixed proportions
What is a mixture?
2 or more elements or compounds not chemically combined together
How can mixtures be separated?
Can be separated by physical processes
What are the 5 physical separation processes?
Filtration, crystallisation, simple distillation, fractional distillation, chromatography
What is filtration and how does it work?
Insoluble solid (a solid that doesn’t dissolve) is mixed up with a liquid.
-use a filter paper to separate the insoluble solid (residue) from the liquid
- liquid goes through filter paper (filtrate)
What is crystallisation and how does it work?
Separating a soluble solid from a liquid
- use bansen burner to heat and evaporate the copper sulphate
- liquid evaporates and crystals (dry salts) are formed
What is fractional distillation and how does it work?
Separating liquids with different boiling points (cold at the top, hot at the bottom)
- mixtures will be heated at the bottom, evaporate and then turns into liquids as they moves up the column (cooler)
- turn back into liquids at different temperatures depending on they’re boiling point (e.g. crude oil)
What is Chromatography and how does it work?
Separating mixtures into their components
- stationary phase (piece of paper) , mobile phase (water/solvent moving up)
- draw pencil line on paper and samples
- put chromatography paper into the solvent so it rises up the paper
- colours release at different points based on their solubility
Atomic structure:
Protons- in the nucleus, relative mass of 1, relative charge of +1
Electrons- in the shells, relative mass: very small, relative charge of -1
Neutrons- nucleus, relative mass of 1, relative charge of 0
What are isotopes?
Atoms of the same element (protons) with different number of neutrons
Mass vs atomic number:
Mass number- number on top of element (protons and neutrons)
Atomic number- number on the bottom of element (protons)
Relative atomic mass:
(% of element x atomic mass) + (% of element x atomic mass)
All divided by the sum of both %’s
Dalton model:
Atoms are little individual spheres
Plum pudding model ( JJ Thompson)
-Discovered atoms have electrons
- develops plum pudding model
- big ball of positive charge with electrons inside
Alpha scattering experiment ( Ernest Ruthford)
-Alpha particles: radio active decay (2 protons, 2 neutrons)
-firing particles at thin sheet of gold foil
-expecting particles would pass through sheet and be the same all over
-only some particles reflected back , realised most of the atom was empty space with a nucleus in the centre
Neil’s Bohr model:
-Electrons in shells at different distances from the nucleus
James Chadwick’s model:
- discovered neutral masses in the centre of the nucleus along with protons and neutrons
How are elements arranged today?
- in order of their atomic number (no. Of protons)
- each group has similar properties meaning they have the same number of electrons in their outer shell
How did Mendeleev arrange the period table before?
- initially were arranged according to atomic weight
- left gaps for unknown elements
What are metals? And what are their properties?
- elements that react to form positive ions
-malleable (change shape)
-conductive (heat/electricity) because of their delocalised electrons
-high melting/boiling points because of the strong metallic bonds in them
-shiny
What are non-metals? And what are their properties?
- elements that react and don’t for positive ions
-poor conductors of electricity
-brittle (break easily)
-low melting/boiling points because of weak forces of attraction
What happens when metals react with water?
Metal hydroxide and hydrogen gas are formed
Difference of reactivity between group 1 and group 7:
- group 1 is more reactive as you go down the group
- group 7 is more as you go up the group
What is displacement:
When elements that are more reactive displace elements that are less reactive in a compound
