Atomic structure and periodic table Flashcards
what is a molecule
a group or 2 or more atoms held by chemical bonds-
eg -o2 cl2 n2 c2o c2o
what are compounds
substances that contain 2 or more different elements
eg- h2o,c2o,
what is a key feature of compounds
they are always found in the same proportion
what are mixtures
2 or more substances that are not chemically combined
- only physically mixed together
soluble
dissolves in solvent
solute
substance that dissolves
solvent
liquid it dissolves in
solution
liquid formed
what does filtration seperate
insoluble solids from liquids through filter paper in filter funnel
how do we get a dissolved soluble solid from a solution
evaporation or crytallisation
explain evaporation
place solution in evaporating dish on tripod
slowly heat with bunsen burner
solvent evaporates and remaining solution becomes more concentrated
leaves us with dry solid crytals
issues with evaporation
some solids decompose when heated(thermal decomposition)
it is broken down into something other than what we need
explain crystallisation
place solution into evaporating dish
heat gently with water bath rather than bunsen burner
when some of solvent evaporates and crystals start to appear leave it to cool so more crystals form( solids are less soluble at lower temp)
filter out crystals from the remaining solutions and dry crystals by leaving it somewhere warm or warming it in an oven
why is simple distillation used
to seperate liquid from solution or liquid mixture
explain simple distillation and equipment
flask with bung with thermometer fit through containing solution
connected to a condenser coated by a water jacket with stream of flowing cold water(goes in through bottom and out through top)2`
at the end there is a beaker to collect the pure liquid
we need a heating device under flask like mixture
explain simple distillation
heat mixture so desired liquid so it evaporates and high pressure will send it down condenser and the cold water will cool the vapour which will run down the pipe and enter beaker leaving only solute in the flask
equipment for fractional distillation
flask contains solution and is heated to temp of the liquid with the lowest bp
The vapour pass through fractionating column (full of glass rods, cooler at top than bottom)
passes into condenser and condenses to liquid into the beaker.
atomic theory
back in 500 bc democritus suggested everything was made of small indivisble spheres which were surrounded by empty space
in 1800s who and what was involved in the development of atoms
John Dalton: described atoms as solid spheres and suggested that different types of spheres make up the different elements
in 1897 who contributed to development of the atom and how
JJ thompson came up with the plum pudding model
He did experiments that proved atoms couldnt be just solid spheres and must have contained negative charged particles
His model was a ball of positive charge with discreet electrons stuck in it
what happened in 1909 in development of the atom
ernest rutherford: in 1909 took + charged alpha particles and fired them at thin sheet of gold
resulted in some alpha particles reflected to side and some sent back completely- deflected
proved jj thompson theory wrong - idea that spread out positive charge wouldnt be strong enough to stop alpha particles and would be spread out
he suggested a nuclear model which said there was a compact nucleus with all positive charge and negative charge was in a cloud around central nucleus
flaw was that there was nothing stopping cloud of negative electrons rushing in to +nucleus
what in 1913 developed atom
Neils bohr:in 1913 suggested that electrons orbited nucleus and were held in shells which prevents the atom from collapsing
what did further experiments by rutherford suggest
+ charge of nucleus is made up of small discrete particles called protons
what is meant by an atom being unstable
it wants to react with another atom to gain a full outer shell
when drawing ions what 2 things do you need to do
the charge in the top right corner
square brackets all around the ion
what did mendeleev do
-he devised the periodic table that organised all of known elements
-he predicted undiscovered elements
what are the elements arranged by
increasing atomic number(no of protons)
what is the mass number
total number of protons and neutrons
why did mendeleev create periods
he found that the elements displayed patterns of chemical properties that repeated at regular intervals and formed new rows which we call periods
list some trends in group 1 elements
-they become more reactive as you go down the group
-they all react violently with water
what are trends with halogens
they become less reactive as you go down the group
what do atoms in the same period(rows) have the same
no of shells
metals form what when they react
positive ions(eg Ca2+)
-they lose electrons
what do non metals form
negative ions (eg:chlorine)
or don’t form ions (eg:carbon)
-they gain or dont gain electrons
what does the positive nucleus do in an atom and why is this important
if the electrons are far away the nucleus cant hold on to them as strongly and so they are easily lost to form positive ions
atoms further down the group are more reactive because
they are more likely to lose their electron during a reaction
physical properties of metals
-they have metallic bonds
-malleable
-high melting point and boiling points
-shiny
-sonorous
-good heat and electricity conductors
what are physical properties of non metals
-dull
-brittle
-low melting points and boiling points many being gaseous at room temp
-poor conductors of electricity
-low density
what are the extra properties transition metals have over other metals
-they can form more than 1 ion which are often coloured (eg chromium which forms 2+(which is blue) 3+(which is green ) and 6+(which is orange)
-very good catalysts(eg iron in the haber process )
list some features of alkali metals
-low density
-low melting point
-soft
-more reactive
-react vigorously with water /oxygen and group 7 elements
why do alkali electrons become more reactive going down the group
the radius increases so the outer shell gets further from positive nucleus.
this means the attractive force between the positive nucleus and the atoms outer most electron meaning the electron can be lost more easily increasing the atoms reactivity
how do alkali metals and halogens form ionic compounds
the halogen will gain the alkali metals outer shell electron so both have full outer shells forming oppositely charged ions which are attracted to each other by electrostatic forces called an ionic bond
an example of this is table salt
they generally form white solids and dissolve in water to form colourless solutions
how do alkali metals react in water
reacts vigourously forming metal hydroxide +hydrogen gas
after pottasium reacts with water the energy released ignites hydrogen gas .What form do we see this in?
as flames
how do alkali metals when heated with chlorine gas
they form white metal chloride salts
what happens when alkali metals react with oxygen
they form metal oxides
potassium +oxygen forms
ko2 or k2o2
sodium +oxygen
na2o2 or na2o
what type of molecules are halogens
-diatomic molecules
list trends that occur with halogens as you go down the group
-reactivity decreases
-boiling and melting points increase
why does the reactivty decrease in halogens
because as you go down the group the outermost shell gets further away from the positive nucleus so the force of attraction to pull in extra electron gets weaker
how do they react and form ionic bonds with metals
they form halide ions with a 1- ions and these are most common with alkali metals
what are all noble gases
-group 0 colourless gases-exist as single atoms and are non flammable
-their melting and boiling points increase going down the group
what are some colour changes that take place in halogen displacement reaction
Halide salts (e.g. KCl, KBr, KI) are colourless
Bromine water is orange
Chlorine water is colourless
Iodine water is brown
list the colours and physical states of the halogens at room temperature
-Fluorine is a poisonous yellow coloured gas and is the most reactive halogen
-Chlorine is a green coloured gas.
-Bromine is a red-brown volatile liquid which is also poisonous.
-Iodine is a grey coloured solid with purple vapours.
noble gases trend
bp increases down group
have full outer shell (not 8)
