Chemichal Periodicity Flashcards
What is chemical periodicity
Tye regular, repeating pattern of properties obvserved jn the elements in the periodic table . This regular recurrence of properties allows elements to be placed in groups each having similar physical and chemical properties
What is group 0 known as
The noble gases are all colourless extremely interactive gases that do not form compounds with other elements as they already have a full outer shell of electrons so are very stable. Monoatomic
Why is their variation in properties as groups are descended
The distance of the outer electrons from the pull of the positively charged protons in the nucleus increased down the group as you add an extra shell
What happens as you go down the noble gases
Become denser , increase in boiling point
Helium
Filling party balloons and airships - helium is much less dense than air
Provides a protective layer by sitting on top of rare documents
Neon
Luminiscente lighting
Argon
Provides an inert atmosphere e.g in lightbulbs prevents the oxidation of the filament beacuse it won’t react with argon
Krypton
In lasers
Xeneon
In flash lamps for cameras
Why does the boiling point of the noble gases jnrease with the RAM
Beacuse the strength between particles increase as the atom size increases
What are the properties of group 1
The alkali metals they have a relatively low density - lithium sodium potassium float on water
Shiny - when freshly cut they rapidly tarnish by reacting with oxygen from ye air .
They are soft - can be easily cut with a shark knife
They have relatively low melting point s- caesium melts in the hand
They are silvery metals except for caesium which is a place hold
They are very reactive - most reactive metal group and are stored under oil or in an argon atmosphere to prevent their reaction with oxygen and moisture in the air
What happens as you descend the alkali metals
They become more reactive , softer , more dense
Why do the alkali metals change as you descend the group
Because the outer electron shell becomes further from the pull of the protons in the nucleus and therefore becomes easier to remove the metals outer electron and turn the atom into a positive ion so the metals become more reactive , all the number of protons in the nucleus also increases but is compensated for by the effect of the increased number of inner electron shells
How do alkali metals react with oxygen
To form oxides e.g 4na +02 = 2(Na20)
How do alkali metals react to form hydroxides
2K + 2h20 = 2koh + h2
To form hydroxides and hydrogen
How does lithium react with water
Very vigorously , fizzing around on the surface of the water and appearing to dissolve as it forms soluble lithium hydroxide . Doesn’t melt because the reaction is slower so heat isbt produces so quickly and it’s melting point is higher
How does sodium react with water
Very vigorously fizzing around rapidly on the surface and appearing to dissolve as it forms soluble sodium hydroxide . With more heat produced and sodiums lower melting point the sodium beacones molten and forms a ball of liquid metal
How does potassium react with water
Violently fizzing around very rapidly in a molten ball and appearing to dissolve as it forms soluble potassium hydroxide . Enough heat is produced to ignite the hydrogen gas created by the reaction so a purple flame is seen
How can you detect the presence of hydroxide ions
By adding an indicator e.g methyl orange which will turn yellow
What are the halogens
Group 7 , reactive non metals that consist of diatomic molecules
How should the halogens be used
With caution and in a fume cupboard beacuse of their poisonous vapours
What are the properties of fluorine
Pale yellow has very toxic and extremely reactive
Chlorine
Pale green gas dense and toxic
Bromine
Dense dark red liquid that gives off red brown vapour . Toxic and corrosive
Iodine
Dark grey solid , sublimes to give a purple vapour . Forms a brown solution in water and a purple solution in hexane
Trends of halogens
On descending the group they become
Less reactive - the further the element is down the group , the further it’s outer shell of electrons is from the nucleus , so the more difficult it becomes to attract an electron to fill the outer shell and form a negative ion
Becomes darker in colour
Increase in melting / boiling point
What do the halogens do when heated with the alkali metals
Burn vigorously to form white crystalline halide salts. These are ionic compounds , electrons are transferred from the metal to the non metal forming negatively charged halide ions
2na + cl2 + 2NaCl
How can you displace a halogen from its Compound e.g reaction between chlorine and sodium bromide
By using a more reactive halogen , these reactions are done in an aqueous solution
Chlorine + sodium bromide = sodium chloride +bromine colourless. Bromine is oxidised
An orange solution is formed due to the formation of aqueous bromine
How do chlorine and sodium iodide react
To form sodium chloride and iodine
Causing a brown solution to form beacuse of aqueous iodine
How do you test for iodine
Add a small amount of hexane and shake forming a layer which floats on the aqueous solution and the iodine is absorbed into the hexane layer , forming a purple solution
What are the industrial uses of chlorine gas
Used as bleach as sodium chlorite , dissolved in water supply in small amounts to kill bacteria .
How do you test for chlorine
Moist Blue litmus is turned white
What are halide salts
White salts that dissolve readily in water to form colourless solutions .
How can you test for halide ions
Add nitric acid then silver nitrate. Silver ions react with the halide ions to form a precipitate as silver halides are insoluble in water
White - chloride
Cream - bromide
Yellow - iodide
What are hydrogen halides
Are colourless gases formed from covalently bonded molecules . When they are dissolved in water , these molecules split up , giving H+ ions and therefore an acidic solution . If dissolved in other solvents the covalent molecules do not split up and no H+ ions are formed and the solution is not acidic.
E.g hcl + h+ and cl-
They are steamy acidic poisonous gases
Why do noble gases boiling points increase as you go down the group
Tye attractions between one molecule and it’s neighbour get stronger as the atoms get bigger . More energy is needed to break the stronger intermolecular attractions
Properties of halogens
Poor conductors of heat and electricity beacsur they are non metal , when they are solid their crystals will be brittle
What is the problem with bromine
Very corrosive
How does flourine react with hydrogen
Violent explosion
Chlorine and hydrogen
Violent explosion if exposed to a aflame of sunlight
Bromine and hydrogen
Mild explosion if exposed to a flame
Iodine and hydrogen
Partial reaction to form hydrogen if iodine vapour is heated continuously with hydrogen
What happens as you descend the halogen group
As molecules get larger melting and boiling points increase and they become less reactive
Explain the trend in reactivity in the halogens
The incoming electron is further away from the nucleus as you go down the group so it is less strongly attracted , this means the ion is less easily formed and the oxidising ability of the halogens falls as you go down the group
Transition metals properties
Good conductors of heat and electricity
Workable and strong with high densities
High melting points
Less reactive than group 1 and 2
