C2 Flashcards
At what rate were chemists discovering element during the 19th century ?
Rapidly . Finding them every year
What was the goal of chemists during the 19th century for the periodic table?
Trying to find pattern in the behaviour of elements which would allow them to be ordered
What did John dalton do about the periodic table?
Arranged elements in order of their atomic weight. He was on of the first suggestions. In 1808 he published his table of elements
How did John Newlands build on Daltons ideas in 1864?
Realised every 8th element had similar properties. Released ‘law of octaves’, which assumes all elements had been found. His pattern broke down
How are elements in the periodic table arranged?
Atomic number ( number of protons) , so elements with similar properties are in ‘groups’.
Why the periodic table has its name?
Similar properties occur at regular intervals.
What is common about elements in the same group in terms of electronic structure?
Same number of electrons on the outer shell, this gives them similar chemical properties
What was the problem with the early periodic tables?
Incomplete and some elements were placed wrongly
Who was Mendeleev?
Russian chemist
What was mendeleevs breakthrough?
1869, ordered them in atomic weight, and with a periodic pattern so their properties could be seen
How many elements had been discovered by 1869?
50
What was the most important aspect of mendeleevs periodic table?
He left gaps for elements not yet discovered
What confirmed that mendeleevs periodic table was close to being correct?
Mendeleev predicted properties of elements to fit in spaces and years after his predictions matched reality.
What was the problem with mendeleevs periodic table?
Did not account for isotopes. Argon could not fit for example. Ordering by mass would put argon (noble gas) in the group 1 with the reactive metals
What change was made to mendeleevs periodic table during the 20th century?
Ordered it in terms of the elements proton number. The structural components of the element had been discovered now making this change easier. The table could now account for protons.
How was the periodic table measured before the discovery of protons, neutrons and electrons?
By mass of the atom (atomic weight)
How many groups are in the periodic table ?
8
What does the group number tell us about the electronic structure of the element?
The number of the group is the number of electrons on the valence shell.
How do metals and non metals react with electricity ?
- metals conduct electricity
- non metals do not , they are an electrical insulator
What is the difference in boiling points , comparing metals and non metals ?
Metals usually have higher boiling and melting points .
What are physical properties of metals and non metals ?
Metals are ductile and malleable, non metals are brittle
Where are non metals found in the periodic table?
Top right , about the staircase
How do group ,5,6 and 7 elements react to form ions?
Gain electrons to form a negative ion . They then have the electronic structure of a noble gas.
Where are metals found in the periodic table ?
Left hand side and the centre.
How do group 1,2 and 3 elements react to form ions?
Lose electrons and form positive ions. They then have the same electronic structure as the noble gas.
How many electrons do noble gases have on their valence shell?
8 , a full valence shell
Features of a noble gas?
- very stable
- unreactive
- exist as a single atom , they are a monatomic gas
- do not form molecule as they have no tendency to react and modify their electronic structures
- boiling points increase going down the group
What is the boiling point of the first and last element in group 8?
- Helium -269 degrees Celsius
6. Radon -62 degree celsius
What are transition metals?
- block of metals in the middle of the periodic table. Not usually reactive , some like silver and gold are very unreactive.
Where are the alkali metals found?
First group on the left
What are the alkali metals ?
Lithium , sodium , potassium , rubidium , caesium and francium
How reactive are alkali metals?
Very reactive, have to be stored in oil to stop them from reacting with oxygen
What is the trend in terms of reactivity in group 1?
As you go down the group the elements become more reactive
What elements are too reactive to be used in school?
Rubidium , caesium and francium. Francium is dangerously radioactive
How dense are alkali metals?
Have a very low density’s . Sodium , lithium and potassium have density’s lower than 1g/cm^3 . Which means they float on water.
How hard are alkali metals?
Soft , can be cut with a knife.
How do alkali metals react with oxygen?
Silvery and shiny at first , but once its reacted with oxygen it goes dull and forms a layer of oxide on the shiny surface.
What is the equations for the reaction between oxygen and sodium?
Sodium +oxygen —-> sodium oxide
What happens if a hot alkali metal is put into a gas jar of oxygen?
Burns vigoursly forming a white smoke of their oxides
What decides the properties of an element?
Electronic structure. Group 1 elements are unstable as they have only 1 valence shell electron
What does an alkali metal need to do to gain stability?
Loose one electron, to get the stable state of a noble gas
What happens if a group 1 metal reacts with a non metal?
Lose outer shell electron forming a metal carrying a 1+ charge eg. Na+ , k+ they always form an ionic compound
What is the trend for group one metals boiling and melting points?
Go down the group the boiling and melting points get lower. Group 1 metals have low boiling points compared to other metals.
How do lithium , sodium and potassium react with water?
- float on water , moving around and fizzing
- fizzing happens because the metals react with water to form hydrogen gas
What happens when potassium reacts with water?
It is so vigorous , the hydrogen gas ignites. It burns with a lilac flame
What does a reaction between an alkali metal and water produce ?
- metal hydroxide
- hydrogen gas
What happens when the metal hydroxide is formed ?
It is soluble in water. It leaves a colourless solution with a high ph .
What is the equation for an alkali metal reacting with water?
Metal +water —-> metal hydroxide +hydrogen
What other non metals do group 1 gases react vigorously with?
Chlorine gas
What does a reaction between a metal and chlorine gas produce?
Metal chloride. Which is a white solid
What happens to the metal chloride once it is formed ?
Dissolves into water to form a colourless solution.
What is the trend going down group 1 for the reaction with chlorine gas?
The reaction gets more and more vigorous, as it becomes easier to lose the single electron on the valence shell, forming a 1+ ion.
What is the equation for the reaction between sodium and chlorine gas ?
Sodium + chlorine —–> sodium chloride
What are group 7 halogens?
Group of toxic non metals that have coloured vapours. They have fairly typical properties of non metals.
What are the trends for the boiling and melting point of group 7 halogens?
Increase going down the group . Relatively low
What sort of conductors are group 7 halogens?
Poor conductors of heat and electricity
How many electrons do group 7 halogens have on their valence shells?
7
What does the electronic structure determine for the halogen?
How it reacts
What does the halogen need to do to become a noble gas?
Gain an extra electron
What happens if a halogen reacts with a non metal ?
Gain an extra electron by sharing pairs of electrons with another atom.
What is the trend of reactivity in group 7 halogens?
Less reactive going down the group
What happens when halogens react with metals?
Gains an electron , forming a 1- charge
What is the rule for displacement reactions between halogens?
More reactive halogen will displace a less reactive halogen from solutions of its salt .
What happens when chlorine dissolved in water mixes with potassium bromide solution?
Colour of solution is due to less reactive of pair of halogens which is left in the solution as the aqueous molecule.
What colour is chlorine , bromine and iodine when they react with a non metal?
Chlorine=green
Bromine=yellow
Iodine=red / brown
Chlorine + potassium bromide is equal to what?
Potassium chloride +bromine
What halogen displaces all of them?
Fluorine
What is the trend in group 1 metals In terms of reactivity ?
Gets higher going down the group
What is the trend of reactivity for group 7 halogens?
Less reactive going down the group
What explains the trends in elements?
Electronic structure
What happens as you go down a group in the periodic table?
- Increases the shells
- atoms get larger
What is the rule for displacement reactions between halogens?
A more reactive halogen will displace a less reactive halogen from a solution of its salt.
What halogen displaces all other halogens?
Fluorine
What happens to large atoms electronic structure?
- lose electrons more easily , going down the group
- gain electrons less easily going down the group
What are the reasons for larger atoms having those particular features?
Valence electrons are further away from the nucleus and its attractive forces
The inner shells screen or shield out electrons from the positive charge of the nucleus
What happens to alkali metals when forming chemical bonds?
Lose electrons
What happens to halogens when forming chemical bonds?
Gain electrons
Why does reactivity increase going down group 1?
Atoms get larger so the single electron in the valence shell is attracted less strongly to the positive nucleus . Electrostatic attraction with the nucleus gets weaker because the distance between the valence electron and nucleus increases.
What do the shells do to the electrostatic forces between the nucleus and valence shell?
Weaken them
What does the amount of protons in the nucleus mean?
A greater attraction
Does going down the group lead to a greater attraction between protons and valence electrons in group 1?
No , there is a shielding effect by the shells that outweighs the increased positive charge
Why does reactivity decrease going down group 7?
- size of the atom
- shielding affect of inner electrons
- nuclear charge
