C2: The Periodic Table Flashcards
Why is the periodic table called the periodic table?
Periodic - occurring at regular intervals.
In the table, elements with similar properties occur at regular intervals.
Why do elements in the same groups react in similar ways?
They have the same number of electrons on their outer shells.
Describe Dobereiner’s Triads
Dobereiner noticed elements with similar properties occurred in threes.
From this, scientists began to wonder whether elements could be arranged in a logical order.
Describe Newlands’ Octaves
Newlands arranged elements in order of increasing atomic weight, and noticed that every 8th element reacts in a similar way.
What are the problems with Newlands’ octaves?
By always sticking to the exact order of atomic weight, sometimes elements were grouped together when they had very different properties, meaning his law was not taken seriously by other scientists.
Describe Mendeleev’s table
He started by arranging all the elements in order of increasing atomic weight.
He then switched the order of specific elements, so they fit the pattern of the same group.
He then realised that some elements had not been discovered, so he left gaps in his periodic table where he thought an element was missing.
He also predicted the properties of undiscovered elements based on the other elements in the same groups. These were discovered several years later and matched his predictions. Because of that, other scientists now accepted that his table was correct.
What are the differences between the modern periodic table and Mendeleev’s periodic table?
The elements are arranged in order of atomic number ( increasing number of protons) - when Mendeleev developed his table, protons had not been discovered, so he ordered the elements in order of increasing atomic weight.
Modern table has noble gasses - which were not fully discovered when Mendeleev published his table.
What is the problem with ordering elements in order of atomic weight?
Elements can appear in the wrong order due to the presence of isotopes.
What are the properties of Group 0 elements?
Inert - highly unreactive
Have a full outer shell
Extremely low b.p. (lower than room temp) - all gasses
Why are noble gasses so unreactive?
All noble gasses have full outer energy levels, meaning they are stable and will not react.
Where are the metals found in the periodic table?
Left and the centre of the table (squiggly line down from boron)
How can metals be divided?
Left side - highly reactive metals
Centre - less reactive transition metals
How do metals react?
Lose electrons to form a full outer shell.
Giving them the same electronic structure as a group 0 element. (?)
What ions do all metals form?
Positive ions.
What are the properties of Group 1 metals (alkali metals)?
All have 1 outer electron in their outer shell.
Soft
Highly reactive - reactivity increases going down the group
Low density
How do the alkali metals react with oxygen?
React rapidly with oxygen to form a metal oxide.
How do the alkali metals react with chlorine?
Rapidly, form metal chloride e.g. lithium chloride (LiCl)
How do alkali metals react with water?
React rapidly with water, with increasing reactivity going down the group.
We can see effervescence (fizzing) - gas (H) is produced.
Universal indicator turns purple as an alkaline solution is formed.
Metal moves around
Metal floats.
Flame - potassium
Produce metal hydroxides + hydrogen
Why do alkali metals get more reactive down the group?
There is a greater distance between the negative outer electron and the positive nucleus, resulting in less attraction between the two. This means that the outer electron is easier to lose.
What are the properties of Group 7 elements (Halogens)?
Have 7 electrons in their outer shell
Diatomic
M.p. and b.p. increases going down the group
Molecules get bigger going down the group
Form covalent compounds when reacting with other non-metal atoms
All have a 1- charge.
A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt.
Why does the reactivity of halogens decrease going down the group?
Going down the group, elements have more outer shells, and therefore more nuclear shielding (also greater distance between outer energy level and nucleus). This means that it is harder for the positive nucleus to attract a negative electron to form a full outer shell, and therefore results in a lower reactivity.
Describe how a more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt
e.g. sodium bromide + fluorine
What are the properties of transition metals?
Dense
