How did Newlands and Mendeleev attempt to classify the elements?
by arranging them in order of their ATOMIC WEIGHTS
In the periodic table, elements with similar properties are….
in the same GROUP
Why is the periodic table called the periodic table?
because similar properties occur at regular intervals
Why was Newlands criticised when attempting to classify the elements in the periodic table?
- as he put elements in groups that did not have similar properties
- mixed up metals and non metals
- didn’t leave gaps for elements that had not yet been found
(he placed elements in inappropriate groups because the strict order of atomic weights was followed)
Why did Newlands end up placing some elements into the wrong groups when attempting to classify the elements?
As he did not leave gaps for elements that had not been found
What did Newlands notice when attempting to classify the elements?
that every 8th element had similar properties, so he listed them into rows of seven
- Newlands’ Octaves
How did Mendeleev overcome some of the problems in classifying the elements?
by leaving gaps for elements that he thought had not been discovered
Why did scientists at first regard the periodic table of elements first as curiosity?
as at the time there was not much evidence to suggest that the elements really did fit together in that way
When did scientists realise that the periodic table was a useful tool and an important summary of the structure of atoms?
After Mendeleev released his work, newly discovered elements fitted into gaps he left- convincing evidence
in 20th century- discovery of neutrons, electron , protons- provided more evidence in favour
What happened to the order of the periodic table when protons, electron and neutrons were discovered in the 20th century?
the periodic table was arranged in order of (atomic numbers)
In the periodic table, what does the group number show?
how many electrons are in the outer shell
Elements in the same group have the same number of…..
electrons in their highest occupied energy shell
What are the elements in group 1 called?
the alkali metals
Describe some of the properties of the alkali metals
- low density (first 3 are less dense than water)
- react with nonmetals to form ionic compounds (in which the metal ion carries a change of +1.) The compounds are WHITE SOLIDS that DISSOLVE IN WATER to form colourless solutions
- react with water, releasing hydrogen
- form hydroxides that dissolve in water to give alkaline solutions
What is the test for hydrogen?
A lighted splint will indicate hydrogen by producing a squeaky pop
In group 1, the further down the group an element is……
- the more reactive the element
- the lower its melting and boiling point
Why in group 1, the further down the group, the more reactive the element?
In elements further down the group, there is a greater distance between the nucleus and the outer electrons because there are more shells. This means there is a weaker attraction between the nucleus and outer electrons due to SHIELDING. This means it is easier to lose electrons.
Compared to group 1, transition elements….
- have higher melting points (except for mercury)
- have higher densities
- are stronger and harder
- are much less reactive and so do not react as vigorously with water or oxygen
Who first started to classify the element?
Newlands and then Mendeleev
Many transition elements have ions with…..
- different charges
- form coloured compounds
- and are useful as catalysts
What are the elements in group 7 of the periodic table called?
the HALOGENS
What do elements in group 7, the halogens, react with?
with metals to form ionic compounds in which the halide ion carries a charge of -1 (gains an electron)
In group 7, the further down an element is….
the less reactive the element
the higher its melting and boiling point
Why in group 7, the further down the group, the less reactive the element?
Because it is harder to gain an electron because the outer shell is further from the nucleus
There is less attraction from the nucleus pulling electrons into the atom
