The Periodic Table - Topic 1 Flashcards
What is the periodic table?
a table that contains all known elements (approx. 100)
How many elements occur naturally?
92
How are elements represented?
by their symbols
How are elements arranged in the Periodic Table?
- Elements are arranged in order of increasing atomic number in rows called periods
- Elements with similar chemical properties are placed in the same vertical columns called groups
What is the number of electron energy levels (shells) of an element on the Periodic Table the same as?
the period number of the element in the Periodic Table
What is the number of electrons in the outer energy level (shell) the same as?
the group number of the element in the Periodic Table
What happens to elements as you go down Group 2 in the Periodic Table?
they get more reactive
What do elements in the same group share?
elements in the same group share similar chemical properties
Group 2 Metals: What is more reactive magnesium or calcium?
calcium is more reactive than magnesium
acid + metal –>
salt + hydrogen
acid + metal carbonate –>
salt + water + carbon dioxide
water + metal –>
metal hydroxide + hydrogen
What is the test for hydrogen?
To test for the hydrogen we placed a lit splint at the neck of the test tube and if a squeaky pop sound was made then hydrogen was present
Periodic table:
table of elements arranged in increasing atomic number and such that elements with similar properties are grouped together (in the same column)
Group:
- a column of the periodic table
- elements of the same groups have similar chemical properties
Period:
- a row of the periodic table
- elements of the same row have the same number of shells
How did Mendeleev arrange the elements?
- in 1869 Russian scientist Dimitri Mendeleev arranged the elements in a periodic table using the chemical properties of these elements and their compounds
- ordered his table in terms of atomic mass but not always strictly i.e. he would change the order based on atomic weight
- he left gaps in his table where elements didn’t match certain properties
- he swapped the order of some elements
Examples where Mendeleev switched the order of two elements:
- iodine (I - 127) and tellurium (Te - 128)
How did Mendeleev justify his change of leaving gaps in the table and swapping some elements?
- as the reactivities wouldn’t match up if he didn’t leave gaps
- to make patterns fit (to keep families together)
- that they would be occupied by undiscovered elements
- used his table to predict the existence and properties of some elements that hadnt been discovered as he realised elements with similar properties belonged in the same groups in the periodic table so was able to leave gaps and place the discovered elements where they fit best
- elements with properties predicted by Mendeleev were later discovered and filled the gaps
How did Mendeleev’s predictions of the properties of Eka-aluminium compare to the properties of gallium?
- properties very close
- density is an especially good agreement of chemical and physical properties
What effect did the discovery of gallium have on the development of the Periodic table?
- it provided evidence that Mendeleev’s idea to leave gaps in the periodic table was correct - table became accepted by mosts scientists
3 important differences between Mendeleev’s table and the modern periodic table:
- his periodic table was ordered in terms of atomic mass and now the modern periodic table is ordered in terms of atomic number
- lanthanoid, actinides and transition metals added - more groups addes
- addition of noble gases - no Group 0 in Mendeleev’s table