Atomic structure and the periodic table 2 Flashcards
The periodic table
How were elements classified in the early 1800s?
By atomic weight.
What had not been discovered in the early 1800s?
Protons
Neutrons
Electrons
Describe two changes that Mendeleev made to early periodic tables.
He left gaps in order to keep elements with similar properties in the same group.
He switched the order of elements based on their properties, even if their atomic weights were no longer in order.
What are the problems with the early periodic tables?
They were incomplete.
Some elements were placed in inappropriate groups if the strict order of atomic weights was followed.
What did some of the gaps left by Mendeleev indicate?
The existence of undiscovered elements.
Mendeleev could predict what their properties might be.
Elements with properties predicted by Mendeleev were…
…discovered and filled the gaps.
When they fit the patterns, this helped confirm Mendeleev’s ideas.
Knowledge of isotopes made it possible to do what?
Explain why the order of elements in early periodic tables, based on atomic weights, was not always correct.
Isotopes of the same element have different masses but the same chemical properties so occupy the same position in the periodic table.
What do we call atomic weight now?
Relative atomic mass
Where does the periodic table get its name?
Because similar properties of elements occur at regular intervals - ‘periodically’. This was noticed at early stages.
Date of Dmitri Mendeleev’s table of elements.
1869
How many elements were in Mendeleev’s original table of elements?
50
Give an example of Mendeleev changing the periodic table from order of atomic weight because of the properties of elements.
Te and I
Iodine has a smaller atomic weight (relative atomic mass) but is placed after tellurium as it has similar properties to the elements in group 7.
How are the elements of the periodic table arranged?
In order of increasing atomic (proton) number.
This means that elements with similar properties are in columns - known as groups.
What do elements in the same group in the periodic table have in common?
They have the same number of electrons in their outer shell (outer electrons).
This gives them similar chemical properties.
What are the vertical columns on the periodic table called?
Groups
How do we work out how many electrons are on the outer shell of atoms of an element?
The group number tells you this (1,2,3,4,5,6,7,) apart from group 0.
Elements in the same group are likely to react…
…in a similar way.
Using the fact that elements in the same group have similar properties, what can we do?
Predict the properties of unknown elements.
Make predictions about reactivity.
What are the rows called on the periodic table?
Periods.
What does the period of an element tell you?
How many electron shells there are (start at hydrogen as period 1!)
Chlorine reacts in a similar way to bromine. Suggest a reason why.
Both chlorine and bromine are in group 7 and so have the same number of electrons in their outer shell.
Metals
Elements that react to form positive ions.
Non-metals
Elements that do not form positive ions when they react.
Are most of the elements in the periodic table metals or non-metals?
Metals