Flashcards in Chemistry a Deck (121)
Until recently, what were the two ways of categorising elements ?
1. Their physical and chemical properties
2. Their relative atomic mass
Why did atomic number not exist in the 1800s ?
They had no idea about atomic structure or of protons and electrons
How were the elements first ordered ?
Relative atomic mass
In what year did new land form his element arrangement ?
What did Newland notice ?
That every 8th element had similar properties - Newlands Octaves
Why was Newland's element arrangement criticised ?
1. His groups contained elements that didn't share properties
2. He mixed up metals and non metals
3. Didn't leave gaps for undiscovered elements
In what year did Mendeleev create his own periodic table ?
What did Mendeleev do ?
He put the elements in order of atomic mass
What did Mendeleev find when grouping his elements ?
He had to leave gaps in order to keep elements with the same properties in the same column
Why was the fact he left gaps so influential ?
He predicted the properties of undiscovered elements
Why did many scientists think that the periodic table wasn't important ?
There wasn't much evidence to support the periodic table
What evidence was soon found that suggested Mendeleev's periodic table was correct ?
New elements were found and they fitted into the gaps he left
What happened in the 19th century which meant that nearly all scientists accepted that the periodic table was useful ?
Scientists discovered protons, neutrons and electrons
What does the periodic table allow us to do ?
Predict element's chemical properties
What do elements in the same group have ? (Excluding transition metals)
The same number of electrons in their outer shell (highest energy level)
What does the group number represent ?
The amount of electrons on the outer shell
How are electrons held in place ?
The positive charge of the nucleus attracts the negative electrons.
The further away from the nucleus, the...
The less attraction the electron has
What is shielding ?
When the attraction of the nucleus is reduced because the 'inner electrons' get in the way
What is energy level ?
The amount of shells of electrons an atom has
Why do group 1 metals become more reactive as you go down the periodic table ?
The combination of an increased distance and increased shielding means that an electron in a higher energy level is lost more easily.
As you go down group 1, what happens to the boiling and melting points ?
Why can some group 1 metals float ?
They have a lower density than water
What are the group 1 metals also known as and why ?
The alkali metals - when they mix with water they form a metal hydroxide which dissolves to form an alkali solution
What are the first three group 1 elements ?
What do group 1 metals have on their outer shell ?
What compounds do the alkali metals form ?
Ionic compounds because they lose the electron (ionic bonding)
What happens when you add alkali metals to water ?
They float on the surface and fizz. The metal displaces the hydrogen in the water, forming hydrogen gas and metal hydroxide
What happens to the metal hydroxide in the water ?
It dissolves in the water, forming an alkali solution. It would turn universal indicator purple