SC3-4 Flashcards
Who made the first periodic table?
Dmitri Mendeleev
What did the first periodic table look like?
He arrogance around 50 elements known at the time.
- He arranged elements in order of increasing atomic mass.
- He put some with similar properties into vertical columns called groups.
- He arranged elements into rows called periods.
- He left gaps in his table for elements to be discovered.
What is similar and what is different in the periodic table now?
Similar - both have groups and periods.
Difference - there are no gaps now, and its now ordered by atomic number not mass.
What is the order for electrons allowed in each shell?
1st - 2
2nd - 8
3rd - 8
What do groups and periods tell you?
Groups - how many electrons on the outer shell.
Periods - how many shells.
What is the history of the atom?
1 - Dalton (1800) = He described atoms as solid spheres and believed they couldn’t be separated.
2 - Thomson (1904) = plum pudding model. He discovered the electron and believed atoms too be made up of positively charged material, with electrons embedded within it.
3 - Rutherford and Bohr (1911-21) = showed the plum pudding model was wrong. Created the modern theory of the atom based on experimental evidence. Positive nucleus with electrons orbiting it.
4 - Chadwick (1932) = modern theory of atomic structure - nucleus with protons and neutrons, electrons in quantum shells.
What was Rutherfords and Bohrs experiment?
Gold foil experiment.
- They fired positively charged alpha particles at a thin sheet of gold.
- They were expecting the particles to pass straight through the sheet or be slightly deflected at most. This was because the positive charge of each atom was thought to be very spread out, through the ‘pudding’ of the atom.
- Whilst most of the particles did go straight though the sheet, some were defected, more than expected, and a small number were deflected backwards.
So the plum pudding model must have been wrong.
What do atoms contain?
Protons - positively charged
Neutrons - neutral
Electrons - negatively charged
What is in the nucleus of an atom?
Its in the middle of the atom.
It contains protons and neutrons.
It has a positive charge because of the protons.
Almost the whole mass of the atom is concentrated in the nucleus.
The nucleus is small compared to the rest of the atom.
Where are the electrons in an atom?
They move around the nucleus in the shells.
They’re negatively charged.
They’re tiny but their shells cover a lot of space.
The size of their shells determines the size of the atom.
Electrons have a tiny mass.
Why are atoms neutral?
Because they have the same number of protons and electrons.
What is an ion?
Its where the number of protons doesn’t equal the number of electrons.
What does the atomic number tell you?
How many protons an atom has.
What does the atomic mass/mass number tell you?
The total number of protons and neutrons.
What are isotopes?
They’re different forms of the same element, which have the same number of protons but a different number of neutrons.
