The Atom Flashcards
What did John Dalton do?
At the start of the 19th century
He described atoms as solid spheres
He said that different spheres make up different elements
What did JJ Thompson do?
In 1897
He made the plum pudding model
His measurements of charge and mass lead him to believe that atoms contain even smaller negatively charged particles (electrons)
What did Rutherford and his students Geiger and Ernest Marsden do?
In 1909
They conducted the gold foil experiment
They shot alpha particles at an extremely thin sheet of gold.
The results show the positive charge must be concentrated in the centre of the atom.
He came up with the nuclear atom which was a tiny positive nucleus surrounded by a ‘cloud’ of electrons.
What did Niel Bohr do?
Scientists realised that if there was a ‘cloud’ of electrons atoms would collapse.
He suggested that electrons were placed in fixed orbits (or shells) around the nucleus, and nowhere else.
What are the three subatomic particles in an atom
Protons, neutrons and electrons
What is the relative mass and relative charge of a proton
Relative mass = 1
Relative charge = +1
What is the relative mass and the relative charge of a neutron
Relative charge = 0
Relative mass = 1
What is the relative mass and relative charge of an electron
Relative mass = 0.0005
Relative charge = -1
What are the three key points about the nucleus
Made up of protons and neutrons
Has a positive charge because of the protons
Almost the whole mass is concentrated in the nucleus
What are the three points about electrons
They move around the nucleus in shells
They are negatively charged
They have hardly any mass
There are the same number of electrons and protons (means there is no overall charge)
Why are atoms neutral
Because they have the same number of protons (+) and electrons (-)
That charges are opposite but equal so they cancel each other out
What is the mass number
The relative atomic mass of an atom
The number of protons and neutrons in an atom (larger number on the periodic table)
What is the atomic number
Number of protons in a nucleus (therefore the number of electrons) (smaller number on the periodic table)
How do you work out the number of neutrons in an atom
Mass number - atomic number
What is an isotope
Different atoms of the same element which have the same number of protons but different number of neutrons. (same atomic number, different mass number)
