Download Early Models of Atom

Early Models of the Atom
Dalton: an English teacher who proposed that atoms are the smallest particles of matter.
Model:
1. Each element is composed of indivisible particles called atoms
2. In an element, all of the atoms are identical. Atoms of different elements have different
properties, such as mass.
3. In chemical reactions atoms are neither created nor destroyed.
4. In compounds atoms of more then one element combine.
5. Samples of a given compound always have the same relative numbers of atoms.
J.J.Thomson
British physicist who discovered electrons.
The cathode ray (blue line) was deflected by the electric field (yellow).
High voltage electricity was passed through a glass tube containing metal electrodes and
produced a radiation with negative electric charge (cathode rays). It was deflected from
the negative electrode (the anode)
Model:
An atom is a positively charged jellylike mass with electrons scattered throughout (like
plum pudding)
Rutherford
New Zealand physicist who proposed yet another new model.
Alpha particles (positively charged) were passed down the gold foil.
Observations:
Most particles passed through yet some deflected back.
Results:
Most of the atom is empty space. Yet there is a dense positively charged nucleus that has
most of the mass of the atoms. Electrons are present in space around the nucleus.
Identifying Elements: Names, Symbols, Atomic numbers, Atomic Masses, Neutrons,
Protons and Electrons
1. # of protons is always equal to atomic number
2. In a neutral atom, # of electrons is equal to number of protons
3. Mass number = # of protons + number of neutrons
Isotopes = atoms of the same element with different mass numbers.