Download We know now that it is composed of protons and neutrons.

In the second term you studied
Rutherford´s atomic model, which
stated:
Atoms are divided into a tiny core, called the nucleus, and an
electron shell.
Between the nucleus and the electron shell there is empty space.
Most of the atom is empty space.
The nucleus of an atom is positively charged and contains almost
all the mass of the atom. We know now that it is composed of
protons and neutrons.
Electrons orbit around the nucleus in circular orbits. The nucleus
holds the electrons by means of an electric force between
positive and negative charges.
But other models were made
after Rutherford´s model to
explain better the properties
of atoms.
Bohr´s atomic model (1913)
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Electrons orbit around the nucleus (which, as we know
now, is formed by protons and neutrons) in different
layers.
In each layer there is a maximum number of electrons:
In the first layer there are 2 electrons at most, 8 in the
second layer, 18 in the third layer... In the layer n there
are 2n2 electrons at most.
Each layer has different energy.
The energy and the radius of each orbit is quantized,
that means it has an specific value (it can´t be any
number).
Bohr´s atomic model (1913)
Bohr´s atomic model (1913)
Inner layers have lower energy and outer layers have higher
energy.
An electron can absorb energy and go to a higher layer. Or it
can go to a lower layer and release energy.
Bohr´s atomic model (1913)
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As atoms absorb or release energy in the form
of light, absorption and emission spectra of the
elements are explained.
The spectra of each element is specific and
unique for that element.