Topic 1 – Atomic Structure and the Periodic Table
Part one
. Chemistry 4.1 .
Atoms, elements and compounds .
● Atoms make up all substances and are the smallest part of an element that can exist
● Chemical symbols represent an atom of an element e.g. Na represents an atom of
sodium
● Compounds are formed from elements by chemical reactions. Chemical reactions
always involve the formation of one or more new substances, and often involve an
energy change
● Compounds contain two or more elements chemically combined in fixed proportions
and can be represented by formulae using the symbols of the atoms from which they
were formed e.g. HCl is a compound containing 1 atom of hydrogen and 1 of chlorine
per molecule
● Compounds can only be separated into elements by chemical reactions
Mixtures
● A mixture consists of two or more elements or compounds not chemically combined
together. The chemical properties of each substance in the mixture are unchanged. (this
is different to a compound)
● Can be separated by: filtration, crystallisation, simple distillation, fractional
distillation
and chromatography. These are physical processes, so do not involve chemical
reactions
and no new substances are made.
The development of the model of the atom
● First: atoms were thought to be tiny spheres that could not be divided
● Discovery of electron-> plum pudding model (atom is a ball of positive charge with
negative electrons embedded in it)
● Alpha particle scattering experiment-> conclusion that the mass of an atom was
concentrated at the centre (nucleus) and that the nucleus was charged
Scattering experiment:
● A beam of alpha particles was aimed at very thin gold foil and their passage
through was detected
● Some of the alpha particles emerged from the foil at different angles, and some
even came straight back
● the positively charged alpha particles were being repelled and deflected by a
small concentration of positive charge in the atom (nucleus)
● Neil Bohr: suggested electrons orbit the nucleus at specific distances (supported by
experimental data)
Later experiments: positive charge of any nucleus could be subdivided into a whole
number of smaller particles, each particle having the same amount of positive charge
(protons)
● James Chadwick’s work: provided the evidence to show the existence of neutrons
within the nucleus (had been an accepted scientific idea for about 20 years already)
Part one
. Chemistry 4.1 .
Atoms, elements and compounds .
● Atoms make up all substances and are the smallest part of an element that can exist
● Chemical symbols represent an atom of an element e.g. Na represents an atom of
sodium
● Compounds are formed from elements by chemical reactions. Chemical reactions
always involve the formation of one or more new substances, and often involve an
energy change
● Compounds contain two or more elements chemically combined in fixed proportions
and can be represented by formulae using the symbols of the atoms from which they
were formed e.g. HCl is a compound containing 1 atom of hydrogen and 1 of chlorine
per molecule
● Compounds can only be separated into elements by chemical reactions
Mixtures
● A mixture consists of two or more elements or compounds not chemically combined
together. The chemical properties of each substance in the mixture are unchanged. (this
is different to a compound)
● Can be separated by: filtration, crystallisation, simple distillation, fractional
distillation
and chromatography. These are physical processes, so do not involve chemical
reactions
and no new substances are made.
The development of the model of the atom
● First: atoms were thought to be tiny spheres that could not be divided
● Discovery of electron-> plum pudding model (atom is a ball of positive charge with
negative electrons embedded in it)
● Alpha particle scattering experiment-> conclusion that the mass of an atom was
concentrated at the centre (nucleus) and that the nucleus was charged
Scattering experiment:
● A beam of alpha particles was aimed at very thin gold foil and their passage
through was detected
● Some of the alpha particles emerged from the foil at different angles, and some
even came straight back
● the positively charged alpha particles were being repelled and deflected by a
small concentration of positive charge in the atom (nucleus)
● Neil Bohr: suggested electrons orbit the nucleus at specific distances (supported by
experimental data)
Later experiments: positive charge of any nucleus could be subdivided into a whole
number of smaller particles, each particle having the same amount of positive charge
(protons)
● James Chadwick’s work: provided the evidence to show the existence of neutrons
within the nucleus (had been an accepted scientific idea for about 20 years already)
