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Elements
are substances which cannot be broken down into simpler componenets by chemical reactions.
Atom
is the smallest unit of an element.
Dalton’s proposition
All matter is composed of tiny indivisible particles called atoms.
Atoms cannot be created nor destroyed
Atoms of the same element are alike in every way.
Atoms of different elements are different.
Atoms can combine together in small numbers to form molecules.
Thompsons plum pudding
Negatively charged electrons positioned in a positively charged sponge-like substances.
Ernest Rutherford
The atom is mainly empty space
Nucleons
Neutrons and protons.
Bohr’s model of the hydrogen atom
He pictured the hydrogen atom as a small ‘solar system’ with an electron moving in an orbit around the psoitively charged nucleus of ne proton.
Atomic number
The number each element is given that describes their relative position in the table.
The number of protons in the atom.
The number of electrons in an atom.
The mass number
The number of protonsplus the number of neutrons in an atom.
Ions
Atoms loses or gain electrons to form ions
Cation
Atom loses electron and forms positive ions
Anion
Atom gains electron to form negative ions
Isotopes
Atoms of the same element with different numbers of neutrons.
Isotopes shpw the same chemical properties, since the diffrence in th number of neutrons makes no difference as to how atoms react.
They lead to different physical properties such as boiling and melting points.
Average relative mass of isotopes
relative average mass = (total mass) / (number of atoms)
Radiosotopes
A nucleus which either contains too many or too few neutrons to be stable.
They emit radioactivity.
Note
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