Atomic Structure

It used to be thought that atoms were small indivisible particles. It was thought that the only difference between the atoms of one element and those of another was their size. John Dalton

Ernest Rutherford We now know that atoms are more complicated than this. An atom is not a simple solid sphere, but is made up of smaller sub-atomic particles We now think of an atom as being like a small solar system, with a central nucleus and smaller particles in orbit around it. Niels Bohr

Atom protonneutron electron positive chargenegative chargeno charge found in nucleus found in orbit around nucleus mass 1 amu mass 1/2000 amu mass 1 amu

nucleus containing protons and neutrons energy levels or shells containing electrons in orbit Rutherford-Bohr Model of an Atom

C 12 6 proton number mass number total number of protons in an atom of the element total number of protons plus neutrons in an atom of the element chemical symbol for the element

protons + neutrons protons - mass number = proton number number of neutrons

- mass number = proton number number of neutrons Example: To work out the particles present in an atom of fluorine, 19 F 9 the proton number = number of protons = 9 the proton number is also = number of electrons = = 10 the number of neutrons = 10

Hydrogen 1 H 1 1p

Helium 4 He 2 2p 2n complete energy level

Lithium 7 Li 3 3p 4n

Berrylium 9 Be 4 4p 5n

Boron 11 B 5 5p 6n

Carbon 12 C 6 6p 6n

Nitrogen 14 N 7 7p 7n

Oxygen 16 O 8 8p 8n

Fluorine 19 F 9 9p 10n

Neon 20 Ne 10 10p 10n complete energy level

Sodium 23 Na 11 11p 12n

Magnesium 24 Mg 12 12p 12n

Aluminium 27 Al 13 13p 14n

Silicon 28 Si 14 14p 14n

Phosphorus 31 P 15 15p 16n

Sulphur 32 S 16 16p 16n

Chlorine 35 Cl 17 17p 18n

Argon 40 Ar 18 18p 22n complete energy level

Potassium 39 K 19 19p 20n

Calcium 40 Ca 20 20p 20n