Structure of an Atom

Discovery/ies: the form of the periodic table is evolving due to knowledge-challenging discoveries thus enhancing its function of showing trends in the physical and chemical properties of the element.

GLOBAL CONTEXT: Scientific and technical innovation periodic table, Orientation in Space & Time

Timeline of an atom

(Name of scientist - Year of discovery - Discovery description)

Democritus – 400 BC – Found atoms are not all the same, why atoms were so small, made the sphere model.
John Dalton – 1803 – he had the most useful
J.J Thomson – 1897 – He found out about electrons and subatomic particles. He also made the plum pudding model.
Ernest Rutherford – 1911 – ionised gas using radiation.
Niels Bohr – 1913 – Structure of the storm and their radiation. Also he made the quantum theory.
Erwin Schrodinger & Werner Heisenberg – 1920 – he made the 'electron cloud model’.

Solar System model or Planetary model

Protons = positive charge +1
Neutrons = no charge 0
Electrons = negative charge -1
1nm = a billionth of a meter
Protons and neutrons are in the middle of the atom (in the nucleus). The cloud around the nucleus is known as a shell.

Using Helium as an example:
4 : p + n (is the atomic mass [A])
He: Helium
2 : e (is the atomic number [Z])
NUMBER OF ELECTRONS = NUMBER OF PROTONS
p + n = 4
p = 2
n -> 4 – p = 2
e- = p+ = 2

Definitions

“Definitions of unknown words encountered in this unit”

Mass Number: the number of protons and neutrons in an atomic nucleus.
Proton Number: also known as atomic number, is the number pf protons in an atom of an element.
Isotope: two or more forms of the same element that contain equal amounts of protons & electrons but different # of neutrons and in addition to this they differ in RAM but not in chemical properties.
Ions: an atom with a charge due to the loss or gain of one or more electrons.
Displacement Reaction: when one element is replaced by another in a compound.
Flame Test: by taking pure compounds which are held in the flame at the end of a platinum wire and observing the colours of flame.
RAM: Relative atomic mass which is the mass of the atom in relation to hydrogen (with number 1 as a RAM).