STRUCTURE OF AN ATOM. STRUCTURE OF AN ATOM. ELECTRON - the NEGATIVE particles surrounding the nucleus of an atom. discovered by JOSEPH JOHN THOMPSON. STRUCTURE OF AN ATOM. PROTON – positively charged particle in the nucleus of the atom Discovered by Eugene Goldstein. STRUCTURE OF AN ATOM.
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NEUTRON – a neutral subatomic particle present in the nucleus of an atom
Discovered by James Chadwick in 1932
1) Matter is made up of extremely small indestructible particles called atoms.
2) All atoms of a given element are alike
John Dalton – English chemist that proposed the first atomic theory in 1803
3) Atoms enter into combination with other atoms to form compounds, but remain unchanged during ordinary chemical reactions.
4) Atoms can combine in simple numerical ratios such as 1:1, 1:2, 2:3 and so on.
Dalton’s Atomic Model
Law of Conservation
There is no detectable change in the masses of substances before and after the course of an ordinary chemical reaction. Mass is conserved.
Dalton’s 3rd postulate
Law of Definite
Proportions or composition.
A pure compound always contains the same elements combined in the same proportions or percentage by mass.
% C = Mass of C / mass of CO2 x 100
% O = Mass of O/ mass of CO2 x 100
Dalton’s 2nd and 3rd postulate
Law of Multiple
When two elements combine to form more than one compound, the masses of one element which combine with a fixed mass of the other element are in a ratio of SMALL whole numbers
Hydrogen: a proton surrounded by an electron cloud
A Hydrogen Atom
Hydrogen Atomic Mass = 1 Atomic Number = 1
Deuterium Atomic Mass = 2 Atomic Number = 1
Two isotopes of hydrogen