Reasoned that atoms were indivisible and indestructible.
The smallest particle of an element that retains its identity in a chemical reaction.
Transformed Democritus ideas on atoms into a scientific theory.
Dalton’s Atomic Theory 1.
All elements are composed of tiny indivisible particles
Dalton’s atomic theory 2.
Atoms of the same element are identical. The atoms of any one element are different from those of another.
Dalton’s atomic theory 3.
Atoms of different elements can physically mix together or can chemically combine in simple whole number ratios to form compounds
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Dalton’s atomic theory 4.
Chemical reactions occur when elements are separated from each other, joined, or rearranged in a different combination.
Negatively charged subatomic particles
Experiment performed by Thomson. One electrode became positively charged, one became negative. The result was a glowing beam.
Robert A. Millikan
Carried out experiments to find the quantity of an electrons charge. Oil drop experiment.
One unit of negative charge
Subatomic positively charged
Subatomic negatively charged
Plum pudding model
Good foil experiment
Tiny central core of an atom and is composed of protons and electrons
Has a positively charged nucleus. Electrons are distributed around the nucleus and occupy almost all the volume of the atom.
Elements are different
They all contain a different number of protons
The number of protons in that element.
The total number of protons and neutrons
Atoms that have the same number of protons but different numbers of neutrons.
They have different mass numbers because they have a different number of neutrons.
Atomic mass unit (amu)
1/12 of the mass of a carbon atom
Weighted average mass of the atoms naturally occurring sample of the element.
Calculating atomic mass
Mass of each isotope x natural abundance, and then add the products.