Chapter 4 Flashcards
Democritus
Greek philosopher
believed atoms were indivisible/indestructable
John Dalton
used experimental methods to transform Democritus’s ideas on atoms into a scientific theory
Dalton’s Atomic Theory
- All elements are composed of tiny indivisible particles called atoms.
- Atoms of the same element are identical. The atoms of one element are different from the atoms of another element.
- Atoms of different elements can physically mix together or can chemically combine in simple whole-number ratios to form compounds.
- Chemical reactions occur when atoms are separated, joined, or rearranged.
Flaws in Dalton’s Atomic Theory
- FALSE- bc atoms are divisible (subatomic particles)
- FALSE- bc atoms of same element aren’t necessarily identical (isotopes)
- atoms can’t “physically mix”
The Atom
smallest particle of an element that retains its identity during a chemical reaction
2 parts: nucleus, electron cloud
Protons
(+) charge
in nucleus
Mass: 1.67 x 10^-24 grams
Electrons
(-) charge outside nucleus (electron cloud) Mass: much smaller than protons and neutrons; negligible so 0 amu
Neutrons
no charge
in nucleus
Mass: 1.67 x 10^-24 grams
atomic number
above symbol of element
= number of protons and electrons
atomic mass
weighted average of the mass numbers of all isotopes of that elementp
mass numbers
sum of protons and neutrons in an atoms
ions
atoms that have gained or lost electrons
isotopes
atoms of the same element with a different number of neutrons (and mass numbers)