Democritus 460 BC 370 BC First scholar to suggest that atoms existed. Believed that atoms were indivisible and indestructible.
Democritus 460 BC 370 BC Problems with theory: 1. Did not explain chemical behavior 2. No experimental support
John Dalton 1766 1844 Dalton s Atomic Theory 1.All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical.
All element A atoms are identical. All element B atoms are identical, but they are different than element A
John Dalton 1766 1844 Dalton s Atomic Theory 3. Atoms of different Elements can physically mix together or can chemically combine in simple wholenumber ratios to form compounds.
John Dalton 1766 1844 Dalton s Atomic Theory 4. Chemical reactions occur when atoms are separated, joined, or rearranged. Atoms of one element, however, are never changed into atoms of another element as a result of a chemical reaction.
Cathode Ray Tube (CRT) Developed by Sir William Crooke
Cathode Ray Tube (CRT) Used by J.J. Thomson
J.J. Thomson 1856-1940 Used a CRT and electric plates in his experiment. Discovered the corpuscle (later known as the electron ) in 1897. Found the charge-to-mass ratio of the electron in the cathode ray. Reached the conclusion that electrons must be parts of the atoms of all elements
J.J. Thomson 1856-1940 Called his atomic theory the Plum pudding model
Plum-pudding Model Electrons are evenly distributed throughout an atom filled uniformly with positively charged material.
Robert Millikan 1868-1953 Oil drop experiment Found the charge on an electron. Used that value to calculate the mass of an electron. The mass of an electron is 9.11 x 10-28 gram
Eugen Goldstein (1850 1930) Observed a CRT and noticed rays traveling in the direction opposite to that of the cathode rays. He called the rays canal rays. These canal rays were made up of positively charged particles which became known as protons
James Chadwick (1891 1974) Was the assistant of Marie Curie. Discovered the neutron in 1932.
Ernest Rutherford 1871-1937 Improved on the Atomic Theory through his gold-foil experiment. The atom is made up of mostly empty space. 99.9% of the mass of the atom is in the nucleus which is where the protons are. The electrons surrounded the nucleus.
Ernest Rutherford 1871-1937 Gold-foil experiment
Alpha particles scatter from the gold foil.
Atomic Number number of protons in the nucleus of the atom. Mass Number = protons + neutrons Atomic Mass the average mass of all the atoms in a naturally occurring sample of the element.
Isotope atoms that have the same number of protons but different numbers of neutrons. Lithium - 6 6 3 Li Lithium - 7 7 3 Li
Nuclear Notation ₃Li ⁷ ₃Li ⁶ ₂₀ ₂₁ ₂₂ ₁₀Ne ₁₀Ne ₁₀Ne
The 3 isotopes of neon
Ions atoms that have the same number of protons but a different number of electrons. 40 19 9 Ca 20 2+ F 1-13 22 N 7 3- Na 11 1+
Atomic Mass is defined as one-twelfth of the mass of a carbon-12 atom. It is a weighted average mass of the atoms in a naturally occurring sample of the element.
Weighted Grades A student has the following points in chemistry class: Homework 8 / 10 9 / 15 1 / 5 7 / 10 Labs 19 / 20 9 / 10 4 / 10 Quizzes/ Tests 20 / 25 47 / 50 Homework is worth 10%, Labs are worth 20% and Tests are 70%.
Homework average percentage: 62.5% Lab average percentage: 80.0% Quiz/Test average percentage: 89.3% Homework is 10% so 62.5% x.10 = 6.25% Labs are 20% so 80.0% x.20 = 16.0% Quiz/Test are 70% so 89.3% x.70 = 62.5%
Of all chlorine atoms, 75.771% are chlorine-35. Chlorine-35 atoms have a mass of 34.96885 amu. All other chlorine atoms are chlorine-37 and these have a mass of 36.96590 amu. What is the average atomic mass of chlorine?
Neon has three different isotopes. 90.51% of neon atoms have a mass of 19.992 amu. 0.27% of neon atoms have a mass of 20.994 amu. 9.22% of neon atoms have a mass of 21.991 amu. What is the average atomic mass of neon?