Alchemist- Next 2000 years –tried to turn cheap materials into gold. Some elements and compounds were discovered, and some procedures were developed

Law of Conservation of Mass- Mass is neither created nor destroyed in a chemical reaction. The same number and types of atoms will be found in the products as in the reactants. They are simply rearranged. H2H2 O 2 H2OH2O

Dalton’s Atomic Theory John Dalton ( ) developed the first useful atomic theory of matter around Dalton's exceptional gift for recognizing and interpreting patterns in experimental data lead him from a problem in meteorology to the idea of atoms as fundamental constituents of matter. He realized the vital theoretical connection between atomic weights and weight relations in chemical reactions. He was the first to associate the ancient idea of atoms with stoichiometry. Dalton's atomic theory rests on the following postulates.

All matter consists of tiny particles called atoms. Atoms are indestructible and unchangeable. All atoms of the same element are identical. Atoms combine in new ways during a chemical reaction. DALTON’S ATOMIC THEORY

Could anything at first sight seem more impractical than a body which is so small that its mass is an insignificant fraction of the mass of an atom of hydrogen? --which itself is so small that a crowd of these atoms equal in number to the population of the whole world would be too small to have been detected by any means then known to science." Recording made in From the soundtrack of the film, Atomic Physics

What would J. J. Thomson’s atom look like? He called his model of the atom plum pudding.

Ernest Rutherford Rutherford began his study of the structure of the atom as a colleague of J. J. Thomson. He naturally viewed the atom as Thomson did.

To examine the structure of the atom Rutherford designed an experiment where he aimed alpha particles so they would strike a thin sheet of gold foil. He expected the dense high speed alpha particles to go straight through the gold foil.

Rutherford and his coworkers repeated this same experiment using foils made of many other elements besides gold. After finding similar results with these experiments, Rutherford and his coworkers were able to show that the centralized nucleus of any type of atom has several fundamental properties. A nucleus has a positive charge which is equal in magnitude the the overall negative charge of the electrons surrounding the nucleus. A nucleus makes up over 99.9% of the total mass of the atom. (Just how dense is the nucleus? Consider this: a piece of nuclear material the size of a pea would have a mass of 250 million tons, which is about the mass of 170 million cars! A nucleus has a diameter that is merely 0.01% the length of the atom itself. ( If an atom were enlarged to the size of a football stadium, its nucleus would have the size and position of a bee on the 50-yard line, and the electrons would occupy the stadium seats!

Describe Thomson’s model of the atom and how did it differ from Dalton’s model of the atom

Describe Rutherford’s model of the atom.

In the Rutherford gold foil experiment, the fact that most of the alpha particles were not deflected as they passed through the gold foil indicates that (a) the nucleus is positively charged. (b) the atom is mostly empty space. (c) atoms are solid spheres touching each other in the solid state. (d) gold is very dense. (e) none of the above is correct.

The Neutron Scientists were confused as they realized that the total mass of the atom was more than just the sum of the masses of the protons and electrons. They suspected that the atom contained a third type of subatomic particle that contributed to the atomic mass. However, as this particle did not have an electrical charge, and therefore was neutral, it was more difficult to detect than the electron and proton. In 1932, an English scientist named James Chadwick showed that an atom contains a third kind of subatomic particle which he called a neutron. A neutron has about the same mass as a proton and is also found in the nucleus of the atom. However, unlike the proton, the neutron does not have an electric charge.

The Atom An atom is the smallest particle of an element that displays all the properties of that element. All atoms of an element have the same number of protons. Atoms have equal numbers of protons and electrons. Isotopes are atoms of the same element (same number of protons) but differ from each other in the number of neutrons in their nucleus. Nucleons are components of the nucleus = protons and neutrons. Electrons are outside the nucleus. The nucleus has most of the mass of the atom but occupies only about 1/10,000 the total volume of the atom. The atom is mostly space.

Which of the following particles has the smallest mass? (a) an electron (b) a proton (c) a neutron (d) a hydrogen atom (e) a hydrogen nucleus

Which statement is false? (a) Ordinary chemical reactions do not involve changes in nuclei. (b) Atomic nuclei are very dense. (c) Nuclei are positively charged. (d) Electrons contribute only little to the mass of an atom. (e) The nucleus occupies nearly all the volume of an atom.

The atomic number of a certain element is 19, and its mass number is 39. An atom of the element contains _____ protons, _____ neutrons, and the chemical symbol for the element is _____.

Give the number of protons, neutrons, and electrons in the ion.

What is the symbol for a species composed of 35 protons, 44 neutrons, and 36 electrons?

Which response includes all the following statements that are true, and no false statements? I. Isotopes of an element differ only in the number of protons. II.The number of protons in an atom is its atomic number. III.The mass number of an atom is the sum of the number of protons plus electrons in the atom. IV.The volume occupied by the nucleus of an atom represents a large percentage of the total volume of the atom. (a) I and III(b) II, III, and IV (c) II and IV(d) II (e) I and IV

Mass Number VS. Atomic Mass The mass number is the sum of the protons and neutrons for an isotope. Since each element has more than one naturally occurring isotope, and the periodic table is a table of elements not isotopes, the mass number is not on the periodic table.

The atomic mass of an element is on the periodic table. It is a weighted average of the masses of all the isotopes of an element. It is weighted based on the relative abundance (decimal %) of each isotope.

Formula for finding Atomic Mass (mass x r.a.) + (mass x r.a.) + (mass x r.a.)... isotope 1 isotope 2 isotope 3

Why is the atomic weight of chlorine instead of exactly 35?

Copper has 2 naturally occurring isotopes. Copper- 63 is 69% abundant the remaining isotopes are copper-65. What is the average atomic mass of copper?

A hypothetical element consists of the following naturally occurring isotopes. What is the atomic mass of the element? Isotopes Mass Abundance amu 26.00% amu 58.00% amu 16.00%