1. Atomic Structure Power Point First Part Chemistry I-AAHS Dr. Gray

2. Atomic structure Matter is comprised of elements, which are the most basic, fundamental units of structure Elements are composed of atoms. The atom has its own set of components-known as sub-atomic particles (electrons, protons, and neutrons)

3. Atomic Structure Dalton (1808) created the atomic model of matter: Three main parts to his model 1. An element is composed of tiny particles called atoms. Atoms of the same element have the same chemical properties. 2. In a given chemical reaction, an atom moves from one substance to another, but no atom disappears or is transformed to an atom of another element.

4. Atomic Structure (Dalton continued) 3. Compounds are formed when atoms of two or more elements combine. From Daltons definition, the atom is the smallest particle of an element that can enter into a chemical reaction.

5. Atomic Structure The discovery of the sub-atomic particles. 2 scientists are given this distinction-both Nobel laureates. - Thomson (Cambridge) -Rutherford (McGill-Montreal)

6. Atomic Structure Sub-atomic particle knowledge was first developed with experiments with electricity through gases at low temps. Thomson used his cathode ray tube experiment to justify the existence of negatively charged particles which he called electrons.

7. Atomic Structure As the cathode rays passed through a evacuated glass tube, they were then passed between both magnetic plates of opposite charge and electric plates of opposite charge. The cathode rays had a tendency to be bent (deflected) in the in the direction of the positively charged electric plate. Based on this Thomson claimed that the sub-atomic particles had a negative charge and he called them electrons.

8. Atomic Structure Rutherford helped to establish the existence of the nucleus and the proton. This was demonstrated by the gold foil experiment. He bombarded a thin sheet of gold oil with positive alpha particles. A few of these particles were deflected sight back at the alpha projector (source of alpha particles)

9. Atomic structure The points at which alpha particles were deflected straight back were determined by Rutherford to be a locus of positive charge. He referred to this locus as a nucleus. He concluded there were sub-atomic particles found in the nucleus which gave it a positive charge. These were referred to as protons.

10. Atomic Structure Rutherford was responsible for the establishment of a locus of positive charge at the center of the atom referred to as the nucleus. He was able to do this with his alpha particle scattering experiment.

11. Atomic Structure Every atom of a given element contains a definite number of protons. All atoms of hydrogen contain 1 proton. All atoms of uranium contain 92 protons. Neutral hydrogen and neutral uranium have an equal number of electrons to their protons. These electrons are arranged in the outer perimeter of an atom where they establish a cloud of negative charge.

12. Atomic Structure The number of protons within a given atom of an element is designated by the atomic number, Z. You can always identify an atom of a given element based on its number of protons (Z). The atomic number of a given atom of an element doesn’t change

13. Atomic Structure While the number of protons of an atom are constant- the number of neutrons may be different from one atom of an element to the next This difference in the number of neutrons is referred to as “isotopes” of a given element.

14. Atomic Structure The total number of protons and neutrons in a given nucleus of an atom is referred to as the mass number. This is represented by the letter “A” So, # of protons of a given atom + # of neutrons of a given atom = Mass Number

15. Atomic Structure The masses of each of the sub-atomic particles are summarized as follows: 1. electron= 1/2000 the mass of the simplest known element (hydrogen). 2. proton and neutron are very similar in their masses. However, the neutron is slightly greater in mass. So isotopes of a given element with a greater mass number, also have a greater atomic mass.

16. ANY QUESTIONS?