Chemistry 101 Chapter 2 Atoms, Molecules, and Ions 1-19 جامعة الامير مقرن скачать в хорошем качестве

Chemistry 101 Chapter 2 Atoms, Molecules, and Ions 1-19 جامعة الامير مقرن

Atomic Theory of Matter The theory that atoms are the fundamental building blocks of matter re-emerged in the early nineteenth century, championed by John Dalton. Dalton’s Postulates 1) Each element is composed of extremely small particles called atoms. 2) All atoms of a given element are identical to one another in mass and other properties, but the atoms of one element are different from the atoms of all other elements. 3) Atoms of an element are not changed into atoms of a different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions. 4) Atoms of more than one element combine to form compounds; a given compound always has the same relative number and kind of atoms. Law of Conservation of Mass ➢ The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place. ➢ This law was one of the laws on which Dalton’s atomic theory was based. Law of Multiple Proportions ➢If two elements, A and B, form more than one compound, the masses of B that combine with a given mass of A are in the ratio of small whole numbers. ➢Dalton predicted this law and observed it while developing his atomic theory. ➢When two or more compounds exist from the same elements, they can not have the same relative number of atoms. Discovery of Subatomic Particles • In Dalton’s view, the atom was the smallest particle possible. Many discoveries led to the fact that the atom itself was made up of smaller particles. ➢Electrons and cathode rays ➢Radioactivity ➢Nucleus, protons, and neutrons The Electron (Cathode Rays) • Streams of negatively charged particles were found to emanate from cathode tubes, causing fluorescence. • J. J. Thomson is credited with their discovery (1897). The Electron Thomson measured the charge/mass ratio of the electron to be 1.76 x 10^8 coulombs/gram (C/g). Millikan Oil-Drop Experiment (Electrons) ▪ Once the charge/mass ratio of the electron was known, determination of either the charge or the mass of an electron would yield the other. ▪ Robert Millikan determined the charge on the electron in 1909. • Radioactivity is the spontaneous emission of high-energy radiation by an atom. • It was first observed by Henri Becquerel. • Marie and Pierre Curie also studied it. • Its discovery showed that the atom had more subatomic particles and energy associated with it. The Atom, circa 1900 • The prevailing theory was that of the “plum pudding” model, put forward by Thomson. • It featured a positive sphere of matter with negative electrons embedded in it. Three types of radiation were discovered by Ernest Rutherford: alpha particles (positively charged) Beta particles (negatively charged, like electrons) Gamma rays (uncharged) Discovery of the Nucleus Ernest Rutherford shot  particles at a thin sheet of gold foil and observed the pattern of scatter of the particles. The Nuclear Atom Since some particles were deflected at large angles, Thomson’s model could not be correct. • Rutherford postulated a very small, dense nucleus with the electrons around the outside of the atom. • Most of the volume is empty space. • Atoms are very small; 1 – 5 Å or 100 – 500 pm. • Other subatomic particles (protons and neutrons) were discovered. Subatomic Particles • Protons (+1) and electrons (–1) have a charge; neutrons are neutral. • Protons and neutrons have essentially the same mass (relative mass 1). The mass of an electron is so small we ignore it (relative mass 0). • Protons and neutrons are found in the nucleus; electrons travel around the nucleus. #chemistry #chemistry101 #generalChemistry #chapter2 #learning #exam #class #تسريبات #بنك_اسئلة #quiz #exam #education #تعليم #تجميعات #course #كيمياء #جامعة_الامير_مقرن #السعودية #مصر #ksa #egypt