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Chapter 4 - Chapter 4 Atoms and Elements 4.1 o Experiencing...

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Chapter 4: Atoms and Elements 4.1 o Experiencing atoms at Tiburon The key to connecting the microscopic world with the macroscopic world is the atom. Atoms compose matter; their properties determine matter’s properties. An atom is the smallest identifiable unit of an element. 4.2 o Indivisible: the atomic theory Democritus: First person to theorize small, indivisible particles that he called “atomos” or atoms Suggested that if you divided matter into smaller and smaller pieces, you would eventually end up with tiny, indestructible particles—atoms. John Dalton Atomic theory: o Each element is composed of tiny indestructible particles called atoms o All atoms of a given element have the same mass and other properties that distinguish them from the atoms of other elements o Atoms combine in simple, whole-number ratios to form compounds. 4.4 o The nuclear atom J.J. Thompson: Discovered the electron Electron: negatively charged particle smaller and lighter than atoms, and are uniformly present in many different kinds of substances. This discovery showed that even ‘Indestructible’ can be chipped into something smaller
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Ernest Rutherford: Attempted to give evidence to Thomspon’s theory, but disproved its validity instead. His experiment shot atoms into a gold piece of foil, but rather than every shot going straight through the foil, some deflected or bounced straight back. In order to explain the deflections he observed, the mass and positive charge of an atom must all be concentrated in a space much smaller than the size of the atom itself. Nuclear theory of the atom: o Most of the atom’s mass and all of its positive charge are contained in a small core called the nucleus. o Most of the volume of the atom is empty space through which the tiny, negatively charged electrons are dispersed. o There are as many negatively charged electrons outside the nucleus as there are positively charged particles (protons) inside the nucleus, so that the atom is electrically neuteral. Nucleus: the area of an atom that contains protons and neutrons Proton: a positively charged particle in an atom contained in the nucleus Neutron: a particle in the nucleus that contains no net charge. 4.4 o The properties of Protons, Neutrons, and electrons Atomic mass unit (amu): one twelfth of the mass of a carbon atom containing six protons and six neutrons A proton has the mass of 1.0073 amu A neutron has a mass of 1.0087 amu An electron has a mass of 0.00055 amu
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