Chapter 5 Review
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Chapter 5 Review
5.1
o Early Models of the Atom
o Democritus
 Greek teacher who lived in the 4th century B.C.
 Was the first to suggest the existence of particles, atoms
 Believed these structures were indivisible and indestructible.
 His ideas were not useful in explaining chemical behavior.
* Lacked experimental support
o John Dalton
 The modern process of discovery regarding atoms began with him.
 Was an English school teacher
 Unlike Democritus, Dalton performed experiments to test and correct his atomic theory.
 Dalton's atomic theory
* All elements are composed of tiny invisible particles called atoms
* Atoms of the same element are identical. The atoms of any one element are different from those of any other element.
* Atoms of different elements can physically mix together or can chemically combine with one another in simple whole-number ratios to form compounds
* 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.
 Much of Daltons theory is accepted today
* Except we now know atoms are divisible and can be broken down into even smaller, more fundamental particles.
o Atom
 The smallest particle of an element that retains the properties of that element.
 Scanning tunneling microscopes provide a visual image of individual atoms.
5.2
Three kinds of subatomic particles
o Elections
o Negatively charged subatomic particles.
o Electrons were discovered by J.J Thompson
o Thompson performed an experiment that resulted with a cathode ray, a glowing beam formed between the electrodes
o Thompson discovered the beam attracted to positive metal plates and repealed negative plates
o He proposed that the cathode ray is a stream of tiny negatively charged particles moving at high speeds.( electrons)
o He concluded electrons must be parties of the atoms of all elements
o E. Goldstein
 Concluded the discovery of protons
o James Chadwick
 Confirmed the existence of neutrons
o The atomic nucleus
o Ernest Rutherford
 Conducted an experiment aiming a beam of alpha particles at a gold foil.
 Most f the particles passed through the foil with no deflection but a few didn't
 Thus, Rutherford suggested the atom is mostly empty space- which explains the lack of deflection for most of the alpha particles.
 All of the positive charge and almost all the mass are concentrated in a small region that has enough positive charge to account for the great deflection of some alpha particles- the nucleus.
5.3
o Atomic Number
o Protons and Neutrons make up the small dense nucleus.
o Electrons surround the nucleus and occupy most of the volume of the atom.
o Elements are different because they contain different numbers of protons
o The atomic number of an element is the number of protons in the nucleus of an atom of that element.
 The number of protons= number of electrons
o Atoms are electrically neutral.
o This is why the number of electrons must equal the number of protons.
o Mass Number
o The total number of protons and neutrons in an atom is called the mass number.
o For any atom, the number of neutrons can be determined by:
 Number of neutrons= mass number - atomic number
o Shorthand notation
 The chemical symbol appears with two numbers on the left.
 The atomic number is the subscript( a number positioned lower)
 The mass number is the superscript ( a number positioned higher)
 Ex:
197
Au
o Isotopes
o Isotopes are atoms that all have the same number of protons and electrons, but different neutrons.
o Isotopes are chemically alike because they have identical numbers of protons and electrons.
o Atomic Mass
o Mass Spectromer- instrument used since the 1920s that makes it possible to determine the tiny masses of atoms
o It is more useful to use a reference isotope as a standard because the values found
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