Chapter 5 Review

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o Thompson discovered the beam attracted to positive metal plates and repealed negative plates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