Chapter 4: Atoms and Elements

Sec. 4.2,3 History of Atomic Theory

Greek philosophers Leucippus (5th century BC) and Democritus (460-370 BC) were the first to suggest that there was a smallest unit of matter, with Democritus coining the word “atom” because it means “indivisible”. Their ideas were not widely accepted.

John Dalton (1808) , building on the work of many others, proposed an atomic theory and constructed experiments to support his ideas.

Matter is made of very small indivisible particles called atoms.

All atoms of a certain element are identical, while atoms of different elements are different. [Every carbon atom is like every other carbon atom, but carbon atoms are different from hydrogen atoms.]

During chemical reactions, atoms combine in whole number ratios to form compounds, or they may separate from other atoms or rearrange.

Dalton was unaware that each element may exist as more than one isotope and therefore atoms may not be identical.

He was also not aware that matter is sometimes destroy (changed into energy) during nuclear reactions.

Know about Thomson’s contributions to atomic theory:

Discovered electrons (1897) using cathode ray tube.

Calculated the ratio of mass to charge for electrons.

Plum pudding model

Cathode ray tube demo: CLICKCathode Ray Tutorial

Know how Millikan built on Thomson’s work:

Determined exact mass and amount of negative charge on electrons

1901

Millikan Oil Drop Experiment

Know Rutherford’s contributions to atomic theory:

Discovered densely-packed nucleus,containing positive particles called protons, taking up essentially no volume and containing essentially all of the atom’s mass (1911)

Be able to explain the gold foil experiment in detail (telling what experimental evidence allowed Rutherford to make each conclusion about the nucleus)

Nuclear model

Rutherford's Gold Foil Experiment

James Chadwick proved the existence of neutrons in 1932. In 1968 scientists discovered that protons and neutrons are made of smaller particles called quarks.

Sec. 4.4,5 Subatomic particles and Atomic Number

Remember that very small masses (such as on the atomic level) are often given in units called ______, which is defined as having a mass that is equal to ______the mass of a ______atom.

Elements are defined by the number of ______, which is also calledthe ______. Since atoms are electrically ______, this will also be the number of ______.

The mass number tells the number of ______plus ______since those subatomic particles weigh approximately ______times more than electrons. Essentially all of the mass of an atom is found ______, although it occupies essentially ______of the volume.

Sec. 4.6 Periodic Law and Periodic Table

Know this material which is review from Chem 1. Be able to locate and identify metals, nonmetals, metalloids, main group elements, transition metals.

Know properties of metals, nonmetals, metalloids, semiconductors.

After Mendeleev’s PT was arranged according to atomic mass, Moseley suggested rearranging according to charge on nucleus (# protons) which worked better for some elements that seemed to be out of place.

Be sure to know all vocab in bold print.

Alkali metals (Group ______)

  • Their predominant characteristic is their extreme ______.
  • For this reason they are only found in nature as ______.

Akaline Earth metals (Group ______)

  • Fairly ______and found in nature only as ______.
  • Together these two groups are sometimes called the ______metals.

Halogens ( Group ______)

  • ______nonmetals therefore they are only found in nature as ______.

Conceptual Check point 4.3

Which statement is NEVER true?

(a) An element can be both a transition element and a metal.

(b) An element can be both a transition element and a metalloid.

(c) An element can be both a metalloid and a halogen.

(d) An element can be both a main-group element and a halogen.

Sec. 4.7 Ions

  • Atoms be definition are electrically ______containing equal numbers of protons and electrons.
  • Charged particles are called ______, which form by atoms gaining (negative ______) or losing (positive ______) electrons.
  • For main group elements (Groups #______), the last digit of the group number tells how many ______(outer shell) electrons.
  • For main group elements, ion charges are often predictable.

Group 1 ______Group 2 ______Group 13 ______

Group 15 ______Group 16 ______Group 17 ______

Group 14 tends to form ______.

Group 18 elements don’t react.

  • Transition metal ion charges are difficult to predict and will be memorized.

Skillbuilder 4.4

Determine the charge of each ion.

(a) a Ni ion with 26 electrons______(b) aBr ion with 36 electrons ______

(c) a P ion with 18 electrons ______

Skillbuilder 4.5

Determine the number of protons and electrons in the S-2 ion.

______protons and ______electrons

Conceptual Checkpoint 4.7

If an atom with mass number of 27 has 14 neutrons, it is an isotope of which element?

(a) Si(b) Al(c) Co(d) Nb

Conceptual Checkpoint 4.8

If a carbon atom is drawn as a black sphere, would C-12 and C-13 need to be represented differently? Why or why not?

Sec. 4.8,9 Isotopes and Average Atomic Mass

  • Most elements occur in nature as a mixture of ______, which are different forms of the same element (same # ______protons) with differing masses (due to different # ______).
  • Unless some of the isotopes of a given element are ______, isotopes of an element have identical physical and chemical properties.
  • The relative amounts of each individual isotope in a naturally occurring same of that element are always the same. These are called the percent natural abundance.
  • Mass number (#______plus #______) must be a whole number. Abbreviated A.
  • Atomic number (#______) is abbreviated Z.
  • The masses on the PT are both relative and average atomic masses. They are relative to ______most common isotope, which is assigned a value of ______. They are a weighted average of the ______isotopes of the element. Be able to calculate average atomic masses as in Ex. 4.9. The mass on the PT is generally closest to the mass of the most abundant isotope of the element in nature.

Conceptual Checkpoint 4.9

A fictitious element is composed of isotopes A and B with masses of 61.9887 and 64.9846 amu, respectively. The atomic mass of the element is 64.52. What can you conclude about the natural abundances of the two isotopes?

(a) The natural abundance of isotope A must be greater than the natural abundance of

isotope B.

(b) The natural abundance of isotope B must be greater than the natural abundance

of isotope A.

(c) The natural abundances of both isotopes must be about equal.

(d) Nothing can be concluded about the natural abundances of the two isotopes from

the given information.

Virtual Lab #1Virtual Lab #2