Chapter 4: Atomic Structure

Subatomic Particles

Symbol Notation

Isotopes

Average Atomic Mass

DemocritusAtom: smallest part of an element that retains the identity of that element.

Democritus (460-370 B.C.): believed in tiny, indivisible, indestructible particles he called “atomos.”

He had NO experimental proof!

John Dalton’s Atomic Theory (1803-1807)

All elements are composed of tiny indivisible particles called atoms.

Atoms of the same element are identical; atoms of different elements are different.

Atoms of different elements can mix in whole number ratios to form compounds.

Chemical reactions cause atoms to separate and recombine, NOT change into different atoms.

Subatomic Particles

Charge Mass (amu)

Location Discoverer

proton

1+ 1 nucleus Thomson

neutron 0 1 nucleus Chadwick

electron 1-

1/1840 outside

nucleusThomson

Comparing Subatomic Particles

The proton gives identity to an atom, the electron gives personality.

Mass Number & Atomic Number

Mass Number = Number of protons + neutrons

Atomic Number = Number of protons

Complete the Table

Symbol Atomic Number

Mass Number

Number of p+

Number of n0

Number of e-

9 10

Na 15

47 25

55 25

S2- 32

Ga3+ 39

Mass of AtomsMass of atom is very small!Heaviest atom is 4 x 10-22g.Diameters of atoms: 100-500 pm (1-5 angstroms)

1 A = 10-10mBoth pm and A are commonly used for diameters.

Isotopes Have the Same…

Number of protons

Atomic Number

Number of electrons

Isotopes Have Different…

Number of neutrons

Mass Number

Mass

n0

Isotopes of Hydrogen

Hydrogen-1 Hydrogen-2 Hydrogen-3

Protium Deuterium Tritium

Atomic Mass Unit (amu)

carbon-12 isotope used as standard 1 atom of carbon-12 = 12 amu carbon-12 has 12 particles with mass mass of proton = 1 amu mass of neutron = 1 amu 12

C 6

Average Atomic Mass

Weighted average of all isotopes

Seen as mass number on periodic table

Units in amu

To Calculate Average Atomic Mass You Need…

Number of Isotopes

Mass of Isotopes

Percent Relative Abundance

Calculating Average Atomic Mass

Mass x Rel. Abundance

Mass x Rel. Abundance

Average Atomic Mass

Isotope A

Isotope B