Ch. 4 - Atomic Structure

Democritus’s Atomic Philosophy• Greek philosopher, first to

propose idea of atoms

• a tomos – “un cuttable”

• Failed theory:– Lacked experimental support– Couldn’t explain chemical behavior

Democritus (400 BC)

Defining the AtomAtom

– The smallest particle of an element that retains the chemical identity of that element (pg. 101)

• Law of Conservation of Matter (Antoine Lavoisier)

• Law of Constant Composition (Joseph Proust)– Elements combine in whole-number ratios to form

compounds.

– e.g., water (H2O) is always 2 hydrogen to 1 oxygen

Btw, by early 1800’s, there was no connection between elements and atoms; all atoms were assumed to be identical.

Dalton’s Atomic Theory

John Dalton 1803

Dalton’s Atomic Theory1. All matter (elements) is composed of tiny indivisible

particles called atoms.

2. Atoms of the same element are identical – but different from those of another element.

3. Atoms of different elements can physically mix, or combine in whole-number ratios to form compounds

4. Chemical reactions involve the rearrangement of atoms. No new atoms are created or destroyed.

Dalton’s Atomic Theory

Atoms of Element A Atoms of Element B

PHYSICALLY mixed CHEMICALLY combined

Fig. 4.2, pg. 102

Sizing Up the Atom

• Scanning Tunneling Microscope (STM)– “Nanotechnology”– Instrument used to “see” atoms

Avg. atomic radius = 5×10-11 m – 2×10-10 m

Kanji characters for atom, “original child.”

4.1 Homework#1, 2, 4 – 7

4.2 Homework#8,

Ch. 4 Atomic Structure

4.2 The Nuclear Atom

pgs. 104 - 108

Subatomic Particles

• Atoms are divisible.

• 3 subatomic particles1. Proton, p+

2. Electron, e-

3. Neutron, no

Subatomic Particles

J.J. Thomson• “Found” the electron, a

negatively charged particle with very small mass.

• Cathode-ray tube, 1897

Deflected Cathode-ray

Thomson’s “Plum-Pudding” Model

The Atomic Nucleus

Ernest Rutherford• “Discovered” atomic nucleus,

tiny central core of an atom• Gold-foil experiment, 1911

Rutherford’s Gold-foil exp.

The Nuclear Atom

The nucleus of the atom is much smaller than the atom yet contains most of its mass.

4.3 Distinguishing Among Atoms

pgs.110 - 119

Ch. 4 Atomic Structure

Periodic Table Intro

Periodic Table Intro

• Family (or group) – vertical column; elements within a family share similar chemical properties.

• Period – horizontal row;

Periodic Table Intro

Atomic Number

• the number of protons in the nucleus of an atom.• Each element has a unique number of protons.• For neutral atom, the number of protons equals the

number of electrons.

Mass Number

• the total number of protons plus neutrons.

• For neutral atom, the number of protons equals the number of electrons.

• e- mass not included; negligible.

Chemical Symbols (pg. 161)

Ion

• a charged atom or group of atoms.• formed when atoms gain or lose electrons.

• Cation – positive ion; p+ > e-

– lose electron(s)

• Anion – negative ion; p+ < e-

– gain electron(s)

CA ION

Isotopes

• atoms that have the same atomic number but different mass numbers;

• same number of protons, but different number of neutrons.

Atomic Mass

• a weighted average mass of all naturally occurring isotopes;

• determined from mass and relative abundance for each isotope.

• Average Atomic Mass =

(massisotope 1 × rel. abundanceisotope 1) +

(massisotope 2 × rel. abundanceisotope 2) + …