Atoms, Molecules, and Ions
Dalton’s Atomic Theory
Based on 4 postulates o Elements are composed of extremely small particles, called atoms.
o All atoms of the same element are identical, having the same size, mass and chemical properties.
The atoms of one element are different from the atoms of all other elements.
o Compounds are composed of atoms of more than one element. In any compound, the ratio of numbers of atoms pf any of the two elements present is either an integer or a simple fraction.
o A chemical reaction involves only the separation, combination, or rearrangement of atoms; it does not result in their creation or destruction.
Dr Erdal Onurhan General Chemistry I CHM 111 Slide 1

Atoms, Molecules, and Ions
Representation of Dalton’s Atomic Theory
Note that atoms of element X combine with atoms of element Y in a 2:1 ratio here. Atoms are neither created nor destroyed in the process
General Chemistry I CHM 111 Dr Erdal Onurhan Slide 2

Atoms, Molecules, and Ions
Laws of Chemistry
•
Law of Conservation of Mass
–
Matter can neither be created nor destroyed – expressed by Lomonosov in 1748 and placed on experimental footing by Lavoisier in 1774 – Dalton’s 4 th hypothesis is in conformity with this law
•
Law of Definite Proportions
– different samples of the same compound always contain its constituent elements in the same proportion by mass
– expressed by Proust in 1799 – Dalton’s 3 rd hypothesis is in conformity with this law
•
Law of Multiple Proportions
– if two elements can combine to form more than one compound, the masses of one element that combine with a fixed mass of the other element are in ratios of small whole numbers – arrived at by Dalton through the 3 rd hypothesis.
Another one will be studied later.
Dr Erdal Onurhan General Chemistry I CHM 111 Slide 3

Atoms, Molecules, and Ions
Cathode-Ray Tube
Dr Erdal Onurhan
The cathode ray tube has an electric field perpendicular to the direction of the cathode rays and an external magnetic field.
The symbols N and S denote the north and south poles of the magnet. The cathode rays will strike the end of the tube at A in the presence of a magnetic field, at C in the presence of an electric field, and at B when there are no external fields present or when the effects of the electric field and magnetic field cancel each other out.
Slide 4 General Chemistry I CHM 111

Atoms, Molecules, and Ions
Millikan’s Experiment
Millikan studied the motion of single tiny drops of oil that picked up static electricity from ions suspended in air through a microscope and arrived at a value for electronic charge.
Slide 5 General Chemistry I CHM 111 Dr Erdal Onurhan

Atoms, Molecules, and Ions
Rutherford’s Experiment

-particles are produced by radioactive sources and they are positively charged.
Rutherford used very thin gold foils.
General Chemistry I CHM 111 Dr Erdal Onurhan Slide 6

Atoms, Molecules, and Ions
Rutherford’s Model of the Atom
General Chemistry I CHM 111 Dr Erdal Onurhan Slide 7

Atoms, Molecules, and Ions
Structure of the Atom and Relative Size
General Chemistry I CHM 111 Dr Erdal Onurhan Slide 8

Atoms, Molecules, and Ions
Fundamental Properties of Subatomic Particles
*The column entitled ‘Mass (amu)’ is a measure of relative mass and will be discussed later.
The above discussion shows that an atom is composed of three types of subatomic particles. These, in turn, are not differentiable from one atom to another. They are exactly the same whatever the source is, i.e. they are fundamental building blocks of any atom.
General Chemistry I CHM 111 Dr Erdal Onurhan Slide 9

Atoms, Molecules, and Ions
Atom Symbolism
Z
A
X
X is the symbol for the element
Dr Erdal Onurhan General Chemistry I CHM 111 Slide 10

Atoms, Molecules, and Ions
Periodic Table
Rows are termed as
Periods
Columns are termed as
Groups
Slide 11 General Chemistry I CHM 111 Dr Erdal Onurhan

Atoms, Molecules, and Ions
Formulas and Models
General Chemistry I CHM 111 Dr Erdal Onurhan Slide 12

Atoms, Molecules, and Ions
Some Organic Functional Groups
2
Dr Erdal Onurhan General Chemistry I CHM 111 Slide 13