Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 1

Dalton’s Atomic Theory

Based on 4 postulateso 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.

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 2

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

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 3

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 4th 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 3rd 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 3rd hypothesis.

Another one will be studied later.

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 4

Cathode-Ray Tube

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.

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 5

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.

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 6

Rutherford’s Experiment

-particles are produced by radioactive sources and they are positively charged. Rutherford used very thin gold foils.

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 7

Rutherford’s Model of the Atom

diameter ~ 10-15

m

diameter ~10-10

m

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 8

Structure of the Atom and Relative Size

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 9

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 sub-atomic 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.

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 10

Atom Symbolism

XAZX is the symbol for the element

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 11

Periodic Table

Rows are termed as Periods

Columns are termed as Groups

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 12

Formulas and Models

Atoms, Molecules, and Ions

General Chemistry I CHM 111 Dr Erdal Onurhan Slide 13

Some Organic Functional Groups

- OH Alcohols- COOH Acids - O - Ethers- CO- Ketones- CHO Aldehydes- NH2 Primary Amines