Atoms Molecules & Ions

Atomic Theory of Matter Atoms – from the Greek word atomos meaning indivisible John Dalton developed the Modern theory of the atom In an attempt to explain how and why elements would combine with one another in fixed ratios and sometimes also in multiples of those ratios, Dalton formulated his atomic theory

elements consisted of tiny particles called atoms all atoms of an element were identical and that in particular they had the same mass compounds consisted of atoms of different elements combined. Compounds have constant composition because they contain a fixed ratio of atoms chemical reactions involved the rearrangement of combinations of those atoms

Discovery of Atomic Structure In 1897 the British physicist Joseph John (J. J.) Thomson (1856–1940) discovered the electron in a series of experiments He studied nature of electric discharge in a high-vacuum cathode-ray tube  Thomson interpreted the deflection of the rays by electrically charged plates and magnets as evidence of "bodies much smaller than atoms"  He calculated the charge-to-mass ratio.

Figure: 02-04

In 1906, Millikan began experiments at the University of Chicago to attempt to measure individual electron charge  use of oil drops

Diagram of Millikan's apparatus, from his Physical Review paper

Figure: 02-05

 Millikan showed that the charge of the droplets were always a whole number multiple of 1.592 x10-19C  The accepted value is 1.602x10-19C Millikan could now calculate the mass of an electron with Thomson’s ratio of charge to mass       m = 9.10 X 10-28 g 

Radioactivity Spontaneous emission of radiation. Rutherford discovered 3 types

Figure: 02-08

The Nuclear Atom Thomson – Plum Pudding model

Figure: 02-09

Rutherford discovered a dense nucleus from his work with the gold foil expt

(a) Expected Results of the Metal Foil Experiment if Thomson's Model Were Correct (b) Actual Results

A Deeper Look into the Atom Particle Mass (kg) Charge Discoverer Electron, e- 9.11E-31 -1 J.J. Thomson Proton, p+ 1.67E-27 +1 E. Rutherford Neutron, n0 Chadwick Other

Modern view of the atomic structure The atom consists of protons (p+), electrons(e-), and neutrons(no). Atoms are electrically neutral (#p+ = #e-) An atom is defined by #p+ = Z = atomic number As single atom is measured in amu ( 1 amu = 1.66054 x 10-24 g) An atomic ion is #p+ ≠ #e- resulting in a net nonzero charge on the species

Isotope Atoms which have the same Z (same # p+) but a different A (different # n0) Most elements have isotopes that occur in nature in precise proportions (fractional abundances, %).

Naturally occurring C: 98.892 % 12C + 1.108 % 13C. Atomic Weights Average Atomic Masses Relative atomic mass: average masses of isotopes: Naturally occurring C: 98.892 % 12C + 1.108 % 13C. Average mass of C: (0.98892)(12 amu) + (0.0108)(13.00335) = 12.011 amu. Atomic weight (AW) is also known as average atomic mass (atomic weight). Atomic weights are listed on the periodic table. Chapter 2

The Periodic Table

Periodic Table An arrangement of elements according to increasing atomic number (Z) Rows = periods Columns = groups or families Metals, Nonmetals, Semimetals Main group (A), Transition Metals, Lanthanides and Actinides

Figure: 02-16

Chemical Bond Types IONIC: metal + nonmetal COVALENT: nonmetal + nonmetal METALLIC: metal + metal

Figure: 02-20a-h

Figure: 02-21

Names and Formulas for Acids The names of acids are related to the names of anions: -ide becomes hydro-….-ic acid; -ate becomes -ic acid; -ite becomes -ous acid.

Chapter 2

Some Simple Organic Compounds Alkanes Organic chemistry: the chemistry of carbon compounds. Alkanes contain only C and H and are called hydrocarbons. The names of alkanes all end in the suffix –ane. Alkanes are named according to the number of C atoms in their backbone chain: Methane has one C atom (CH4) Ethane has two C atoms (CH3CH3) Propane has three C atoms (CH3CH2CH3)

Some Derivatives of Alkanes Replace H atoms in alkanes with heteroatoms (atoms other than C or H), we have introduced a functional group into the alkane Replace H with –OH, then we form an alcohol. Alcohols are also named by the number of C atoms. Consider propanol: there are two places for the OH: on an end C or the middle C. When the OH is located on the end C, we call the substance 1-propanol When the OH is on the middle C, we have 2-propanol.

Replace a single bonds in an alkane with one or more double bonds, then we form alkenes. Forming a double bond between C and O, forms carboxylic acids, ketones, aldehydes, and esters Any organic molecule with double or triple bonds is called unsaturated.