Chem ch. 1

Structure and Classification of Matter, Scientific Method and Chemical Laws, Mass Laws and Quantitative Relationships, Dalton’s Atomic Theory and Interpretation, Atomic Structure, Notation, and Ions, Experimental Evidence and Atomic Models

Plumb-Pudding Model

J.J Thomson

• atoms consist of electrons held in place by a diffuse cloud of positive charge

• electrons are randomly embedded in this cloud of positive charge

• discovered the measured charge/mass ratio of the electron

Gold-Foil Experiment

E. Rutherford
The nucleus

• Expected outcome: alpha particles would pass through or be slightly deflected

• actual outcome: most of the particles passed straight through, but some were deflected at very large angles or reflected completely

• explanation: positive charge and most of the atomic mass is in a very small and dense area, called the “nucleus”
  *atoms are mostly empty space

Nucleus contains..

protons (+1, p+)

neutrons (n^o) 0

electrons (-1, e^-)

atomic symbols

number of protons in nucleus distinguishes elements

X= atomic symbol

Z= atomic number

A= mass number (number of protons + number of neutrons)

A
X
Z

isotopes

• atoms of a given element that differ in number of neutrons (and mass)

• Dalton was wrong (assumed all atoms of a given element were identical)

• properties of isotopes for an element are nearly identical

how to determine amount of protons, neutrons, and electrons in atom

number of protons= atomic number

number of neutrons= atomic mass - number of protons

number of electrons= number of protons

neutral atoms

contain equal #s of protons and electrons to balance charge

forming ions

• remove or add electrons

• never add or remove protons (it will change identity of atom)

• add onee electron for each - charge, or subtract one electron for each + charge

ex) Br^- : 35 p+, 36e^-

ex) Sr²⁺ : 38p+, 36e^-

scientific method

the process of studying natural phenomena, involving observations, forming laws and theories, and testing of theories by experimentation.

measurement

the characteristic that any measurement involves estimates and cannot be exactly reproduced.

hypothesis

one or more assumptions put forth to explain the observed behavior of nature.

theory

a set of assumptions put forth to explain some aspect of the observed behavior of matter.

model

a set of assumptions put forth to explain the observed behavior of matter. The models of chemistry usually involve assumptions about the behavior of individual atoms or molecules.

natural law

a statement that expresses generally observed behavior.

law of conservation of mass

mass is neither created nor destroyed

law of definite proportion

a given compound always contains exactly the same proportion of elements by mass.