# CHEM103 Study Guide - Midterm Guide: Rutherford Model, Oil Drop Experiment, Chemical Formula

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20 Apr 2012
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Alexander Hunt
Chemistry 103 Midterm Notes
1.5 – Units of measure
Density= mass/volume
Temperature- a measure of how hot or cold a substance is when compared to another
substance
Heat – the energy that is transferred from one substance to another. Heat is always
transferred from the warmer object to the cooler one.
1Celcius degree = 9/5 Fahrenheit degree
T (K) = T(C) + 273
1.6 – significant digits
Zeroes aren’t counted unless followed by a period.
Ex. 5400=2 sig where 5400.= 4sig
For multiplication and division, the answer contains the same amount as the measurement
containing the least.
For addition and subtraction, the answer has the same number of decimals places as the
measurement with the fewest.
Rules for rounding off (only the special ones):
-If the digit removed is 5, the preceding number is increased by one if it’s odd, and if the
preceding number is even, is remains unchanged
Exact numbers can have as many sig figs as they want!
Systematic error – where the values are all higher or all lower than the actual value. A
result of a faulty measuring device, misreading it.
Random error – where values are both higher and lower than the actual value
2.3 – Dalton’s atomic theory
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Dalton’s postulates:
- Matter is composed of atoms called particles and they cannot be created or destroyed, nor
divided any further
- Atoms from one element can’t be transformed into atoms from another element
- Each element’s atoms are different
- Compounds are the result of the combination of a specific ratio of atoms (law of definite
composition)
The law of definite composition:
No matter what its source, a particular compound is composed of the same element in the
same parts by mass. Each element in a compound constitutes a fixed fraction of the mass.
2.4 – Observations that led… nuclear atom model
-Thomson discovered that atoms could be separated (contrasts Dalton’s postulate),
discovered the electron
-Millikan measured the charge of the electron with his oil drop experiment
-Rutherford’s gold foil experiment lead to the discovery of the nucleus. With Thomson’s
plum pudding model in mind, he expected only minor deviations as the particles passed
through, yet there were particles which took a deflection of more than 90 degrees. He
concluded that the nucleus contains all the positive charge and mass of an atom.
- Chadwick discovered the neutron in the nucleus
2.5 – Atomic theory today
The atomic number (Z) – the number of protons in the nucleus of each of its atoms
The mass Number (A) – the total number of protons and neutrons in the nucleus
Number of neutrons = mass number – atomic number
An element may have isotopes which are particles with different numbers of neutrons in
the nucleus. All isotopes have nearly identical chemical properties
The mass of an atom is measured relative to a standard, the atomic mass unit, (amu) which
is 1/12 of a carbon-12 atom. It has a mass of 1.66054E-24
Modern atomic theory
-All matter is composed of atoms, which can be divided further.
-A chemical reaction can never change an atom into another element, although this is
possible in nuclear reactions
-Elements form compounds in specific ratios
2.7 – intro to bonding
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