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Chem 103 Midterm.doc

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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 Rules for sigs in answer: 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 1Dalton’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 2Ionic compounds are between a metal and a non metal and there is a transfer of an electron, the metal gives up it’s electron to the non-metal. They are neutral compounds and their attractive force is determined largely by Coulombs law Covalent (molecular) compounds are between two non-metals and consist of a “charing of electrons”. As the molecules get closer together, the opposing nuclei pull the electrons from the other atom in closer, this forms a covalent bond. 2.8 – formulas, names and masses The empirical formula shows the relative number of atoms in a compound and is the simplest forumula. Ex. Hydrogen peroxide HO The molecular formula shows the actual number of atoms in each compound Ex. H 2 2 The structural formula shows the atoms and the bonds between them Ex. H-O-O-H Naming rules for metals with more than one ion: -The suffix –ous is given to the ion with the lower charge -The suffix –ic is given to the ion with the higher charge (table on page 67) *Tin is stannous and stannic* Naming rules for Oxoanions -These compounds are usually a non metal bonded to one or more oxygen atoms. When there are only two types of oxoanions in the family, the following applies: -the ion with fewer O gets the suffix –ate -the ion with more O gets the suffix –ite Ex. Nitrate and nitrite When there are four oxoanions in the family, the following applies: -the ion with the most O has the prefix, per- and also the suffix –ate -the ion with one fewer has just the suffix –ate -the ion with two less has the suffix –ite -the ion with three fewer, has the prefix hypo-, and the suffix –ite *know Organic Chemistry* 7.1 The Nature of Light 3The Wave Nature of light: The speed of light is a constant and it is based on two inversely related principles, frequency and wavelength. C=v*(lamda) The amplitude defines the intensity of the wave but does not change the wavelength The EMR spectrum: When talking about visible light, red light has the lowest energy, and violet has the highest energy. ROYGBIV (lowest to highest in that order) Characteristics of Waves: -as the wave enters another medium, the change in speed causes refraction, which gives the wave another angle (angle of refraction) -if a wave strikes the edge of an object, or passes through a slit with the approximate width of it’s wavelength, then diffraction occurs. This is a bending around a corner of an object, or in the case of the slit, the propagation on the
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