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Chapter 1

Chemistry Chapter One Notes

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Louise Dawe

1.1 Atoms, Molecules, and Compounds Atoms- fundamental unit of a chemical substance. - Extremely small, not visible to the eye. Atoms – basic particles from which matter is composed. Atoms consist of a nucleus (protons and neutrons) and electrons. Atoms may be combined with others (of the same or different element) to form molecules.
 Atoms in molecules are associated by sharing electrons in covalent bonds. We will study this in Chapter 7: Theories of Chemical Bonding. Other types of associations include coordinate covalent bonds and ionic bonding. More about that in Chapter 6: Fundamentals of Chemical Bonding! Atoms are often represented by spheres, with different colours differentiating the different elements. Your textbook uses the following convention: Molecules- atoms when come together in orderly ways become molecules. (only takes two atoms to make one molecule, which is termed diatomic) Chemical Formulas - Chemical compound: contains more than one type of element in fixed, relative amounts. - This ratio is expressed as a chemical formula - Chemical formulas are composed of each element type present (chemical symbol) followed by a whole-number subscript which represents the number of atoms of the type in the molecule. - There are different ways to represent molecules, different shapes and colours depending on what is being analyzed and why. 1.2 Measuring in Chemistry Physical Properties- length, area, and volume measure the size of an object. Every object possesses a certain quantity of matter called mass. Time is also used to know how long it takes for chemical transformation to occur. Temperature is the property of matter that determines the direction of heat flow. -quantitative measurements - each measurement gives a numerical result that has three aspects: 1. a numerical magnitude 2. an indicator of scale called a unit 3. a precision Physical changes – do not alter the chemical composition of a substance. Chemical changes- result from processes that change the chemical composition of a substance. Magnitude- values range from vanishingly small to astronomically large. Units- scientists use an international sustem of units (SI). It consists of seven base units that can be used to derive other units and prefixes that are used as decimal base multipliers. Liters are not included in the SI however, 1L= 1dm 3 Temperature – kelvin to Celsius is -273.15 and Celsius to kelvin is +273.15 Precision and Accuracy - the exactness of a measurement is precision. - how close a measurement is to the true value is accuracy. Significant Figures 1. When adding or subtracting, the number of decimal places in the result is equal to the least number of decimal places of the numbers being added or subtracted 2. when multiplying or dividing, the number of sig.figs in the result is equal to the least number of sig.figs of the numbers being multiplied or divided. 3. postpone adjusting result to the correct number of sig.figs until a calculation is complete. 1.3 Chemical Problem Solving Step 1: Determine what is asked for. - What type of problem is it? What are you asked to find? Step 2: Visualize the problem. - Draw pictures that illustrate what takes place. - Is chemical changes occur, draw molecular pictures. Step 3: Organize the data. - What data are available? - How are the data related to what is asked for? Step 4: Identify a process to solve the problem. - What concepts are required? What equations apply? Step 5: Manipulate the equations. - If necessary, do calculations in step. Solve for what is asked for. Step 6: Substitute and calculate. - Keep track of units. - Use the correct number of sig.figs Step 7: Does the result make sense? - Are the units consistent? Is the result sensible? 1.4 Counting Atoms: The Mole Mole- the amount of substance that contains as many elementary entities ( atoms, molecules, or other particles) as there are atoms in 12 exactly 12g of C. Avogadro’s number- 6.022142 x 10 atoms/mol Molar mass- of an element is a weighed avg. of the masses of all the isotopes of one element. Once calculated, it is the mass of one mole of atoms of the elements. Elemen
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