# Unit 1: Atomic Structure Unit 1: Atomic Structure Part 1 CH1120 Chemistry The study of the properties and behavior of matter

States of matter Solid Liquid Gas Fundamentals of Measurement 1960 international agreement on measurement units for scientific measurements

SI units (Systeme International dUnites) Seven base units Fundamentals of Measurement Prefixes used to represent fractions or multiples of base units

Examples What is the name of the unit that equals 10-9gram? 10-6second? 10-3meter? Temperature

Measure of kinetic energy of a substance Scales include Celsius, Fahrenheit, and Kelvin Temperature Celsius () Based on the properties of water

Kelvin (K) SI temperature scale Fahrenheit () Not generally used in science Temperature

K = + 273.15 = ( - 32) = () + 32

Volume Most common units for volume are liters (L) and milliliters (mL) 1mL = 1cm3 Density

Mass per unit volume Accuracy and Precision Precision is a measure of how closely individual measurements agree with one another

Accuracy refers to how closely individual measurements agree with the correct value Accuracy and Precision Significant Figures Suppose you determine the mass of a dime on a balance capable of measuring to the nearest 0.0001g,

You could report the mass as: 2.2405 0.0001g The shows the magnitude of uncertainty of your measurement Significant Figures

In science we drop the It is understood that there is always some uncertainty in the last digit reported for any measured quantity All digits in a measurement including the final digit (the uncertain one) are called significant figures

Significant Figures A measurement of 4.1g has 2 significant figures (sig figs) A measurement of 4.0012g has 5 sig figs

There are rules to follow for sig figs that you will be expected to use in all coursework Significant Figures Counting numbers and constants have an infinite number of sig figs

For other numbers we must first identify if there is a decimal point or not For numbers that have exponential characters we ignore the exponent 6.0432 x 1045 we would only use 6.0432 for sig figs Significant Figures

If there is a decimal point we count sig figs from the LEFT If there is no decimal point we count sig figs from the RIGHT Significant Figures

Sig fig counting begins with the first non-zero digit 2.003948 7 sig figs 1900 2 sig figs

0.00475 3 sig figs Significant Figures For addition and subtraction we look at decimal places

Our answer will have the same number of decimal places as the measurement with the fewest decimal places Significant Figures 20.42 2 decimal places 1.322 3 decimal places + 283.1 1 decimal place 304.842 Round!

304.8 Significant Figures For multiplication and division we look at sig figs Our answer will have the same number of sig figs as the measurement with the fewest

sig figs Significant Figures Area = (6.221cm) (5.2cm) = 32.3492cm2 Round! =32cm2 Dimensional Analysis This method focuses on units and avoids the memorizing of most equations

The key to dimensional analysis is the correct use of conversion factors to change one unit to another or cancel the units Dimensional Analysis Example: 2.54cm = 1inch

Dimensional Analysis 1. Identify the given and desired units 2. Select the appropriate form of the conversion factor 3. Check that units cancel out properly to give you the desired unit 4. Perform the calculation Dimensional Analysis

Dimensional Analysis Convert 8.50 inches to cm. Given: 2.54 cm = 1 inch Dimensional Analysis Convert 8.00 m to inches Given: 2.54cm = 1 inch Composition of Matter

Matter is the physical material of the universe Matter is anything that has mass and occupies space

Properties are characteristics that allow us to recognize a particular type of matter Composition of Matter Atoms are the tiny building blocks of matter Atoms are unique to each element

Molecules are made up of two or more atoms that are joined in specific shapes Composition of Matter Elements are substances that cannot be decomposed into simpler substances Each element is made up of only one type of atom

Compounds are substances composed of two or more elements and contain two or more kinds of atoms Mixtures are combinations of two or more substances each substance retains its chemical identity

Composition of Matter Composition of Matter Chemical symbols are used to denote each element These are made up of one or two letters

The first letter is capitalized Derived mostly from the English names of the element but sometimes from foreign languages like Latin Composition of Matter Know the following elements:

Elements 1-20 Common Metals: Cr, Mn, Fe, Co, Ni, Cu, Zn, Ge, Ag, Pd, Cd, Cs, Ba, W, Pt, Hg, Pb, Sn, Au, U Other: Br, I, Rn Use your periodic table to help memorize these elements

Composition of Matter Molecular elements are those elements that are found as molecules in nature HOBrFINCl is used to remember the diatomic elements Those elements found in pairs

P and S are also molecular elements (P4, S8) Composition of Matter Law of Constant Composition Law of definite proportions

In a given compound, the relative numbers and kinds of atoms are constant Water (H2O) always has the same chemical formula and contains 2 hydrogens and 1 oxygen atom A pure compound should always have the same composition and properties, regardless of its source

Law of Multiple Proportions If two elements combine to form more than one compound the masses that combine are in the ratio of small whole numbers H2O 2gH combines with 16gO (1:8) H O 2gH combines with 32gO (1:16) 2 2