CH.1 Matter & Measurements

Transcription

1 CH.1 Matter & Measurements Chemistry- the study of matter and its behavior and properties. Matter- anything with mass and takes up space. If you can find it on the periodic table its matter. Atom- Building blocks of matter Substance- has distinct properties and a composition that does not vary. Element- an atom with a unique make up, substance that cannot be decomposed into simpler substances. Compound- made of two or more different kinds of elements, substance that can be decomposed into simpler substances. 4 CLASSIFICATIONS OF MATTER: States of Matter: Solid-ice Liquid-water Gas- water vapor Classification of Mater Based on Composition: Matter Uniform Throughout No Heterogeneous Mixture Yes Homogeneous Mixture Variable Composition No Pure Substance Yes Homogeneous Mixture More Than 1 Atom No Element Yes Compound/Molecule EX: H2O (compound) Mixtures- exhibit properties of the substances that make them up. Heterogeneous- mixtures that vary in composition throughout a sample. Homogeneous- mixtures have the same composition throughout a sample. AKA: solution. 1. Law of Constant Composition (Law of Definite Proportions) water is always H2O, and H2O is always water Compounds have a definite composition, which means that every compound has a

2 set number of atoms of each element in the compound, and the number is the same in every sample. Types of Properties: 1. Physical properties- observed without changing the substance into another substance EX: boiling point, density, mass, volume 2. Chemical properties- only observed when substance is being changed into another substance EX: flammability, corrosiveness, reactivity with acid 3. Physical changes- changes in matter that don t change the composition EX: change in state, temperature, volume 4. Chemical changes- results in a new substance, breaks or makes bonds EX: combustion, oxidation, decomposition 5. Intensive- independent of amount EX: density, boiling point, color 6. Extensive- dependent on amount of substance present EX: mass, volume, energy Separating Mixtures: Mixtures can be separated based on physical properties of the components of the mixture. Some methods used are: Filtration- separate solid from liquid/solution Distillation- uses difference in boiling point of the substance to separate a homogeneous mixture into its components. Chromatography- technique that separates substance based on their differences in the ability to adhere to solid surfaces. Units of Measurements- SI Units The base units used in the metric system: Mass: gram (g) Length: meter (m) Time: second (s or sec)

3 Temperature: degrees Celsius ( o C) or Kelvins (K) Amount of a substance: mole (mol) Volume: cubic centimeter (cc or cm 3 ) or liter (l) Metric System Prefixes: Temperature- how hot or cold an object is, used to determine the flow of heat. F=1.8C+32 K=C Density- physical property derived from mass and volume D=m/V (units: g/ml, g/cm 3 ) Exact numbers- are counted or given by definitions (ex: 12= 1 dozen) Inexact numbers/ measured numbers- depend on how they are determined Instruments have limitations. Accuracy- how close to the truth Precision- how close to other answers Significant Figures- refers to the digits that were measured. When rounding calculated numbers, do not overstate the accuracy of the answer.

4 RULES: 1. All nonzero digits are significant. 2. Zeroes between two significant figures are themselves significant. 3. Zeroes at the beginning of a number are never significant. 4. Zeroes at the end of a number are significant if a decimal point is written in the number. When addition or subtraction is performed, answers are rounded to the least significant decimal place. When multiplication or division is performed, answers are rounded to the number of digits that corresponds to the least number of significant figures in any of the numbers used in the calculation. We use dimensional analysis to convert one quantity to another. Most commonly, dimensional analysis utilizes conversion factors (e.g., 1 in. = 2.54 cm).

5 CH. 2 Atoms, Molecules, Ions Law of Conservation of Mass The total mass of substances present at the end of a chemical process is the same as the mass of substances present before the process took place. H2 + O2 H2O 4(1.01 g) + 2(16.00) 2(18.02) Law of Multiple Proportions If two elements, A and B, form more than one compound, the masses of B that combine with a given mass of A are in the ratio of small whole numbers. H2O not H4O2 When two or more compounds exist from the same elements, they can not have the same relative number of atoms. CO and CO2

6 Atomic Mass Atoms have extremely small masses. The heaviest known atoms have a mass of approximately g. A mass scale on the atomic level is used, where an atomic mass unit (amu) is the base unit. 1 amu = g Elements are represented by a one or two letter symbol. This is the symbol for carbon. All atoms of the same element have the same number of protons, which is called the atomic number, Z. It is written as a subscript BEFORE the symbol. The mass number is the total number of protons and neutrons in the nucleus of an atom. It is written as a superscript BEFORE the symbol. Isotopes are atoms of the same element with different masses. Isotopes have different numbers of neutrons, but the same number of protons. Atomic Weight Because in the real world we use large amounts of atoms and molecules, we use average masses in calculations. An average mass is found using all isotopes of an element weighted by their relative abundances. This is the element s atomic weight. Atomic Weight = Ʃ [(isotope mass) (fractional natural abundance)]. Note: the sum is for ALL isotopes of an element.

7 Periodicity-When one looks at the chemical properties of elements, one notices a repeating pattern of reactivities. Groups Known by their names: Metals are on the left side of the periodic table. Some properties of metals include shiny luster. conducting heat and electricity. solidity (except mercury). Nonmetals are on the right side of the periodic table (with the exception of H).