* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Chemistry 2: matter is made up of atoms
Survey
Document related concepts
X-ray fluorescence wikipedia , lookup
X-ray photoelectron spectroscopy wikipedia , lookup
Photoelectric effect wikipedia , lookup
Auger electron spectroscopy wikipedia , lookup
Electron scattering wikipedia , lookup
State of matter wikipedia , lookup
Rutherford backscattering spectrometry wikipedia , lookup
Atomic orbital wikipedia , lookup
Degenerate matter wikipedia , lookup
Chemical bond wikipedia , lookup
History of thermodynamics wikipedia , lookup
Transcript
Chemistry 2: Scientific Measurement • Quantitative measurements give results in a definite form, usually as numbers • Qualitative measurements give results in a descriptive nonnumeric form Accuracy and Precision • Accuracy is how close a measurement comes to the actual dimension or true value of whatever is measured • Precision is concerned with the reproducibility of the measurement Significant Figures in Measurements • The significant figures in a measurement include all the digits than can be known precisely plus a last digit that must be estimated. • 1. Every nonzero digit is significant. • 2. Zeros appearing between nonzero digits are significant. • 3. Zeros appearing in front of all nonzero digits are not significant. • 4. Zeros at the end of a number and to the right of a decimal point are significant. • 5. Use scientific notation whenever possible. The Metric System • • • • • • • • • • • Length Mass Time Electric current Temperature Amt of substance Light intensity Pressure Energy Force Capacitance meter kilogram second ampere kelvin mole candela pascal joule newton farad m kg s A K mol cd pa J N F Units of Length, meter • kilo • deci • centi • milli • micro • Nano • Pico k d c m m n p 1000 1/10 1/100 1/1000 103 10-1 10-2 10-3 10-6 10-9 10–12 Units of Volume, liter • A liter is the volume of a cube that is 10 cm on each edge (10cmx10cmx10cm=1000cm3=1 L Units of Mass, kilogram • A kilogram is the mass of 1 L of water at 4 oC. • A gram is defined as the mass of 1 cm3 of water at 4 oC. Density and Specific Gravity • Density is the ratio of the mass of an object to its volume. • Density = mass / volume • Specific gravity is a comparison of the density of a substance to the density of a reference substance, usually at the same temperature. • Specific gravity = density of substance (g/cm3) /density of water (g/cm3) Measuring Temperature • Temperature is the degree of hotness or coldness of an object. • Heat transfer occurs when two objects at different temperatures contact each other. • Swedish astronomer Anders Celsius (17011744)—the Celsius scale takes the freezing point of water as 0 oC and boiling point at 100 oC at one atmosphere pressure. • Scottish physicist Lord Kelvin (1824-1907)—the Kelvin scale, the freezing point of water is 273 K, and the boiling point is 373 K. • The zero point (0 K) on the Kelvin scale is absolute zero. It is –273 oC. Measuring Heat • English physicist James Joule (18181889) formulated heat conversion. • 1 J = 0.239 cal and 1 cal = 4.18 J • 1 calorie is the quantity of heat that raises the temperature of 1 g of pure water 1 oC. • 1 kcal = 1000 cal = 1 Cal. Specific Heat Capacity • The quantity of heat required to change an object’s temperature by exactly 1 oC is the heat capacity of that object. • The specific heat capacity, or simply the specific heat, of a substance is the quantity of heat required to raise the temperature of 1 g of the substance 1 oC. Matter is made up of atoms • Joseph Proust, in 1799, observed that water consists of 11% hydrogen and 89% oxygen: in a ratio of 1:8 by mass • Antoine Lavoisier, in 1774, discovered the law of conservation of matter • John Dalton in 1800s proposed the atomic theory Dalton’s Atomic Theory • 1. All matter is made up of atoms • 2. Atoms are indestructible and cannot be divided into smaller particles (not true anymore) • 3. All atoms of one element are exactly alike, but they are different from atoms of other elements The Methods of Science • Repeated observation give rise to hypothesis, which is tested by experiments • Repeated experiments either confirm the hypothesis or revise the hypothesis • After a hypothesis has been verified my other scientists, it becomes a theory • More experiments will give rise to a revised theory • When the theory is firmly established without exceptions, it becomes a law The Discovery of Atomic Structure • J.J. Thomson, in 1897, discovered the electron using the cathode-ray tube, and that electrons are negatively charged • Rutherford’s gold foil experiments showed that atoms have positively charged nuclei • Thomson’s atomic model: electrons embedded in a ball of positive charge • Nagaoka’s atomic model: electrons orbit around the positive nucleus like planets round the sun Atomic Numbers and Masses • Atomic number is the number of protons in the nucleus of an element • Mass number is the sum of protons and neutrons in the nucleus. It is the average of all isotopes of an element • Isotopes are different forms of an element having the same number of protons but different number of neutrons, hence their masses are different • Atomic mass, 1 u = 1/12 the mass of C-12 Common Particles of an Atom • Particle, symbol, charge, Z, mass in u • Proton p+ 1+ 1 1.01 • Neutron n0 0 1 1.01 • Electron e10 0.00055 Electrons in Motion • Niels Bohr proposed that electrons have energies to move round the nucleus • Now electrons are considered as particles and waves • Electrons move round the nucleus near the speed of light • Electrons cannot be accurately located, only the probability of finding it The electromagnetic spectrum • All forms of radiant energy can be placed in the electromagnetic spectrum, from radio waves, AM, FM, microwaves, infrared, visible spectrum, UV, X-rays, to gamma rays, which are very energetic and have very short wave-lengths Electron and Light • Hydrogen can be shown to consist of many energy levels, which are similar to the rungs on a ladder • The electron cloud model of an atom suggests that energy levels are concentric spherical regions of space around the nucleus • Electrons in the outermost energy level are called the valence electrons Lewis Dot Diagrams • A Lewis dot diagram illustrates valence electrons as dots around the chemical symbol of an element. Each dot represent one valence electron • Chemical changes only involve the outermost electrons of an element