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GEN CHEM - Notes on general chemistry
General Chemistry I (CH 7)
Ateneo de Manila University
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MODULE 1
Chemistry is the study of Matter Matter - Anything that occupies space and has mass Mass - Measure of the amount of matter that an object contains Chemistry and Its Methods 1) Hypothesis: A tentative explanation or prediction based on experimental observations 2) Law: A concise verbal or mathematical statement of a behavior or a relation that seems always to be the same under the same conditions. 3) Theory: a well-tested, unifying principle that explains a body of facts and the laws based on them. It is capable of suggesting new hypotheses that can be tested experimentally Qualitative Observations - No numbers involved - Color, appearance, statements like “large” or “small” - Stating that something is hot or cold without specifying a temperature - Identifying something by smell - No measurements Quantitative Observations - A quantity or attribute that is measurable is specified - Numbers with units are expressed from measurements - Dimensions are given such as mass, time, distance, volume, density, temperature, color specified as a wavelength etc... Goals of Science: Prediction, Control, Understanding, & Explaining Dilemmas and Integrity in Science - Experimental results should be reproducible - Furthermore, these results should be reported in the scientific literature in sufficient detail so that they can be used or reproduced by others - Conclusions should be reasonable and unbiased - Credit should be given where it is due Sustainability and Green Chemistry - Prevent waste - Synthetic methods should maximize materials - Chemical synthesis should reduce toxicity - Energy requirements should be minimized - Raw materials should be renewable and practical - Chemical products should not persist in the environment - Substances should be chosen to minimize risks States of Matter 1) Solid: Definite Shape, Definite Volume, Lowest Kinetic Energy 2) Liquid: Indefinite Shape, Definite Volume, Intermediate Kinetic Energy 3) Gas: Indefinite Shape, Indefinite Volume, Highest Kinetic Energy *Gas can be compressed so it is the densest phase of matter
Classifying Matter
Mixtures: Homogeneous and Heterogeneous 1) Homogeneous mixture – consists of two or more substances in the same phase. No amount of optical magnification will reveal a homogeneous mixture to have differe nt properties in different regions. (Uniform Composition) 2) Heterogeneous mixture – Its components are easily visually distinguishable. (Nonuniform Composition) - When separated, the components of both types of mixtures yields pure substances. - Mixtures may be separated by physical properties
Physical Property Means of Separation
Density Decantation, Centrifugation
Boiling Point Distillation
State of Matter Filtration
Intermolecular Forces Chromatography
Vapor Pressure Evaporation
Magnetism Magnets
Solubility Filtration
Pure Substances - A pure substance has well defined physical and chemical properties. - Pure substances can be classified as elements or compounds. - Compounds can be further reduced into two or more elements. - Elements consist of only one type of atom. They cannot be decomposed or further simplified by ordinary means Element – Cannot be converted to a simpler form by a chemical reaction. (sodium and helium) Compound – Combination of two or more elements in a definite, reproducible way (water-H2O) *Kinetic energy of a substance increases with heat Chemical Compounds - composed of two or more atoms - All compounds are made up of molecules or ions. - A molecule is the smallest unit of a compound that retains its chemical characteristics. - Ionic compounds are described by a “formula unit” - Molecules are described by a “molecular formula.” Physical Properties - Characteristics that can be evaluated without changing the composition of the material - Color, Odor, Density, Melting point, Thermal conductivity, Volume, Hardness, State
MODULE 2
Subatomic Particles - Atoms composed of smaller subatomic particles - Charged (+ or -) - Uncharged (neutral) - Electrical nature of the atom was crucial to discovering its subatomic structure Law of Electrostatic Attraction - Like charges repel - Unlike charges attract Atomic Composition - The atom is mostly empty space - Protons and neutrons in the nucleus - The number of electrons is equal to the number of protons - Electrons in space around the nucleus - Extremely small - one teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water Protons - Positive electrical charge - Mass = 1 x 10-24 g - Mass = 1 atomic mass units (u) Electrons - Negative electrical charge - Relative mass = 0 u Neutrons - No electrical charge - Mass = 1 u One proton or neutron has a mass of 1 amu (Atomic Mass Unit) a.k. “Dalton” or u Atomic Structure Atoms are neutral (numbers of protons and electrons must be equal) Atomic Mass = p + n - Don’t have to worry about mass of e- since they have such a small mass - Numbers of neutrons are determined from atomic mass Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z
Atomic Weight - The atomic mass of one atom of an element is relative to one atom of another - Example: an O atom has approximately 16 times more mass than an H atom. - The standard is based upon the carbon-12 isotope - The mass of one C-12 atom is 1 x 10-23 g - The atomic mass of a C-12 atom is defined as exactly 12 u. - Therefore: 1 u = (the mass of one C-12 atom ÷ 12) = 1 x 10-24 g Mass Number, A - A = mass number = # protons + # neutrons - The following notation is often used
- The subscript Z is optional because the elemental symbol tells us what the atomic number must be
Carbon - A C-12 atom has 6 protons and 6 neutrons - Carbon-12 has a mass # of 12 u - Carbon-13 has a mass # of 13 u (6 + 7) and so on Fluorine; symbol = F - atomic number = 9 (this is the number of protons in the nucleus) - number of e = 9 (same as the number of protons for a neutral atom) - mass number = 19 - atomic weight from the periodic table = 18. - mass number = p + n - neutrons = 19 – 9 = 10 Isotopes
- Elements with different number of neutrons
- Existence of isotopes means all atoms of an element are not exactly the same all atoms of the same element have the same number of protons in the nucleus atoms of the same element can have different numbers of neutrons in the nucleus
- Isotopes have the same Z but different total number of nucleons (A) Mass Spectrometer
- The masses of isotopes and their abundances are determined experimentally by mass spectrometry
Isotope Abundance
The mass spectrometer gives information on the mass and relative abundance of each elementʼs isotopes.
Each isotope is represented by a Relative Abundance Hydrogen Isotopes
Lanthanide and Actinide series Periodic Table Features
Compounds and Molecules COMPOUNDS are a combination of 2 or more elements in definite ratios by mass The character of each element is lost when forming a compound. MOLECULES are the smallest unit of a compound that retains the characteristics of the compound (non-metal combined with a non-metal).
Molecular Models
Chemical Equations Word description - methane reacts with oxygen to yield carbon dioxide and water Symbolic representation of a chemical reaction
Naming Molecular Compounds Non-metals Combining
Naming Monatomic Ions Cation - name of the element followed by ion - Na+ sodium ion Anion - name of the element with an ide ending - Cl– chloride ion Metal Ions Names
- Main group elements
- All metal cations are named after their representative elements followed by the word “ion.”
By losing or gaining electrons, an atom has the same number of electrons as the nearest Noble gas atom. Polyatomic Ions - A special class of ions where a group of atoms tends to stay together-an ion that contains atoms covalently bound together - Polyatomic anions are groups of atoms (molecules) with a net charge.
Formulas of ionic compounds - Metal cation combining with nonmetal anion - Ionic compounds are neutral - net charge is zero - amount of +charge = amount of –charge - Ion charge of main group (1A-7A) elements (representative elements) is predictable - 1A-3A lose e- cations - 5A-7A gain e- anions Transition Metal Cations - These elements may have more than one charge states. - Oxidation Number (charge) is found from the formula.
Writing Chemical Formulas Given Individual Ions - Use crossover rule to make sure that the overall charge is ZERO - This applies to monatomic ions as well as polyatomic ions... polyatomic use of a parenthesis as needed
Electrostatic Forces
The Force depends directly on the charges on the ions and inversely on the distance between them
The oppositely charged ions in ionic compounds are attracted to one another by ELECTROSTATIC FORCES
These forces are governed by COULOMBʼS LAW
The bond distance in an ionic compound is measured as a function of the sum of the individual ionic radii Effect of Coulomb’s Law
MgO with the greater charge and smaller bond distance has the higher melting point Mole
Hydrates - A hydrate is a substance composed of an inorganic salt and physically bound water - n = is the ratio of moles of water to 1 mole of the salt
Naming Hydrates - Salt name + prefix hydrate - prefix: mono, di, tri, etc...
Heating Hydrates - When a hydrate is heated, the water is liberated - For every one mole of hydrate, n moles (in this case 2) of water are liberated. - After heating, any mass that remains is due to the salt residue. - Therefore, any mass loss in heating is due to the water loss.
Hydrate Formulas - From the mass of the water lost, one can find the mols of water associated with the hydrate - Knowing the mass and chemical identity of the anhydrous salt... - One can determine the mols of the anhydrous salt. - The ratio of moles of water to mols of salt (n) is found by
MODULE 3
Atomic Structure - A model describing the structure of an atom. - When Atoms react it is the ELECTRONS that react - Much of our understanding of ELECTRONS comes from Analysis of the Absorption or Emission of Light Electromagnetic Radiation ● Atoms gain energy and they become excited ● Added energy is absorbed by electrons and then released in the form of“ Electromagnetic Radiation” ● energy traveling through space ● c = v𝜆 c = speed of light (2×10 8 ms-1) 𝜆 = wavelength (lambda typically nm) - Radio waves - m - Visible light - nm (10-9 m) v = frequency (nu s-1 or a hertz (Hz) ● Consists of oscillating electric and magnetic fields traveling through space ● Travel at the same rate-----speed of light in a vacuum ● Aka Light ● Composed of two orthogonal vectors: An electric wave and a magnetic wave
● The intensity of light is a function of the wave’s amplitude ● A point of zero amplitude is called a node ● Light is characterized by its wavelength and frequency ● The visible region of the electromagnetic spectrum is only a small portion of the entire spectrum Quantization of Energy ● Max Planck (1858-1947) (1918 Nobel Prize) proposed that light waves existed as discrete packets of energy, quanta in order to account for the prediction that an ideal black body at thermal equilibrium will emit radiation with infinite power. ● According to classical physics, the intensity of emitted light approaches infinity as the wavelength of the light approaches zero ● Packet of energy ● Energy = hv (h = 6 x 10-34 J s) ● Energy is restricted
E = hv, E = 2hv, E = 3hv,...
Energy is quantized ● Since hv is small, macroscopic level energy appears to be continuous. ● An object can gain or lose energy by absorbing or emitting radiant energy in QUANTA ● A quanta of energy is the smallest unit of energy that may be exchanged between oscillators or emitted as radiation. It is too small to be observed in the classical world in which we live. ● Energy of radiation is proportional to frequency Planck’s Law ● E = hv and v = c/𝜆
as electrons go from higher to lower energy, light is emitted ● Excited atoms emit light of only certain wavelengths. ● The wavelengths of emitted light are unique to each individual element Atomic Spectra and Niels Bohr ● One view of atomic structure in early 20th century was that an electron (e-) traveled about the nucleus in an orbit
- Any orbit should be possible and so is any energy
- But a charged particle moving in an electric field should emit energy.
- End result should be destruction! ● Bohr asserted that line spectra of elements indicated that the electrons were + ● Bohr asserted that line spectra of elements indicated that the electrons were confined to specific energy states called orbits
● The lines (colors) corresponded to “jumps” or transitions between the levels.
● Bohr said classical view is wrong. ● Need a new theory—now called QUANTUM or WAVE MECHANICS ● e- can only exist in certain discrete orbits—called stationary states. ● e- is restricted to QUANTIZED energy states. ● Energy of state = -c/n 2 ● Where n = quantum no. = 1, 2, 3, 4, ....
● Line Spectra of H, Hg, and Ne
Bohr Model ● Line Spectra of H, Hg, and Ne ● E is negative (-) for all values of n - Lower (more -) values — more stable ● Lowest E for n = 1 — most stable ● Zero (0) for n = ∞ Line Spectrum of Hydrogen
Energy Transitions ● ground state - lowest energy level (n =1) ● excited state - higher energy level than the ground state (n >1) ● E = 0; electron completely separated from H nucleus (n = ∞) The Balmer Equation ● Mathematical relationship among observed frequencies.
Bohr Model - Summary ● Successes - describes the line spectra of the hydrogen atom ● Limitations - only works for 1-electron systems (H, He+) ● Bohr - 1929 Nobel Prize ● “If light can be viewed in terms of both wave and particle properties, why cant particles of matter, such as electrons, be treated the same way?” DeBroglie ● Matter has wave properties
● 1 J = 1 kg m 2 s- ● h = 6 × 10-34 J s Planck’s constant ● m = mass ● v = velocity Wavelength of a Golf Ball ● 82 g, v = 255 km/hr (150 mph) ● 𝜆 = 1 × 10-34 m ● big particle; very short wavelength Wavelength of an Electron ● 9 × 10-28 g, v = 3 × 10 7 m/s ● 𝜆 = 2 × 10-11 m ● small particle, longer wavelength Wave or Quantum Mechanics ● Taking on the ideas of Bohr, de Broglie and Heisenberg, Irwin Schrödinger proposed that matter can be described as a wave
● In this theory, the electron is treated as both a wave and a particle. ● An electron is described by a Wave Function “Ѱ“ that completely defines a system of matter. Quantum Mechanics ● e- has only certain allowed energies
- sound tube demo ● results presented
- from mathematical relationship of Schroedinger (Nobel Prize, 1932)
- wave function Ѱ - no physical meaning
- Ѱ 2 - probably of finding an electron in a region in space (orbital)
From the book in search of Shrodinger’s cat ● If it were ever possible to know the position and velocity of every particle in the universe, then it would be possible to predict with utter precision the future of every particle and therefore the future of the universe. Uncertainty principle ● Heisenberg (1932 Nobel Prize) ● for an electron, cannot know simultaneously both - Position - momentum ● observation affects behavior - Mouse - flashlight analogy - stick in stream analog Orbitals ● The solutions to the Schrödinger equation yields the probability in 3-dimensons for the likelihood of finding an electron about the nucleus. ● It is these probability functions that give rise to the familiar hydrogen-like orbitals that electrons occupy ● The region in which an electron can be found within an atom Quantum Numbers & Electron Orbitals ● Quantum Numbers are terms that arise from the mathematics of the Schrödinger equation. They describe location of an electron in a particular orbital much like an address. ● Each electron in an orbital has its own set of three quantum numbers 1) Principal Quantum Number n = 1, 2, 3, 4.. to infinity 2) Azimuthal or Angular Quantum Number “l” = 0, 1, 2, 3.. to a maximum of n – 1 (sub-shell) 3) Magnetic Quantum Number “ml” ml may take on the value an integer from -l to +l (individual orbitals)
GEN CHEM - Notes on general chemistry
Course: General Chemistry I (CH 7)
University: Ateneo de Manila University
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