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Atoms and Elements

REVIEW CHAPTERS 3, 5, 10 and 11. Atoms and Elements. A. Atoms make up all matter B. ~91 different naturally occurring elements Indivisble: The Atomic Theory A. Democritus (~400 BC) B. Dalton (early 1800's) 1. Each element is composed of tiny indestructible particles called atoms

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Atoms and Elements

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  1. REVIEW CHAPTERS 3, 5, 10 and 11 Atoms and Elements A. Atoms make up all matter B. ~91 different naturally occurring elements Indivisble: The Atomic Theory A. Democritus (~400 BC) B. Dalton (early 1800's) 1. Each element is composed of tiny indestructible particles called atoms 2. All atoms of a given element have the same mass and other properties that distinguish them from atoms of other elements 3. Atoms combine in simple, whole-number ratios to form compounds -Law of conservation of matter

  2. The Atomic Structure and Nucleus A. Positive and negative charges (Thompson)-plum pudding model B. Mostly empty space (Rutherford) C. Current nuclear theory of the atom 1. Most of the atom's mass and all of its positive charge is contained in the nucleus 2. Most of the atom is empty space with small fast moving electrons 3. Number of protons = number of electrons in neutral atoms The Properties of Protons, Neutrons, and Electrons -Atomic Number = Number of protons - Mass Number = # of Protons + # of neutrons A. Masses expressed in atomic mass units (amu) B. Protons and neutrons about 2,000 more massive than electrons C. Nature of electrical charge 1. Electrical charge is a fundamental property of protons and electrons 2. Species of opposite electric charge are attracted to each other 3. Species of the same electric charge repel each other 4. Species of opposite electric charge cancel to make a neutral atom

  3. Mass # 35 Cl 17 At. # Isotopes: When the Number of Neutrons Varies in an element A. Isotopes have the same chemical properties, but different masses B. Some isotopes are more prevalent than others C. Chemical symbol with mass number indicates which isotope D. Some elements have many isotopes, some very few Elements: Defined by Their Number of Protons A. Identity of atom comes from the number of protons B. Atomic number (Z) = number of protons C. Chemical symbol is a shorthand notation of chemical name 1. C = carbon = 6 protons 2. O = oxygen = 8 Ptrotons 3. Co = cobalt = 27 Protons Atomic Mass A. Value on periodic table represents average mass of all isotopes B. No chlorine atom weighs exactly 35.453 amu

  4. Looking for Patterns: The Periodic Law and the Periodic Table A. Mendeleev (1834 - 1907) B. Periodic law C. Metals (usually loose electrons to form cations) D. Nonmetals (usually gains electrons to form anions) E. Metalloids, also known as semiconductors F. Individual group names 1. Group 1 – alkali metals +1 ion only 2. Group 2 – alkali earth metals +2 ion only 3. Group 7 – halogens usually –1 ion 4. Group 8 – noble gases Periodic Trends: Ionization Energy, Atomic Size, and Metallic Character A. Atomic size 1. Decreases as you move to the right along a row (Period) 2. Increases as you go down a column (group) B. Ionization energy 1. Increases as you move to the right along a row (Period) 2. Decreases as you go down a column (group) C. Metallic Character Decreases as you move to your right along the period.

  5. Modern Model of Atom Light: Electromagnetic Radiation A. Light is not matter, it is pure energy B. A photon is a particle of light 1. Wavelength is distance between adjacent wave crests 2. Frequency is the number of cycles that pass a point per unit time The Electromagnetic Spectrum A. Gamma rays 1. High energy 2. Low wavelength B. X-rays C. Ultraviolet D. Visible 1. Very narrow band 2. Does not affect biological molecules E. Infrared F. Microwaves G. Radio waves Classical vs Quantum physics for matter and light

  6. The Bohr Model: Atoms with Orbits A. Electrons exist in quantized Circular orbits B. Electrons get excited to a higher energy level by absorbing energy C. Electrons emit light when relaxing from higher levels D. Absorbed and emitted light correspond to energy difference between states E. Higher the principal shell# higher is the energy of the electron (away from nucleus) The Quantum-Mechanical Model: Atoms with Orbitals A. Orbitals instead of Circular orbits B. Electrons do not move in predictable paths C. Probability maps-different shapes- called as ORBITALS Quantum-Mechanical Orbits A. Quantum numbers 1. Principal shell 2. Subshell: s (2e), p(6e), d( 10e), f(14e) B. Electronic configuration 1. Gives location of each electron in the atom 2. Li: 1s22s1 C. How do the electrons fill in the atom 1. Auf-Bau Principle, Hund’s rule 2. Electron spin-Pauli exclusion principle Filling order 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s-MEMORIZE

  7. Electron Configurations and the Periodic Table A. Valence electrons (outermost shell electrons with highest principal shell#) B. Core electrons C. Writing electronic configurations 1. Noble gas core 2. Locations of valence electrons 3. Highest n value is equal to row value 4. d electron group is equal to row number – 1 Compound Formation A. Valence electrons dictate chemical reactivity B. Elements in the same group have similar reactivity as they have SAME VALENCE ELCTRONIC CONFIGURATION C. Compound formation and Octet rule with Chapter 5 Periodic Trends: (once more!) A. Atomic size 1. Decreases as you move to the right along a row (period) 2. Increases as you go down a column (group) B. Valnce electrons – Increase as you move to your right and stay same down the group. C. Ionization energies and electronegativity both increase as one moves from left to right with in a period both decrease as one moves down a group D. Metallic character - Increase as you move to your right and slightly decreases as you down the group.

  8. Molecules and Compounds • Sugar and Salt • A Molecular View of Elements and Compounds • A. Atomic elements exist in nature as single atoms • B. Molecular elements exist as diatomic molecules, H2, N2, O2, F2, Cl2, Br2, I2 • Compounds held by covalent bonds • Molecular compounds formed between two or more nonmetals • Attractive forces maximum at bond position • - Sharing of electrons • A. Every sample of a compound has the same proportions of constituent elements • Representing Valence Electrons with Dots (LEWIS SYMBOLS) • A. Valence electrons in outermost shell electrons • B. Lewis Structure is simply chemical symbol + # valence electrons around it • C. Most atoms "want" eight electrons around them (octet rule) • D. Exception: duet rule for hydrogen and helium • E. A covalent bond is a shared pair of electrons to get an octet around each atom

  9. Covalent Lewis Structures: Electrons Shared A. Two bonded nonmetals share electrons such that both get an octet (duet) B. Both species get "credit" for all electrons in bond C. Two species can share two, four, or six electrons 1. Two electrons shared is a single bond 2. Four electrons shared is a double bond 3. Six electrons shared is a triple bond Writing Lewis Structures for Covalent Compounds A. Write the correct skeletal structure for the molecule B. Calculate the total number of valence electrons C. Distribute electrons among atoms giving each an octet (duet) D. If any atoms the lack an octet, form double or triple bonds as necessary E. Exception to the octet rule 1. Duet rule for hydrogen 2. Odd number of electrons 3. Boron usually has only six electrons about it 4. Some elements in the third row and beyond may have more than eight electrons around them.

  10. A. Ionic compounds formed between a metal and one or more nonmetals B. Groups of atoms are set off by parentheses, e.g. Mg(NO3)2 Writing Formulas for Ionic Compounds A. Ionic compounds always contain positive and negative ions B. Formula units form neutral species Electronegativity and Polarity: A. Electronegativity B. Bond dipoles C. Pure covalent bonds D. Polar and nonpolar bonds E. Ionic bonds

  11. THE SHAPES OF MOLECULES • Predicting the Shapes of Molecules (around central atom) • A. VSEPR Theory • 1. Electron groups repel each other • 2. Electron geometry • a. Linear • b. Trigonal planar • c. Tetrahedral • B. Predicting structures • 1. Draw the Lewis structure • 2. Count the number of electrons groups (Steric number) • 3. Determine the number of bonding groups and lone pairs 4. Determine molecular geometry • Polarity of molecules • Add up dipoles, if everything cancels, NON polar (m = 0) • Dipoles do not cancel out – Polar molecule ((m ≠ 0) • Lone pair on central atom usually causes molecules to be polar • Unsymmetrical molecule- POLAR

  12. MEMORIZE ELECTRON GROUPS AND MOLECULAR GEOMETRY

  13. Sample Questions for Second Test Which of these elements have the highest electronegativity? (a) Al (b) S (c) O (d) B Give the electronic configuration and outershell configuration (i.e. 4s24p1) of the following elements and state the number of valenceelectrons (i.e. 3). (DO NOT use the shorthand “noble gas” notation) Full ConfigurationValence config.Number of valence e- Na Draw the Lewis structure, give the geometry of the molecule, and state whether the molecule is polar (has a dipole) or nonpolar for the following: Lewis Structure GeometryPolarity 1. CO2

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