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Chapter 4 Chemical Foundations: Elements, Atoms, and Ions

Chemistry 101. Chapter 4 Chemical Foundations: Elements, Atoms, and Ions. Element: is a substance consists of identical atoms. Cannot be divided by chemical & physical methods. Carbon, Hydrogen, Oxygen 116 elements – 88 in nature. Millions of compound are composed of these 116 elements.

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Chapter 4 Chemical Foundations: Elements, Atoms, and Ions

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  1. Chemistry 101 Chapter 4 Chemical Foundations: Elements, Atoms, and Ions

  2. Element: is a substance consists of identical atoms. Cannot be divided by chemical & physical methods. Carbon, Hydrogen, Oxygen 116 elements – 88 in nature Millions of compound are composed of these 116 elements.

  3. H: 0.9% Ti: 0.6% Others: 0.9% Element abundance on earth O - O O2 Almost half of the mass is oxygen. 20% of atmosphere.

  4. Element Symbols The first letter or two first letters of element name: Oxygen O Silicon Si Carbon C Argon Ar Sometimes, two letters are not the first letters: Chlorine Cl Zinc Zn Sometimes, old names are used (Latin or Greek): Iron (Ferrum) Fe Lead (Plumbum) Pb

  5. Dalton’s Atomic theory • All matter is made up of very tiny, indivisible particles (atoms). • All atoms of a given element have the same chemical properties. • Compounds are made up of two or more different kinds of atoms. A compound has the same relative numbers and types of atoms. 2 H H2O or 2 : 1 = 1 O 1 C CO or = 1 : 1 O 1 Compound always has the same properties. Law of constant composition: Compound always has the same composition.

  6. Dalton’s Atomic theory 4. Atoms are not created or destroyed in chemical reactions. A chemical reaction changes the way the atoms are grouped together. Law of conservation of mass: C + O  CO

  7. Chemical Formula Compound Formula Identifies each element Ratios H2O Subscript (number of each atom) Subscript 1 is not written.

  8. H2O O H H Molecular formula Space-filling model Structural formula Ball-and-stick model H H C H H Molecular models CH4

  9. - - - - - - - Atom + (Source of  particles)

  10. Atom Nucleus: positive charge Atoms are neutral. Atomic mass unit (amu) = 1.6605×10-24 g mass of proton = 1 amu mass of neutron = 1 amu mass of electron = 5.48×10-4 amu

  11. Mass number (A) 12 C Atomic number (Z) 6 Atom Mass number: Protons + Neutrons Atomic number: Protons

  12. 14 12 13 C C C 6 6 6 Isotopes Isotopes: atoms with the same number of protons and electrons but different numbers of neutrons. different mass number 6 P + 6 N 6 P + 8 N 6 P + 7 N Carbon-12 Carbon-13 Carbon-14 Almost the same properties

  13. Atomic number 17 Cl Atomic weight 35.45 Atomic Weight Atomic weight: of an element is average of the masses (in amu) of its isotopes found on the Earth. Cl 37 35 Cl Cl 36.97 amu 34.97 amu 17 17 (75.77/100 × 34.97 amu) + (24.23/100 × 36.97 amu) = 35.45 amu

  14. main-group elements: 1A to 8A transition elements: 1B to 8B (3 – 12) inner transition elements: between B3 & B4 (58 to 71 and 90 to 103) Column: the same properties (main group) Row or Period (7 rows)

  15. Group 2A: Alkaline metals or earth metals Be-Mg-Ca-Sr-Ba-Ra reactive, solid metal Group 1A: Alkali metals Li-Na-K-Rb-Cs-Fr too reactive, unstable, solid metal 2Na + 2H2O 2NaOH + H2 2Na + Cl2 2NaCl

  16. Group 7A: Halogens F-Cl-Br-I-At reactive, colored, gas, nonmetal Group 8A: Noble gases He-Ne-Ar-Kr-Xe-Rn non reactive, stable, gas, nonmetal

  17. Classification of the elements metals nonmetals metalloids Metals: solid (except mercury), shiny, conductors of electricity and heat, ductile, malleable Nonmetals: solid, liquid or gas, do not conduct electricity (except graphite) Metalloids (Semimetals):between metals and nonmetals

  18. Monatomic Diatomic Polyatomic Ar He N2 O2 S8 Most elements are reactive and they cannot be found in nature in free form. They occur in compounds. Noble metals: unrecative metals Ag, Au, Pt Noble gases

  19. Allotropes Different forms of an element Carbon: Buckminsterfullerene & Nanotube Graphite Diamond

  20. Metallic properties More metallic More metallic

  21. Ions Total number of protons = Total number of electrons Atom is neutral (zero net charge). Ion: atom with any charges (positive or negative). Na → Na+ + e- Cation Cl + e-→ Cl- Anion Number of protons and neutrons in the nucleus remains unchanged.

  22. 11- 10- + e- 11+ 11+ Na+ Na Ions & Ionization Na + energy → Na+ + e- ion The size of the cation is smaller than the neutral atom.

  23. Ions & Ionization Cl + e-→ Cl- ion 17- 18- + e- 17+ 17+ Cl Cl-

  24. Ionization Energy Ionization energy: the energy required to remove the most loosely held electron from an atom in the gaseous state. Ionization energy Ionization energy

  25. Cation (Y+) Metals: lose 1, 2 or 3 e- Ions Nonmetals: gain 1, 2 or 3 e- Anion (X-) 1A 2A 8A 4A 5A 6A 7A 3A Transition elements

  26. Ionic Compounds • Ionic compounds are salts containing cations and anions. • The positive charge of the cation(s) must balance the negative charge of the anion(s) to form a neutral compound.

  27. Ionic Compounds Sometimes several cations balance one anion. Sometimes one cation needs several anions.

  28. Ionic Compounds Mg → Mg2+ + 2e- Cation Cl + e-→ Cl- Anion Mg2+ 2Cl- MgCl2

  29. Ionic Compounds Li → Li+ + e- Cation S + 2e-→ S2- Anion 2Li+ S2- Li2S Al → Al3+ + 3e- Cation O + 2e-→ O2- Anion 2Al3+ 3O2- Al2O3

  30. MEMORIZE

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