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Atomic Structure

Atomic Structure. Atom = the smallest particle of an element that retains the properties of that element. Law of Conservation of Mass. Matter cannot be created or destroyed . Law of Definite Proportions.

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Atomic Structure

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  1. Atomic Structure Atom = the smallest particle of an element that retains the properties of that element

  2. Law of Conservation of Mass • Matter cannot be created or destroyed

  3. Law of Definite Proportions • A chemical compound contains the same elements in exactly the same proportions by mass regardless of the size or source of the sample • H2O is water, all water is H2O, or it’s NOT water • H2O2 is hydrogen peroxide, NOT WATER

  4. The Law of Multiple Proportions • Copy this law into your notes and see sample exercise 2.1 on page 45 • Briefly describe how Dalton’s observation of this phenomenon contributed to his atomic theory

  5. 2 regions of the atom • Nucleus • Protons (p+) • Neutrons (n0) • Electron cloud • Electrons (e-) Protons, electrons, and neutrons are called subatomic particles

  6. Electrons Thomson’s Cathode Rays • e- have large charge:mass ratio • Mass of e- was determined by measuring charge and calculating mass based on ratio • Mass of e- = 9.109 x 10-31 Negligible and not counted in atomic mass calculations

  7. Atoms are electrically neutral • Negatively charged e- are balanced by positively charged particles (p+) • Charge of p+ = charge of e- • # p+ = #e- • n0 has NO charge

  8. Forces in Nucleus • + attracts – • + repels +, so how are the p+ in the nucleus held together? • When p+ are in close proximity to other p+ and n0, strong forces are created = nuclear forces • But a nucleus can only hold so many protons in proximity and remain stable

  9. Atomic Number and Mass Number • Atomic # = # p+ • #p+ = #e- • Mass number = #p+ + #n0 • Remember: mass of e- is negligible • The atomic number or # of p+ determines the atom’s identity (which element) • The atomic number for every element can be found in the Periodic Table Element builder

  10. Atomic # appears above symbol • Atomic mass appears below symbol • Why is it a decimal?

  11. Average Atomic Mass • The mass number on a PT is the average atomic mass • Isotopes = atoms of the same element that have different numbers of neutrons and therefore different atomic masses • A specific type of isotope is also called a nuclide • The average atomic mass is the average mass number of all the atoms of a given element including isotopes

  12. Nuclides of Hydrogen • Protium (99.9885% of H) = 1p+ • Deuterium (0.0115% of H) = 1p+ +1n0 • Tritium (negligible in nature, can be synthesized) is radioactive = 1p+ +2n0 How many e- do these isotopes have?

  13. Most isotopes/nuclides don’t have names….. • Isotopes are referred to by the element name and the mass number (#p+ + #n0) • Ex. Carbon • Carbon-14 (14 = 6p+ + 8n0) = radioactive • Carbon-12 (12 = 6p+ + 6n0) = most common • NOTICE: both types of carbon have same number of protons • What if the atom had 7 protons?

  14. Atomic mass and mass units • Metric unit for mass = gram • Too large to measure mass of something so small, so we use amu (atomic mass units) to measure atomic mass • Relative atomic mass = the mass of an atom expressed in relation to a defined standard (carbon-12 atom) • The carbon-12 atom has a relative mass of 12 amu, so 1 amu = 1/12 mass of C-12 atom

  15. Calculating average atomic mass • Depends on mass and relative abundance of isotopes • Avg. atomic mass = %A1m1 + %A2m2 + …..

  16. The mole • Mole = the amount of a substance that contains as many particles as there are atoms in exactly 12 g of C-12 • 1 mol of atoms = 6.022 x 1023 atoms Just like… • 1 dozen eggs = 12 eggs Avogadro’s number The mole is a counting unit, just like a dozen

  17. Molar Mass • Mole = the amount (mass) of a substance that contains Avogadro’s number (6.022 x 1023) of particles • The mass of 1 mole of a substance = molar mass (found under symbol for each element in PT) Molar mass for neon = 20.18 g/mol

  18. Chemical Bonding • In order to become more stable, many atoms form bonds with other atoms • Covalent bonds result from • Ionic bonds result from

  19. Energy Levels • e- are located outside the nucleus in energy levels • The innermost energy level can hold a maximum of 2 e- and the outermost energy level can hold a maximum of 8 e- • Atoms with a full outer energy level or 8 valence e- is stable and generally will not react or combine with other atoms • These atoms occur in the inert (Noble) gases of group 18 on the Periodic Table

  20. Ions • Ions are atoms that are not neutral • + ions = cations • - ions = anions What happens to an atom to give it electrical charge?

  21. The Periodic Table • Shows all known elements • Arranged in a systematic way based on properties of elements • Group/family = column • Period = row

  22. Metals • Found on the left side • Typically form cations • Properties • Luster • Malleability • Ductility • Conductivity Alkali metals, group 1 Alkaline earth metals, group 2 Transition metals, group 3-12 Lanthanides Actinides

  23. Nonmetals • Found on far right of PT • Either form anions or bond covalently • Properties • Varied • Poor conductors Halogens, group 17 Noble gases, group 18

  24. Metalloids • Intermediate btw metals and nonmetals (step ladder)

  25. Groups • The elements of each group have similar properties in relation to bonding, i.e. they form ions with the same electrical charge • Alkali metals from +1 ions • Alkaline earth metals form +2 ions • Halogens form -1 ions • Transition metals are more varied and some single elements can form several ions with different charges

  26. Naming Compounds • Inorganic binary compounds • Cation named first, anion second • Cations take name from element • Anions take name from element with suffix –ide added • NaCl = sodium chloride • KI = • CaS = • Li3N = • CsBr = • MgO =

  27. Type II binary ionic compounds • Formed when the metal (transition metals) can form more than one type of cation. • e.g. CuCl = copper (I) chloride • CuCl2 • Fe2O3 • FeO • PbCl2 • PbCl4 See table 2.4

  28. Ionic Compounds with Polyatomic Ions • See table 2.5 for some common polyatomic ions • There is a list on the website of the polyatomic ions that you should know PRINT IT OUT AND MEMORIZE THEM TONIGHT • Name • Formula • Charge

  29. Oxyanions • Polyatomic ions with different numbers of O atoms • e.g. NO2, NO3, SO3, SO4, et. al.

  30. Binary Covalent Compounds

  31. Acids

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