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Honors chemistry section 3.3

Honors chemistry section 3.3. Counting Atoms. Atoms. Atoms Atomic Number (z) – Number of Protons In neutral atom – Number of Electrons Mass Number = Protons + Neutrons Isotopes – Same Element/Different Number of Neutrons – still have same chemical behavior. Isotopic Notation. Two Forms

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Honors chemistry section 3.3

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  1. Honors chemistrysection 3.3 Counting Atoms

  2. Atoms • Atoms • Atomic Number (z) – Number of Protons • In neutral atom – Number of Electrons • Mass Number = Protons + Neutrons • Isotopes – Same Element/Different Number of Neutrons – still have same chemical behavior

  3. Isotopic Notation • Two Forms • Hyphen notation • Element’s name – Mass Number • Carbon – 14 • Symbol Notation • Ex. • Ex.

  4. Practice • How many protons, neutrons and electrons are in Carbon -13? • What is the symbol notation for Oxygen-16?

  5. Relative Mass • Standard is Carbon-12 – mass is 12.00 atomic mass units (amu) • Hydrogen – 1 is 1.007825 amu • Oxygen – 16 is 15.994915 amu. • Used for the masses of single atoms

  6. Average Atomic Mass • Most Elements exist as a mixture of isotopes. • Separate isotopes and find abundance with a mass spectrometer

  7. Average Atomic Mass • Used in most calculations • Found on the Periodic Table • Calculated by:

  8. Example Problem • Note: • Abundance must be a decimal for the calculations • Always use atomic mass to 2 decimal places!!!!

  9. Key Terms for Atoms in a Sample • Mole – the amount of substance which contains the same number of particles as in 12 g of Carbon – 12. • Avogadro’s Number – 6.022 x 1023 particles in a mole (Just a number like dozen, gaggle, gross or ream • Molar mass – the mass of one mole of a pure substance – grams/mole. Numerically equivalent to the atomic mass but in grams rather than amu.

  10. Solving Mole Problems molarmass (grams) 1 mole 1 mole 6.022 x 10^23particles Grams Moles Particles (Atoms, molecules or formula units)

  11. Practice Problems • What is the mass in grams of 3.6 moles of C? • How many moles of Cu are in 3.22 g of Cu?

  12. Practice Problems (cont.) • How many moles of C are in 2.25 x 1022 C atoms? • How many moles of O are in 2,000,000 atoms of O?

  13. Practice Problems (cont.) • What is the mass in grams of 5.0 x 109 atoms of Ne? • How many atoms of C are in 0.020 g of C?

  14. Practice Problems (cont.) • How many grams of Ag contain the same number of atoms as 10.0 g of B?

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