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Assignment

Assignment. What is an atom? Write your thoughts and ideas in your journals. Ch. 3 – Atoms: The Building Blocks of Matter. An atom is the smallest particle of an element that retains its chemical properties Atom is Greek for indivisible What is an atom made up of? Nucleus

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Assignment

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  1. Assignment • What is an atom? • Write your thoughts and ideas in your journals.

  2. Ch. 3 – Atoms: The Building Blocks of Matter • An atom is the smallest particle of an element that retains its chemical properties • Atom is Greek for indivisible • What is an atom made up of? • Nucleus • Proton – positive charge • Neutron – neutral charge • Electron clouds (energy levels) • Electrons – negative charge

  3. Atomic Theory • 1700s most chemist accept the definition of an element as a substance that can’t be further broken down by ordinary chemical means • Accept that elements can be combined to form compounds that will differ in physical and chemical properties • Chemical reaction is the transformation of substance(s) into one or more new substances.

  4. Law of Conservation of Mass – states that mass is neither created nor destroyed during ordinary chemical reactions or physical change. • Law of Definite Proportions – a chemical compound contains the same elements in exactly the same proportions by mass regardless of the size of sample or source of the compound. • Law of Multiple Proportions – If two or more different compounds are composed of the same two elements, then the ratio of the masses of the second element combined with a certain mass of the 1st elements is always a ratio of small whole numbers.

  5. John Dalton • School teacher in 1808 developed the theory which have developed in laws of chemistry. • Modern Atomic Theory

  6. Atoms of different elements may combine to form chemical compounds. • In chemical reactions atoms are either combined, separated, or rearranged • Atoms cannot be created nor destroyed. • Each element can have more than 1 atom. • Ex. Cl2 • MASS # - ATOMIC # = NEUTRONS

  7. Atoms of the same element may have different masses. These are called isotopes. • Ex. Hydrogen has 3 isotopes  Protium, deuterium, tritium. • What does the atomic number tell you? • Number of protons in each atom of an element. • What does the mass number tell you? • Total number of protons and neutrons in the nucleus of an atom. • If an element has isotopes for that element they are called nuclides.

  8. An atomic mass unit is a standard unit used for comparison. • Carbon has exactly 12 atomic mass units (U) and is used as a standard for comparison. • Each element on the periodic table has an average atomic mass. • Why do you suppose it is an average? • Average atomic mass is the weighted average of the atomic masses of the naturally occurring isotopes of an element. • Ex. Cu  69.17% is Cu – 63; 30.83% is Cu – 65.

  9. Mole, Molar Mass, and Avogadro’s number all help describe an element. • CD ROM • Mole – Roughly the mass of a substance that is has 6.02 x 1023 particles (atoms or molecules). • All of the average atomic masses on the periodic table is equal to 1 mole (mol.). • Ex. B 10.81g = 1 mol. • Ex. Zn 65.39g = 1 mol.

  10. Avogadro’s number is 6.02 X 1023 particles. • The number of particles (atoms or molecules) in exactly one mole is always 6.02 X 1023. • Ex. B 10.81g = 6.02 X 1023. • Ex. Zn 65.39g = 6.02 X 1023. • Molar mass – the mass in grams of one mol. Of a pure substance. • Basically the average atomic mass in grams. • Ex. B 10.81g = 1 mol. = 6.02 X 1023. • Ex. Zn 65.39g = 1 mol. = 6.02 X 1023.

  11. The molar mass of all elements will always contain the same number of atoms, which is 6.02 X 1023. • Which atoms are heavier? • Do the heavier atoms have more atoms in one mole? • Pg. 90 • Sample Problems from pg. 82-85.

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