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Honors ch 4.3.  An English scientist  Discovered each element contains a unique positive charge in the nucleus  The number of protons in the nucleus.

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Presentation on theme: "Honors ch 4.3.  An English scientist  Discovered each element contains a unique positive charge in the nucleus  The number of protons in the nucleus."— Presentation transcript:

1 Honors ch 4.3

2  An English scientist  Discovered each element contains a unique positive charge in the nucleus  The number of protons in the nucleus of an atom identifies the element – atomic number

3  Because all atoms are neutral, the number of protons and electrons in an atom must be equal  Atomic number = # protons = # electrons

4 ElementAtomic #ProtonsElectrons Pb

5 ElementAtomic #ProtonsElectrons Pb

6 ElementAtomic #ProtonsElectrons Pb82 O888 30

7 ElementAtomic #ProtonsElectrons Pb82 O888 Zn30

8 How many protons and electrons are in: a. radon b. magnesium  An atom of an element contains 66 electrons. What element is it?  An atom of an element contains 14 protons. What element is it?

9  Dalton was incorrect about atoms being indivisible and stating that all atoms of an element are identical. (#2 and #5)  All atoms of a particular element have the same number of protons and electrons but the number of neutrons in the nucleus can differ.  Isotopes – atoms with the same number of protons but different numbers of neutrons

10  All Isotopes of a specific element have the same chemical behavior (determined by electrons)  Isotopes are identified with a mass number Mass number = atomic # + # neutrons

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12  In nature most elements are found as a mixture of isotopes  Ex: copper – two types found naturally - 29 protons and 34 neutrons - 29 protons and 36 neutrons Cu – 63; Copper – 63, 63 Cu, Cu Cu – 65; Copper – 65, 65 Cu, Cu

13  Atoms are measured in amu (atomic mass units). (based on carbon -12)  1 amu is almost equal to 1 proton or neutron  Atomic mass – the weighted average mass of the isotopes of that element. Because isotopes have different masses, the weighted average mass is NOT a whole number.

14 ElementAtomic #Mass # Neon1022 Calcium2046 Oxygen817 Iron2657 Zinc3064 Mercury80204

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16  Calculate the atomic mass of unknown Element X. Identify the unknown element. IsotopeMass (amu)Percent Abundance 6X6X % 7X7X %

17 Boron has two naturally occurring isotopes: boron-10 (abundance =19.8%; mass = amu) and boron-11 (abundance = 80.2% and mass = amu). Calculate the atomic mass of boron.


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