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2 Atoms Molecules & Ions

# 2 Atoms Molecules & Ions - Chapter 2 Atoms Molecules...

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1 Atoms, Molecules, and Ions Chapter 2 2 S t r u c t u r e o f t h e a t o m According to Dalton’s theory, an atom is the basic unit of an element that can enter into chemical combination A t o m Nucleus Electrons (-1) Protons (+1) Neutrons Number of protons = number of electrons. An atom has n o net electrical charge

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2 How to represent an element? X A Z symbol of the element mass number atomic number Atomic Number, Mass Number and Isotopes Atomic number Z: number of protons in the nucleus Mass number A: the sum of the number of protons and neutrons 4 What is the number of protons, neutrons and electrons for the fluorine atom? F 19 9 The mass of an electron is so small we ignore it. Example: Z= number of protons =9 = number of electrons A= mass number = protons + neutrons = 19 neutrons = 19 - 9 = 10
3 Atomic Number, Mass Number and Isotopes (cont) Definition : Two Isotopes are two atoms that have the same atomic number (Z) but different mass numbers (A). E x a m p l e : Hydrogen has three isotopes H 1 1 1 2 1 3 H H Hydrogen Deuterium Tritium (0 neutrons) (1 neutron) (2 neutrons) 6 Example: What is the number of protons, neutrons and electrons for the isotopes of carbon below? 11 14 6 6 C C Atomic Number, Mass Number and Isotopes protons electrons neutrons 6 6 5 11-6= 6 6 8 14-6=

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4 Average Mass E x a m p l e : Carbon is naturally composed of 98.93% 12 C and 1.07% 13 C Averare atomic weight =(0.9893)(12 amu) + (0.0107)(13.00335)=12.01amu Atomic weight of the elements are listed in the periodic table 1 amu=1.66054 x 10 -24 g
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2 Atoms Molecules & Ions - Chapter 2 Atoms Molecules...

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