Chapter 3 Sec 3 Counting Atoms All atoms are composed of the same three particles, but not all atoms are the same. Atomic number – of an element is the number of protons in the nucleus. The number of protons makes the element that specific element. As a NOTE elements have the same number of electrons as the number of protons. Atomic mass – of an element is number of protons and neutrons combined in the nucleus.

Isotopes Isotopes of elements have the same number of protons but a different number of neutrons in the nucleus. Isotopes have different masses because of the additional neutrons but they don’t differ significantly is their chemical properties. Nuclide is a general term for a specific isotope of an element

isotopes To find the number of neutrons any element has: Atomic mass – atomic number = number of neutrons for that element Hydrogen - 1 atomic mass – atomic number = # neutrons 1 - 1 = 0 neutrons But hydrogen has 2 isotopes Protium – has 1 p , 1 e and 0 n (hydrogen – 1 ) Deuterium – has 1 p , 1 e and 1 n (hydrogen – 2 ) Tritium – has 1 p , 1 e, and 2 n (hydrogen – 3 )

Elements nuclear symbol The nuclear symbol is a way to write elements information Hydrogen – 1 𝑎𝑡𝑜𝑚𝑖𝑐 𝑚𝑎𝑠𝑠 𝑎𝑡𝑜𝑚𝑖𝑐 𝑛𝑢𝑚𝑏𝑒𝑟 atomic symbol 1 1 H Hydrogen – 2 Carbon 12 6 C Helium 4 2 He 2 1 H

Hyphen notation Element name – element’s atomic mass (rounded to whole number) Hydrogen – 1 Hydrogen – 2 Helium – 3 Helium - 4

Atomic mass units Atomic mass units (amu) Atomic mass unit ( amu) = the atomic mass of an element Helium has an atomic mass of 4.005 so helium has 4.0 amu Magnesium has an atomic mass of 24.31 so magnesium has 24.31 amu

Calculating Average atomic mass Since elements and their isotopes are found in the same area, to calculate the average atomic mass we have to include the percent of the isotope and well as the percent of the element: %natural atomic mass occurance Copper – 63 69.15 62.929601 Copper – 65 30.85 64.927794 69.15 x 62.929601 + 30.85 x 64.927794 = 63.546 amu

The MOLE Mole is a term we use for the number 6.022 1314 x 1023 1 mole is 602 billion trillion Abbreviated mol and 6.02 x 1023 1 mole = 6.02 x 1023 Just like dozen is used for the number 12 We could have 1 mole of anything Soda cans 1 mole would equal 602 billion trillion soda cans Pop corn kernels 1 mole would equal 602 billion trillion popcorn kernels

The Mole To give you a better idea of how many 6.02 x 1023 popcorn kernels would be: 602 billion trillion popcorn kernels would cover the United States to a depth of over 9 miles 602 billion trillion soda cans would cover the Earth to a depth Depth of 200 miles

The Mole 6.02 x 1023 is often referred to as Avogadros numbers. Amedeo Avogadro, discovered while working with gases that no matter what the gas was there was the same number of molecules present.