Representing Elements and Atoms

Atomic Number   The number of protons in an atom = atomic number   The atomic number identifies an atom as a specific element Ex. Atomic number = 6 means this atom has 6 protons in it Only carbon has 6 protons If a proton is somehow added to this atom, it is no longer carbon. It becomes nitrogen (atomic number 7), a completely different element

Mass Number  Mass number = # protons + # neutrons   If I know the mass number, how can I determine the number of neutrons in an atom? # neutrons = mass number – atomic number = total # P & N – # P # neutrons in Na = 23 – 11 = 12

Number of Subatomic Particles   So far, you have learned how to find the number of protons and neutrons in an atom.   Now, how do you find the number of electrons? In a neutral atom, positive charge = negative charge Therefore, # protons must = # electrons since they have equal but opposite charge

Number of Electrons   Ex. In a neutral carbon atom, how many electrons are there? Carbon’s atomic number is 6. Therefore, there are 6 protons. Since there are 6 protons, there must also be 6 electrons to balance the charge (+6) + (-6) = 0 6 protons x (+1) charge each 6 electrons x (-1) charge each Gives you an atom with no overall charge

Shorthand Notation for Elements   The same way it is easier to write 5678 instead of five thousand six hundred seventy-eight, we need a shortcut for atoms of elements   Each element has its own symbol. This is a universal ‘language’ for all scientists. Na  sodium K  potassium C  carbon

Shorthand Notation for Elements   The symbol is always a capital letter first Ar Ne B   In “Standard Atomic Notation”: Mass number goes at the top Atomic number goes below

Isotopes  Isotopes: Atoms with the same number of protons but a different number of neutrons.  Different varieties of the same element  2 common isotopes are Carbon-14 and Carbon-12.  Both isotopes are carbon because they each have 6 protons  Both isotopes are carbon because they each have 6 protons  They are different because C-14 has 8 neutrons and C-12 only has 6  While C-12 is the most abundant (common) isotope of carbon, both are called isotopes

Isotopes  Here is the isotopic notation for carbon 14.  From looking at the isotopic notation, you can determine the number of protons, neutrons and electrons for a given atom.  How many protons, neutrons and electrons? Protons- The atomic number is 6, therefore there are 6 protons Protons- The atomic number is 6, therefore there are 6 protons Electrons- If the atom is neutral, the number of protons = the number of electrons, therefore there are also 6 electrons. Electrons- If the atom is neutral, the number of protons = the number of electrons, therefore there are also 6 electrons. Neutrons- The mass number equals the number of protons + neutrons, therefore 14-6 leaves 8 neutrons. Neutrons- The mass number equals the number of protons + neutrons, therefore 14-6 leaves 8 neutrons.

Shorthand Notation for Elements   Your text book tries to simplify…   They have AM on the bottom and AN on the top Remember: Atomic number = a whole number (no decimal) Atomic mass = usually a decimal (an average of the # neutrons)   Write the standard atomic notation for Hydrogen Calcium Oxygen (Hint: Use your periodic table!)

Standard Atomic Notation   Homework: Learn the first 20 symbols Learn the first 20 element names in order (Atomic numbers 1-20) Spelling included!

Homework Element symbolElement name 1HHydrogen 2HeHelium 3LiLithium 4…… 5…… …etc……