Atomic Number & Atomic Mass

The periodic table includes each element’s: name atomic number symbol atomic mass Carbon 6 C 12.011

Atomic Number The atomic number is the number of protons an element has. The periodic table lists elements by their atomic number (the whole number) The number of protons is the same as the number of electrons. The atomic number NEVER changes

Atomic Number Give name and symbol for…the element that has the atomic number 2 10 9 7 4

Atomic Mass Atomic mass is the weighted average of all the masses of all the isotopes for a particular element so it has a decimal value Atomic mass is given (in decimal form) for each element on the periodic table (round to the nearest whole number) … What is the atomic mass for carbon?

What is the atomic number? 6 How many protons? 6 How many electrons? 6 Carbon 6 C 12.011 How many protons? 6 How many electrons? 6 What is the atomic mass? 12 How many neutrons? 6

How can I write this? Write the element symbol C Write in the Atomic Mass (round to nearest whole #) Write in the # of protons below the atomic mass 12 6

Isotopes Elements that are chemically identical but have different mass numbers Number of protons atom has will never change An isotope is the same element but atomic mass is different because different number of neutrons

Example C carbon has 6 protons Atomic Mass # → 11 = 6 + 5 Atomic # → 6 if you know this carbon isotope has 5 neutrons Atomic Mass = # of protons + # of neutrons = 6 + 5 = 11 Atomic Mass # → 11 C Atomic # → 6

Write isotope symbols for: Li with 2 neutrons Li with 3 neutrons Li with 4 neutrons C with 6 neutrons C with 7 neutrons F with 7 neutrons

Conversely, if you know the isotope symbol, you can use the mass number to find out the number of neutrons the isotope has. e.g. Atomic Mass # = #p + #n So… #n = Atomic mass # - #p #n = 14 - 6 #n = 8