The Atom

 An atom is the smallest particle of matter that still has the same properties of that element. What is an atom? Atoms = Building Blocks Na Mg H

1.Protons  Positively charged particles inside the nucleus What makes up an atom? 2.Neutrons  Neutrally charged particles inside the nucleus 3.Electrons  Negatively charged particles outside the nucleus

 Atomic Number: tells the number of protons in the nucleus.  Each element is unique- no two elements have the same number of protons/ atomic number. Counting Atoms  Mass number: tells the total number of particles in the nucleus. Mass # = #p + #n

Helpful Information How to read the Periodic Table How to write symbols 11 Na Atomic # Element Symbol Average Atomic Mass Mass # X 11 Atomic #

Example 1 ElementAtomic #Mass ## protons# neutrons # electrons symbol Oxygen O P + N = Mass 8 + N = 16 N = 8 # electrons = # protons

Example 2 ElementAtomic #Mass ## protons# neutrons # electrons symbol Li P + N = Mass 3 + N = 7 N = 4 If the atomic # is 3, look at the PT to find out which element is 3 The atomic # tells us the # p in the nucleus 3Lithium

Example 3 ElementAtomic #Mass ## protons# neutrons # electrons symbol Ar P + N = Mass 18 + N = 40 N = 22 If the symbol is Ar, the element name is Argon From the symbol, the top number is 40 (mass #) From the symbol, the bottom number is 18 (atomic #) The atomic # tells us the # p in the nucleus Argon # electrons = # protons