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Drill – What do you know? 1. Write your definition of an ATOM. 2. What is inside an atom? 3. What determines the identity of an atom? The Atom What is an atom? • We know that an element is a substance that cannot be separated into simpler substances… • An atom is the smallest unit of an element that maintains the chemical properties of that element. Gold = Element Atoms of Gold How little is an atom??? • If you expand a hydrogen atom to the size of an apple, the apple would expand to the size of the Earth. is to as is to How little is an atom??? • A human hair is about 1 million carbon atoms wide. • A speck of dust contains about 3 trillion atoms. Atoms of Gold Gold = Element Each Individual Gold Atom • The nucleus is a very small region in the center of the atom that is made up of protons and neutrons • Surrounding the nucleus are electrons Inside the atom • Subatomic Particles: Particle Charge Mass (kg) Relative Mass (amu) Proton Positive 1.7x10-27 1 Neutron Neutral 1.7x10-27 1 Electron Negative 9.1x10-31 0 Protons: An atom’s identity is determined by the number of protons. If you change the number of protons, you change the element. Neutrons: Neutrons maintain stability. If you change the number of neutrons, you have an ISOTOPE. Electrons: Electrons determine an atom’s behavior. If you change the number of electrons, then you have an ION. What the Periodic Table tells us! Atomic Number (Z): 3 Li Lithium 6.941 The number of protons An atom, which is neutral, will have an equal number of protons and electrons…so that the positive and negative cancel out (not true for ions) What the Periodic Table tells us! 3 Li Lithium 6.941 Average Atomic Mass: The weighted average of the atomic masses of the naturally occurring isotopes of the element The Average Atomic Mass rounded to a whole number is the MASS NUMBER Because protons and neutrons are much larger than electrons, they are the only 2 particles that impact the mass of the atom. Therefore: Mass Number = # of protons + # of neutrons # of neutrons = Mass Number - # of protons What the Periodic Table tells us! Average Atomic Mass: The weighted average of the atomic masses of the naturally occurring isotopes of the element Isotopes are atoms of the same element that have different masses (ie same protons, different neutrons) Isotopes are written using the name of the element followed by a hyphen and then the mass number. Ex: Hydrogen-1, Hydrogen-2, & Hydrogen-3 are isotopes What is a weighted average? • Mrs. Tang’s English Class: – 20% Homework – 45% Test – 35% Essay If Sue got a 94% on Homework, a 82% on Tests, and a 89% on Essays, what is her English grade? What is a weighted average? • Sue’s English Grade: Homework: (.20)(.94) = 0.19 Test: (.45)(.82) = 0.37 Essay: (.35)(.89) = 0.31 Add all three up and you get: 0.19 + 0.37 + 0.31 = 0.87 = 87% Now let’s do an actual example: • Copper consists of 69.15% copper-63 and 30.85% copper-65. Calculate the Average Atomic Mass of copper? Electrons • If electrons are added or removed, we ION This is indicated with a + or – have an ____. charge. NEGATIVELY • Since electrons are ____________ charged, if we have extra electrons the atom will be NEGATIVE _____________. If the atom has lost an POSITIVELY electron, the atom will be _____________ charged. Ca2+ Cl- O-2