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Name __________________________ Unit 3 Notepack – Atomic Structure Unit 3 Objectives: 1. Describe the structure of the atom including: protons, electrons, and neutrons. 2. Explain why isotopes differ. 3. Diagram the Bohr Model of an atom. Objective 1: Describe the structure of the atom including: protons, electrons, and neutrons. Atoms and Atomic Theory • Atoms – the smallest _______________ of a given type of _______________. • Atomic Theory – the idea that _______________ is made up of fundamental particles called _______________. Early Ideas About Matter Democritus – 400 B.C. – atomos – Lavoisier Law of conservation of matter- When a chemical reaction occurs, matter is neither nor , but only changed. John Dalton – Father of the Modern Atom • Dalton’s Atomic Theory. 1.) All matter is made of . 2.) All atoms are and cannot be divided into smaller particles. 3.) All atoms of one element are , but they are different from all other elements. 1 Subatomic Particles • Electrons • Protons • Neutrons Diagram: Electrons • J.J. Thomson – Discovered the electron using a • Symbol: • Mass = 1/1837 amu • 1 amu ~ the mass of a hydrogen atom • Charge = (-1) ray tube. Protons • Symbol: • Mass = 1 amu • Charge = (+1) Thomson’s Model • Thomson put both the electron and proton together and proposed the “ ” model of the atom. Diagram the Plum Pudding Model: Neutrons • Symbol: • Mass = 1 amu • __________ charge 2 Nucleus • Discovered by Ernest Rutherford. • Using the “Gold Foil” experiment, Rutherford determined: – An atom is mostly . – There is a – The • in the middle of the atom containing the protons. orbit a large distance away from the nucleus. Proposed the nuclear model of the atom. Atomic Number • Designates the number of • Each element has a characteristic • The number of electrons in a of an atom. . the atomic number in a neutral atom. Mass Number • Designates the total number of and in an atom. • Number of neutrons = - • Atoms of the same element can have different mass numbers. Objective 2: Explain why isotopes differ. Isotopes • Atoms with the same number of • Isotopes of an element have the same • Nuclear Symbol or isotopic symbol – shows , but different numbers of . number, but different mass numbers. of protons, neutrons and electrons in an atom. • Isotopes may also be described by labeling the name following by the number. (Example: carbon-12) Diagram the nuclear symbol for lithium – 7, Helium – 4, Titanium – 48: 3 Atomic Mass • Weighted mass of the atoms in naturally occurring sample of an element. • Masses are based off of the atomic mass unit (amu) defined as one the mass of a carbon-12 atom. Atomic Mass Example • In nature carbon is composed of 98.89% 12C atoms and 1.11% 13C atoms. 12C has a mass of 12 amu and 13C has a mass of 13.0034 amu. What is the average atomic mass of carbon? Objective 3: Diagram the Bohr Model of the atom. Bohr Model • Niels Bohr (1913) – Bohr Model stating travel around in energy levels. • Uses to show the energy levels. • The number of rings should match the the element is in on the periodic table. Bohr Model Diagram • The in the nucleus = the . • The in the nucleus = the mass number - the atomic number. • Electrons = number of protons. Fill the shells from to until the correct number of electrons are added. • This model works for the first Diagram Lithium-7 . Diagram Aluminum-27 4 Diagram Nitrogen-14 Diagram Calcium-40 Valence Electrons Electrons in the __________________ energy level. Ex: Li = 1, F = 7 Corresponds with the group number for Groups 1-2, 13-18. Lewis Dot Structures Show __________________ electrons. Look at the __________________ number. This is how many dots you draw for each atom. Ex: Potassium Fluorine Sulfur Xenon Phosphorous Silicon Aluminum Beryllium 5