Transcript atoms
Chapter 17 cp Atoms 4.2/4.3 The Structure of the Atom & Modern Atomic Theory JOURNAL: 1. 2. 3. QUIETLY work on the Atomic Math worksheet FIRST Then, work on the“Not So Bohr-ing Atoms” Worksheet from the back table. Use the Periodic Table I gave you to help you. Studying Atoms ANCIENT GREEKSDEMOCRITUS: “atomos” = indivisible, uncut Different types of atoms with specific properties ARISTOTLE: Only 4 elements No limit to divisions Studying Atoms DALTON’S ATOMIC THEORY: all matter is made of particles that cannot be divided Evidence: Compounds have fixed compositions H2O Chemical reactions are a rearrangement of solid atoms. Studying Atoms THOMSON’S ATOMIC THEORY: all matter is made of particles that CAN be divided EVIDENCE: Particles collected on metal plate The particles ALWAYS had a mass 1/2000 of a Hydrogen atom. The beam was always attracted to the positive side Thomson’s “plum pudding” Atomic Model Explained neutral atoms with charges Studying Atoms RUTHERFORD’S ATOMIC THEORY: all atoms positive charge is concentrated in the nucleus Thomson’s “plum pudding” Atomic Model Studying Atoms RUTHERFORD’S ATOMIC THEORY: all atoms positive charge is concentrated in the nucleus Discovered: Uranium emits fast moving positive particles Studying Atoms RUTHERFORD’S ATOMIC THEORY: all atoms positive charge is concentrated in the nucleus If you shoot these positive particles at other atoms (Thomson’s plum pudding atom), what would happen to the particle? SHOULD GO STRAIGHT THROUGH!! Studying Atoms – Gold Foil Experiment 4.1 The Gold Foil Experiment RUTHERFORD’S ATOMIC THEORY: all atoms positive charge is concentrated in the nucleus Studying Atoms – Modern Atomic Theory Bohr Atom: Electrons are in energy levels Electrons move when they gain or lose energy (example) Parts of an ATOM: Subatomic particles – distinguished by mass, charge and location Subatomic particle PROPERTIES Protons (p+): In the nucleus Charge of 1+ Mass of 1 DEFINES THE ELEMENT (equals the ATOMIC NUMBER) Protons (p+): Atoms of DIFFERENT elements have DIFFERENT numbers of protons Subatomic particle PROPERTIES Neutrons (n°): In the nucleus NO charge Mass of 1 Protons + neutrons = the ATOMIC MASS Neutrons (n°): Atoms of the same element with DIFFERENT numbers of neutrons are called ISOTOPES Neutrons (n°): ISOTOPES of Hydrogen. Same Atomic #, different Mass # Electrons (e-): In ENERGY LEVELS around the nucleus Charge of 1Mass of 1/1836 of a p+ Equal to the number of protons The outermost shell of electrons is called the VALENCE SHELL which holds the VALENCE ELECTRONS. Take out Bohr Diagram Sheet. Electrons (e-): Change ENERGY LEVELS when the atom GAINS or LOSES energy The most stable electron arrangement Electrons (e-): CurrentTheory – “Electron Cloud Model” (p116-17) Orbitals that show most PROBABLE location of electrons Electrons (e-): Atoms of the same element with different number of ELECTRONS are called IONS IONS: form to make the outermost shell stable 4.2/4.3 The Structure of the Atom & Modern Atomic Theory OCTET RULE: Take out a lined sheet of paper, draw a circle for a nucleus and then three rings around the nucleus. 2 electrons in 1st shell Protons and neutrons in nucleus 8 electrons in 2nd shell 8 electrons in 3rd shell Atomic Number Practice Use your periodic table to find the atomic number of the following elements: Aluminum (Al) Titanium (Ti) Tin (Sn) Osmium (Os) Erbium (Er) Al = 13 Ti = 22 Sn = 50 Os = 76 Er = 68 How many protons does each atom have? The number of protons are equal to the atomic number. Mass Number The mass number of an atom is the sum of the number of protons and neutrons in the nucleus. Element Protons Neutrons Mass Number Boron 5 6 5+6 11 Carbon 6 6 6+6 12 Oxygen 8 8 8+8 16 Sodium 11 12 11+12 23 Copper 29 34 29+34 63 Practice Determine the number of protons and neutrons in the following atoms: Lithium – Atomic Number = 3 Mass Number = 7 Argon – Atomic Number = 18 Mass Number = 39 Strontium – Atomic Number = 38 Mass Number = 88 Atomic Number & Mass Number If you know the atomic number and mass number, you can determine the number of neutrons. Mass Number - Atomic Number Number of Neutrons Answers Determine the number of protons and neutrons in the following atoms: Lithium – Protons = 3 Neutrons = 7 – 3 = 4 Argon – Protons = 18 Neutrons = 39 – 18 = 21 Strontium – Protons = 38 Neutrons = 88 – 38 = 50 Neutral Atoms In the nucleus, which particles have charge? What charge do they have? Protons Positive What particle is opposite that charge? Electrons Neutral Atoms In the atom: The number of protons equals the number of electrons. Li has 3 protons, so has a charge of +3. Li also has 3 electrons that add up to -3. ADDED TOGTHER, the overall charge is: (+3) + (-3) = 0, so the atom is neutral. Practice Determine how many electrons the following atoms have: Magnesium, Protons = 12 Beryllium, Protons = 4 Nitrogen, Atomic Number = 7 Bromine, Atomic Number = 35 12 Electrons 4 Electrons 7 Electrons 35 Electrons Bohr Models of the Atoms Each atom has shells in which the electrons can fit. 1st Shell: fills to 2 electrons 2nd Shell: fills to 8 electrons 3rd Shell: fills to 18 electrons 4th Shell: fills to 32 electrons Start filling the smallest/closest shell first. REVIEW 1. Draw a Bohr Atom Model of Hydrogen, Carbon, and Oxygen on the back of your worksheet. 2. Which subatomic particles belong in the nucleus? 3. Which subatomic particles belong on the rings? 4. What is the difference between ‘ground state’ and ‘excited state’ of an atom?