The Atom SC1. Obtain, evaluate, and communicate information about the use of the modern atomic theory and periodic law to explain the characteristics of atoms and elements. a. Evaluate merits and limitations of different models of the atom in relation to relative size, charge, and position of protons, neutrons, and electrons in the atom. b. Construct an argument to support the claim that the proton (and not the neutron or electron) defines the element’s identity. d. Construct an explanation that relates the relative abundance of isotopes of a particular element to the atomic mass of the element. e. Construct an explanation of light emission and the movement of electrons to identify elements.

The History of the Atom You should be familiar with the findings of: Democritus Dalton Thomson Rutherford Bohr Schrödinger/Heisenberg Chadwick

Subatomic Particles Particle Symbol Charge Relative Mass Electron e- 1- 0 (1/1836) amu Proton p+ 1+ 1 amu Neutron n0 none 1 amu

Location of Subatomic Particles 1 angstrom = 10-10 m

Atomic Number Counts the number of PROTONS in an atom

Atomic Number on the Periodic Table 11 Na Atomic Number Symbol

All atoms of an element have the same number of protons 11 Na 11 protons Sodium

Learning Check State the number of protons for atoms of each of the following: 1. Nitrogen A) 5 protons B) 7 protons C) 14 protons 2. Sulfur A) 32 protons B) 16 protons C) 6 protons 3. Barium A) 137 protons B) 81 protons C) 56 protons

Solution State the number of protons for atoms of each of the following: 1. Nitrogen B) 7 protons 2. Sulfur B) 16 protons 3. Barium C) 56 protons

Mass Number Counts the number of PROTONS and NEUTRONS in an atom

Atomic Notation atomic number Shows the mass number and/or atomic number Gives the symbol or name of the element mass number Na sodium-23 atomic number 23 11

Number of Electrons An atom is neutral The net charge is zero Number of protons = Number of electrons Atomic number = Number of electrons

Subatomic Particles in Some Atoms 16 31 65 O P Zn 8 15 30 8 p+ 15 p+ 30 p+ 8 n 16 n 35 n 8 e- 15 e- 30 e-

Isotopes Atoms with the same number of protons, but different numbers of neutrons. Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35Cl 37Cl 17 17 chlorine - 35 chlorine - 37

Learning Check Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 13C 14C 6 6 6 #p _______ _______ _______ #n _______ _______ _______ #e _______ _______ _______

Solution 12C 13C 14C 6 6 6 #p 6 6 6 #n 6 7 8 #e 6 6 6

Learning Check An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom 1) 30 2) 35 3) 65 B. Number of neutrons in the zinc atom C. What is the mass number of a zinc isotope with 37 neutrons? 1) 37 2) 65 3) 67

Solution An atom of zinc has a mass number of 65. A. Number of protons in the zinc atom 1) 30 B. Number of neutrons in the zinc atom 2) 35 C. What is the mass number of a zinc isotope with 37 neutrons? 3) 67

Learning Check Write the atomic symbols for atoms with the following subatomic particles: A. 8 p+, 8 n, 8 e- ___________ B. 17p+, 20n, 17e- ___________ C. 47p+, 60 n, 47 e- ___________

Solution B. 17p+, 20n, 17e- 37Cl 17 47 16O A. 8 p+, 8 n, 8 e- 8 C. 47p+, 60 n, 47 e- 107Ag 47

Atomic Mass on the Periodic Table 11 Na 22.99 Atomic Number Symbol Atomic Mass

Atomic Mass Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom. Measured in amu (atomic mass units)

Example of an Average Atomic Mass Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine. 35 x 0.755 = 26.4 35.5 37 x 0.245 = 9.07

Learning Check Magnesium has 3 stable isotopes: Mg-24 (78.99%), Mg-25 (10.00%), and Mg-26 (11.01%). Determine the average atomic mass.

Learning Check Copper has 2 naturally occurring isotopes. Cu-63 has an atomic mass of 62.9296 amu and an abundance of 69.15%. Identify the second isotope.

Energy Levels Electrons are found outside the nucleus in energy levels, or shells There are a maximum of 7 shells n is used to identify the shell n=1 for 1st energy level, n=2 for 2nd, up to n=7 for 7th

Energy Levels There is a limit to the number of electrons per energy level Max number of e- = 2n2 2nd shell can have up to 8 e- 6th shell can have…?

Energy Levels Energy levels increase in size and energy as the distance increases from the nucleus

Atomic Spectra An important consequence of the energy level concept is the understanding of atomic spectra. When substances are heated, the electrons are excited into unstable energy levels. It takes a discrete amount of energy (quantum) for an electron to be “bumped up” E=hf (or hν)

Atomic Spectra The electrons immediately return to their more stable energy levels, called ground state, releasing the absorbed heat energy in the form of light. Because each element’s atom has a unique distribution of electrons among the energy levels, the release of the energy is uniquely associated with that element, and can allow that element to be identified.

Atomic Spectra Emission spectrum for H Absorption spectrum for H

Atomic Spectra