Atomic Structure

What Is an Atom? Atom: the smallest unit of matter that retains the identity of the substance.

Atomic Structure Atoms have two regions: Nucleus: the center of the atom that contains protons and neutrons which is most of the mass of the atom. Electron Cloud: surrounds the nucleus and takes up most of the space of the atom.

Inside the Atom’s Nucleus Protons: positively charged subatomic particles. Mass of 1 amu Neutrons: neutrally charged subatomic particles. Mass of 1 amu

Inside the Electron Cloud Inside the electron cloud are electrons which are subatomic particles with a negative charge and relatively no mass.  Mass of ~ 1/1836 amu

Subatomic Particles

Protons Atomic Number = Number of Protons in an Atom Ex: Hydrogen’s atomic number = 1 Hydrogen has one proton Ex: Carbon’s atomic number = 6 Carbon has six protons The number of protons identifies the atom. It is the atom’s fingerprint.

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

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

Neutrons Atomic Mass = Number of Protons and Neutrons in an Atom # of Neutrons = Atomic Mass - Atomic Number Ex: Lithium’s atomic mass = 7 Lithium’s atomic number = 3 # Neutrons = 7 – 3 = 4 Lithium has 4 neutrons

Electrons Most atoms are neutral--having no overall charge. Because the only charged subatomic particles are the protons and electrons… they must balance each other out in an electrically neutral atom. Therefore.. # p+ = # e- …in a neutral atom.

Calculating p+, n, and e- Beryllium Protons = Neutrons = Electrons = Magnesium

Calculating p+, n, and e- Beryllium Protons = 4 Neutrons = (9 – 4) = 5 Electrons = 5 Magnesium Protons = 12 Neutrons = (24 – 12) = 12 Electrons = 12

Subatomic Particle Arrangement All of the protons and the neutrons Orbit 3: holds up to 8 e- Orbit 1: holds up to 2 e- Orbit 2: holds up to 8 e-

Carbon’s Arrangement Atomic Number = 6 Atomic Mass = 12 e- = 6 6 p and 6 n live in the nucleus

Atomic Mass Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom. Atomic Mass Unit = amu Your remember this. 1 amu the mass of 1 p+ or 1 n You do NOT have to remember this. Atomic Mass Unit (amu) is defined as one-twelfth the mass of a carbon-12 atom. Atomic Number 11 Na 22.99 Symbol Atomic Mass

Why “Average” Atomic Mass? Q: How heavy is an oxygen atom? A: It depends because there are different oxygen isotopes. We are more concerned with the average atomic mass. This is determined based on the abundance of each isotope. The standard unit for mass = grams. But, for atomic mass amu (atomic mass unit) is used. It is too small to use grams.

Calculating Average Atomic Mass Cl-35 is about 75.5% and Cl-37 about 24.5% of natural chlorine. 35 x 75.5 = 26.43 100 35.50 37 x 24.5 = 9.07

Calculating Average Atomic Mass for Carbon Isotope Symbol Composition of the nucleus % in nature Carbon-12 12C 6 protons 6 neutrons 98.89% Carbon-13 13C 7 neutrons 1.11% Carbon-14 14C 8 neutrons <0.01% Atomic mass is the average of all the naturally occurring isotopes of that element. Carbon = 12.011

Dalton’s Atomic Theory Dalton’s first postulate was wrong. Atoms of the same element can be different. They can have different # of neutrons. Thus, different mass numbers. These are called isotopes.

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

Isotopes Elements occur in nature as mixtures of isotopes.

Hydrogen Isotopes Hydrogen–1 (protium) 1 Hydrogen-2 (deuterium) Protons Electrons Neutrons Nucleus Hydrogen–1 (protium) 1 Hydrogen-2 (deuterium) Hydrogen-3 (tritium) 2

LecturePLUS Timberlake 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 _______ _______ _______ LecturePLUS Timberlake

LecturePLUS Timberlake Solutions 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 ___6___ ___6___ ___6___ #n ___6___ ___7___ ___8___ #e ___6___ ___6___ ___6___ LecturePLUS Timberlake

LecturePLUS Timberlake Learning Check An atom of zinc has an atomic mass of 65 amu. Find the atomic number then answer the questions. 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 LecturePLUS Timberlake

LecturePLUS Timberlake Solutions An atom of zinc has an atomic mass of 65 amu. Find the atomic number then answer the questions. 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 LecturePLUS Timberlake

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

Solutions Write the atomic symbols for atoms with the following: A. 8 p+, 8 n, 8 e- ___________ B. 17 p+, 20 n, 17 e- ___________ C. 47 p+, 60 n, 47 e- ___________ 16O 8 p+, 8 n, 8 e- 8 17p+, 20n, 17e- 37Cl 17 47p+, 60 n, 47 e-107Ag 47

Isotope Nomenclature We name the isotope based on its mass number. Carbon-12 C-12 12C Carbon-14 C-14 14C Uranium-235 U-235 235U