Atoms vs. Molecules Matter is composed of tiny particles called atoms. Atom: smallest part of an element that is still that element. Molecule: Two or more atoms joined and acting as a unit. Copyright © Cengage Learning. All rights reserved

Oxygen and Hydrogen Molecules Use subscripts when more than one atom is in the molecule. Copyright © Cengage Learning. All rights reserved

A Chemical Reaction One substance changes to another by reorganizing the way the atoms are attached to each other. Copyright © Cengage Learning. All rights reserved

Atomic Theory Atoms are building blocks of elements Similar atoms in each element Different from atoms of other elements Two or more different atoms bond in simple ratios to form compounds 4

Subatomic Particles ParticleSymbol Charge Relative Mass Electron e Proton p Neutron n0 1 5

Location of Subatomic Particles cm electrons protons neutrons cm 6 nucleus

Atomic Number This refers to how many protons an atom of that element has. No two elements, have the same number of protons. Bohr Model of Hydrogen Atom Wave Model

Atomic Number on the Periodic Table 11 Na 8 Atomic Number Symbol

All atoms of an element have the same number of protons 11 Na 9 11 protons Sodium

Learning Check State the number of protons for atoms of each of the following: A. Nitrogen B. Sulfur C. Barium 10

Solution State the number of protons for atoms of each of the following: A. Nitrogen 7 protons B. Sulfur 16 protons C. Barium 56 protons 11

Mass Number Counts the number of protons and neutrons in an atom 12

Atomic Symbols Show the mass number and atomic number Give the symbol of the element mass number 23 Na sodium-23 atomic number 11 13

Number of Electrons An atom is neutral The net charge is zero Number of protons = Number of electrons Atomic number = Number of electrons 14

Subatomic Particles in Some Atoms O P Zn p + 15 p + 30 p + 8 n16 n35 n 8 e - 15 e - 30 e - 15

Isotopes Atoms with the same number of protons but different numbers of neutrons. Show almost identical chemical properties; chemistry of atom is due to its electrons. In nature most elements contain mixtures of isotopes. Copyright © Cengage Learning. All rights reserved16

Atomic Mass and Isotopes While most atoms have the same number of protons and neutrons, some don’t. Some atoms have more or less neutrons than protons. These are called isotopes. An atomic mass number with a decimal is the total of the number of protons plus the average number of neutrons.

Two Isotopes of Sodium Copyright © Cengage Learning. All rights reserved18

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 35 Cl 37 Cl17 chlorine - 35 chlorine

Learning Check Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C #p _______ _______ _______ #n _______ _______ _______ #e _______ _______ _______ 20

Solution 12 C 13 C 14 C #p #n #e

Learning Check An atom of zinc has a mass number of 65. A.What is the number of protons in the zinc atom? B.What is the number of neutrons in the zinc atom C. What is the mass number of a zinc isotope with 37 neutrons? 22

Solution An atom of zinc has a mass number of 65. A.Number of protons in the zinc atom 30 B.Number of neutrons in the zinc atom 35 C. What is the mass number of a zinc isotope with 37 neutrons? 67 23

Learning Check Write the atomic symbols for atoms with the following: A. 8 p +, 8 n, 8 e - ___________ B.17p +, 20n, 17e - ___________ C. 47p +, 60 n, 47 e - ___________ 24

Solution 16 O A. 8 p +, 8 n, 8 e - 8 B.17p +, 20n, 17e - 37 Cl 17 C. 47p +, 60 n, 47 e Ag 47 25