Atoms & Elements •What is an atom? An atom is the smallest particle of an element that retains its identity in a chemical reaction. Word origin: atom comes from the Greek word atomos meaning “ indivisible” •Elements & Compounds • What would atoms of an element, mixture and compound look like at a microscopic level? •Subatomic Particles • The parts that make up an atom! • protons • neutrons • electrons electron proton nucleus neutron •Subatomic Particles Protons • Found in the nucleus • Found in the nucleus • Identifies the element • Plays no role in chemical behavior • • #of protons = specific element Responsible for chemical and physical properties Electrons Neutrons • Purpose: to put space between protons • • • Spin around in set regions outside of nucleus Most important in chemical reactions Farthest electron away from nucleus determines how atoms chemical to combine to one another. •Subatomic Particles Name Symbol Charge Relative Mass Proton p+ +1 1 Neutron no 0 1 Electron e- -1 0 (1/1840) How big is an atom? Imagine the nucleus is the size of a marble located in the middle of the football field, the electron would be in the classroom the size of a period! •Periodic Table Greatest Cheat Sheet Ever! •Periodic Table Categories: Metals • Rows: periods • • 7 periods Columns: groups or families • 18 Groups • 1A: Alkali Metals • 2A: Alkaline Earth Metals • 7A: Halogens • 8A: Noble gases • B Groups: Transition and Inner Transition Metals Nonmetals Metalloids (B, Si, Ge, As, Sb, Te, At) •Periodic Table 14 Symbol Si Silicon 28.086 Atomic Mass Atomic Number Element name •Important Numbers • Atomic • Number Counts the number of protons in an atom within the nucleus 14 Si Atomic Number = # of protons Silicon has 14 protons •Atomic Number • State the number of protons for atoms of each of the following: • A. Nitrogen • B. Potassium • C. Neon •Atomic Number • State the number of protons for atoms of each of the following: • A. • • B. • • C. • Nitrogen 7 protons Potassium 19 protons Neon 10 protons •Number of Electrons • An atom is neutral • The net charge is zero • Number • Atomic of protons = Number of electrons number = Number of electrons • Remember: proton = +1 electron = -1 •Number of Electrons 14 electrons 14 14 protons Si -14 +14 = 0 neutral •Important Numbers • Mass Number 14 Si Silicon 28.086 • • Atomic Mass Counts the number of protons and neutrons in an atom OR Determined by: the whole number closest to the Atomic Mass •Mass Number • Atomic Symbols Show the mass number and atomic number • Give the symbol of the element • Mass Number Atomic Number 28 14 Si silicon-28 •Determine the Mass Numbers 4 Be 27 Co 10 Ne 9.0122 58.933 20.179 9 59 20 •Write the Symbol and Name for each 4 Be 9.0122 9 Be 4 beryllium-9 27 Co 10 Ne 58.933 20.179 59 Co 27 20 Ne 10 cobalt-59 neon-20 •Mass Number • The total number of particles in the nucleus • • # of protons + # of neutrons To determine the number of neutrons • Mass number – Atomic number = # of neutrons 16 8 O 31 15 P 65 30 Zn #p 8p+ 15p+ 30p+ #n 8no 16no 35no 8e- 15e- 30e- #e •Isotopes • • The identifies the element, but an element may have atoms with several different . Most elements consist of several different isotopes • Same number of protons , Different number of neutrons •Isotopes of Hydrogen • Naturally occurring hydrogen consists of 3 isotopes, protium (H-1), deuterium (H-2), and tritium (H-3). State the number of protons, neutrons, and electrons. 1 1 #p #n H 1 0 #e 1 2 1 H 3 1 H 1 1 1 2 1 1 •An atom of Calcium (Ca-40) • A. Number of protons • B. number of neutrons • C. What is the mass number of a calcium isotope with 19 neutrons? •Atomic Mass • This is NOT a whole number • A given element can have atoms with several different mass numbers. • Average mass of the atoms with all possible mass numbers • We will calculate later •Write the atomic symbol • A. 11p+, 12no, 11e- • B. 17p+, 20no, 17e- • C. 47p+, 60no, 47e- •Write the atomic symbol • A. 11p+, 12no, 11e- 23 11 Na • B. 17p+, 37 17 • C. 47p+, 60no, 47e- 20no, 17e- Cl 107 47 Ag •Ions • • • Atoms with a charge (positive or negative) Remember atoms are neutral, therefore if an atom has a charge we call it an ion. Ions- Atoms which gain or lose an electron atom #p 11 #e 11 ion 11 10 Na1+ atom #p 17 #e 17 ion 17 18 Cl1- Why do the electrons change? •Why? • If protons change…new______?________ • If neutrons change…new______?______ • If electrons change….new _____?______ •Why? • If protons change…new element • If neutrons change…new isotope • If electrons change….new ion •Ions #p atom 12 ion 12 #e 12 10 #p atom 8 ion 8 #e 8 10 Mg 2+ O 2- •Complete Atomic Symbol combines isotopes and ions 27 Al 13 • • 3+ What does each represent? How many of what subatomic particles does each represent? •Complete Atomic Symbol combines isotopes and ions Mass number 27 Al 13 3+ Ionic charge Atomic number 13p+ 10e- 14no •How many protons, neutrons, & electrons? 14 7 N3- 7p+ 7no 10e- 32 15 P3- 15p+ 17no 18e- 65 30 Zn2+ 30p+ 35no 28e- •Atomic Mass Coming back to this… Atomic mass is the weighted of all the atomic masses of the isotopes of that atom. So we involved all the different forms of ATOMS of an element (ions not an issue here) and how frequent they are •Average Atomic Mass cont. • To find the Average Atomic Mass (generally referred to as the atomic mass of an element) we need to use two things • • • The mass of the isotope Multiplied by its frequency Then we add all the forms up. •Example of Average Atomic Mass Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine. 35 x 75.5 = 26.4 100 35.5 37 x 24.5 = 9.07 100 • Rubidium has two common isotopes, Rb-85 and Rb-87. If the abundance of Rb-85 is 72.2% and the abundance of Rb-87 is 27.8%, what is the average atomic mass or rubidium?