Chapter Two Atoms & The Periodic Table

Section 2.1 Atoms First

Atoms Atoms are the smallest quantities of matter that still retain the property of that matter

A brief history Democritus was the first to develop this idea of an atom in the 5th century John Dalton was the first to formalize the idea of an atom with Dalton’s atomic theory Known as the “father of atomic theory” The word “atom” comes from the Greek word “atomos” meaning “uncuttable.”

Dalton’s Atomic Theory All matter is made up of atoms Atoms are indivisible Atoms of the same element are identical Atoms of one element are different than atoms of another element Atoms come together to form compounds

Dalton’s Law of Multiple Proportions If two elements can combine to create multiple compounds, then the ratios of the masses of the second element which combine with a fixed mass of the first element will be ratios of small whole numbers CO CO2 100 g of C 100 g of C 133 g of O 266 g of O

Section 2.2 Subatomic Particles & Atomic Structure

Subatomic Particles & Their Discovery Who Discovered It How was it Discovered Electron (and Charge-to-Mass ratio) J.J. Thomson Cathode Ray Tube (Cathode Ray Experiment) Charge of the Electron Robert Millikan Oil Drop Experiment Proton & Nucleus Ernest Rutherford Gold Foil Experiment Neutron James Chadwick Beryllium Bombardment

Comparing All 3 subatomic Particles Charge Location Contribution to Atom Proton +1 In the nucleus Mass Neutron Electron -1 Outside nucleus Volume

Section 2.3 Atomic Number, Mass Number and Isotopes

Element Symbols

Isotopes Not all atoms of a given element are identical Most elements have 2 or more isotopes (atoms with same # of protons, different # of neutrons)

Isotopes Isotopes behave like each other Named after their mass number Ex: U-235 (“Uranium two thirty five”) If mass number is not given, use rounded atomic mass from PT. If mass number is given (or if protons & neutrons are given), use that value instead of on the PT. If mass # is different than what’s on PT, it is an isotope

Ions Atoms with charges (different # of electrons) Positive ions called cations Negative ions called anions

Let’s Do Some Structural Practice!

Fill Out the Table Below # of Protons # of Neutrons # of Electrons Mass Number Atomic Number Ion? Isotope? 14 18 20 6 13 10 29

Practice List the number of protons, neutrons, and electrons in the following elements: Carbon-14 Iodine-128 An atom has a mass number of 114 and 66 neutrons. Write the isotope notation for this atom.

Section 2.4 Average Atomic Mass

Average Atomic Mass Mass of an atom in atomic mass units (a.m.u) Based off of 1/12 of a carbon atom Most elements are mix of isotopes in nature Average Atomic Mass is reported

Practice The atomic masses of two stable isotopes of copper, copper-63 and copper 65, are 62.929599 and 64.927793 amu, respectively. If copper-63 is 69.17% and copper-65 is 30.83%, what is the average atomic mass of copper?

One More The atomic masses of 34Cl and 35Cl are 34.0578 amu and 35.0147 amu, respectively. Calculate the natural abundance of these two isotopes. The average atomic mass of Cl is 35.45 amu.

Section 2.5 The Periodic Table

The Periodic Table Mostly metals (left of stair step) Good conductors of heat/electricity Non metals (right of stair step) Poor conductors of heat/electricity Metalloids/Semi-metals (on stair step) Properties of both metal and nonmetal B, Si, Ge, As, Sb, Te, Po, At

The Periodic Table

The Periodic Table Groups: vertical columns Periods: horizontal rows Elements in the same group share similar chemical properties 18 groups Periods: horizontal rows Elements transition from metal to nonmetal across a period

The Periodic Table

Section 2.6 The Mole and Molar Mass

The Mole A unit of quantity (how much) Mole = mol 1 mole = 6.022 x 1023 “particles” “particles” can be atoms, molecules, or formula units This number is called Avogadro’s Number

Molar Mass Molar Mass = the mass of ONE MOLE of a substance g/mol

Molar Mass 1 mole of water = 18.02 grams 1 mole sodium chloride = 58.44 g 1 mole helium gas = 4.003 g

Molar Mass Molar mass is found by Listing elements in compound Determining their mass found on periodic table Multiplying by how many atoms there are Adding these values Ex: H2SO4

A helpful guide

Conversions How many molecules of magnesium chloride (MgCl2) are there in 67.35 grams of magnesium chloride? How many chlorine atoms are there in the same mass of magnesium chloride?

Group Quiz 1)Write the appropriate isotope notation for the following: Z=29, A=64 2)How many protons, neutrons, & electrons in 3)Rb-85(72.17%) is 84.911794. If the average atomic mass of Rb is 85.4678, what is the atomic mass of Rb-87(27.83%). 4)How many grams is 5.30 x 1023 molecules of K2O? +3