Chapter 5: Atomic structure & the Periodic Table College Prep Chemistry

Section 5.1 – The Atom Atoms: the smallest particle of an element that retains the properties of that element. (Greek: atomos = indivisible) Democritus (Greek teacher in the 4th century) First suggested that atoms existed

The Atom 1700’s – chemists were able to relate changes to individual atoms Average atom size: Mass = 1 x 10 –23 g Diameter = 1 x 10-8 cm How small is that?100,000,000 copper atoms in a row would = 1 cm in length!

John Dalton’s Atomic Theory 1. All elements are composed of tiny indivisible particles called atoms. 2. Atoms of the same element are identical. The atoms of any one element are different from those of any other element.

Atomic Theory (cont’d) 3. Atoms of different elements can combine with one another in simple whole number ratios to form compounds. H2O C12H22O11 NOT H2.5O¾ 4. Chemical reactions occur when atoms are separated, joined or rearranged. Atoms of one element are not changed into atoms of another!

Atomic Theory (cont’d) 5. Atoms can not be infinitely subdivided.

Just how small is an atom? 100,000,000 copper atoms in a row would = 1 cm in length!

Section 5.2 – Structure of the Nuclear Atom Most of Dalton’s Atomic Theory is accepted One revision includes that idea that atoms are indivisible…. There are 3 parts to an atom…. 1. electrons 2. protons 3. neutrons

Electrons (e-) Negatively charged subatomic particles J.J. Thomson discovered in 1897 Passed a electric current through gases called a “Cathode Ray” Opposites attract and the electrons were attracted to the positive ends and lights up!

Electrons (cont’d) How televisions work!

2. Protons (p+) Positively charged particles 1,840 times heavier then an electron

3. Neutrons (no) Subatomic particles with no charge Discovered by Sir James Chadwick Mass is nearly the same as a proton

Summary of Subatomic Particles Symbol Relative Charge Approx. Relative Mass (amu) Actual Mass (g) Electron e- 1- 1/1840 9.11x10-28 Proton p+ 1+ 1 1.62x10-24 neutron no

Atomic Nucleus Discovered by Ernest Rutherford (1911) Gold Foil Experiment

Gold Foil Experiment

Atomic Nucleus- Rutherford’s Model The alpha particles were positively charged - Like things repel Therefore – there must be a densely, positively charged center Nucleus – has a positive center - with an electron cloud

Atomic Nucleus: Bohr’s Model Niehls Bohr Atom has a nucleus but electrons orbit in definite energy levels

Section 5.3 – Distinguishing Between Atoms Atomic Number - the number of protons in the nucleus of an atom of an element Atoms are electrically neutral Tells how many electrons there are also! Periodic Table #1 – Hydrogen: has 1 p+ and 1 e- #6 – Carbon: has 6 p+ and 6 e-

On the Periodic Table Mass Number – total number of protons and neutrons in a nucleus # of neutrons = mass # - atomic # = (# p+ + # no) - (# p+) Beryllium – 9 The number “9” is the mass number # of p+? # of no? # of e-?

Determining Mass Number: # of protons = atomic number # of electrons = # of protons (in a neutral atom) # neutrons = Mass # - Atomic #

Atomic Notation:

Ions: Atoms with a charge (results from gain/loss of electron) If an atom GAINS an electron = ANION Negative charge Ex: Cl- If an atom LOSES an electron = CATION Positive charge Ex: Ca2+

Isotopes Definition – atoms that have the same number of protons but different numbers of neutrons Different types of the same element Ex) Carbon – has 3 isotopes 1) Carbon – 12 2) Carbon – 13 3) Carbon – 14 Differ by # of no

Isotopes of Carbon All have the same # of p+ 1) Carbon – 12 If not, it would be a different element All have 6 protons 1) Carbon – 12 Has 6 neutrons 2) Carbon – 13 Has 7 neutrons 3) Carbon – 14 Has 8 neutrons

Isotopes of Hydrogen Hydrogen-1: 1 p+ and 0 no Relative abundance = 99.985 % Commonly called normal “hydrogen” Hydrogen-2: 1 p+ and 1 no Relative abundance = 0.015% Commonly called heavy hydrogen or “deuterium” Hydrogen-3: 1 p+ and 2 no Relative abundance = ~0.00% Commonly called “tritium”

Atomic Mass Definition – weighted average mass of the atoms in a naturally occurring sample of the element Carbon-12 = 98.89 % abundant Carbon-13 = 1.11% abundant Carbon-14 = ~0.0000001% abundant

Atomic Mass Formula: Formula: Atomic = relative mass relative mass mass abund. x # + abund. x # + Repeats for however many isotopes exist for that element….

Atomic Mass Sample Problem: Chlorine has 2 isotopes: chlorine-35 which is 75.77% abundant and chlorine-37 which is 24.33% abundant. What is the atomic mass of chlorine?

Atomic Mass 35 Cl = 75.77% abundant 37 Cl = 24.33% abundant = (35 amu x 0.7577) + (37 amu x 0.2433) = (26.5195 amu) + (9.0021 amu) = 35.5 amu Compare to value on Periodic Table = 35.45 amu which rounds to 35.5 amu

Section 5.4 – The Periodic Table: Organizing the Elements Dmitri Mendeleev (1834-1907) – first person to organize the elements in a chart Organized about 70 elements by increasing atomic mass Left blank spaces for elements which were not discovered yet

Mendeleev’s Periodic Table

Arranged by increasing atomic number instead! Periodic Table Henry Moseley (1913) – rearranged Mendeleev’s periodic table to the current configuration Arranged by increasing atomic number instead! Also grouped elements by their properties

Moseley's Periodic Table What is the mass of potassium and argon? #19 Potassium = 39.01 amu #18 Argon = 39.95 amu If Mendeleev’s Periodic Table was our arrangement, the gas Argon would be lined up with the metals!

Modern Periodic Table Arrangement: Groups/Families = columns Periods = rows Periodic Law: when the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties

Periodic Table

Parts of the Periodic Table Line of Demarcation: jagged “stairs” which separate the left and right side Metals = left and below the line of demarcation Nonmetals = right and above the line of demarcation Metalloids = elements along the line

Parts of the Periodic Table Metals Conduct electricity & heat Malleable Strong High melting and freezing points Mostly solids Have Luster

Parts of the Periodic Table Nonmetals Insulators – do not conduct well Brittle Low melting and freezing points Contain gases and liquids Are dull

Parts of the Periodic Table Metalloids – have properties of both metals and nonmetals Ex) Silicon -semi-conductor -brittle

Groups of the Periodic Table Group 1 = Alkali Metals Violently react with water http://video.google.com/videoplay?docid=- 2134266654801392897

Groups of the Periodic Table Group 2 = Alkali Earth Metals Very common in the earth’s surface Ex) Beryllium Magnesium Calcium Strontium Barium Radium

Groups of the Periodic Table Group 3-12 = Transition Metals Most of the common metals Lanthanide & Actinide Series = Inner Transition Metals

Groups of the Periodic Table Group 13-16: Either metals, metalloids, or nonmetal Depends on their side of the line Group 17: Halogens Highly reactive Fluorine Chlorine Bromine Iodine

Groups of the Periodic Table Group 18: Noble Gases All gases Do not react or combine with any other element

Chapter 5 Review Problems Page: 129 #33, 36, 38-43, 45-46, 48-49, 53, 57