chapter 3

Chapter 3The Evolution of Atomic Theory

Homework Pg. 113 #3.25, 3.27, 3.30

The Law of Conservation of Matter

• When a chemical reaction takes place, matter is neither created nor destroyed

The Law of Constant Composition

• Multiple samples of any pure chemical compound always contain the same percent by mass of each element making up the compound

Aristotle

•400 BC

•Matter was made of smaller and smaller infinitely divisible particles.

Democritus

•400 BC ish

•Matter is made of tiny indivisible particles he called atoms

John Dalton• Beginning of modern

atomic theory• Early 1800’s• Created his model of

the atom to explain the way matter behaves based on a number of laws about how matter behaves during a chemical reaction. Model

The Law of Conservation of Matter

• Matter is neither created nor destroyed when a chemical reaction takes place.

Marie & Antoine Lavoisier

1775

Experiments in sealed containers

Proved that matter was conserved

The Law of Constant Composition

• Multiple samples of any pure chemical compound always contain the same percent by mass of each element making up the compound

Example Percent by Mass• 300.0g wasps and hornets• Component parts 60.5g of Wasps and 239.5g of hornets

Example Percent by Mass• 300.0g wasps and hornets• Component parts 60.5g of Wasps and 239.5g of hornets

Example Percent by Mass• 50.0g of pure water• H2O• Component parts 44.4g of Oxygen gas and 5.6g

Hydrogen gas

Mass of Hydrogen in compound = 5.6g =11.2%Total mass of Compound 50.0g

Mass of Oxygen in compound = 44.4g =88.8%Total mass of Compound 50.0g

Example Percent by Mass• 50.0g of pure water• H2O• Component parts 44.4g of Oxygen gas and 5.6g

Hydrogen gas

Mass of Hydrogen in compound = 5.6g =11.2%Total mass of Compound 50.0g

Mass of Oxygen in compound = 44.4g =88.8%Total mass of Compound 50.0g

• Work patch and practice problems

Warm up 10-28• A tablet of Tylenol has a mass of 0.611g. It

contains 251 mg of its active ingredient, acetaminophen, C8H9NO2.

(don’t forget to make the units the same.)

a.) What is the mass percent of acetaminophen in a tablet of Tylenol?

The Law of Conservation of Matter

• Matter is neither created nor destroyed when a chemical reaction takes place.

Marie & Antoine Lavoisier

1775

Experiments in sealed containers

Proved that matter was conserved

Homework Check

Homework Pg. 113 #3.25, 3.27, 3.30

Dalton’s Atomic Theory

1. All matter is made up of atoms2. Atoms can neither be created nor destroyed3. Atoms of a particular element are alike in size,

mass and properties4. Atoms of different elements are different from

each other in size, mass and properties5. A chemical reaction involves either the union

or the separation of individual atoms

Dalton’s Atomic Theory Almost

1. All matter is made up of atoms (atoms are made of smaller particles like protons, neutrons and electrons)

2. Atoms can neither be created nor destroyed (atoms can be created and destroyed fission and fusion)

What Do atoms Look Like

1897 Thompson discovered the first subatomic particle…..the electron!

You should know:

1. All atoms contain electrons and all electrons were identical

2. Very light 1/1836th the mass of a Hydrogen atom

3. Negative electrical charge (-1)

The mass of a raisin is about 1gThe mass of one H atom 0.000 000 000 000 000 000 000 001 67 g

10 years later in 1907 James Chadwick discovers the proton

You should know:

1. Protons are very heavy. Almost equal in mass to a Hydrogen atom.

2. Positive electric charge (+1)

25 years later in 1932 Chadwick demostrates the existence of a third subatomic particle the neutron

You should know:

1. A neutron has the same mass as a proton;

2. 2. no electric charge

Early Model of the Atom

1909 Ernest Rutherford developed a new model of the atom

Based on his study of alpha particles

1. Chunks of positively charge matter that are spontaneously given off by radioactive elements. (2 protons & 2 neutrons)

2. 7000 times more massive than electrons

3. He “Shot” alpha particles at a film of pure gold only a couple 1000 atoms thick.

4. Rutherford expected the alpha particles to cruises right through the foil.

experiment

Size of an atom

• An atom is mostly empty space• An atom is roughly 100,000 times larger

than its nucleus• The Problem of Electrons in motion and

quantum physics

The Structure of an Atom

Particle Location Charge SizeProton (P) Nucleus Positive (+1) Relatively

massive

Electron (e-) Outside the Nucleus

Negative (-1) Relatively small

Neutron (n) Nucleus No Charge Same size as the proton

Atomic Number (Z)

• The number of protons in the nucleus is the atomic number

• Determines the identity of the atom• The atomic number is so important the

periodic table is arranged according to increasing atomic number

Mass Number

• = number of protons plus the number of neutrons in the nucleus

• Remember!!!! It is the atomic number and the atomic number only, not the mass number, that determines the identity of an atom. The mass number can change because there can be more neutrons in the nucleus.

Isotope

• Isotopes are the same element (same atomic number) that contain different numbers of neutrons in their nuclei (different mass number)

• Because they are the same element they have the same chemical properties

• See page 87

Atomic Mass

• Mass of the atom.• The exact mass of the specific isotope• Reported in Atomic Mass Units (amu)• 1 amu is 1/12th the mass of one 12C atom• 1 amu = 1.660 54 x 10-24g• Can you calculate the mass in grams of

one carbon atom? (12 amu)

Atomic Number(A)

# of Protons # of Protons = # of electrons

Mass Number(Z)

# of Protons + # of Neutrons

Isotope Determined by mass number

Different number of Neutrons

Atomic Mass Specific to each isotope. (P+N)

Complete Table14N

7

24Mg12

23Na11

59Fe26

Mass Number

Atomic Number

# of Protons

# of Neutrons

# of Electrons

Complete Table14N

7

24Mg12

23Na11

59Fe26

Mass Number

14 24 23 59

Atomic Number

7 12 11 26

# of Protons 7 12 11 26

# of Neutrons

7 12 12 33

# of Electrons

7 12 11 26

The Nature of Light

• 186 000 miles per second• 671 000 000 miles per hour• c=3.00 x 108m/s• Photons: particles or packets of energy• Wave of energy

• Wavelength (λ): distance between identical points on the wave

• Red Light has a wavelength of 700nm• Violet light has a wavelength of 400nm• Smaller wavelength more energy

Visible Light

Electromagnetic Spectrum

Energy in Electromagnetic Radiation

E=hc/λ

Where;

E=energy of the electromagnetic radiation

c=3.00 x 108 m/s (speed of light)

h=6.626 x10-34js

λ=wavelength of electromagnetic radiation

Conversion factor 1 x 10-9 m/nm

Bohr Model

• Electrons can only “orbit” certain distances from the nucleus.

• That is electrons have certain “Quantized” energies

• Like a person on a ladder• This model is not completely accurate

Important Vocabulary

• Shells• Principal Quantum number (n)

4 main features of the Bohr model

• Orbits (shells) gets larger, their radius increases as the principal quantum number, n, increases

• Electrons in the n=1 orbit have the lowest energy

• Each shell can hold a maximum of 2n2

electrons (2, 8, 18, 32)• The inner orbits are filled first.

Law of Mendeleev

• Properties of the elements recur in regular cycles (periodically) when the elements are arranged in order of increasing atomic mass

• Predicted the properties of elements yet to be discovered. (C, Si, ?, Sn)

Modern Periodic Table

• Arranged by Atomic number not mass.• Each column is called a group• Each row is called a period• See page 98

Three Broad Groups on the Periodic Table

• IA – VIIIA are called the representative elements or the main group of elements.much of early chemistry was based on these elements.Strongest periodic relationship on the table.law of octaves: Chemical properties repeat every 8 elements when dealing with the representative elements.

Other Groups

• Transition Metals• Lanthanides (or Rare Earth Metals)• Actinides

Group VIIIA Noble Gases

• All gases at STP 1atm and 25 degrees Celsius

• Extremely unreactive• Called noble gases or rare gases• All are found in trace amounts in the

atmosphere except Helium.• Radon is the only radioactive noble gas

Metals

• Most elements are metals• Shiny solids• Malleable• Bendable• Conduct heat & electricity (conductors)

Nonmetals

• Tend to be brittle• Do not conduct heat or electricity

(insulators)

Metalloids

• Depending on conditions can act like either metals or nonmetals

• Si Silicon• Ge Germanium• As Arsenic• They neither conduct electricity as well as

metals or insulate as well as nonmetals

Transition Metals

• Form a bridge between the two parts of the representative elements

• Mercury (Hg) is the only metal that is a liquid at STP

• Nickel, silver, gold, copper, zinc, chromium, titanium, platinum

Lanthanides & Actinides

• Less common• Eg. Uranium and plutonium

Alkali Metals & Alkaline Earth Metals

• Group IA – Alkali Metals• Group IIA – Alkaline Earth Metals• When placed in water these elements

react to make the water alkaline (Basic)

Chalcogens

• Group VIA• Oxygen, Sulfur, Selenium, Tellurium,

Polonium• Most copper containing minerals contain

oxygen or sulfur

Halogens

• Group VIIA • Halo = Salt genes= Born• Fluorine, Chlorine, Bromine, Iodine,

Astatine

Noble Gases (again)

• Group VIIIA• Helium, Neon, Argon, Krypton, Xenon,

Radon

Hydrogen

• Not an Alkali metal even though it is in group IA

Atomic Size

• Atomic Radius increases as you go down a group

• Atomic Radius decreases as you move from left to right in a period

Ionization energy

• Atoms are electrically neutral• An atom where there is a net charge is an

Ion• Ions are created by adding or removing

electrons• Anions - negatively charged ions• Cations – positively charged ions

• The amount of energy required to remove an electron from an atom is called the first ionization energy(IE)

• Ionization energy decreases as you move down a group

• Ionization energy increases as you move left to right in a period

Remember this!

• The only way to turn a neutral aton into an ion (cation + or anion -) is to add or remove electrons

• Removing electrons takes energy

• The amount of energy required to remove an electron from an atom is called the first ionization energy(IE)