Atomic Theory

Atomic Theory

The Chemistry of Energy Part 1

"If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creature, what statement would contain the most information in the fewest words? I believe it is the atom hypothesis that all things are made of atoms - little particles (MATTER) that move around in perpetual motion (ENERGY), attracting each other when they are a little distance apart, but repelling upon being squeezed into one another.

- Richard Feynman

Matter and Energy• Matter: anything that occupies space and has

mass• Energy: anything that has the ability to move

matter, has no mass and does not occupy space.

• Albert Einstein showed that matter (mass) can be converted into energy and visa versa

• The total amount of energy (in Joules) contained in m (kg of mass) is

E = m x c2

– Where c is the speed of light (3 x 108 m/s)

The Law of Conservation

• The total mass and energy of the universe never changes (i.e. it is conserved)

• Mass + Energy = Constant

• We extract energy by converting a tiny amount of mass into energy

• In practice, the amount of mass converted to energy is always small!

Composition of Matter

• Matter is composed of atoms• Atoms are constantly in motion • The “speed” of the atoms determines the

state of matter - solid, liquid or gas.– Gases have no defined shape or defined

volume– Liquids flow and can be poured from one

container to another– Solids have a definite volume

States of Matter• H2O is found on the surface of earth in three

states, ice, liquid water, water vapor• The difference between these forms is the

motion or speed of the molecules.– Ice (Solid) = slowest atomic motion– Liquid Water (Liquid) = faster atomic motion– Water Vapor (Gas) = fastest atomic motion

IceLiquidWater

WaterVapor

Increasing Atomic Motion

Basic Structure of an Atom

• An atom consists of negatively charged electrons surrounding a positively charged nucleus

• The nucleus consists of both positively charged protons and neutral particles called neutrons

Atomic Mass

• The nucleus consists of two particles:

1. protons (positive charge)

2. neutrons (no charge)

• Protons and neutrons are roughly equal in mass, but they are almost 2000 times more massive than the electron

• The total number of neutrons and protons is the ATOMIC MASS

Atomic Number

• The number of protons in the nucleus determines the chemical properties of an atom.– Gold is different than silver because it has a

different number of protons• The number of protons in the nucleus of a

particular atom is its ATOMIC NUMBER

• Example: Carbon atoms have six protons so the atomic number of carbon is six

Elements

• An element is a group of atoms with the same atomic number, thus the same number of protons in the nucleus, thus the same chemical properties.

• Another definition of an element is a pure substance which cannot be broken down into anything simpler by either physical or chemical means.

Periodic Table of the Elements

The periodic table is made up of rows of elements (periods) and columns (families).


• Elements in column have similar physical properties

• For example, Gold (Au), Silver (Ag) and Copper (Cu) are in the same column

• All three are soft metals that are good conductions of heat and electricity.

11

Na

22.99


Atomic Number

Symbol

Atomic Mass

Modeling the Carbon Atom

• How many protons does carbon have?

• Carbon has an atomic number of 6, therefore it has 6 protons.

Atomic Number

Modeling the Carbon Atom• How many neutrons does carbon have?• The average atomic mass for carbon is 12.• Since the number of protons plus the number

of neutrons equals the atomic mass, the number of neutrons can be determined by subtracting the atomic number from the atomic mass.

12 (atomic mass)

– 6 (atomic number)

= 6 neutrons

Isotopes and the Atomic Mass

• Isotopes have the same atomic number but a different atomic mass

• That is, the number of protons is the same, the number of neutrons is different

• The atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.

Notation

• Sometimes, the atomic mass of an isotope is indicated after the name of the element, e.g.– uranium-238– carbon-14

• Sometimes, the atomic mass is written as a superscript preceding the symbol for the element, e.g.– 238U or 14C

Isotopes of Hydrogen

• Hydrogen has three isotopes called hydrogen, deuterium and tritium (each has only one proton)

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. What is the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C #p 6 6 6

#n 6 7 8

#e 6 6 6

Isotopes of Carbon

Isotopes of Carbon

• Since the average atomic mass of Carbon is 12.01, the most common isotope of carbon is C-12.

• C-13 and C-14 are very rare

Electrons

• The electron is a negatively charged particle that is thousands of times lighter than the lightest atom

• The electrons adds almost no mass to the atom

• In an uncharged atom the number of electrons (negative) = the number of protons (positive)

Electrons Shells or Energy Levels

• Each electron orbits the nucleus in a shell• A shell is considered an energy level.• Each shell has a maximum electrons that

it can contain (see next slide).• Valence electrons are those electrons

that occur on the outer shell of atoms.• The Octet Rule: Atoms attempt to acquire

an outer shell with eight valence electrons through chemical bonds

Electrons Shells or Energy Levels


• What is the number of electrons in a carbon atom?

• Since this carbon atom has no charge, the number of electrons is equal to the number of protons (6)

• The first two electrons occupy the first shell while the remain electrons occupy the second shell.

6p+

e-

e-

e- e-

e-

e-


• What is the number of valence electrons in a carbon atom?

• Valence electrons are the electron occupying the outermost shell

• The carbon atom has 4 valence electrons

6p+

e-

e-

e- e-

e-

e-

Ions

• An ion is an atom with a charge.• A charge results when the number of

protons and electrons are not equal.• An atom with more electrons than protons

has a negative charge and is called an anion.

• An atom with more protons than electrons has a positive charge and is called an cation.

Example of a Cation

• This carbon atom has a positive two charge and is called a cation.

• It has two less electrons (-) than protons (+).

• Therefore, this atom has 6 protons and only 4 electrons.

• Note that this carbon atom has only 2 valence electrons.

C2+

6p+

e-

e-

e-

e-

Example of a Anion

• This carbon atom has a negative two charge and is called a anion.

• It has two more electrons (-) than protons (+).

• Therefore, this atom has 6 protons and only 8 electrons.

• Note that this carbon atom has 6 valence electrons.

C2-

6p+

e-

e-

e- e-

e-

e-

e-

e-

Chemical Bonding

• Though the periodic table has only 118 or so elements, there are obviously more substances in nature than 118 pure elements.

• This is because atoms can react with one another to form new substances called compounds.

• Formed when two or more atoms chemically bond together, the resulting compound is unique both chemically and physically from its parent atoms.

Chemical Bonding

• Recall that atoms are most stable when the outermost shell or energy level contains the maximum amount of electrons.

Chemical Bonding

• Carbon has 6 total electrons and 4 valence electrons

• It needs 4 more valence electrons to become stable.

C

Chemical Bonding

• Oxygen has 8 total electrons and 6 valence electrons

• It needs 2 more valence electrons to become stable.

O

Chemical Bonding• If one carbon atom and two oxygen atoms bond

then they can fill their outer shells by sharing electrons

• This results in a new compound, Carbon Dioxide (CO2), one of the most important molecules that we will study in this class!

O OC

• The element sodium is a silver-colored metal that reacts so violently with water that flames are produced when sodium gets wet.

• The element chlorine is a greenish-colored gas that is so poisonous that it was used as a weapon in World War I.

• When chemically bonded together, these two dangerous substances form the compound sodium chloride, a compound so safe that we eat it every day - common table salt!

Chemical Bonding

+ =

Na+1

cationCl-1

anion

Atom Review Question

• For the atom listed below, list the number of protons, neutrons, electrons, and valence electrons. Also indicate if the atom is an ion and if it is the most common isotope of that element.

16 O3-

Step #1: Protons

• Determine the number of protons of oxygen using your Periodic Table.

• Oxygen is Atomic Number 8, therefore it has eight protons.

Atomic Number

Step #2: Neutrons

• Determine the number of neutrons of this oxygen atom by subtracting the number of protons (8) from the Atomic Mass listed on the left.

• Subtract the number of protons (8) from the Atomic Mass (16).

• 16 (Atomic Mass) - 8 (Protons) =

8 Neutrons

Atomic Mass

16 O3-

Step #3: Electrons

• In an uncharged atom, the number of electrons (-) should equal the number of protons (+).

• For example, in an uncharged atom of oxygen, there would be 8 negative electrons (-) to balance the 8 positive protons.

• However, this oxygen atom is an ion has a charge of 3-

Charge

16 O3-

Step #3: Electrons (Continued)

• The 3- charge indicates there is 3 more electrons (-) than there are protons (+).

• Since number of protons in oxygen is always 8, the number of electrons must be 11.

• 8(+) + 11(-) = 3-

Charge

16 O3-

Step #4: Drawing a Model of the Atom

• This oxygen atom has eight protons and eleven electrons.

• List the eight protons in the nucleus

• Place the 11 electrons in the shells.– The first shell can only

hold two of the four.– The next eight in the

second shell – And the final electron in

the outermost shell.

8p+

e-

e-

e- e-

e-

e-

e-

e-e-

e-

e-

Step 5: Valence Electrons

• Valence electrons are the electrons in the outermost shell.

• Based on your drawing, this oxygen atom has 1 valence electrons

8p+

e-

e-

e- e-

e-

e-

e-

e-e-

e-

e-

Final Two Questions

• Is this atom is an ion?

• YES. The atoms has a charge

Charge

16 O3-

Final Two Questions

• Is this atom the most common isotope of the element?

• Compare the mass listed next to the atom with the mass on the periodic table

• The rounded mass of the periodic table is the most common isotope of the element.

Atomic Mass

16 O3-

Final Two Questions

• Is this atom the most common isotope of the element?

• The mass provided is 16 and the most common isotope of oxygen is 16.

• Thus, this atom is the most common isotope of this element.

Atomic Mass

16 O3-

• Number of protons = 8 • Number of neutrons = 8• Number of electrons = 11• Number of valance electrons = 1• Is this atom an ion? Yes • Is this atom the most common isotope of this

element? Yes

16 O3-

Education

Atomic Theory