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 .
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
Where c is the speed of light (3 x 10 8 m/s)
The Law of Conservation The total mass and energy of the universe never changes (i.e. it is conserved) 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 H 2 O 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 Ice Liquid Water Water Vapor Increasing Atomic Motion
Water Vapor (Gas) = fastest 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: protons (positive 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).
Periodic Table of the Elements 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.
Periodic Table of the Elements 11 Na 22.99 Atomic Number Symbol Atomic Mass
Modeling the Carbon Atom How many protons does carbon have? Atomic Number
Carbon has an atomic number of 6, therefore it has 6 protons.
Modeling the Carbon Atom How many neutrons does carbon have? The average atomic mass for carbon is 12. 12 (atomic mass) – 6 (atomic number) = 6 neutrons
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.
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.
Sometimes, the atomic mass is written as a superscript preceding the symbol for the element, e.g.
Isotopes of Hydrogen
Hydrogen has three isotopes called hydrogen, deuterium and tritium (each has only one proton)
Isotopes of Carbon
Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. What is the number of protons, neutrons, and electrons in each of these carbon atoms .
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
Modeling the Carbon Atom 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) 6p+ e- e- e- e- e- e-
The first two electrons occupy the first shell while the remain electrons occupy the second shell.
Modeling the Carbon Atom What is the number of valence electrons in a carbon atom? Valence electrons are the electron occupying the outermost shell 6p+ e- e- e- e- e- e-
The carbon atom has 4 valence electrons
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. C 2+ 6p+ e- e- e- e-
Note that this carbon atom has only 2 valence electrons.
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. C 2- e- e- 6p+ e- e- e- e- e- e-
Note that this carbon atom has 6 valence electrons.
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.
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 C
It needs 4 more valence electrons to become stable.
Chemical Bonding Oxygen has 8 total electrons and 6 valence electrons O
It needs 2 more valence electrons to become stable.
Chemical Bonding If one carbon atom and two oxygen atoms bond then they can fill their outer shells by sharing electrons O O C
This results in a new compound, Carbon Dioxide (CO 2 ), one of the most important molecules that we will study in this class!
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. Chemical Bonding + =
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!
Na +1 cation Cl -1 anion
Atom Review Question 16 O 3-
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.
Step #1: Protons Determine the number of protons of oxygen using your Periodic Table. Atomic Number
Oxygen is Atomic Number 8, therefore it has eight protons .
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). Atomic Mass 16 O 3-
16 (Atomic Mass) - 8 (Protons) =
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. Charge 16 O 3-
However, this oxygen atom is an ion has a charge of 3-
Step #3: Electrons (Continued) The 3- charge indicates there is 3 more electrons (-) than there are protons (+). Charge 16 O 3-
Since number of protons in oxygen is always 8, the number of electrons must be 11.
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 8p+ e- e- e- e- e- e- e- e- e- e- e-
And the final electron in the outermost shell.
Step 5: Valence Electrons Valence electrons are the electrons in the outermost shell. 8p+ e- e- e- e- e- e- e- e- e- e- e-
Based on your drawing, this oxygen atom has 1 valence electrons
Final Two Questions Charge 16 O 3-
YES. The atoms has a charge
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 Atomic Mass 16 O 3-
The rounded mass of the periodic table is the most common isotope of the element.
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. Atomic Mass 16 O 3-
Thus, this atom is the most common isotope of this element.
Number of valance electrons = 1 16 O 3-
Is this atom the most common isotope of this element? Yes