1.1 What Is Chemistry? Matter is anything that has mass and occupies space. Chemistry is the study of the composition of matter and the changes that matter undergoes. Chemical changes that occur in leaves can cause brilliant displays of color.

1.1 Why Study Chemistry? What are three general reasons to study chemistry?

An Example of a Chemical Reaction 1.1 Why Study Chemistry? #1 - Explaining the Natural World An Example of a Chemical Reaction

Why Study Chemistry? #2 - Preparing For a Career 1.1 Even after the invention of the digital camera, many photographers still work with film. They use chemical processes to develop film and produce prints in a darkroom. Inferring Why isn’t film developed under natural light conditions?

Why Study Chemistry? #3 - Being an Informed Citizen 1.1 By registering to vote, these citizens in Chicago, Illinois, can have a say in the decisions made by their government. Those decisions include how much money to provide for scientific research.

Organization of Matter The flow chart summarizes the process for classifying matter. Any sample of matter is either an element, a compound, or a mixture. Interpreting Diagrams What is the key difference between a substance and a solution?

Looking at the History of the Atom Classification of Matter Practice w/ whiteboards http://www.mrwiggersci.com/chem/tutorials/ch3-rev-pract-classify-matter--blacksburg.htm Introduction to Atoms Looking at the History of the Atom https://www.youtube.com/watch?v=-4Us5PTb4J8

History of Atom All atoms share the same basic structure During past 200 years, scientists have proposed different models

Dalton’s Model All matter is composed of tiny, indivisible particles called atoms Atoms of each element are exactly alike Atoms of different elements have different masses Atoms of different elements can join to form compounds

Dalton’s Model

Thomson’s Model End of 1800s Thomson discovered that atoms were not simple, solid spheres Atoms contained subatomic particles Very small, negatively charged Called them ELECTRONS

Thomson’s Model Also knew that atoms were electrically neutral Must contain enough positive charge to balance negative charge of electrons Developed model where electrons were stuck into a positively charged sphere Like chocolate chips in cookie dough

Thomson’s Model

Rutherford’s Model By early 1900s, scientists knew that positive charge of atom comes from subatomic particles called PROTONS 1911—Rutherford begins to test theory His experiments led him to believe that protons are concentrated in a small area at center of atom Called this area the NUCLEUS

Rutherford’s Model Rutherford’s model describes an atom as mostly empty space, with a center NUCLEUS that contains nearly all the mass Like the pit in a peach Contained the PROTONS (+)

Bohr’s Model Modified Rutherford’s model in 1913 Proposed that each electron has a certain amount of energy Helped electron move around nucleus Electrons move around nucleus in region called energy levels Energy levels surround nucleus in rings, like layers of onion

Bohr’s Model Has been called planetary model Energy levels occupied by electrons are like orbits of planets at different distances from the sun (nucleus)

Electron Cloud Model Model accepted today Electrons dart around in an energy level Rapid, random motion creates a “cloud” of negative charge around nucleus Electron cloud gives atom its size and shape

Electron Cloud Model

FOCUS ON ELEMENTS Simplest form of matter Unique set of chemical & physical properties Identified by number of protons

Atomic Number Number of protons Symbol is “Z” Found on periodic table (check the legend) Elements are different because they contain different numbers of protons Protons found in dense nucleus HMMM – How do protons stay “TOGETHER” in the nucleus if they are all positive?

Practice Finding Number of Protons Aluminum Bromine Carbon Potassium Tungsten

Mass Number Number of protons + number of neutrons Symbol is “A” 4.3 Mass Number Number of protons + number of neutrons Symbol is “A” NOT found on periodic table Neutrons found in dense nucleus

How Many Electrons Do you Have? 4.3 How Many Electrons Do you Have? Neutral (no charge) electrons = protons Positive charge subtract electrons Negative add electrons

Practice Counting Subatomic Particles in IONS (atoms with a charge) Mass Number # Protons # Neutrons # Electrons Al3+ 27 O2- 16 Cu2+ 64 Ca 40 Ca2+

Isotopes How are these atoms alike? How are they different? 4.3 Neon-20, neon-21, and neon-22 are three isotopes of neon, a gaseous element used in lighted signs. Comparing and Contrasting How are these isotopes different? How are they similar?

Isotopes Same element Same number of protons Change number of neutrons 4.3 Isotopes Same element Same number of protons Change number of neutrons Different Mass Numbers

Draw a model of each of the atoms listed. Chromium-58 Chromium-63 # of protons # of neutrons # of electrons Nitrogen-15 Nitrogen-20 # of protons # of neutrons # of electrons