Basic Chemistry. What is matter? Atomic Structure 8/25/2016

Transcription

1 Basic Chemistry What is matter? Any substance in the universe that has mass and occupies space. All matter is composed of atoms. Atoms are the smallest building block of chemistry. Smallest unit in chemical reactions. Sub-atomic particles are the realm of physics and nuclear reactions. (not for this course) Atomic Structure Atoms are composed of Protons Positively charged particles Located in the nucleus Neutrons Neutral particles Located in the nucleus Electrons Negatively charged particles Found in orbitals surrounding the nucleus Physical Review Letters: "Hydrogen Atoms under Magnification: Direct Observation of the Nodal Structure of Stark States." 1

2 Elements A substance made of atoms that have the same number of protons ---the same kind of atom. Pure substances, not compounds. Example: Oxygen is an element: O 2 Water is not an element: H 2 O Nice Periodic Table to Download National Institute of Standards and Technology: Science Notes: How to use the periodic table: Four most common elements in living things: CHON 2

3 Four most common elements in living things: approx. percent Oxygen 65% Carbon 18-19% Wait, that s not 100% (approx. 96%). Smaller amounts of: Sodium Magnesium Phosphorus Sulfur Hydrogen 9-10% Nitrogen 3.5% What s the rest? Chlorine Potassium Calcium Iron Chemical Bonds Moleculesare groups of atoms held together in a stable association. O2 Compoundsare molecules containing more than one type of element. Ex: H2O Atoms are held together in molecules or compounds by chemical bonds. Basic types of bonds Ionic Positive and negative atoms attract (ions) Covalent Sharing electrons Hydrogen Sharing an H atom with weak positive charge Ions Trying to become stable, atoms can lose or gain an electron. When this happens, the atom is no longer neutral. Becomes either a positive or negative ion. Positive ion: Cation Negative ion: Anion Ionic bond formed when opposites attract. 18 3

4 Covalent Bonds Sharing of electrons in order to become stable. Valence: Number of electrons needed for stability. Ex: valence of Carbon is 4 and Oxygen is 2. CO 2 Example: 20 Chemical reactions Chemical reactions involve the formation or breaking of chemical bonds. Atoms shift from one molecule to another without any change in number or identity of atoms. Reactants = original molecules Products = molecules resulting from reaction 6H 2 O + 6CO 2 C 6 H 12 O 6 + 6O 2 reactants products 21 What can change in an atom? Electrons: Can change = ions Protons: Do not change ever = atom identity Neutrons: Can change = isotopes Atoms of an element that have different numbers of neutrons are called isotopes. Most elements in nature exist as a mixture of different isotopes. Some common, some rare. 24 4

5 Radioactive Isotopes Some isotopes are unstable and thus radioactive. Radioactive isotopes decay over time turning into a different atom (element). The original radioactive isotope is called the parent isotope. The element that it decays into is called the daughter isotope. Half-lifeis the amount of time it takes for one half of the parent isotope to turn into the daughter isotope. 5

6 Parent Isotope Daughter Isotope Half-Life Uranium-238 Lead billion years Potassium-40 Argon billion years Uranium-235 Lead million years Uranium-234 Thorium ,000 years Carbon-14 Nitrogen-14 5,700 years Your happy instructor when everyone dresses properly for lab What happens when flip flops show up in lab The Wizard of Oz, Warner Brothers