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Basic Chemistry

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Basic Chemistry CH 2- THE CHEMISTRY OF LIFE Atoms . The study of chemistry begins with the basic unit of matter, the atom. The Greek philosopher Democritus called the smallest fragment of matter the atom, from the Greek word atomos. Atoms (cont.) . Placed side by side, 100 million atoms would make a row only about 1 centimeter long. Atoms contain subatomic particles that are even smaller. Atoms (cont.) . What three subatomic particles make up atoms? Atoms (cont.) . The subatomic particles that make up atoms are . protons . neutrons . electrons Atoms (cont.) . Smallest property of an element that still has the properties of that element . “The building blocks of matter” . Atoms are made of smaller (subatomic) particles arranged in a particular way . p+ (proton) . n° (neutron) . e- (electron) Atoms (cont.) . Protons and neutrons have about the same mass. Protons are positively charged particles (+). Neutrons carry no charge (◦). Strong forces bind protons and neutrons together to form the nucleus, which is at the center of the atom. Atoms (cont.) . The electron is a negatively charged particle (−) with 1/1840 the mass of a proton. Electrons are in constant motion in the space surrounding the nucleus (e- cloud). Atoms (cont.) . The subatomic particles in a helium atom. Atoms (cont.) • Electrons are attracted to the positively charged nucleus but remain outside the nucleus because of the energy of their motion. • Because atoms have equal numbers of electrons and protons, and because these subatomic particles have equal but opposite charges, atoms are neutral. Atoms (cont.) . Atomic number- # of p+ AND electrons in an atom . Mass number- total # of p+ + n° in an atom . # of neutrons- mass number- atomic number . Ion- charged atom (can gain or lose electrons) . If an atom gains e-, does it have a positive or negative charge? . What if the opposite is true? . LEP-GEN (Lose Electrons Positive, Gain Electrons Negative) . Where can the characteristics of all atoms be found? Practice . Atomic #? . Atomic mass? . # of neutrons? More Practice . Atomic #? . Atomic mass? . # of neutrons? Elements . Substances that can’t be broken down into simpler substances . Pure substance made of only ONE type of ATOM . Represented by one or two letter symbol (Ex. C, H, O, Al, Fe, He, Ga, Pt, Au) . Noble gases . Elements that can exist alone (don’t combine with other atoms…usually!) . Ex. He, Ne, Ar . Mike Stanfill, Private Hand - Flash Animation - The Elements, by Tom Lehrer Elements (cont.) . Sodium . Reaction of Sodium with Water . Mercury Elements (cont.) • More than 100 elements are known, but only about two dozen are commonly found in living organisms. Isotope . Atoms of the same element that have different #’s of n° . Ex. C-14 and C-12 . Both have 6 p+ . C-14 (8 n°), C-12 (6 n°) Isotopes (cont.) . Isotopes are identified by their mass numbers. For example, carbon has three isotopes—carbon-12, carbon-13, and carbon-14. Each isotope has a different number of neutrons. Isotopes (cont.) . Q- How are all of the isotopes of an element similar? Isotopes (cont.) . A- Because they have the same number of protons and electrons, all isotopes of an element have the same chemical properties. Isotopes (cont.) Isotopes of Carbon 6 electrons 6 protons 768 neutrons Isotopes (cont.) . Radioactive Isotopes . Some isotopes are radioactive, meaning that their nuclei are unstable and break down at a constant rate over time. Although the radiation these isotopes give off can be dangerous, they have important scientific and practical uses. Isotopes (cont.) • Radioactive isotopes can be used: . to determine the ages of rocks and fossils. to treat cancer. to kill bacteria that cause food to spoil. as labels or “tracers” to follow the movement of substances within an organism. Chemical Compounds . Chemical Compounds . In nature, most elements are found combined with other elements in compounds. A chemical compound is a substance formed by the chemical combination of two or more elements in definite proportions. The physical and chemical properties of a compound are different from the elements from which it is formed. Chemical Compounds • Scientists show the composition of compounds by a kind of shorthand known as a molecular formula. • Water, H2O, contains two atoms of hydrogen for each atom of oxygen. • The formula for table salt, NaCl, indicates that sodium and chlorine combine in a 1 : 1 ratio. Molecular Formulas . Shows numbers of molecules and atoms . Molecules = coefficient (the number in front) of molecular formula (ex. 3H2O = 3) . Atoms = # of atoms in compound (ex. H2O = 2 Hydrogens, 1 Oxygen = total of 3 atoms in this compound) . Total # of atoms = (Coefficient) x (# of atoms) . How many molecules and atoms do each of the following have? . 3 H2O . 2 C6H12O6 . 4 NaCl . CO2 Structural formulas . Shows how the atoms are connected in a compound. Each element requires 1-4 lines to connect it to other atoms (see periodic table) . Ex. C2OH6 . Is there a problem in drawing this? H H H H | | | | H - C - C - O - H H - C - O - C - H | | | | H H H H Isomers . Have same molecular formula but different structural formulas . C3H8O Energy shells . Located in the e- cloud . 1st shell holds a maximum of 2 e- . All other shells hold up to 8 e- Electron Configuration . Drawing of how many e- are in each orbital. Must know atomic number so know how many protons (and therefore how many electrons) an element has . Ex. O has atomic # of 8 therefore has 8 e- . Electron configuration = 2) 6) . Ex. Al has atomic number of 13 . Electron configuration = 2) 8) 3) Valence . Shows how elements bond together by sharing e- . Several steps involved in determining valence . What is an e- orbital? . How many e- can fit in each orbital? . What do we have to know before we can determine valence? Valence electrons . Number of e- in the outermost energy shell - . Ex. O2 has _______ valence e Valence (cont.) . Where are the valence e- located? . Answer: In the LAST orbital!!! . _______ +7 2) 5) . _______ +5 2) 3) . Each orbital wants to be FULL to be happy!! . To determine valence, always take the path of least resistance (always choose the lowest number to gain or lose to make the orbital full) Valence (cont.) . If an atom loses e-, does it become more positive or more negative? . This positive or negative will always be the sign in front of the valence . The valence number is found by figuring out how many e- must be lost or gained to make the atom happy (have the last orbital full!) Valence (cont.) . In summary, to find valence: 1. Look up the atomic number (# of p+) 2. Determine the electron configuration 3. Determine the # of valence e- (# of electrons in last shell) 4. Determine if it is + or – valence (if it gains e- it becomes more negative and vice versa) 5. Determine valence by how many e- it would have to lose or gain to be happy Valence (cont.) . Want an easier way to find valence? . Label your periodic table! Chemical bonds . Forces that hold atoms together . Can be single, double, or triple bond . Depends on how many pairs of electrons are shared between elements . Single bond . Double bond . Triple bond Bond Lines . All elements have the ability to bond with other element(s) . Can have anywhere between 1 and 4 bond lines . How do we know how many bond lines each element has? . Answer: the number of bond lines is the same of the valence of the element (without the + or – sign) Bonding (cont.) . Ex. Cl has a valence of -1, so it has one bond line. Ex. C has a valence of ±4, so it has four bond lines. Ex. N has a valence of -3, so it has three bond lines. Bonding rules . Each element must have the correct # of bond lines attached to it . # of bond lines is determined by _________? . Ex. O2 has valence of -2, so it has _________ bond lines. Ex. C has a valence of ± 4, so it has _________ bond lines. Bonding rules (cont.) . All coefficients and subscripts must be satisfied. Ex. 2C2H6- Must draw two molecules each having 2 carbons and 6 hydrogens Changing molecular formulas to structural formulas . All bond lines, subscripts, and coefficients must be satisfied. Ex. H2O Changing structural formulas to molecular formulas . All coefficients and subscripts must be satisfied. Ex. H – O – H ―> H2O . Ex. H – Cl H – Cl ―> 2HCl Types of bonds . Covalent . Chemical bonding where pairs of electrons are shared . Strongest type of bond (gets stronger as more pairs of electrons are shared) . Polar covalent bond . Present in water molecules . Because electronegativity difference between O and H, a bond forms where the O has a partial negative charge and H a partial positive charge Types of bonds . Ionic bond . Weak bond formed between two oppositely charged ions . Type of bonds in salt (NaCl) . Hydrogen bond . Caused when hydrogen and an electronegative atom bond . Weakest type of bond Organic compound . Must contain carbon (C) . Usually associated with living things . Ex. Carbohydrates, lipids, proteins, nucleic acids . What is inorganic???? Chemical Bonds . What are the two main types of chemical bonds? Chemical Bonds . The main types of chemical bonds are: . ionic bonds . covalent bonds Chemical Bonds . Chemical Bonds . The atoms in compounds are held together by chemical bonds. Bond formation involves the electrons that surround each atomic nucleus. The electrons that are available to form bonds are called valence electrons. Chemical Bonds . Ionic Bonds . An ionic bond is formed when one or more electrons are transferred from one atom to another. An atom that loses electrons has a positive charge. An atom that gains electrons has a negative charge. These positively and negatively charged atoms are known as ions.
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