(Almost) Everything You NEED in Chemistry An atom consists of a central portion, the NUCLEUS (made up of Protons and Neutrons) and Electrons which are found outside the nucleus. An uncharged atom has an equal number of protons (positive charge) and electrons (negative charge). ATOMIC NUMBER is the number of protons in the nucleus. This determines what element the substance is. Q1. What is the Atomic Number of the Li atom shown? (see answer sheet) ATOMIC WEIGHT is the weight of the atom. This includes the mass of the Protons plus the mass of the Neutrons. Electrons have much less mass, and are not counted. Q2. What is the Atomic Weight of the Li atom shown? RADIOACTIVITY is the property of matter in which an unstable nucleus gives off a particle or energy (or both). Electrons are arrange in orbitals or shells. The number of electrons that fit into an orbital is shown below. Shell/ Energy Level Maximum # of electrons shell can hold First 2 Second 8 Third 8 The CHEMICAL PROPERTIES of an element are the ways in which it reacts or combines with other elements. The CHEMICAL PROPERTIES of an element are determined by the number of electrons in the outer shell. An atom will donate/accept/share electrons to get a FULL outer shell. Q3. What would the Li atom shown above do to have a full outer shell? 1
Atoms combine with other atoms by forming CHEMICAL BONDS. Chemical Bonds result from gaining, losing or sharing electrons. IONIC BONDING results when one atom loses and electron and another atom gains an electron. An example of Ionic Bonding can be found with table salt, NaCl (sodium chloride). Na has one electron in its outermost shell, and Cl has seven. If Na gives away the outer electron, it will have a full orbit underneath. Cl will get the extra electron, moving from seven to eight electrons, making a full shell. So now, both Na and Cl have a full outer shell. This type of bond is called IONIC BONDING, and is very strong. It takes a lot of energy to break this kind of bond. Note that the total charge on the Na atom becomes Positive when it gives away a negative electron. The total charge of the Cl atom becomes NEGATIVE when it takes on that electron. It is the attraction between the positive and negative charges that account for the bonding. COVALENT BONDING occurs when atoms SHARE electrons. For example, look at the oxygen molecule. Each atom of O has two electrons in the inner shell, and six electrons in the outer shell. A complete shell would have 8 electrons. If two oxygen atoms SHARED a pair of electrons, both would have a complete outer shell. Atoms with the same number of electrons in the outer shell combine in similar ways. For example, Cl and Br both have 7 electrons in the outer shell, so they would combine with H as HCl or HBr A chart showing this similarity is called the Periodic Table. 2
POLAR MOLECULES result when atoms in a molecule share electrons unequally. Water is the prime example of a polar molecule. Note in the water molecule that the electrons from the H atom stay close to the O atom. This gives the O atom a partial positive change and the H atoms a partial negative charge. Like dissolves like. Polar substances will dissolve in polar solvents. So water would not dissolve fats, which are not polar. HYDROGEN BONDING results when the partially charged ends of separate molecules are attracted to one another. (see below). These are weak bonds, but are critically important in physiology. DNA strands are linked by hydrogen bonding. Note the attraction here between the Oxygen atom with a negative charge and the Hydrogen atom with a partial positive charge. 3
DNA strands are held together by H Bonding, as shown by the dotted line in this picture. Q. 4 Chlorine has seven electrons in its outer shell. How would two chlorine atoms combine so that each had a complete outer shell (eight electrons)? Try writing out the diagram to show this sharing, 4
IONS a charged atom or molecule. Na+, Cl-, PO4-2 are all IONS. Strictly speaking, substances which dissolve to give IONS (charged particles) in water are called ELECTROLYTES. In fact, we usually refer to these ions themselves as electrolytes. So Na+, K+, Ca+2 are all electrolytes. ACIDS and BASES Substances which give off a H+ ion when dissolved in water are ACIDS. HCl --> H + + Cl - HCl is an ACID because it dissolves to give H + ions. H 2 SO 4 --> 2 H + + SO4-2 H 2 SO 4 is an ACID because it dissolves to give H+ ions. BASES are substances that release ions that would COMBINE WITH H +. What would combine with H +?? OH - + H+ --> H2O So NaOH --> Na + + OH- NaOH is a BASE ACID and BASE concentrations [critically important info] The amount of acid or base in a water solution is measured by the ph. ph is a measure of the amount of acid in a solution. It is the negative of the log of the H+ ion concentration (written in brackets [H+] ) so if [H+] is10-7 the ph is 7. The ph of distilled water is 7. This is the NEUTRAL ph. (Neither ACIDIC nor BASIC) ph less than 7 are ACIDIC ph more that 7 are BASIC The LOWER THE ph, the MORE ACID. let me repeat that. The LOWER THE ph, the MORE ACID. let me repeat that. The LOWER THE ph, the MORE ACID. let me repeat that. The Higher the ph the LESS ACID. Q. 5 Which solution has more acid? #1 ph of 7.4 #2 ph of 7.3 5
Normal ph in the body is 7.35 to 7.45 Less than 7.35 is ACIDOSIS More than 7.45 is ALKALOSIS Inorganic substances CO2 O2 etc. Will be covered in your course as you need them. Organic compounds. A more detailed explanation will be provided in your coursework. Made up of Carbon and other atoms. CARBOHYDRATES Made up of C, O, H Dissolve in Water Used for energy animals glycogen] Used to STORE energy [plants starches, Simple Carbohydrates have one or two sugars. Complex carbohydrates have long chains of sugars. 6
LIPIDS This group includes fats, phospholipids, and steroids. Do NOT dissolve in water. Lipids are an important constituents of cell membranes. Fats are used for energy and used to store energy. Fats are made up of glycerol and 3 fatty acids. These are triglycerides Phospholipids Used to make cell membranes. The PO4-2 end is POLAR, and the two fatty acid chains are NON- polar. Steroids Made from cholesterol. Used in cell membranes, and to make steroid hormones, like Estrogen or Testosterone. PROTEINS Made up of strings of amino acids, linked by 7
covalent bonds, called peptide bonds. Two amino acids are linked in the diagram. A protein would contain hundreds or thousands of amino acids held together by such linkages. Proteins have primary, secondary, tertiary and sometimes quaternary structure. Secondary, tertiary, quaternary structure depend on H- bonding, and will be broken up when the protein is DENATURED. Proteins can form ENZYMES, which are CATALYST- molecules that make a chemical reaction go faster, but don t participate in it. NUCLEIC ACIDS the building blocks of DNA, the genetic code. Made of a fivecarbon sugar, a phosphate group and a base. The Phosphate groups link the sugars in each chain, the bases form hydrogen bonds that link the two strands together. 8